Considering building the latest boutique 6mm caliber. Need advice for twist rate for Bartlein 5r barrel @ 26” finished length. Thanks.
What is best twist rate for 6mm GT?
- Thread starter IndianaRem5r
- Start date
what bullet and what speed
7.5, 7.7, 8. they'll should all work just fine
Twist Rate Stability Calculator
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bergerbullets.com
7.5, 7.7, 8. they'll should all work just fine
Most barrels I see reported are 7.5 twist but lots of 7.0 and 7.7 as well. Not sure you can go wrong. Most important thing you should absolutely make sure is that the minor diameter of the bore is 0.237” and NOT 0.2365” or 0.236” or you could see early pressure signs.
here is a decent comparison and a good read http://bulletin.accurateshooter.com...ew-6gt-cartridge-tested-in-3-tactical-rifles/
here is a decent comparison and a good read http://bulletin.accurateshooter.com...ew-6gt-cartridge-tested-in-3-tactical-rifles/
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As well as the tighter bore can increase bullet failure as well. No reason for a tight bore with good quality match bullets.
Groove size effects pressures more than the bore does (the bore is the tops of the lands) but anytime you start changing the total surface area of the bore you you start effecting pressures.
Later, Frank
Bartlein Barrels
I"m considering a 6mm GT build. I want to shoot 105s, so 7.5 shoudl be good. But gunsmith said go 1:7 cause you'll want to shoot 115s eventually. Thoughts?
Shouldn’t the appropriate twist be 6.9 for gay tiger?
Not a guarantee either way. Worst case is that you just cannot push bullets to the higher speeds of 2900-3000 and you may need to settle on ~2850. I have early pressure signs in the form of ejector rings all over my brass and I’m running 108elds and 109s at 2880. No sticky or heavy bolt lift and the primers still look sexy. I don’t know exactly what is causing it. Could be soft brass, small neck diameter in the chamber or smaller bore. Doesn't seem to be a big issue since this barrel has 1200 rounds on it and 50 pieces of the Hornady brass now have 10 firings on them and are still good to go. I would stay optimistic if I were you.
