9mm Non-dedicated Rig

[CrowCommand]

My 9mm upper was an 8", I used Endo mags.

I used a KVP BCG with a Rifle (Green) spring.
You pretty much want the reciprocating mass around 21 - 23oz.
I was using a Law folder and had to cut the carrier's internal weight off a bit to fit the adapter for the folder, with an A5H4 buffer I was at 22oz.
Ran like a champ and didn't trash the brass on the way out.
Vltor has dedicated 9mm buffers now up to 10oz I believe.

My 5.56 upper is using an A5 action.
To use The 9mm upper I used a 5/8" nylon spacer for the A5 tube with the A5H4 and green spring.
A regular carbine tube doesn't need a spacer.

Also very useful information. Thanks.

I may run an a5 in this, I have one in the parts bin.

[1168]

This may be the route I go, thank you. Building out as mainly a fun gun, most likely will not be competing with it.



Curious what your reasoning for this is….I would think 9mm wouldn’t need a real long barrel to stabilize.

This will be going on a pistol lower, so I guess my point is that I’d prefer it longer than hand gun barrel length, but shorter than 16”. Leaning 10.5” at the moment.

No suppressors in my state, unfortunately.

Thanks to everyone else too, I will be referencing this thread as I build.

As a training analog, not for ballistic prowess. A 10.5” or 11” would be perfectly fine, ballistically (as much so as any other pistol cartridge gun), and won’t rattle your fillings like a 5.56 version.

The 1/2” longer bit is because blowback barrels don’t need a barrel extension to house the bolt lugs, so a 5.56 barrel is externally a half inch longer than the same internal (ATF) length blowback 9 barrel. Sometimes manufacturers (like New Frontier) just cut the barrel longer than advertised to account for that. Most do not.

If you’re the type that likes a handguard to go all the way to the muzzle, that 1/2 inch will matter when you do the math. If not, it won’t.

[26 Inf]

What BCG, buffer and spring did you run?

Don't remember that, it was several years ago. I know a KAW Valley BCG, standard carbine spring, don't remember the weight of the buffer used. Sorry couldn't be more help.

[CrowCommand]

As a training analog, not for ballistic prowess. A 10.5” or 11” would be perfectly fine, ballistically (as much so as any other pistol cartridge gun), and won’t rattle your fillings like a 5.56 version.

The 1/2” longer bit is because blowback barrels don’t need a receiver extension to house the bolt lugs, so a 5.56 barrel is externally a half inch longer than the same internal (ATF) length blowback 9 barrel. Sometimes manufacturers (like New Frontier) just cut the barrel longer than advertised to account for that. Most do not.

If you’re the type that likes a handguard to go all the way to the muzzle, that 1/2 inch will matter when you do the math. If not, it won’t.

I figured it was a training aspect. Did not know about the RE. Good to know.

Been watching a lot of YouTube videos on the subject. Blowback9, I believe is the channel, has a lot of good info for others interested.

[1168]

I figured it was a training aspect. Did not know about the RE. Good to know.

Been watching a lot of YouTube videos on the subject. Blowback9, I believe is the channel, has a lot of good info for others interested.

My post should have said “barrel extension” not “receiver extension”. I’ll fix that.

[CrowCommand]

My post should have said “barrel extension” not “receiver extension”. I’ll fix that.

Didn’t catch that, but I understood what you meant.

[Red*Lion]

I read that a good compromise of shortest barrel length and performance is 7.7". Part of the reason that I recently got a Scorpion 3 + with a 7.8" barrel. I have not shot it yet though.

[CrowCommand]

Just ordered a BKing firearms BCG, weighing in at 14.6 oz, and a 7.5 oz KVP 9mm buffer. That brings the reciprocating weight to right around 22oz, which, according to Blowback9, is the desired weight for a 9mm rig….

Upper is arriving tomorrow. I’ll have to go start my paperwork on a new pistol lower, and I suppose A5 system is out of the question now. Will have to research what buffer spring I will run.

This leaves me with a partially non dedicated lower, as I can always bail on the 9mm and swap out the guts to run 5.56.

[CrowCommand]

Endo mag guts will be next. Another reversible component. Thanks to all who’ve contributed.

[TonyAngel]

I just did this. Put together a 9mm upper to swap out with a 5.56 upper with minimal fuss.

For the barrel and BCG, I went with a CMMG radial delayed barrel and bolt kit. It drops right into a standard upper. It was a little pricey at $350, but I also didn't need to buy any special buffers or springs either, and those add up. I'm running an H buffer and standard spring in my 5.56 rig and the 9mm runs perfectly as well.

For mags, I tried both glock and colt pattern adapters and they both worked well with ball ammo. I settled on ejectorless endomag inserts. They were the most reliable over a broader range of ammo types.

When I switch from 5.56 to 9mm it is literally a matter of swapping uppers. No mag adapters, no changing buffers or springs. One to the other in less than a minute.

If you go blowback, I ran a Vltor A5SH 3 or 4 buffer with a sprinco blue spring. Although the recoil was harsh, it ran very well. I also used the endomags with ejectors, but they are kind of delicate. They will quit working at some point.