Brand new to the forum, first post. I'm currently working on 2 builds, one for myself and another for a very good friend. My buddy chose for me to build him a Pistol. My indecision comes in what caliber to go with being he wants a 7.5" barrel. He also doesn't want a suppressor.  I've been told and read very few things on 5.56 being extremely loud with such a short barrel. I've been thinking of going 300BLK. Can anyone tell me if that would be my better option? Again I've heard for optimal use 300 BLK should be maybe built within the realm of a 10.5" barrel with a 4" suppressor mounted.. I guess I've rambled on without saying much... Better option? 7.5" 300 BLK unsurpressed or 7.5" 5.56?

I would do a blackout, easier to make it work at 7.5 than a 223/5.56.

Depends on what he's wanting to do with it. If it's just for the range and targets, build him a 5.56 AR-15. I would make the barrel a little longer for the AR-15 though. Ammo for the 300 BLK is still kinda expensive but if that's not a concern with him, go with it.

Yes, a 7.5" pistol is louder compared to a 16" rifle. Unless you're shooting suppressed, the louder bang, won't be a problem for you or anyone around you.

If he ever gets to shoot a suppressed gun he may change his mind, or not




yes very loud.  but at dusk or later without a muzzle device it creates a great fireball, especially with wolf .223




That depends what you are going to be shooting for.  and what the end use is going to be.  I happen to love 300blk and it fulfills everything I need it to except long range precision.  and I don't really do long range precision so it does what i need.  from plinking, HD, and hunting.



not sure where you heard that or who it was that said it, or what their knowledge was, but I happen to love my 8.5 inch barrel suppressed for all kinds of use.  optimal is subjective again for what the end use will be.  a 4 inch suppressor will do ok with subs and help tame supers, but a better suppressor will do wonders for subsonic.  My next 300blk AR barrel will be 7.5 or shorter




since unsuppressed seems to be the thing he wants.  then simply for ammo cost 5.56. unless he reloads, oh and a good set of ear plugs and ear muffs.   But again it would depend on his desired use

Yea my initial opinion was going 5.56 regardless of it making more noise than usual. The ammo is more affordable, available and from the little I've read it seems more things can go wrong with such a short barrel unsurpressed for 300blk. But again that's just what I've read I have no experience personally just yet with that caliber.

in my opinion a short barrel unsuppressed 300 blk runs just fine as long as it is built with the correct components.  I can run subs and supers unsupressed with no issues out of a 8.5 as well as a 16 inch 300blk with carbine gas.

So what would be the "key factor" components?

for a short barrel

pistol gas length
correct size gas port (would have to research based on length)
correct buffer either standard or perhaps an H2 but I don't use an H2 I use standard.  and not anything heavier
carbine recoil spring
Standard ar15 bolt carrier although a M16 bolt carrier may work.  I use standard AR15 carriers

Sorry for the maybe dumb question... What's a carbine recoil spring?

For anything other than a range toy, a 7-8" 300BLK is much more effective than a 7-8" 5.56.

For a good working 7-8" 300BLK build, you need:

Pistol gas port in the .110-.125 range
1:7 twist rate to stabilize heavier subsonic rounds
Standard weight carbine buffer and action spring (H2 or H3 buffers will cause cycling problems with subsonics)

An adjustable gas block is highly desirable. The energy difference between full-power supersonic rounds and subsonic rounds is almost 3x (~1400 ft-lb vs ~500 ft-lb), compared to about a 1.25x difference between .223 Remington and 5.56mm. If you adjust the action for subs, supers will cycle unnecessarily vigorously, increasing felt recoil and wear on the gun. If you adjust cycling for supers, subs will not cycle.

A standard carbine recoil spring versus a heavy duty, a light one or a rifle length recoil spring

An adjustable gas block is not necessary with the 300blk.  it is not a bad thing to have but it is not necessary.

I do have one on my 16 inch carbine gas, but it has not been adjusted in since I put it on and it shoots subs and supers suppressed and unsuppressed.  And I have not experienced any issue with excessive recoil or cycling