Best twist rate

[hellcat370]

Looking at having a barrel custom made and was wondering whats the best twist rate for the Grendel. I shoot pretty much everything under 130gr.'s, but i'd like to get get good accuracy from heavier bullets as well. Any suggestions?

[Nimrod]

I would recommend 1 in 8", and I recommend you talk to Les Base.

[Bill Alexander]

The barrel length is the first question. Long tubes do well with a 9 twist while 18" and under should be tightened up to account for the lower velocities.

[VASCAR2]

The barrel length is the first question. Long tubes do well with a 9 twsit while 18" and under should be tightened up to account for the lower velocities.

Is there a threshold on a 16" barrel which generally indicates which weight and length bullet might not be stabilized with field grade accuracy. I have a 1 in 9 twist 16" barrel and it shoots factory Hornady 123 A-Max to my satisfaction. I was curious if the slower twist was any different in effect with shorter lighter bullets compared to the longer heavier bullets. I've been satisfied with my handloads using 100/120 grain Nosler BT, 85/100 grain Sierra HP, 120 Sierra Pro hunter and 95 grain V-Max. My rifle does not seem to like Black Hills loaded 123 SMK factor compared to the Hornady 123 A-Max. I bought my 6.5 Grendel for varmint and Hog hunting and assumed the barrel twist would work in a similar manner as with the 5.56 barrels, (77 & 80 grain need 1 in 7 or 8 twist, 69 grain and lighter 1 in 9 twist).

[texasgrunt]

The barrel length is the first question. Long tubes do well with a 9 twsit while 18" and under should be tightened up to account for the lower velocities.

I know this is resurrecting an old thread, but according to Brian Litz data the 8 twist stabilizes all the 264 rounds better (specifically the 108gr scenar where it is an increase in SG from 1.19 to 1.50). I am NOT a ballistics expert and I am asking if there is a good reason to go with a 9 twist which is widely offered. The Litz data does not factor in barrel length that I can tell and I am looking at a 22" pipe.

Thanks all...

Grunt

[Whelenon]

Found this on the web, can't say if it's accurate or not, just FYI.

http://www.varminthunters.com/tech/barreltwist.html

[texasgrunt]

Found this on the web, can't say if it's accurate or not, just FYI.
http://www.varminthunters.com/tech/barreltwist.html

Thanks. That follows the information I have seen elswhere and prior to reading Litz's book. His chapter on stability indicates a best practice of maintaining a SG (stability factor) of over 1.4 and that you can't really have too much spin until it gets extreme and then you have to worry about the slight imperfections in the bullet causing instability. Not that Litz is the guruist of the gurus, but I think he's pretty well respected in the long range game.

Shilen's pretty reputable as well, and probably I am worrying over nothing as the 22" barrel on my current stick is 1 in 9 and it shoots pretty damn tight. But if I can get even more accuracy due to increased stability provided by a tighter twist I want to take advantage. What's the consensus?

Grunt

[stokesrj]

I would go with 1:8, I have several, exactly how many is on a need to know basis, my wife surely doesn't need to know, and they will shoot everything from 81.5 grain Cauterucio bench rest bullets to 140 Berger VLD's superbly. I only have one barrel that isn't 1:8 and it is built specifically for short range and light bullets.
Bob

[blackfoot]

I don't understand the 9 twist either. Why would 50-100 fps make that much difference that you would want to go to a slower twist when the 8 doesn't over stabilize? For punching little holes short range BR guys are on the ragged edge of stability, the the long range BR guys want to spin em fast. Why wouldn't the Grendel lean more toward the long range theory? Very interesting questons that I'm sure Bill knows more about than I could hope to learn all year. Curious about the reasonings if you're willing to share. Is it more about terminal ballistics?

[Bill Alexander]

When we were first working on the Grendel we followed what everyone said about 6.5 calibers and made the barrels with 8 twist rifling. Some barrels would shoot but more often than not the groups were open and the guns were tempremental. One of the very early test rigs had run a 9 twist and it actually shot well despite a less than optimum chamber so out of frustration we ignored conventional wisdom and build some 9 twist units at 24" and 20" barrel lengths. The change in accuracy for the group as a whole was unquestionable. Subsequent production of 9 twist barrels has proven that this is optimum for the caliber.

One of the contributors to the 9 twist is actually the Grendel itself. Pressure limits the ability to slug the bullet to the grooves and the case capacity holds the round to lighter bullets. The 168 grain roundnose nickel steel projectiles are simply not a consideration any more than the 142 and 155 grain SMKs

We have tested barrels as short as 14.5" in 9 twist (not recommended use 1:7.5 this short) with projectiles up to 152 grains and both accuracy and stability are maintained. Equally we have run 9 twist barrels out to 1600 yards (12" group) and the round remains stable and it would appear accurate through the transition velocity. Longer 8 twist barrels often demand velocity reduction for best accuracy

It is our conclusion that the 9 twist offers the best solution for the Grendel for barrels of 20" and longer while the 18" and shorter barrels thrive on 7.5 twist.

[texasgrunt]

And that's what I love (well one of the main things, anyway) about the Grendel round. We have access to the developer and he is happy to share his experiences. I was ready to order the 8 twist based on good information about the .264 bullet, but now I have info on the specific round and how it works with the whole rifle system.

Thanks Bill.

Grunt

[Bill Alexander]

Hold up!

There was a mention of polygonal rifling. This is not territory we have experience in and so the wisdom to date may not apply.

[texasgrunt]

I'm not going polygonal, but thanks for the disclaimer!

[BjornF16]

Schwag173 is considering polygonal...his thread is on "custom builds" (6.5 CSS barrel, .295 or .300?)

[hellcat370]

Thanks for all the info Bill. I was able to get my hands on a 1/9 barrel, but the accuracy isn't great. I tested 4 different loadings, 123gr Lapua, 123gr sp Wolf, 120gr MTP Wolf, and the 90gr TNT Speer. I shot from 25 yds out to 280 with all rounds. Most held around 2.5-3 inch groups at 100yds. The 90gr TNT's did a lil better, and held 3 inches at 280yds. This was on par with the 14.5 1/8 AA Tactical I had a couple years ago, but it did better with the other ammo, save the 123 wolf because I hadn't shot any of that until recently. I also noticed that AA is now offering uppers using the 1/9 twist. Any ideas why this barrel isn't gettin decent accuracy?