9mm AR setup planning

Status
Not open for further replies.
greyling22

greyling22

Member
Joined
Aug 6, 2007
Messages
6,779
Location
East Texas
I am looking hard at converting an AR in 223 that I don't use into a 9mm carbine. If I can do it cheap enough.
Currently I load a 125grn lee rnfp made a wheel weights over 4grn of WSF. bullet is sized .358 and runs about 950-970fps out of my handgun.

I'd like to keep that load, but it is my understanding that 9mm AR's want a relatively hot load to run right, and my load is not hot.

So, here are my questions:
Can I run a lighter spring and get proper function like I had to with my light blackout loads? I know the AR is blowback, not gas operated.
Would a lighter or heavier buffer help ensure that the gun would function?

I have a spare carbine spring that I can cut short for experimental purposes, and I have a spikes st-t2 buffer (4 to 4.3oz according to the website) barrel would be 16", no suppresor.

and finally, I have not shot an ar9 before. I hear if you are running suppressed you get a lot of gas in the face. what if you are not? I shoot left handed.
 
My PSA 9mm does not need a hot load to function. Just the opposite.

I'm a lefty too and I haven't noticed any blowback problem. Less than a surpressed gas gun for sure.
 
greyling22 said:
I am looking hard at converting an AR in 223 that I don't use into a 9mm carbine. If I can do it cheap enough.
Click to expand...
With metal magwell blocks running around $100+ (I do not recommend plastic Promag blocks that will warp/deform over time), I highly recommend buying a dedicated 9mm lower. And using PSA complete upper with hybrid cut bolt will allow you to use either Colt or Glock lowers with probably lowest cost.

Even though you will spend $100+ for dedicated lower and $420 for complete upper from PSA, you will save money over time compared to shooting .223. I switched to 9mm carbines when I had difficulty finding 22LR ammo during the shortage as I could reload 50 rounds of 9mm for less than $5 using RMR 100 gr thick plated bullets pushed to 1500 fps with sub 2" groups at 50 yards - https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-3#post-10245856

index.php

greyling22 said:
Currently I load a 125 grn lee rnfp made a wheel weights over 4 grn of WSF. bullet is sized .358 and runs about 950-970 fps out of my handgun.

I'd like to keep that load, but it is my understanding that 9mm AR's want a relatively hot load to run right, and my load is not hot.

Would a lighter or heavier buffer help ensure that the gun would function? ... I have a spikes st-t2 buffer (4 to 4.3oz according to the website)
Click to expand...
Carbine buffer weights are H1 (3.8 ounces), H2 (4.6 ounces) and H3 (5.4 ounces). PSA 9mm buffer is 5.3 oz.

The key is getting around 19-22 oz range for combined weight of buffer and bolt weight. 16-18 oz combined weight will give you harsher felt recoil and I prefer heavier than 19 oz combined weight. PSA bolt is 14.7 oz so Spikes T2 buffer at 4-4.3 oz will give you 18.7-19 oz. You can try Spikes T2 buffer and see if felt recoil is harsh or comfortable as you can always go with heavier buffer or even try rifle spring.

I run standard carbine spring and PSA 9 buffer in my PSA carbines and even lighter start charge of 3.2-3.3 gr of new IMR Red with RMR 124 gr HCM RN (around 800 fps from Glock pistol) cycled the JR carbine without issues - https://www.thehighroad.org/index.p...ectan-ba-9-5-ba-9.817796/page-2#post-10520702
greyling22 said:
I guess I just need to pick a Glock or Colt style mag system.
Click to expand...
The main difference between Colt vs Glock lowers is Colt lowers retain last round bolt hold open feature and Glock lowers do not. Glock lowers should feed more reliably (in theory) as rounds are fed straight into the chamber from the magazine while Colt lowers bump rounds on a feed ramp before the chamber.

I have built several PSA 9mm carbines on M&P15/Spikes Tactical/Anderson lowers using PSA metal magwell blocks and AR Stoner magazines with stainless steel bodies/4-way anti-tilt followers have worked well and continue to feed reliably (If you search the forums, many experienced feeding issues using magwell blocks and reliable feeding is one of reasons why dedicated 9mm lowers came to market) - http://www.midwayusa.com/product/2228167977/ar-stoner-magazine-ar-15-9mm-luger-stainless-steel-black

I also have Just Right carbine with Glock magwell and recently purchased New Frontier Armory dedicated 9mm Glock lowers sold through Joe Bob Outfitters as Spartan 9mm lowers and have been very happy with them with even more reliable feeding with Glock magazines - https://www.joeboboutfitters.com/Sp...ine_Compatible_Billet_Lower_p/jb-spartan9.htm

Since I have gotten used to JR carbine not having LRBHO feature, I do not mind Spartan 9mm lowers not having LRBHO but currently looking at stripped upper receiver from RR Guns that offer LRBHO - https://www.runnerrunnerguns.com/9mm_Last_Round_Bolt_Hold_Open_Stripped_Upper_p/9mm-upper-r.htm
 
Last edited:
If you plan on switching between 9mm upper and standard 5.56 upper make sure you get a bottom loading mag block. Removing and re-inserting the BHO to swap in/out the block gets old really fast.
Dedicated 9mm lower or mag block, both are viable options, depends on your wants, needs, and budget.

For my first SBR I went with a bottom loading mag block so I could use 5.56 and 7.62x39 "pistol" uppers as well.
 
well, right now I'm looking at a dedicated glock lower from new frontier (rebranded. probably runner runner or joebob), a spinta blem bolt, and trying my carbine spring and st-t2 buffer, with the understanding that I will probably need an H3 buffer in the end. I already have a 16" faxon barrel and the upper, handguard, and lower parts from the 223 AR. I just need a good muzzle device. hoping for just a nitride finished thread protector. need something to cover .58 length of threads and an OD of .728. but I may need a crush washer and flash hider if I can't find something that fits. (open to suggestions. no part is too cheap!)

thanks to all who have provided insight thus far.
 
greyling22 said:
I already have a 16" faxon barrel
Click to expand...
Check the leade length/start of rifling on that Faxon barrel. Another member had problem with rounds not fully chambering in his Faxon barrel and needed to have the barrel reamed - https://www.thehighroad.org/index.p...ch-barrel-chamber.814420/page-2#post-10470284

Measure the depth of your bolt face (should be around .125" +/- a few thousandths) and your rounds' case base should not stick above the chamber than that.

As to muzzle device, I would suggest a thread protector as 9mm loads do not produce much flash out of 16" barrel.
 
Last edited:
bds said:
Check the leade length/start of rifling on that Faxon barrel. Another member had problem with rounds not fully chambering in his Faxon barrel and needed to have the barrel reamed - https://www.thehighroad.org/index.p...ch-barrel-chamber.814420/page-2#post-10470284

Measure the depth of your bolt face (should be around .125" +/- a few thousandths) and your rounds' case base should not stick above the chamber than that.

As to muzzle device, I would suggest a thread protector as 9mm loads do not produce much flash out of 16" barrel.
Click to expand...

ahhh nuts. and I was hoping I had a good barrel. I don't have a bolt yet, but I dropped a few of my rounds into the barrel. I'm getting a little sticking right where the guy in the linked post was. It's not bad, and they pop out easy enough with a fingernail, but they don't drop out. I also tried a few random 9 jacketed rounds I had picked up off the ground at the range. about half passed the plunk test, about half did not.

I'd rather find a thread protector, but all I can find thus far have OD's of .71 or .75, and I need .725ish.
 
greyling22 said:
I hear if you are running suppressed you get a lot of gas in the face. what if you are not? I shoot left handed.
Click to expand...
The heaviest buffer you can find, namely 12oz 9Q-T or equivalent, and you'll have no problem. Select or modify the recoil spring to match your load and you're all set.
 
All I can offer is that I had a factory AR in 9 from rock river. I really enjoyed it- felt like I had a M4 in my hands but shot like an MP5. The downside is that is was so much fun I blazed through 9mm ammo like crazy. Also it fired great with 9mm NATO but lower pressure rounds like 115 grain fiochi or PMC tended to malfunction.
 
You can always use a lighter buffer if light reloads don't function the rifle. My RRA has not had any trouble with anything I have tried in it, but I haven't tried anything that light. The 9MM AR uses a very heavy buffer, so there is a lot of room to lose weight to help function.

My though at first was using a standard lower and a block (Bought an RRA set up like that), and then I would have the ability to remove the mag block and use the lower for .223 etc, but I have never done it, never even removed the mag block. Like others, I just got another AR. I would have no issue with buying a dedicated 9MM lower these days. But then I have more than two standard lowers as well, and don't need to use the 9MM AR lower for something else.

Everyone did buy one or two (Or more) of those on sale $35 or $40 AR lowers, right? And on sale parts kits to go with them? :)
 
Everyone did buy one or two (Or more) of those on sale $35 or $40 AR lowers, right? And on sale parts kits to go with them? :)
Click to expand...

And for anyone who doesn't have a couple sitting on a shelf somewhere, your complaints about the next "shortage" will fall on deaf ears! Mags are also currently cheap and plentiful, no reason not to have enough on hand now!
 
Yeah, I had a spare receiver. it turned into a blackout somehow. Now I never shoot the 5.56 gun I never really liked in the first place. Thus, the 9mm.

But on that faxon barrel, I dropped one of my reloads in the chamber, and I measured .145 poking out. Faxon says you should have .135 out, and I can press my case down to .135 pretty easy and it pulls out easy enough with a fingernail. Maybe it will work?
 
Chamber some factory ammo.

SAAMI spec barrels should chamber 115/124 gr FMJ loaded to 1.169".

At least 1.150"-1.160" if the nose profile/ogive is more blunt.
 
bds said:
Chamber some factory ammo.
Click to expand...
Yep, a lot of 9MM reloads are fatter than factory, unless you are checking them with a good case gauge, and even then factory ammo tends to be skinnier.
 
I'm sure factory ammo would chamber, and I'm sure the faxon chamber is in spec (if on the tight end of spec), but I don't shoot factory ammo. I need a big ol' sloppy chamber.
 
greyling22 said:
but I don't shoot factory ammo. I need a big ol' sloppy chamber.
Click to expand...
I understand that, and I did the same thing for a long time until I got an EMP with a SAMMI minimum chamber (Actually under, SA reamed it and got it to minimum), and I had jams from fat reloads that ran in other guns. I bought a Wilson case gauge and scrap all sized brass which won't fall free of its own weight (About 10 to 15% of range brass). No more issues.
 
 
Last edited:
I would have bought PSA lowers but they won't ship to CA.

So I went with NFA/Joe Bob Spartan 9 lowers and quite happy with the quality and finish. I am building 4 at the moment (2 for my family and 2 for my sister/BIL as 4th of July gifts) using PSA M-Lock/Keymod uppers.

In past testing, 17" Just Right carbine with 1:16 twist rate barrel produced smaller shot groups for me but that was with 16" PSA 1:10 twist rate MOE uppers without free-float barrel so I am looking forward to doing comparison accuracy tests with PSA M-Lock/Keymod free-float uppers.
 
I went with a dedicated Colt style lower for my pistol build. The reason being is that I wanted a LRBHO that works from the start, plus I just prefer the look of the Colt style magazines over the Glock magazines. The lower is a CMMG Mk9 pistol lower. I built the upper using a DPMS A2 receiver with a Rock River 10.5" barrel and CMMG bolt.

BkbOrxD.jpg
 
Status
Not open for further replies.

Similar threads

M1key
  • Locked
AR-15 Carbine Buffers
Replies
17
Views
2K
Dr.Zubrato
D
greyling22
  • Locked
300 blackout short stroking help
2
Replies
25
Views
11K
greyling22
greyling22
S
  • Locked
AR not locking back even when suppressed.
Replies
12
Views
1K
HankC
H
N
  • Locked
Will changing AR stocks/buffers affect function?
Replies
7
Views
1K
ugaarguy
ugaarguy
S
  • Locked
AR15 Build Issue
Replies
10
Views
732
Ramone
Ramone
Back
Top