Building a 9mm Pistol Caliber Carbine

[Mustang51]

I've started collecting parts for a 9mm Pistol Caliber Carbine. Decided on Aero Precision. Plan to complete it as featureless.

AIM surplus recently had parts on sale, so I picked up a 16" "complete" upper (complete in this case does not include the BCG or charging handle), buffer kit and LPK (less grip and fire control parts)



The lowers appear to be out of stock, as do the BCG's.

I've noticed that Toolcraft 9mm BCG's are readily available and much cheaper than the Aero Precision part. I used a Toolcraft 6.5 Grendle BCG in my Aero Precision M4 build without any problem. Anyone have any experience, information or opinions on the Toolcraft PCC BCG's?

I'm planning on a RISE armament drop in PCC trigger, since they are sold on the AP website.

Anyone have any advice for a 9mm PCC builder?

 

[hoardingthemanual]

I chose a standard AR15 buffer spring, Foxtrot Mike BCG (13.4 oz) and KAK industries sliding buffer (8.4 oz). The articles I read recommended a total weight of ~22 ounces to keep the timings correct and prevent out of battery discharges. I know Aero markets a 308 buffer spring but I disregarded that and chose a standard one per my source Blowback9.com – For the 9mm AR enthusiast. No marketing, no sponsors. (wordpress.com).

I have a couple hundred rounds of 115 gr fmj in 9mm with no problems at all. In fact, my 8" barrel is very, very precise.

 

[BreechFace]

One thing to note is most 9mm BCG's should have extra weight in them, often the hole at the back of the BCG is filled in to provide additional mass to keep OOB and bolt bounce from occuring.

There is an inherent risk associated with blow back carbines in an AR platform as bolt bounce causing the hammer to contact the firing pin can occur with the geometry of the BCG. Standard AR's eliminate this possibility with the disconnector and the locking lugs. When the BCG is unlocked in a standard AR the firing pin won't protrude enough to contact a primer, not the case in a blowback pistol BCG.

Refer to: https://www.thehighroad.org/index.php?threads/blowback-9mm-carbines.882984/#post-11811852

The above is just insight, to go into this project with the knowledge that one needs to pay special attention to buffer weights and buffer spring tensions along with what ammo one is "buffered" for.

If someone sets up a light reciprocating mass for 115gr 9mm ammo and has it tuned well for that light projectile and then puts in a binary trigger and cuts loose with 147gr +P ammo, bolt bounce and OOB detonation become a great likelihood.

 

[Mustang51]

Thanks, guys.

I've got a Aero 7.7 oz buffer kit. The Toolcraft 9mm BCG is listed at 14.4 oz, which puts it in the range recommended in your link, BreechFace. It also is only few tenths of an oz less than the Aero BCG.