30BR barrel length for hunting

[opodden]

I'm thinking about building an AR15 in 30BR for hunting up to elk size animals. According to local legislation minimum bullet weight is 140 grains and 275 Joules energy at 100 meters, which means a muzzle velocity of about 2725 fps. If bullet weight is 155 grains or above, the energy requirement is 225 J, which means a muzzle velocity of about 2330 fps.
I would like to keep barrel length as short as possible, and would like advice on this subject. I'm also interested in advice on rifle twist suitable for these loads. I know that bench rest shooters have good results with 21-23" barrels with 1:17 or 1:18 twist. But that is with light bullets in the 115-125 grain range, so I will probably need something like 1:12 or 1:13?

 

[JCummings]

Why in the world would you want an AR based rifle in 30BR for hunting?! The 30BR is a great short range accuracy cartridge normally shot from single shot bolt action rifles. It is not designed to feed well from magazines,although it may work OK). You have to neck up brass and usually neck turn. Why wouldn't you just use a cartridge that is readily available and ready to use as is such as 308, 260REM, 243, 6.5 Creedmore? These can be had ready to shoot from DPMS. No fuss, no muss.

 

[JCummings]

Having said that If you are determined to go with a 30BR I believe the most important thing is barrel twist no length. Any length of 20 inches or more would be fine. Because you need a bullet of at least 140 grains I think you would want at least a 1:14 twist.