Authentic Paper Cartridges
Historically the plugs were coated in beeswax and then inserted into the bullets. The sticky nature of the wax would ensure the plug remains in the bullet throughout its flight. Should the plug fall out, it effectively amounts to reducing the mass of the bullet and changing the center of gravity while the bullet is already on its trajectory. Although the plugs are very light, even the sudden loss of ten grains of weight from a stabilized bullet in flight can shift the center of gravity forward, causing a wobble and loss of accuracy. At close range it may not matter much but we enjoy shooting at long ranges, 300 yards and beyond, and that is where small deviations really add up.
This bullet was fired at an 800 yard target and recovered intact. The plug was missing but it did it's work. Notice the visible evidence of the plug being driven forward. Also notice the vaguely triangular shape of the base of the bullet; this is the result of this relatively small bullet (.550-inch) being forced into the grooves of the rifling, which were .592-inch diameter at the breech.
SHOOTING THE P1853 ENFIELD RIFLE WITH HISTORICALLY ACCURATE CARTRIDGES
A Few Observations on making Authentic Historical Cartridges for the Enfield Rifle; updated August 2017
The paper. When I first tried making Enfield-style cartridges, I used ordinary paper (blank newsprint) and the results were extremely disappointing. Paper made from wood pulp (like virtually all modern paper) soaks up the beeswax lubricant instead of simply being coated by it, and tends to burn when the gun discharges, exiting the muzzle smoldering and smoking. Because it soaks up lubricant, the wood pulp paper sticks to the bullet and destroys any possibility of accuracy.
Captain Hawes gives us a wonderful description of the cartridge paper used in his 1860 work Rifle Ammunition. The historical paper was derived from cotton rag with a 13lb weight. It does not soak up the lubricant. It separates instantly from the bullet upon leaving the muzzle, and does not burn or smolder. There are several suitable modern equivalents, including the often-cited Bienfang 360 translucent marker paper, which has a historically-correct 13.5lb weight. Apparently the Bienfang 360 was not a big seller at my local art store, and they had several pads of the stuff on sale: I bought it all, and shot it all, with good results. Yet the Bienfang paper is very translucent (you can see the bullet clearly, even through two complete thicknesses of paper) and it is not very strong; it gets turned into tiny little bits of confetti when fired. It's also expensive, and when my cheap source of Bienfang paper dried up, I switched to Helix 100% cotton rag tracing vellum. It is noticeably stronger than the Bienfang, much less translucent, but still less than 0.002-inches thick with a 16lb weight, which is close enough to the historical 13lb weight paper for my purposes. The Helix paper is expensive, at about the same cost as the Bienfang, but I find it to be much better. It has all the correct properties of historically accurate cartridge paper: separates instantly from the bullet, doesn't soak up beeswax, and doesn't burn. It is essential (as will be observed later) that the beeswax coats the paper, and does not soak into the paper, for the best anti-fouling performance. Helix 100% rag paper also stays generally intact when fired, leaving large pieces on the ground that can be examined afterwards for signs of rifling cuts (a sure sign that the bullets are expanding and engaging the rifling).
After lead, the paper is the biggest expense of the cartridge, costing more per cartridge than the gunpowder. Because it's so expensive, I have switched over to the late-pattern of Enfield cartridges which utilizes a smaller outer wrapper that must be made from 100% rag paper, and I make the powder cylinder out of ordinary cheap paper that does not need to have any "ballistic" qualities.
This round went downrange with a distinct whistling noise; it's easy to see why. The paper "apron" must have applied a huge amount of drag on this bullet, but it resisted 1100 feet per second of wind resistance and the sudden impact into rocky soil, hopelessly ruining any accuracy.
But the performance of the ammunition was not consistent between all three rifles. Easy loading aside, the Parker Hale and Whitacre progressive barrels provided reasonable accuracy with the service charge of 68 grains powder, while my poor friend with his modern Italian repro could only achieve accurate shooting with 75 grains or more. (This is contrary to my personal experience with my old Italian repro barrel, which shot beautifully with 55 grains and only goes to show that ever rifle is different, especially in this age of multiple manufacturers.) However, when he tried my latest cartridges, made with plugs from "Magic Sculpt" two-part sculpting resin, his Italian repro turned into a tack driver with the standard 68 grain charge. It was absolutely a night and day difference.
As mentioned already, I have switched to the latest pattern of British-made Enfield cartridges, which utilized the smallest size "outer wrapper" that actually formed the paper patch around the bullet. This is the most important piece of paper used in making the cartridge and must be of uniform size. It wraps around the bullet twice. The three cuts made in the paper, where it surrounds the bullet, are essential. Historically the cuts were 1.15 inches long and started below the base of the bullet, and extended just beyond the nose of the 1.09-inch long Pritchett ball. I make the cuts with a razor blade after the papers have been cut to correct size by sharp scissors. Dull scissors tend to leave a rough, serrated cut on the rag paper. I use a tin template to ensure the outer wrappers are all exactly the same size, every single time.
Historically, it was the plug that made the P1853 Enfield a successful military rifle. The effectiveness of the plug was realized by Colonel Hay, the commandant of the School of Musketry at Hythe, and he directed its adoption in 1855 after extensive practical testing. It enabled a generously-undersized bullet to be used (both the 568 and 550), facilitating the rapid and easy loading that the Enfield-style cartridge is best known for. And it made the bullet accurate, by positively forcing an instant expansion into the rifling. To achieve this without a plug would require a thin-skirted bullet with very little windage like the American 575-caliber Burton ("Minie") ball, which is so dreadfully susceptible to difficult loading in a fouled barrel, even after just a few rounds. The plug, then, isn't an unnecessary afterthought, but an essential component of the Enfield rifle cartridge.
For almost ten years, I have been shooting (or trying to shoot) historical black powder muzzleloading rifles. My interest stems from Civil War reenacting, which is unique among hobbies in that reenactors desperately seek to recreate the historical period exactly as it during the period. Or, as Foucault would say, as it was at the moment of its sudden irrruption. My background as a reenactor, and a rather unromantic relationship with graduate level history, means that my interests and motivations in black powder rifle shooting are primarily historical, instead of the far more common pursuit of accuracy. As I have found, however, at the end of the day the seemingly disparate realms historical accuracy and rifle shooting accuracy have happily (and somewhat unexpectedly) converged.
The lubricant. I live in a warm climate and straight beeswax has served me very well as an anti-fouling agent from the very start. Historically, a beeswax and tallow mixture was used until the acidic salts naturally present in the tallow were found to form a white crust on the lead bullets, increasing their diameter and making loading more difficult. Beeswax was used solely thereafter. Being generously undersized, lubricant is not necessary to load a paper-patched Pritchett bullet; the purpose of the lubricant is to control the build-up of black powder fouling, and so facilitate rapid and sustained fire.
In warm weather, any excess wax just peels back from the bullet when loading but it may as well be concrete in cold temperatures, hindering loading. Tallow softens the mixture but in hot weather it can cause the lubricant to get runny, and soak into cartridge paper. The elegant period answer (as most period solutions were) was to gauge the cartridges to ensure, even after the cartridge was dipped in the pure beeswax, the external diameter of the cartridge was less than the diameter of the bore. I gauge my cartridges at .568-inches, and even in very cold weather in the California high desert, in temperatures well below freezing, beeswax-lubricated rounds still load effortlessly.
Shooting observations. Most of my shooting is in the standing position, loading from the period cartridge-box, more or less "plinking" at moderate ranges, so I have geared my cartridges more for this purpose. With an Italian barrel that does not have progressive-depth rifling, I get the best accuracy with charges of 55gr 3F powder. The service charge of 2.5 drams, or approximately 68 grains, is too much for my reproduction rifle with the historically-incorrect constant depth shallow rifling; I get terrible accuracy with the service charge. However, with the correct progressive depth rifling that was used in the P1853 Enfield after 1858, the service charge is necessary to force a .550-caliber bullet into the grooves.
Original English-made Pritchett bullet and boxwood plug on the left, and my cast bullet and clay plug on the right. The N.O.E. 550-cal Pritchett mold throws a bullet with a slightly thicker skirt and a more pointed nose ogive than the original, which has a rounded skirt base instead of flat and a blunt, round nose.
Strong rifling cuts are also visible on many fired bullets. They vary in length; I am not sure why. It could be variations in the material used to make the plug, or variations in the charge, or different softness of the lead I use from batch to batch of bullets, or a combination of these and perhaps other factors. At any rate, any rifling cuts at all are a sign the ball is expanding, engaging the rifling, and imparting the rotation that gives accuracy.
UPDATE August 5, 2017. Recently I've gone shooting twice with friends who also have P1853 rifles, and we have fired over 600 rounds between three rifles. One rifle is mine, with the new Whitacre progressive rifled barrel. Another is an early serial number Parker Hale with a gloriously crisp progressive bore, and the last one is an Italian recent reproduction with constant depth rifling.
The result of expending some 600 rounds of Enfield "Pritchett" ammunition in two days are, once again, a vindication of Colonel Hay's expanding plug (and Boxer's bullet reduction from .568 to .550). The reduced bullet size enables consistent easy loading; after firing 75 rounds, in a hot barrel the weight of the ramrod alone will seat the bullet nearly home. Try doing that with .575 Minie balls!
Magic Sculpt is similar to Milliput, but it cures to an extremely hard plug within about two hours, instead of overnight with the Milliput. Additionally, it is somewhat cheaper. I have determined that the Fimo, Sculpey, Kato, and other oven-cure clays are simply not hard enough to fully answer for their purpose. Kato was the hardest brand, and I achieved very good results with it, but I noticed a disturbing trend: the oven-cured plugs were never (well, almost never) found in the bullets recovered from the ground around my long-range targets. Meanwhile, bullets with Milliput and Bondo plugs were found with the plugs still in place and well driven forward into the cavities. Shooting at close range targets will always turn a soft leaden Pritchett into a splattered unrecognizable blob, but at long range (600 yards and over) the bullets impact the ground at a velocity slow enough that they usually retain their shape. At 800 yards, they can be found nearly intact. When shooting these softer clay plugged bullets, we often notice an unexplained extra little "puff" of dust that is often some distance from the larger plume kicked up by the impact of a 540-grain Pritchett. The cause is easy to determine: the soft clay plugs are falling out of the bullets in flight.
Switching to a harder plug, with Magic Sculpt, seems to have cured the problem of the soft oven-cured polyclay plugs falling out of the bullets. It has also improved the performance of the bullet. The harder the plug, the better it seems to perform. My friend's Italian repro barrel is now printing nice groups on paper at 100 yards with the hard Magic Sculpt plug and a standard 68 grain charge.
Finally, I have changed the way I make the plugs. Originally I purchased the NOE Pritchett plug mold, but this casts a plug that does not fit flush in the base of the bullet. Instead, unlike historical Pritchett bullets, the plug sticks out perhaps 1/16th of an inch beyond the base of the bullet. Various explanations for this have been provided for why they made the plug mold tray this way. I don't like the plug sticking out of the back of the bullet, so I have stopped using the plug mold. Now I take the Magic Sculpt and form pea-sized little balls (its very important to make them all the same size for consistency). I swipe the inside of the Pritchett cavity with a cotton ball dipped in coconut oil, and then insert the pea-sized ball into the cavity. Gently pressed, it fills the cavity and forms a flat base. The coconut oil prevents the Magic Sculpt from adhering to the lead when it cures (the plug needs to move in the cavity when fired). This produces flush-fitting plugs, and they have been found to shoot more accurately at all ranges, especially at distances over 300 yards. For reasons I do not fully understand, the hard plugs do not fall out of the bullets, while the softer oven-cured polyclay plugs do.
There is clear evidence of expansion and rifling cuts on recovered bullets, as well as sharp rifling cuts in the paper. More or less intact recovered bullets have a distinctly noticeable "swell" at the base, where the cavity has expanded due to the action of the plug. Of the overall length of the bullet, only the bottom one-third or one-fourth actually expands to engage the rifling. Comparing a spent bullet with an unfired Pritchett, the expansion of the bullet is readily apparent. It is irrefutable proof that everything is working correctly.
The paper ejected at the muzzle tells an even clearer story. Rifling cuts, burn patterns, and remaining beeswax are tell-tale signs to look for. If the paper is heavily charred, it suggests that the bullet did not expand and hot gas burned the paper as it blew between the bullet and the barrel. Most of the paper I recover is not charred, except for the paper at the base of the bullet on top of the powder (as one would naturally expect). Through examination of the paper, I am quite convinced that the plug forces expansion of the bullet, and obturation of the bore, instantly or nearly instantly with the firing of the charge.
Making cartridges. The cartridges must be carefully and correctly constructed, to ensure that the paper around the bullet separates instantly at the muzzle, without influencing the bullet's flight. Cartridges must be tight; this is achieved by using the correctly-sized mandrels and formers, and properly sized paper templates. The paper must not be loose around the bullet; any wrinkling or bunching of the paper will make the round difficult or impossible to load. Most importantly, in my experience, the bullet end of the cartridge must be choked completely tight with no hole or gap remaining in the "rose" at the base. Examination of historical cartridges confirms that they were choked fully closed, and tied off tightly. The "rose" at the base of the cartridge must not extend beyond the diameter of the bullet; in every original cartridge I've ever seen, the rose is approximately half the diameter of the bullet, to ensure it does not interfere with loading. Just as importantly, it cannot have a hole or gap that could let molten wax flow through the hole when the cartridge is dipped in the lube. The wax hardens and then adheres to the plug and base of the bullet inside the paper, and sticks to the bottom of the bullet when the round is fired.
The bullet. The original Enfield bullet (both 568-cal and 550-cal) was formed by machinery under intense pressure, which ensured a perfectly solid, uniform projectile of exact dimensions. Unfortunately for the modern shooter, the only available "Pritchett" style bullets are cast, with all the associated imperfections of cast bullets. Molds for Pritchett bullets must usually be custom-ordered, which places the historically-accurate shooting of the P1853 Enfield outside the realm of the casual shooter. (If you don't want to spend over $100 for a mold, you can buy Pritchett bullets here.) My mold is an N.O.E. model that throws a 550-caliber bullet at approximately 530 grains. Among historical P1853 shooters, the 568-caliber bullet is more popular because it is accurate with reduced target shooting powder charges (51 grains 3F is common). I chose to recreate the final version of the Enfield cartridge with the .550-caliber bullet, which was adopted in 1858 because of difficulties encountered in loading the tighter-fitting .568-caliber bullets in combat conditions. The .568-cal bullet is a target round; the .550-cal bullet was adopted for the battlefield. Because I like long-range shooting and loading from the cartridge box, I went with the battlefield bullet.
Recovered bullet fired at 800 yards; they can be found reasonably intact and with rifling impressions gloriously evident. Notice the location of the "bulge" in the bullet near the base, where lead has been pushed out to fill a rifling groove. I am convinced this is the work of the plug.
Recovered bullets, showing clay plugs driven well forward into the cavity. Bullet on the far right was fired on top of a 68-grain service charge; other three bullets were fired with a 55-grain charge. They vary in color because I bought a bunch of clay that was on sale at the local craft store.
The P1853 Enfield cartridge. Developed in the mid-1850s for the British Army, the cartridge utilized by the P1853 Enfield rifle-musket elegantly solved the greatest problem of the muzzleloading rifle: the build-up of black powder fouling that harms accuracy and makes loading increasingly difficult. Unlike "American" style cartridges, which simply held the ball and powder together in a "neat and convenient" package, the Enfield cartridge must be very carefully constructed or it will not work. The paper cannot be too thick, but it must be strong, must not soak up beeswax, and must separate from the bullet as it leaves the muzzle. The bullet must be correctly sized. The anti-fouling agent (commonly but incorrectly called "lubricant") must be effective. Every aspect of the cartridge must perform perfectly as intended; if not, the rifle will be inaccurate at best, and outright impossible to load at worst. For me, it was not sufficient to simply make an Enfield-style cartridge that worked. My goal, from the start, has been to replicate the original mid-19th century ammunition as closely as possible.
So What? If you have read this far and your eyes have not glazed over, I hope this has been useful to you. Recreating this historical cartridge has been a lot of fun, and occasionally frustrating. The inherent complexity of the Enfield cartridge makes it a difficult historical black powder cartridge to make, but when it all comes together and everything works, it makes shooting muzzleloaders a fundamentally different experience compared to shooting plain Minie-style bullets.
The dimensions of the paper vary in period sources. Initially I used the dimensions provided in Captain Hawes' seminal Rifle Ammunition of 1860. This pattern worked very well, as the outer wrapper makes slightly more than two complete wraps around a .550-caliber bullet. When using the Bienfang 360 marker paper, the two wraps were essential since the beeswax would tend to soak through the outer wrap of paper but not the inner wrap, thus preventing the paper from adhering to the bullet. I now use the final pattern approved by Colonel Boxer in 1864, which utilizes an even smaller outer wrapper that does not quite make two full wraps around a .550-caliber bullet. Using Helix 100% cotton rag paper, the beexwax does not soak through even the single layer of paper, making this pattern practicable.
Recovered bullets, and the paper that gets blown out of the barrel, tell the full story. My friends hardly want to go shooting with me anymore because, after the last round is fired, I spend the next hour or two digging through the earth behind the target for fired bullets to examine. Many, perhaps as many as 50%, still retain their plugs. Of those found with the plug missing, there is usually clear evidence inside the cavity of the plug doing it's job, with lead visibly displaced as the plug advanced forward upon firing.
The plug. The entire subject of an expanding plug is, rather absurdly, still controversial among modern Enfield rifle shooters even though the issue was decisively settled almost 160 years ago. I rank myself among the vigorous defenders of the expanding plug, because it is historically accurate to begin with, and because they work on the practical scale. I will concede that the modern shooter, unconcerned with historical accuracy and more concerned with accurate shooting, has less need for a plug with the 568-caliber Pritchett than there is with the 550-caliber bullet. To obturate the bore and engage the rifling in a 577-caliber barrel, the 550-caliber bullet must expand 27 thousandths of an inch; that is a huge amount of windage. Obviously, the windage that must be overcome with a .568-caliber bullet is significantly less, especially with a paper patch. Because modern shooters achieve accuracy shooting 568's without plugs, a misconception has been repeated over and over that the plugs were only used by the British in the first place for protecting the skirts of the bullets from damage. This is categorically untrue. The primary purpose of the plug is to achieve positive expansion of the skirt and physically force the bullet into the rifling at the instant of discharge. Period sources (Hawes, Majendie, etc) attest to this fact over and over again. The fact that the plug does also serve to protect the bullet skirt from being deformed or dented is a happy added benefit.
I have tried making expanding plugs out of wood, Bondo automotive body filler, Milliput modeling putty, and clay. Out of all of them, I now use clay exclusively and achieve good results. Initially I used wooden furniture plugs (made to cover up screw heads) but these are expensive and each one must be cut down to the correct size. Bondo is messy, with intense fumes and very short working time before it cures. Milliput is expensive and has to cure overnight. Clay is ideal, since it is cheap, it was historically used, and it works. I am not a physics expert, but from examining recovered fired bullets, the lighter the plugs are the deeper they are driven into the bullet cavity. Additionally, I have found that the plugs do not need to be extremely hard. The "Sculpey" brand modeling clay I now use is baked at low temperature in a household oven (275 degrees F) and is easily cut with a sharp knife after it is cured, while Bondo and Milliput are much harder and very difficult to cut. Yet I consistently recover the softer Sculpey clay plugs from the base of fired bullets, and find them perfectly intact (so perfectly intact, that I use them again!).
UPDATE DECEMBER 2016: I have always wanted a P53 rifle with the correct progressive depth rifling that the originals had. My Enfield was an Italian reproduction and these have constant depth rifling, which is as deep at the muzzle as at the breech. To truly exercise the Enfield cartridge requires the correct barrel. Options are limited for the modern shooter, with three possible choices. First, find an original rifle in good condition and strong rifling. There are originals out there in shootable condition, but even the best preserved originals are 150+ years old and their rifling is worn. Early rifles also have iron barrels, while the latest production P1853's had steel barrels (although many of these steel barrel guns were converted over to Snider breechloaders). This is also the most expensive option: an original rifle with excellent rifling is an investment piece, and not something to shoot thousands of times recreationally. The second option is to find an old Parker Hale P1853; these were made in England on the actual machinery that made the Enfields historically. Old Parker Hale rifles have progressive depth rifling. However, these are also several decades old now, and many have been through a lot of reenacting seasons. Good Parker Hale P1853's in nice condition are worth almost as much as an original P1853 now!
Generally speaking, the paper recovered after firing is either part of the "sabot" that includes the choked and tied base of the cartridge, or thin strips of paper that wrapped around the bullet and usually showing numerous signs of rifling cuts. In the recovered choked base of the cartridge paper, the effectiveness of the three slits cut into the outer wrapper is readily apparent. It helps the paper spread away and separate from the bullet after it leaves the muzzle. As mentioned earlier, before I learned to tightly choke and tie the base of the cartridge, beeswax would get through the little hole (which you can see in a couple examples in the image) and stick to the bottom of the bullet. Occasionally I would find these still attached to the bullets I dug up out of the ground. Once this was corrected, I have no longer been finding any paper downrange with the bullets, and now it litters the ground in front of the muzzle. The "sabots" usually fall about ten feet away, and the lighter strips fall anywhere from three to fifteen feet away. Also visible in the "sabots" are sharp creases, showing where the plug was pressed forward. I have not encountered any evidence of paper being "nipped" by the action of the plug.
So the modern P1853 Enfield shooter has a decision to make when selecting which caliber of bullet to use: 550 or 568? Both are perfectly historical. The .568-caliber bullet, being 18 thousandths larger than the .550, does not have to expand as much to engage the rifling grooves and therefore does not require as strong a powder charge to achieve accurate shooting. Correctly-made cartridges with the .568-caliber bullet load easily and consistently in "non-combat" conditions. The .550-caliber bullet is not as flexible; it needs the full strength of the powder charge to achieve expansion. This makes it less desirable as a short-range target bullet. It's redeeming feature, however, is the absurdly easy loading, and the ability to be loaded and fired with ease and accuracy even when the rifle is dirty. With a .550-caliber bullet, these are "battlefield cartridges" that can be fired indefinitely (201 consecutive rounds is the standing record).
A well-perforated target, after being engaged by a P1853 Enfield at 380 yards
So I ultimately went with the third option: having a custom progressive depth rifled barrel made to replace the Italian rifle barrel. My Armi-Sport P1853 was made in the 1980s and I bought it many years ago for $200. For what it was, it was a good shooter with the old Italian barrel, which was quite accurate. But it was not progressive depth rifled, and my overarching goal was to fire historically accurate Pritchett cartridges from a historically accurate rifle. Daniel Whitacre of West Virginia made my barrel, and contoured it to the original Italian breechplug to ensure it would be a drop-in fit for the stock. I highly recommend his work. For much, much less than the cost of an original rifle or a vintage Parker Hale, Whitacre can make a new barrel with crisp, perfect rifling. Then Whitacre's barrel and the stock and lock went to Todd Watt, who did a complete "defarb" on the rifle. His work is pure artistry. What went in as a hideous 1980s Armi-Sport came back as a correctly stamped 1859 Tower rifle. The cast Italian sights were replaced with machined Rich Cross sights. After nearly ten years of shooting Enfield style cartridges, I finally have a P/53 with progressive depth rifling, and it now looks like an immaculately preserved original, to boot.
The recovered bullet in the pictures demonstrates what happens when the cartridge is not choked and tied off completely closed around the base of the bullet. In this case, the plug (made from Bondo) performed perfectly, being driven well forward into the plug cavity. Yet wax had flowed in through the gap in the paper when dipped in the lube, adhering to the plug and the base of the bullet when it cooled. The wax can be seen still sticking to the plug and bullet, and it stuck so firmly to the paper that the entire bottom of the paper cartridge was carried along the entire flight of the bullet, utterly destroying accuracy. Choking the cartridge base extremely tight, so that no hole or gap remains whatsoever, completely solves this issue.
The grooves in my progressive depth rifle barrel are 15 thousandths of an inch deep at the breech, and become shallower nearer the muzzle, where they are 5 thousandths deep. Consider, therefore, that in a progressive rifled barrel, a .550-caliber bullet has to expand 27 thousandths to reach the lands of the .577-inch bore, and it still has to expand 15 thousandths more to fill up the deepest grooves. That is a total of 42 thousandths. To achieve this incredible amount of expansion, a .550-caliber bullet needs the full force of a period 68 grain service charge (or thereabouts). Nice modest plinking loads of 55 grains, which work great in the Italian constant depth rifle barrel, do not have enough force to completely expand a .550-caliber bullet into a progressive rifle barrel. When Captain Boxer was advocating for the adoption of the .550-caliber bullet, he didn't have 21st century target shooters using reduced powder charges in mind.
With Italian rifling, my Enfield was most accurate with 50 or 55 grain charges. With the Whitacre progressive depth rifled barrel, it did not like my reduced charge loads at all. And by that, I mean it would not hit anywhere close to the point of aim. At 200 yards, the bullets were flying randomly like musket balls; none of the bullets were engaging the rifling and receiving any spin. Some more amateur forensics soon found the problems: the powder charge, and the plug.
Progressive depth rifling is deepest at the bore. A bullet fired from such a barrel expands into the deep rifling at the breech, and is "swaged" as it moves forward into the shallower grooves towards the muzzle. The charge has to be strong enough to expand the ball into these deeper grooves. Apparently my 50 grain charges were not producing enough pressure to drive the plug forward and expand the ball (and this isn't too surprising, considering it has to expand a .550-caliber bullet into .577-caliber lands, with even deeper grooves, which is an enormous amount of windage!). Increasing the charge to 65 grains, very nearly the 68-grain service charge of the period, instantly resulted in much better accuracy.
Yes, I know this is against most muzzleloader shooting conventional wisdom, which preaches that better accuracy is got with lesser charges. This may be so with the much more common (and much tighter fitting) Minie-style bullets with thin skirts which do not need as much pressure, and therefore do not need as heavy a charge, to expand into the rifling. I am also convinced that historical powder was much better than modern powder. The commercial black powder made today are usually made with the readily available and consistently performing alder wood for charcoal (the crucial ingredient). Alder charcoal performs well across a broad spectrum of uses, from pistols to muskets to cannons, in various conditions. Historically, powder was usually made with willow or dogwood for charcoal, and I believe this was much better powder that was slightly stronger and fouled far less. Experiments in the 1830s determined 12 grains of dogwood powder produced 82 cubic inches of gas, while 12 grains alder powder produced only 74 cubic inches; this is a 10% difference!
Even after increasing the charge, I was getting inconsistent accuracy. A couple rounds would fly true, and then the next would zip off into space. Finally I narrowed it down to different batches of cartridges, and found that the cartridges made with plugs of a specific brand of clay were the ones that were hopelessly inaccurate. Cartridges with other plugs performed great. This was very surprising, since they all performed flawlessly in the Italian barrel with constant depth rifling. Apparently the ineffective plugs were too soft, and upon inspection they were found to be slightly rubbery. They squished a very little bit, but still a perceptible amount, when squeezed or pressed against something hard. Other plugs from other clay brands do not yield at all when squeezed by hand. I tested a few in a C-clamp, tightening down on them until they were squashed. All of my clay plugs squashed with relatively little pressure, except some old Bondo and Milliput plugs. The Milliput was hardest of all.
The soft, "rubbery" plugs were Sculpey brand terracotta oven-cured modeling clay. I have discontinued these plugs, and have switched over to Kato brand polyclay. The Kato plugs are nearly as hard as the Bondo and Milliput, and the Kato clay is infinitely easier to work with than either Bondo or Milliput. They are forced deep into the plug cavities of the bullets, visibly displacing lead.
It is absolutely no surprise to me that the British had this all figured out in the 1850s. The plugs used in historical Enfield rifles were made from boxwood, a scarce and exceptionally hard wood. When the British changed from boxwood to clay in 1864, it was because local sources had dried up and the source of boxwood from the Ottoman Empire was unreliable. The requirements for clay plugs were strict, requiring sintered ceramic fired at extremely high temperature. The resulting product was glass hard. When put on top of the 68-grain charge of good English dogwood powder, such a hard plug was instantly and forcefully driven deep into the cavity of the bullet upon the discharge of the piece, compelling the lead to yield and expand into the rifling.
Cartridges made to historical specifications do not make for hyper-accurate short range "bench rest" ammunition. Period cartridges, especially with the .550-caliber bullet, were made with battlefield conditions in mind: dirt, rust, long intervals between opportunities to clean the weapon, and firing at long ranges (300 yards and beyond). This holds true today: modern 7.62 NATO ammunition with M80 ball is well made, but it is manufactured for military weapons with varying chamber sizes that must continue firing even when dirty, and it will be far less accurate than "match-grade" ammunition. I recommend the historically-correct Enfield cartridge for shooters who want to replicate the historical experience, shooting primarily at longer ranges. If you are trying to make cloverleaf groups at 50 yards from a bench rest, historically-made Enfield ammunition is probably going to be less accurate than other bullet options.
Why Enfield cartridges? Simply put, you can shoot them all day. After shooting (or attempting to shoot) the standard 575-caliber Minie balls, I nearly gave up on live-firing historical muzzleloading rifles. Even with Minies correctly swaged to 575-caliber, they become impossibly hard to load after ten or even fewer shots as the barrel fouls, which requires the ritualistic ordeal of cleaning before shooting can resume. In the early 1850s, the laboratory at the Royal Arsenal at Woolwich solved the fouling problem. With correctly-constructed Enfield cartridges, fouling is controlled and the generously-undersized bullets are easy to load, regardless of how long you've been shooting. It is night and day difference when compared to shooting American-style Minies.
Strong rifling impressions visible on the third of the bullet near the base; the result of the plug forcing the cavity open