Best twist rate

[leopard6.5]

hellcat: What manufacturer's barrel did you get?

Were you shooting factory loads?

What is the profile?

What is the length?

Is this a new barrel or is it used?

This should help give Bill and others some idea of what is going on with your barrel and what suggestions to give you.

Good luck and good shooting.

Lee

[hellcat370]

I'm not exactly sure who made the barrell, i just had a gun dealer order one for me. All the ammo was factory loads I got from AA. Its a 18 inch heavy barrel.

[leopard6.5]

hellcat: You probably should ask the gun dealer who made the barrel, especially for your own personal knowledge.

This way if you get it shooting really well you will know whose barrel to ask for next time or if it never shoots well, you will know who to stay away from.

Either way, if you received a rack grade barrel and expect it to shoot like an AA top line barrel or a Satern barrel, etc., it probably never will.

Please let us know what you find out so we can help you further.

Lee

[txgunner00]

I would look at the barrel quality before the twist rate for the cause.

[Schwag173]

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

I was ... but decided to go with standard rifling and I opted for the 1-in-8" twist for the 18" length. If I understand Bill's posts above, I think 8" is about right for my mid-length barrel.

BTW: The barrel is due at my door on 27 March, lower is built and all the upper parts are in a box. Waiting is tough ...

[Zach987]

I'm just wondering why Bill A said to go from 1-in-9 down to a 1-in 7.5 for the shorter barrel. I can see this for the 14.5" barrel, but from a 20 to 18 inch pipe I'm curious why he recommends going to the faster twist for not that much difference in barrel length.

[leopard6.5]

Zach: I can't find where Bill A. said this in going through his posts.

I did find him saying this: " 1 in 7.5, 7 will run at 10" but 9 is for 20" and up"

Where did you see him say to use the 1-in-7.5 for the 20"-18" barrels?

When he said to use 1-in-7.5 he was saying this in reference to a 14" barrel and then 1-in-7 for a 10" barrel.

Thanks for the clarification.

Lee

[Zach987]

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.

I have a 18" barrel ordered with 9 twist and I saw this and was just curious.

[leopard6.5]

Thanks Zach for finding that.

I wonder, and only he could say, if Bill A. typed the wrong number as I have an 18" AA barrel on an upper and it is 1-in-8.75 twist.
I used to have a 16" AA barrel and it was 1-in-8.00 twist.
Even on AA's website, they don't get lower than 1-in-8 twist until you get into the 14" barrels.

Hopefully at some point as he gets a chance, Bill A. will clarify this.

Thanks again for the additional info.

Lee