1 in 15 twist for a 6PPC

JonathanK

JonathanK

New member
At the nationals I watched a shooter keep up with the railguns shooting a bag gun, his barrel was a 1 in 15 twist. I also read in Tony's book that one of the best barrels he ever had was a 1 in 15. This definately peaked my interest but there's not much info on the internet. I was wondering how may people are shooting, or have shot a 1 in 15, what their experience was, and will it stabilize a 68gn bullet?
Thanks,
Jonathan K
 
At 500 a pop, i dont think i would take a chance on a 15 twist barrel, but thats just me. Heck sometimes i wonder if a 68gr BT shoots as good in the winter as the summer time here in the midwest in a 14 twist barrel. Lee
 
If I were disposed to try a 15" twist barrel, I would first find out if there were any "hot" bullets that were being made on .790 and .750 jackets, and what the supply was like.
 
I would first find out if there were any "hot" bullets that were being made on .790 and .750 jackets,
Click to expand...

or any at all. Jef Fowler use to make a 62-grain bullet on a .750 jacket that shot lights-out at 100 yards, but they were a sometimes thing. Don't know if Schieder kept that die or not, or can get jackets.

R.G. Robinett sometimes offers a bullet on the .790 jacket, but lists 1:14 as "ideal" for them. That would be an Sg of 1.5, so they would almost certainly work if you don't like shooting in the snow.

I thought I read on this forum that Bart was making a bullet on the .790 jacket too.

* * *

As soon as somebody mentions "Tony Boyer" a lot of us get quiet. But I do remember reading an interview given by him a while back -- to Dick Wright, I believe -- where he said that [marginally stabilized bullets, as you'd get with] a 15-twist 6PPC and bullets on the .825 jacket, were wind sensitive. Maybe he just needs the challenge?
 
I have a 15 twist lilja barrel. It hates the 68 gr bullets in moderate weather. In hot weather it shoots pretty well. I had intended to use the 60 gr pills i make and even as high as 63 gr on the 750 jackets.
when i get more time {at the range} I think i'll give it a try again with the 60 gr pills.
 
I shot a 3-groove 1:15 in a few matches in 2004. About all it would shoot was a 750 65 grainer that Ed Watson made at the time. The 750/65's did ok at 100 but were really lacking at 200. I still have that barrel. I may make muzzle brakes out of it.
 
I've had a couple 15 twist barrels. If you get a good barrel, you get a good barrel. It is like talking 5R, Ratchet, gain twist, 3,4,6, and 8 groove barrels. I use 66Grn bullets and shot my first teen agg with a 15 twist barrel in 50deg. weather.
Butch
 
The late Skip Otto always used 15 twist Shilen barrels and he was the first to shoot sub-.100 at 200 yards. I am not sure of the jacket length of his bullets, but I believe they were .790. Good shooting....James
 
Down under in the land of Kangaroos, Maddco barrels have produced 15 twist barrels in both 3 and 6 groove for some time now. I had one of the first in 3 groove, as Nev Madden wanted me to do some R&D on it, such as testing out to 300 yards to check stabilisation etc.
That barrel was a pearler, and the first time I shot it was in the LV Nationals. I won the 200 yard agg, and the next day backed it up with a winning .1810 agg at 100 in the HV event. Bullets used were 67gn flat base on .790 jackets. Naturally, I was pretty stoked with the results from that barrel.

OK, that's the good side of the story. I shot the same barrel with the same load a couple of month's later on a cold morning in Portland Vic. It would not shoot worth a damn. I switched to my 1 in 14 twist and shot back in the one's but the agg was in tatters. Since then, a number of Aussie shooters have had a similar experience with the 1 in 15 twist. If the ambient temperature is under about 15 deg C, they are risky to shoot with normal loads. We have seen it too many times to be a coincidence. I guess one could switch back to 62 or 63 grain bullets (I still have some Metzger 62's!), and that might cure the problem.

These days I have switched to Kreiger 1 in 13.5 twist and use 67 BT's on .825 jackets.
 
I had a 6mm 1/15 twist barrel couple years ago. It was ordered as a 1/13.5 twist but somehow came in at 1/15. I did not check the twist. Just had it chambered and started shooting it. It was a teaser. Sometimes it would shoot sometimes it would not, even slight keyhole. I was shooting a variety of bullets, Gentners, Bruno, and a bullet made by a friend. Most were 65-66 grains. The friends bullets were 62's and seemed to shoot the best. I live in Oklahoma, altitude 1126 feet and shoot at Luther and Denton. Nothing over about 1200 feet altitude. The 62 grain bullets measure .800 in length. I would assume made on a .790 jacket. At Raton in 2009 these bullets shot as good as I have ever shot, and this thru the 1/15 twist barrel. Of course I thought it was a 1/13.5. I messed with this barrel for several months trying to get it to shoot. Sometimes it would and sometimes it would shoot 3 inch goups at 100 yards. Finally the light bulb went off. I checked the twist. That was when I found out about the 1/15 twist. Now at Raton which is 6,000 plus altitude that barrel was a hummer, but at lower altitude it was a bummer. I contacted the maker, sent it back and they replaced it free of charge. My gunsmith said I should have kept the barrel and just shot a shorter bullet. Maybe so but it is gone now. Sometimes I think maybe a 14.5 would work good as I don't shoot in real cold weather. Probably never under 45 degrees or so. I did the modified Greenhill formula on that short bullet at 3320 fps which is about where I shot it and if I remember it stated I needed a 14.9 twist. So I guess that is why it sometimes shot and sometimes not. I don't think it hurts accuracy to be a bit overstabilized but I know for sure it does if you are understabilized. That was my only experience with a 1/15 for a 6ppc.

Donald
 
Donald said:
I had a 6mm 1/15 twist barrel couple years ago. It was ordered as a 1/13.5 twist but somehow came in at 1/15. I did not check the twist. Just had it chambered and started shooting it. It was a teaser. Sometimes it would shoot sometimes it would not, even slight keyhole. I was shooting a variety of bullets, Gentners, Bruno, and a bullet made by a friend. Most were 65-66 grains. The friends bullets were 62's and seemed to shoot the best. I live in Oklahoma, altitude 1126 feet and shoot at Luther and Denton. Nothing over about 1200 feet altitude. The 62 grain bullets measure .800 in length. I would assume made on a .790 jacket. At Raton in 2009 these bullets shot as good as I have ever shot, and this thru the 1/15 twist barrel. Of course I thought it was a 1/13.5. I messed with this barrel for several months trying to get it to shoot. Sometimes it would and sometimes it would shoot 3 inch goups at 100 yards. Finally the light bulb went off. I checked the twist. That was when I found out about the 1/15 twist. Now at Raton which is 6,000 plus altitude that barrel was a hummer, but at lower altitude it was a bummer. I contacted the maker, sent it back and they replaced it free of charge. My gunsmith said I should have kept the barrel and just shot a shorter bullet. Maybe so but it is gone now. Sometimes I think maybe a 14.5 would work good as I don't shoot in real cold weather. Probably never under 45 degrees or so. I did the modified Greenhill formula on that short bullet at 3320 fps which is about where I shot it and if I remember it stated I needed a 14.9 twist. So I guess that is why it sometimes shot and sometimes not. I don't think it hurts accuracy to be a bit overstabilized but I know for sure it does if you are understabilized. That was my only experience with a 1/15 for a 6ppc.

Donald
Click to expand...

Wow thanks for the info Donald!!
 
These calculations are from JBM's Drag/Twist section. Keep in mind the theoretical 'perfect' stability number is 1.5. Stability numbers down into the 1.3's will still hold together, but when you get below this things can get herky pretty fast.

Many of the 'tune' issues are the result of an extremely low stability number, coupled with a bullet that doesn't have enough 'straight' length on the shank.

A little time on the JBM calculator can be pretty enlightening......
------------------------------------------------------------------------------
Caliber: 0.243 in Bullet Weight: 68.0 gr
Bullet Length: 0.825 in
Muzzle Velocity: 3400.0 ft/s Barrel Twist: 14.0 in
Temperature: 80.0 °F Pressure: 29.92 in Hg
Stability: 1.118

------------------------------------------------------------------------------------

Caliber: 0.243 in Bullet Weight: 68.0 gr
Bullet Length: 0.825 in
Muzzle Velocity: 3400.0 ft/s Barrel Twist: 13.0 in
Temperature: 80.0 °F Pressure: 29.92 in Hg
Stability: 1.297

-----------------------------------------------------------------------------------
Caliber: 0.243 in Bullet Weight: 65.0 gr
Bullet Length: 0.790 in
Muzzle Velocity: 3400.0 ft/s Barrel Twist: 14.0 in
Temperature: 80.0 °F Pressure: 29.92 in Hg
Stability: 1.208

------------------------------------------------------------------------------------
Caliber: 0.243 in Bullet Weight: 65.0 gr
Bullet Length: 0.790 in
Muzzle Velocity: 3400.0 ft/s Barrel Twist: 13.0 in
Temperature: 80.0 °F Pressure: 29.92 in Hg
Stability: 1.401
 
Hall of Fame member, the late Jef Fowler was famous for his 66 gr. FB bullets made on an .825 jacket, BUT he personally shot the 63 grain .750 bullets. He told me this at his last Super Shoot. Good shooting....James
 
Al,
Interesting..but you might consider using the actual lengths of bullets made on the various jacket lengths, since they end up quite a bit longer. Another thing... I think that the whole thing about 13.5 twist barrels being so good is probably because BTs on .825 jackest may be a little too near the edge, under some conditions, when paired with a true 14" twist. A .390 jacket bullet with a 14 twist would, I think, have similar advantage to a .825 with a 13.5. Perhaps then, the 15 would be best with a .750, over a broad range of conditions. Over the years, Del Bishop has made a lot of high quality bullets on shorter jackets, both .790 and .750.
 
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