I know that a lot does not transfer from Modern High Power and Bench Rest shooting to RB muzzleloaders, but some things certainly do.
In modern high level competition barrels we separate what is normally called the “muzzle crown” into the “muzzle face” and the “crown of the actual rifle bore or bore crown.” This last is also often called the “muzzle crown” and is what piloted crowning tools cut on rifle bores.
Dan is correct the “muzzle face” is basically to prevent damage to the muzzle/bore crown and especially if the barrel is dropped on the face of the muzzle. That’s why G.I. M1903, M1 and M1 carbine barrels were made with a slightly humped or rounded muzzle face – to protect the bore/muzzle crown if the rifle was dropped or hit against something hard like a rock or jeep or truck, etc. at the front end of the barrel.
Modern Bench Rest shooters have experimented with almost every imaginable shape of the muzzle face of the barrel. Some are made with a slight taper going straight down into the bore. Some have an indented surface from the rest of the muzzle face that is near to the bore. They and we found it really didn’t make much difference what the shape of the muzzle face was AS LONG AS it was extremely uniform all the way around the barrel. Uniformity is key as the when the bullet JUST completely escapes the bore, gas coming out behind it can STILL throw a bullet off if that muzzle face surface is not uniform. This because the gas will push the bullet slightly toward the part of the crown that is lowest and thus has the least resistance to the gas coming out of the barrel. Now this may not sound important, but it is. So much so that we learned to crown the very front of M14 flash suppressors on NM rifles for the best accuracy and that spot is well beyond the barrel muzzle.
Once there is a uniform muzzle face, the next thing to address is the bore/muzzle crown. The most accurate way to cut that angle is with a piloted and angled reamer to get absolute uniformity for better accuracy. This is short work on a new barrel, but requires more attention on used barrels because the ends of the lands and grooves do not wear evenly. This is why one MUST be sure that each and every land has a fresh cut all the way across each land for the best “crowning job.” If one leaves even the end of one land where it does not have a full fresh cut, the bullet will go off center towards that worn/uncut spot.
I fully believe this all applies to muzzle loaders because I have used piloted crowning tools this way to improve worn round ball barrel muzzles, including for members of the U.S. International Muzzle Loading Team.
Most of us know to try to put the sprue of the ball in the center of the patch and bore when we load it. Many of us know that sprues are usually not uniform and that introduces a different rotation in the ball from shot to shot and that hurts accuracy. It doesn’t show up much at 25 yards, but it does begin to be noticeable at 50 and especially 100 yards. This is why many of the “Tin Tipi” shooters and International Shooters JUMPED at the chance to use swaged round balls when they became available, that have no sprue and are much more uniformly round, for the most uniform ball rotation in flight and best accuracy – as long as there is a size of swaged round ball that fits your rifle well.
One thing that we are “stuck with” using patched round balls is the patch is not uniform all the way around the bullet, especially in the grooves. This is why we see various non uniform creases in patches that are picked up after firing. This means propellent gas does not push against the patched ball, all the way around it, with the most uniformity. A GREAT advance with some of the earliest breechloading bullets was to “patch” the bullets with paper that was even more uniform than cloth patches. Paper patched bullets were THE thing in the highest levels of long range shooting for decades until technical advances in barrel and bullet construction made them obsolete.
I still think the fact the coned barrels allow the sprues to be loaded less uniformly is a main part of the reason they are not as accurate. Of course, that doesn’t matter as much if one is using a swaged ball with no sprue.
I do believe Dan made an extremely good point that as the patched ball leaves the tightest portion of the bore at the rear of the cone, the patch that already does not seal the bore uniformly, now allows even more uneven gas pressure on the ball as the patch begins to unfold in the barrel and the ball slips around until it leaves the bore. This is even more important as it will do this even with a swaged ball that has no sprue. Matter of fact, it is probably the main reason why coned barrels are not as accurate.
Gus
