Dan, that's an Ed Rayle barrel, isn't it? 1,700fps is a good speed. It took 200gr. 2F GOEX (1987stuff) to get that speed in my 31" .69.
Taylor's 16 bore Lang has a 48" twist, with 12 lands/grooves, seems to me. He shoots 85gr., a .650" ball and .020" patch which actually
cuts on the lands (sharp muzzle), but no burnouts with that load & decent square accuracy at 100 meters - 2 1/2" square for 5 shots.
As far as stripping, not sure that can happen with a tight loads, but thinner patches, of course, would acerbate that problem. My 66" twist
in the .69, showed no stripping & good accuracy with 200gr. (1,700fps) The accidental 330gr. charge produced 1,770fps & lifted me up off the
'chunk' I was sitting on.
As to stripping, my .004" deep 48" twist rifling in the TC I had, got really good accuracy with 110gr. 2F, back in the 70's - no stripping, but I was using
.495" balls and .022" denim.
As to higher velocity with a smooth bored barrel compared to a rifled one, same calibre, our tests were inconclusive. We used a pair of .62's & the velocities
were pretty much identical. Seems to me, IIRC, the rifled tube was slightly faster, but so much would depend on ball size and "tightness of the load" in the bore.
A little late here. Not paying enough attention to the site.
It has barrel from a man in Missouri that no longer makes barrels.
It has 8 lands, shallow and shows a little patch abrasion at the lands but no burning or blowing. I did find some heavy linen canvas at
https://www.fabrics-store.com/ that is pretty heavy after a washing and drying. Might work better if not too thick. Its almost too heavy for my 50 cal GM barrels with .495 ball. But it was perfect in a Douglas 54 I freshed, someone had let it pit from the breech up about 12" and its a Don King Hawken and I did not want to rebarrel it. The heavy linen and a .535 load normal and seems to shoot great, I have not slugged it to be sure how large it is now but I sure got tired of walking back and forth, brushing off chips and then pulling/pushing it back through again.
More thoughts, question about the rifle answered etc. Since we are on the subject. Have not read everything in the thread so I might be repeating something some has posted. And answer some other questions.
104" is too slow IMO, even for a 69, based on your experience and mine. My late English style flintlock, its actually a 15 bore I guess, it shoots a 16 to the pound ball, has an 80" twist and will shoot 140 gr of FF Swiss great. I have shot it with lighter loads but not that much. Its hunting gun so I shoot the hunting load and honestly I have not shot it in perhaps 5+ years. 140 ff Swiss gives 1600 fps with a 30" barrel. It is shallow grooved narrow grooved and will shoot W-W alloy and pure lead to the same point at 50 yards. It has a 1 1/4" breech and a 1 1/8" muzzle. Shop made breech, shop made 303 stainless vent, shop made under rib, shop made sights and patchbox lock is from the Rifle Shop the the recessed breech Manton rifle lock, shop made mainspring, link and tumbler. I don't recall where the buttplate came from but think it might be TRS too since it had cast in engraving. The entry pipe, trigger, trigger bar and TG are from TOW. American grown English Walnut from Dunlap. Once I faced the frizzen it is an extremely reliable lock and ignition is as fast I have shot a few deer with it and intended to shoot a Gbear in AK with it but I had to rebarrel it because of accuracy issues and by the time I got that done Dad, in his 80s, was getting too old to be a good backup so that never happened. Could not afford a guided hunt.
I will say this. The Nock breech is very consistent in ignition will not reliably work with a dirty burning powder that creates flakes of fouling in the bore. If one of these falls into the breech and blocks the passage to the antichamber the vent will have to be primed to get the rifle to fire. Never had a problem with Swiss powder. But I did try the same charge of some Schuetzen powder I had a can of and it gave flakes and "problems". I had an "experience" back when I wore green uniforms that causes neck pain even though the x-rays are now "normal". This video shows one of the reasons i don't shoot this rifle anymore.
Back to twists.
IMO a great many modern ML barrels are twisted too slow. I think a 48" twist is ideal to at least 54 caliber. Note John Baird's Hawken Rifles.." pg 42-43. But people read Forsythe and went a little wild with both powder charges and twist rates especially in calibers under 65 or so IMO. This .67 FL with a Nock patent breech looses efficiency at charges over 140 gr of FF Swiss. Powder increases no longer give meaningful increases in velocity. The twist/stripping patches thing is that the larger balls have lot of rotational inertia due to weight and diameter. When the powder burns the initial acceleration is pretty extreme even compared to grey powder guns and the ball wants to not spin up so a slower lets the ball rotate a little slower. Someone with the inclination can calculate the RPM fora projectile at a given twist and velocity. The RB needs little to be fairly stabilized. But sometimes even a 70-72" 54 can take more powder than I like to use to shoot well. But this is almost a barrel by barrel thing.
Forsythe used 137 gr of "Halls #2" powder (which I think, given the European grading system may have been about like FFF) to give about 1600 fps from a short barreled percussion rifle. I did some work using his trajectory tables and a ballistic program and they gave about 1600 fps. He stated his 69 caliber (14 bore) rifle with a hardened 15 gauge ball would pass through an Indian Elephants head from side to side. I would point out that it seems that the smaller the bore the more powder, in relation to ball weight, needed to get to a velocity for flat trajectory giving 120 yard "point blank" for deer sized game. But the larger balls, 62 cal and up,have a little better BC and will give a decent trajectory at 200 fps less velocity than a 50-54 will. These need about 1/2 ball weight of powder while my the .67 with a ball twice the weight of a .530 uses 1/3 ball weight.
Velocity, smooth vs rifled. I do not think that the smooth bore with "less friction" will give higher velocity than a rifled bore with "more friction". Actually a little more friction may make the powder more efficient and give a little better velocity. So I think that Forsythe was a little off here, but many firearms ballistics ideas of the 19th c were. There are so many factors at play is such things that getting a REAL answer to this is very difficult if not impossible.
I was going to do some shooting today by the weather forecast was right. Wind in the 30s, gusting to around 50 mph.
