Do I want a 7.5" or 10+" barrel SBR?

[CJ]

I would not do a SBR with a 5.56x45. That cartridge really needs a 24" barrel and anything shorter really puts a dampener on the performance.

It was designed for a 20" barrel, and the difference between a 16" barrel and a 24" barrel is about 200fps, which is 17%, negligible. It takes a substanial hit below 14.5" but to say it's only good in 24" is pretty ridiculous. I have a 24" .223 and the only reason is to squeeze every last drop of velocity out of it.

A 6.5mm Grendel, 7.62X39 or 6.8mm SPC would be a much better choice for a SBR. I'd like one with a 12" barrel as that length doesn't totally kill performance.

Better than .223 for sure. .300 is better than all of these in an SBR, and cheaper. In SBR the above calibers specifically lose advantage to .300, in longer barrels they have better range for sure. But .300 is a caliber designed for SBR's. My 9.5" .300 SBR was chronoing 1950fps on a 147gr projectile. Compare that to my friends 6.8" with an 11.5" barrel and he's getting 2300fps with a 110gr. My .300 is delivering the same energy and it's 2 full inches shorter. That's excellent.

[svauto-erotic855]

It was designed for a 20" barrel, and the difference between a 16" barrel and a 24" barrel is about 200fps, which is 17%, negligible. It takes a substanial hit below 14.5" but to say it's only good in 24" is pretty ridiculous. I have a 24" .223 and the only reason is to squeeze every last drop of velocity out of it.

I said 24" because that is what I came up with when doing the paper powder burn test and it has nothing to do with any velocity readings that I have measured.

I have PLENTY of 5.56x45 rifles but I am not a big fan of that cartridge.

The cartridges that I mentioned were because they can normally be bought at big box stores, albeit Cabelas now stocks .300blk.