FYI, there's an active 9mm carbine build thread you can reference for your build -
https://www.thehighroad.org/index.p...es-and-what-parts-did-you-use-and-why.825314/
I have built several 9mm carbines using mag blocks and dedicated Glock lowers along with PSA complete uppers with bolts. In the past, bolts came cut different to clear Colt or Glock magazines but now, most bolt bottoms are cut to clear both Colt/Glock magazines.
With carbine recoil spring, I found 19-22 oz combined weight of buffer and bolt produces more comfortable felt recoil. 16-18 oz combined weight produces harsher felt recoil.
PSA bolt 14.7 oz + PSA buffer 5.3 oz = 20 oz combined weight and produces comfortable felt recoil with various 9mm loads. Since 9mm carbines are blowback, for longest "in battery" time for more consistent chamber pressures (and not get case base bulged brass), use heaviest buffer that will reliably cycle the bolt. With 20 oz combined weight, my 9mm carbines will cycle even lighter target loads (115 gr RMR FMJ with 4.6 gr W231/HP-38 or 4.1-4.2 gr Red Dot/Promo) -
https://www.thehighroad.org/index.p...-what-am-i-in-for.824002/page-3#post-10606695
For reference:
- H1 buffer weighs 3.8 oz
- H2 buffer weighs 4.6 oz
- H3 buffer weighs 5.4 oz
IF you are set on the Glock style, as opposed to the Colt style... keep in mind most Glock type lowers DO NOT have a Last Round Bolt Hold Open The Colt style does.
Last round bolt hold open is nice but it's not a necessity to me.
Well now, shooters of AK variants HAVE NOT complained about not having LRBHO ...
I started building 9mm carbines on AR lowers using mag blocks (both metal and polymer) and would definitely recommend metal mag blocks. BUT since quality mag blocks cost about the same or more than dedicated 9mm lowers, I would suggest considering dedicated lower over mag block option.
If you want LRBHO for dedicated Glock lowers, there are upper and lower receiver options.
I'm about to build an AR9 pistol. I'll be using the Joe Bob Outfitter's Spartan lower that takes Glock mags.
I have built 4 carbines on Joe Bob Outfitter's Spartan Glock lowers and quite happy with them. BTW, Joe Bob Spartan lowers are made by New Frontier Armory but at lower price of $149 and free shipping -
https://www.joeboboutfitters.com/Sp...ine-Compatible-Billet-Lower-p/jb-spartan9.htm
Both NFA and JBO sell LRBHO option for upper receiver.
Joe Bob Outfitter also sells Spike's Tactical dedicated lowers in both Colt and Glock pattern lowers for $157 with LRBHO -
https://www.joeboboutfitters.com/Pistol-Caliber-AR-Lower-Receivers-s/176650.htm
When I did my pistol build, I went with something with a bit more punch and did a .45 APC from Macon Armory.
If you want to shoot multiple calibers, consider Just Right carbine. Since mag well is modular, swapping out barrel/bolt/magwell using conversion kit allows switching to 9mm, 357 Sig, 40S&W, 10mm and 45ACP. Just Right offers mag wells to accept Glock or M&P magazines and with takedown tube, makes swapping barrels quick and easy -
https://www.justrightcarbines.com/product/takedown-tube-2/
Caliber conversion kits -
https://www.justrightcarbines.com/product/caliber-conversion-kit/
Glock mag well -
https://www.justrightcarbines.com/product/glock-magwell-assembly/
M&P mag well -
https://www.justrightcarbines.com/product/mp-magwell-assembly/
Case ejection and bolt are ambidextrous and with 1:16 twist rate barrel (instead of more common 1:10), I find JR carbine to be more accurate than PSA uppers and use 9mm/40S&W/45ACP barrels for accuracy testing -
https://www.thehighroad.org/index.php?threads/testing-pistol-loads-rests.834622/page-2#post-10799867
Here's JR carbine at 2018 Shot Show.