AmericanLongRifles Forums
General discussion => Black Powder Shooting => Topic started by: Gene Carrell on October 27, 2013, 03:29:20 PM
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This may have been beaten to death and if so, I apologize. I have a 62cal gain twist barrel that I am not satisfied that I have found its potential. Is there a 'rule' or other that gain twist bbls. shoot best loaded light or hot as compared to others in their caliber. My reasoning (often off track) is that accuracy in a gain twist bbl. should be found with a charge on the lighter side as stabilization could be established with a lower muzzle velocity. Am I off base or overthinking this? Any experience to share out there? Thanks,
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The very existence of gain twist rifling demonstrates that the old timers were trying to get higher velocity, and longer range, out of muzzleloading guns. That high velocity is not obtainable with light, or moderate, charges. The gain twist was developed, so heavy charges, could be used without stripping the rifling. I think that a sixty two caliber with a gain twist is going to be pretty abusive with charges in the range that will produce the best accuracy, unless its a heavy bench gun. Of all the antique gain twist guns I've examined, I don't recall any of them over fifty caliber. This is probably due to the recoil, from a heavily loaded gun of larger caliber.
Hungry Horse
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My only experience with gain twist barrels is with one I've owned and fired for nearly 50 years. It's a .45 and extremely accurate. The usual load is 60 or 65 grains of 3F but it has done equally well with 70 to 75 grains. I'd have to say they do shine with heavy loads and there must be something to the accuracy claim as well.
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I have recently been shooting a Jim McLemore .50 gain twist barrel in a flintlock I built a while back. (just recently got back to shooting -kids, job, but now retirement !) As I recall, it starts at about a turn in 60" and ends at a turn in 48" or thereabouts. Barrel is 44" long. I am using a .490 ball will the .020 ox yoke prelubed patch and 75 gr. of 2F. Shoots like a house afire at 50 yds off the bench. Will put shots in 1 ragged hole at 50 yds single rest if I do my part. I dont know what your twist is or the gain factor, but I suspect that you will find your best accuracy will come with a load that is somewhat less than maximum. Just my $0.02.
Mike
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I will qualify my previous post after a little thought. If your twist starts out slow, and the gain factor is not too radical, you might find your best accuracy at a point closer to your max load. ( probably closer to $.03 than $.02)
Mike
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Gene, sorry I can't offer any insight on this. Have you tried to contact Bobby Hoyt?
Seams to me the theory of heavier than normal charges makes sense.
I recall my test target was with 65-75grs 2f, and it was very comfortable to shoot. But I wasn't trying to get the tightest group, just making sure everything functioned properly.
Please let me know what you find out.
Thanks!
Tom
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You should be able to get an accurate load with roughly the same charge as you would use with whatever the final twist rate is. The gain twist should also allow heavier charges to be shot accurately (i.e. without ripping the patch), with the additional benefit of a flatter trajectory and lower flight time (which may make it seem relatively more accurate). I suspect a gain twist barrel is just like any other, and you will see some sort of accuracy curve as you change charges. Presumably the difference with the gain twist will be that the "peak accuracy" is over a wider and higher range of charges than a straight twist barrel of the same final twist rate.
Load development with a .62 sounds like fun :)!
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The theory or practice of a gain twist, is that the ball is being increasingly constrained as it leaves the muzzle- by the increased rate of twist.
Harry Pope wrote about this back at the turn of the 19th century.
Today, some smokeless powder Bench Rest shooters have their bores 'scoped'/'measured'/'gauged' and a cross section drawing made of them - PRIOR to them cutting the barrel blank to get their 'screamer' grouping 20 to 24" barrel from the 30" blank.
The scoping/gauging/measuring with today's sophisticated instruments can show that as a barrel is rifled, the rifling slows down and speeds up through-out the barrel - minutely, but it does this very thing. The barrel is then cut off so the last thing the bullet will be doing is speeding up, ie: more tension on the bullet from the rifling inside the barrel. The practice of doing this has produced, in the last 10 years, more rifle barrels that produce screamer groups (sub .1" at 100 yards or sub .2" at 200yards) than ever before.
So - what this actually shows, if not proof of Pope's and others 'gain twist' "theories" is that TREND of increased accuracy from increased tension is "somewhat' repeatable. This increased tension on the ball or bullet could also be attributed to choked or taper bores as well. Diufferentt methods to obtain similar results.
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The rifle is 8 1/2# and relatively straight-stocked with a big wide butt, so it is not terribly punishing. I am loading .610rb with mink oiled 0.022 patching. Using 75gr 3Fg powder I am getting 1.5" groups at 50 yds. off a bench. I just think I can do better. I reviewed my last shooting data and found the group to be closing as the charge increased to 75gr. Hope to get back to the range next week. The rifle is going to Alberta next May for black bear(s).
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Gene - you might find your rifle shoots as well or better, only with about 90 to 100gr. of 2F - or even more. Seems to me, in Taylor's .62, he's up to about 130gr. 2F now for the most accurate load in his Hawken, using similar sized balls and patch.