Blowback 300 project.

[cav_scout_tj]

Originally Posted by redtazdog

357 sig and 400 corbon pistols have barrels that cam back and cause a delay
to reduce the pressure before the slide comes back.
If the barrel came straight back without delay the hi pressures would
make a straight wall case out of a 357 sig or a 400 corbon.
.
Figure out how to delay the bolt from coming back until the hi pressure is dropped and a bottle neck
will work in a AR.

When forming 300W brass from .223 brass, the shoulder needs to be fireformed, and blown out a little. Shooting subsonics does not generate enough pressure to do this, have to use more powder. As such there is no way there is enough pressure straighten out the bottle neck shooting subsonics. Supersonics is another matter....

If you found a way to delay the bolt, then this would not be a blow-back project anymore. It would be direct impingment, or delayed roller lock or short stroke piston or whichever...

[redtazdog]

I know how to fireform brass as I have been for over 20 years,
around 15 years just with the 300 whisper.
I made a 357 sig in a blowback AR a couple years ago just to use sub
ammo and found that the brass would blow out to easy when i used a can so I removed the barrel and made it a 40sw.
If the 300 whisper works as a blowback then great!
but I'm thinking there may be problems so I'm waiting for this build to
get done and tested.