From another thread:
Originally Posted by Truc
it has been proven that with only the primer ignited and before the powder lights the bullet is already moving, that is why the small primer is used in Benchrest (205 Federal shoots better because it don't move the bullet) very little flame.
I've not heard of this until now. But in my experiences with .308 Win. amm0 with primers igniting and no powder in the case, the bullets didn't move at all. Here's the details and facts:
Issued 7.62 NATO ammo, M118 LC66 Match case and primer, 172-gr. FMJBT bullet and IMR4895 powder removed, reloaded with 44 grains of IMR4320 under a Sierra 190 HPMK. The black sealer was not cleaned out; it held the bullets in place with about a 5 to 7 pound release force as measured. (Bullet release force specs for M118 ammo's greater than 40 pounds and is usually about 50.) Rifle was a converted M1 with SA-1965 arsenal 1:12 twist 7.62 NATO barrel.
Had to load 44 rounds to get 22 to fire. All those that were "clickers" and didn't fire had no powder. Overall cartridge length of the clickers was the same as loaded unfired rounds. Pulled bullets from the clickers showed black primer residue on the bullet base as well as the inside of the case. No bullet from the clickers seemed to move forward in the case neck at all.
Others have fired issued ammo handloaded by US military team support folks that also had no powder. Nary a bullet left the case. I've had Eley Tenex rim fire ammo without powder shoot the bullet about 20 inches down the barrel. And 9mm Luger rounds with no powder push the bullet about 1/4 inch into the rifling. Others have reported similar incidents with rimfire and handgun ammo; .38 Special wadcutter target loads without powder locking up the cylinder of a S&W K38 Masterpiece with the bullet halfway into the barrel's forcing cone.
I'll let others chat about the small rifle primer stuff. I used them in Rem. .308 Win. cases and they worked well with 155 and 180-gr. bullets. Others have used the same case with Rem. 7.5 primers with 48 grains of IMR4350 powder under a Sierra 200 gr. HPMK and set records at 600 yards. Check the pictures in the following link's documents and compare large rifle primer flash to small rifle primer flash to see the differences.
An interesting paper on primers' pressure and other stuff is in: