Shooting 40 grainers in a fast twist 20 cal barrel

[Tommie]

For those shooting a 20 caliber with 1-9” or tighter twist:
What kind of performance are you getting with traditional weight bullets? My new build will be mostly for the heavy Bergers but I’d like to have the option of shooting 39 or 40 grainers. I have no prior experience with tight twist 20’s and am wondering if lighter bullets can withstand he high RPM’s. The chambering will be a 20 Wasp and I expect velocities a little below 20 BR levels.

 

[Wirelessguy2005]

39's and 40's work fine out of a 9 twist barrel as long as you don't get carried away with the velocity. I have a 20-223ai that is chambered on a 9 twist Pacnor 3 Groove barrel. The 39 sierra blitzking works good out of this barrel but i don't push them over 3,700 fps.

 

[Tommie]

39's and 40's work fine out of a 9 twist barrel as long as you don't get carried away with the velocity. I have a 20-223ai that is chambered on a 9 twist Pacnor 3 Groove barrel. The 39 sierra blitzking works good out of this barrel but i don't push them over 3,700 fps.

Have you run 55 grain bullets through your rifle? I’m having a tough time deciding on rate of twist.

 

[Wirelessguy2005]

Yep the 9 twist works perfectly fine for 55 bergers as well as some custom 48 grain rebated boat tail bullets I was testing. I have used a 9 twist on a number of builds and they always worked fine with the heavy 20 caliber bullets such as the 55.

Have you run 55 grain bullets through your rifle? I’m having a tough time deciding on rate of twist.

 

[Tommie]

Any indication of yaw at longer yardages?

 

[B23]

Just had a 20-250 built using a Krieger 1-8tw to specifically shoot the 55's. First group out of the gun shot a .154 so I'll be sticking with a 1-8tw for the 55's.

 

[Wirelessguy2005]

I wasn't shooting mine at extended ranges but I have friends that have shot their 9 twist with the 55 berger in excess of 500 yards with great accuracy.
For what it's worth there are plenty of guys running an 8 or even an 8.5 twist barrel with the 55 berger and a hotrod 20 caliber cartridge such as the 20-250 or 20-250ai. What most of them find out is that as soon as they get some rounds down the barrel and start to push the velocity up near 3,800- 3,900 fps the bullets start to come apart due to excessive rpm.

Any indication of yaw at longer yardages?

 

[jcm24m]

I shoot a 20 PPC with a 8.5 twist PAC-NOR barrel. I had to slow the 39 & 40 gr bullets down to 3550 FPS or they would BLOW UP in flight. At this reduced speed, the lighter bullets are very accurate This rifle was made for the 50gr BERGER bullet which I have a lot of them on the shelf. If you want more info, just send me a PM.

 

[Wirelessguy2005]

Interesting that you mention the 50 berger, I built a 20BR ai with an 11 twist barrel a few years back and it shot the 50 bergers into one ragged hole. Funny thing is Berger will tell you that an 8 or 9 twist barrel is required to shoot the 50 berger.

 

[jcm24m]

A 50gr BERGER with my 8.5 twist PAC-NOR with do the same ragged one hole as yours . This is my LONG range P-DOG rifle from 400-600 yards.

 

[ab_bentley]

I shoot a 20 PPC with a 8.5 twist PAC-NOR barrel. I had to slow the 39 & 40 gr bullets down to 3550 FPS or they would BLOW UP in flight. At this reduced speed, the lighter bullets are very accurate This rifle was made for the 50gr BERGER bullet which I have a lot of them on the shelf. If you want more info, just send me a PM.

Who made the light weight bullets? I've run 40s and 32s vmax through an 8t beyond 4k.

 

[jcm24m]

I used 39gr BLITZKING & 40gr VMAX at 3950 fps which I calculated out to over 334588 RPM which is way over the MAX RPM of 300000 RPM'S. When you see a puff of smoke at the 50 yards, you know you are tearing the bullet apart. Also when your bullets are hitting 6 feet to the left or right of your p-dog at 250 yards, I knew my 20 PPC bullets were coming apart and not stable. I just slowed them down to over 3500 fps and no problems after that. Most factory loaded rounds are spinning at the 230000 - 250000 rpm range.

 

[Wirelessguy2005]

Adam,
Are you saying that you are running bullets in excess of 360,000 rpm and they are holding together? If so to what range?

Who made the light weight bullets? I've run 40s and 32s vmax through an 8t beyond 4k.

 

[ab_bentley]

Adam,
Are you saying that you are running bullets in excess of 360,000 rpm and they are holding together? If so to what range?

That's exactly what I'm saying. 600yds is the practical limit. After that the centrifugal force overtakes the velocity and bullets careening off in the blue.

The barrel is a three groove x-caliber

 

[xswanted]

Yep the 9 twist works perfectly fine for 55 bergers as well as some custom 48 grain rebated boat tail bullets I was testing. I have used a 9 twist on a number of builds and they always worked fine with the heavy 20 caliber bullets such as the 55.

What elevation and temperature are you shooting at?

 

[Wirelessguy2005]

elevation is 813 and in a variety of Temps from 50 degrees up to 85.

What elevation and temperature are you shooting at?

 

[MrMajestic]

But when you play with that "ragged edge" terminal ballistics are amazing.

 

[germanlongbow]

I shoot a 20-250 with PacNor 1x9 twist 28 inch barrel. H4350 powder over 55 gr Berges at 3850 fps. Crazy accurate.

 

[steve123]

I shoot a 20-250 with PacNor 1x9 twist 28 inch barrel. H4350 powder over 55 gr Berges at 3850 fps. Crazy accurate.

It's funny all our varied experiences with the faster twist 20's!

I had a 20x47l barrel done in a 9 twist Krieger. At around 300 of the 55 Berger bullets down the barrel they started coming apart/3830fps. Slowing them down didn't help.

Tried 40 vmax, the node being at 4100 fps, they worked - go figure??? I never shot them past 400Y though and haven't used that barrel much since.

I highly suggest sending the 55's slower than the bigger cartridges are capable of sending them and in hind sight wish I had done a 22x47L instead.

 

[B23]

It's funny all our varied experiences with the faster twist 20's!

I highly suggest sending the 55's slower than the bigger cartridges are capable of sending them and in hind sight wish I had done a 22x47L instead.

That's pretty much what I'm doing with my 20-250 and the 55's. I'm not running them very hard, only using 36gr RL16 and with the Berger 55's that gives me right at 3660 with single digit ES and stacks them up into tiny little groups. I don't expect barrel life to be particularly long which is why I went ahead and got an extra Krieger 1-8tw 20 cal barrel so I'll have another ready to go when this one goes south.

What are you guys seeing for barrel life out of the 20x47's or 20-250's? I was thinking 600-ish maybe a little more but probably not much.