Considering doing a gain twist rifle.

[Minesweeper3433]

I am considering doing a 6.5 swede mauser and maybe even an AI version depending on die availability. I would like to shoot the 155BIB bullets I have out of it but don't want the rifle to tear up real quick. My question is would going with a gain twist to start the bullets off slower be better for the purpose of not tearing up the bullet? I was thinking maybe an 8.5 speed up to 7.75? But then again I have not actually started my research into this just yet so need to read up a bit more on gain twist rifles. Any info links or suggestions on this will be appreciated. The barrel would be bartlein 30 inch heavy palma fluted and action will be 700LA currently set up as a 300winmag build by Mike Bryant. I still have the original 30-06 bolt I would use and have lapua 6.5 swede brass on hand which is why I chose this cartridge.

 

[mikecr]

Is there a 26cal 155gr BIB bullet?

 

[Minesweeper3433]

Yes. My 96 swede shoots them to the original irons that were set up for the old 160 class bullets. Only reason I use them in that rifle but I thought it would be fun to take full advantage of what they have to offer.

 

[Win94ae]

My question is would going with a gain twist to start the bullets off slower be better for the purpose of not tearing up the bullet?

A gain twist will tear-up the bullet.

A bullet traveling down a bore with a constant twist, will have rifling marks which match the twist rate.
Here is a pic of a bullet shot from my 30-06.

If the twist rate changes, the lands will scrape the bullet's jacket with the new ratio, in essence causing additional deformity to the bullet jacket.

 

[Rockfish Dave]

I have both a 5R and 5R gain twist. Honestly I don't see any difference, but I have to admit: The Bartlien barrels perform better than I do. If there is any benefit to be had I think you would have to be an execptional marksman to be able to recieve any benefit from the gain twist.

When the "normal" barrel shoots 1/2 MOA (or better), it get's really hard to tell if there is any difference when shooter error is greater than what the barrels are capable of.

 

[Minesweeper3433]

I was thinking with this to do a 9-7.5 twist change but after emailing them about their gain twist barrels the only advantage I might be able to justify is slowing the presure curve which I don't plan on running this cartridge at max all the time. Unless of course that is the best shooting load. I havn't played with this on QuickLoad in a few nights so I might play some more with it tonight. Something I could use is if someone has measured case volume on their 6.5x55AI or has any velocity data. Basically anything I could use to help tweak the numbers in QL.