Thread: Show me your lightweight rifle

Originally Posted by NIMROD

The secret to keeping velocity up in short barrels is to use a powder that burns completely inside the barrel.
If I'd stuck with 2209, half of it would be wasted as muzzle flash outside the barrel.

Thats a bit of an old wives tale really & if anything the opposite is true, the fastest velocity will always be achieved by compressing the slowest burning powder you can fit into a given cartridge. If you can select a slower powder that just barely gets you to your maximum pressure with a very full / compressed load, its always going to have better velocity than a faster burn rate powder that doesnt fill the case entirely. Think of it as the projectile getting a short sharp push with the faster burning powder, vs a push that has the same peak force but lasts longer with the slower burning powder. Even with a very short barrel the principal remains the same as the majority of the combustion process/peak pressure happens in the first couple of inches of barrel.

Your 130gr barnes/2206h combination would still need the best part of 30 inches of barrel to be burning the powder charge in its entirety before the muzzle. Peak combustion pressure has a far bigger impact on how fast the charge will burn, drop the charge weight back a couple of grains and you will then need a much longer barrel to burn all the powder. As you go up in powder charge & pressure increases, so does the speed of combustion.

One of the main reasons 2209 would burn more powder after the muzzle in a short barrel isnt so much that its a slower burning powder (although it does have some effect certainly), but the fact that its more dense & you cant get enough in the case with that same 130gr projectile, so you cant achieve the same pressure & therefore burn speed as you would with 2206h. Without the peak pressure going as high, the powder charge burns much slower as a whole & you get the big flame show.