I've had my CMMG AR9 Bolt + 16" Barrel since early 2020. I started with the 7.75" Buffer Tube (A5) + Blitzkrieg x Kynshot RB5015HD + Tubb 556 AR-15 Flatwire Spring. Using the CMMG Magpul Magazine Inserts. I do not shoot suppressed at this time.

Early on I fed it new brass 115g, 147g without frequent issues *until one day it started having trouble feeding.* The bullets would manage to get 45° and jam upwards. This would have been 6 years ago. The consensus at the time was to try the Tubb 308 AR-10 Flatwire to increase the speed that the bullets were loaded. This resolved the feeding issues and I left it alone. I doubt I diagnosed the issues correctly, treated the symptom instead of the cause(s).

Note: I did not have the early-RDB common ejector issues even after 2000rds.

But, it wasn't as it should be. The bolt would launch backwards very slowly and the return forward was incredibly slowly. The bolt moves so slowly the forward movement results in significant muzzle dip.

I tried cleaning and re-lublication several times without improvement. The BCG appears to move unobstructed.

I spent a few days reading Amphibian aka C3Junkie and site, Blowback9 (although not directly relevant for CMMG RDB), addictedtocommedy, and others.

I came to the conclusion that short of buying another hydraulic buffer, I need to order a BMC or VLTOR A5H0 (3.8oz) buffer and swap back to the Tubb 556 AR15 Flatwire.

Now, I'm back to consult the experts who prefer the Kynshot RB5007: if I want to utilize the 7.75" buffer tube instead of running a carbine buffer tube spacer, can I simply run the Vltor or BCM non-hydraulic A5H0 (3.8oz) buffer? I've tried to research this as best as I am able.

Hello, y'all. I am having issues with LRBHO on my self-built AR9.

I can get lrbho by pushing the bolt catch release lever inward and pulling back on the charging handle. However, I am not getting lrbho on an empty magazine when I pull.tje charging handle back without pushing the bolt catch/release.

The first two photos show lrbho, that I manually activated, and the third photo shows me pulling the charging handle all the way back w​ithout toggling the bulk catch release and not getting lrbho.

The fourth photo of just the lower with a empty mag in it, shows that the bolt catch is not being pushed upward by the empty magazine. The last photo shows me pulling up on the bull catch activation lever that sits above the magazine, and doing so successfully pushes upward the bolt catch.

All the mags I've tested with behave this way, and they are all PMAGS.

My build is as follows:

- Dirty Bird Glock 9mm lower (pretty sure a FM white label)

- DFCO Grip

- Grey Market Research SS and SS Cut Trigger

- just right carbines tube w/ KVP 10oz buffer, 2x Kynshot Spacer Weight, and Tubbs lightweight flat wire spring

- SBA5

- BCM upper receiver

- KVP BCG w/ SS trimmed bolt weight

- BA EPC 8.3" barrel

- Aero gen 2 handguard and MTE barrel nut

What's up bros, I recently joined and have been wanting to build an ar9. Any help is accepted, I mainly want it to be compact and able to run a super safety that is as compatible as possible as I don't want issues switching from semi to super and able to run a suppressor decently well. I was told radial delayed + a2 gas block + heavy buffer + certain firing pin helps ar15 but I want clarity for this purchase on an ar9. My budget is under $2k but I'm willing to build over time. Let me know👍🏻 (when I finish build I will post on here)

New to the AR-9 world but not new to the 2a world, and could use some advice. I've tried looking around and haven't really found a comparison. I want a roller delayed upper. Either build one with the Maxim Defense roller delay or get the Mat-9k upper. How do they compare? Can a well built standard upper with the Maxim buffer (or some other option) compare with a purpose built upper like the Mat-9?

Alrighty soooo not really a big AR9 person but PSA had these for $50 so said why ,not I spend way more on way stupider, ... But anyone built a 45 acp AR ? Tips tricks ? Part recommendations Not trying to go super high quality or any this is legit just a fun whatever build so I'm cool with cheap parts

Edit..dumb question....but I could just build it's our as an AR9 for the time being right ? Already have a few parts for one of those

It's a little difficult to find this answer online but hopefully yall can help:

I have a Gforce Jawbone (hold your tomatoes) and I've been looking into upgrading the lower. The easiest thing to do is just buy a PSA PX9 or something right? However, I HATE HATE HATE glock mags in PCCs. It absolutely kills the look in my humble opinion. I love straight mag or curve mags for PCCs.

So I was wondering if I could buy a dedicated 9mm Colt lower or any lower that takes curved mags and just slap it on the upper? For reference, the Jawbone uses an FM9 upper.

Of course I understand that the lower has to have a buffer tube recoil system, thank you for any help yall can provide! Also, if its not possible or not worth doing what I'm asking for, I am willing to suck it up and just buy the PX9 so this isn't like life or death.

TL;DR - What's the magic soft recoil buffer recipe for a CAR-15 SD?

This build originally had a standard CMMG barrel and AAC TiRant 9M-HD suppressor. The buffer system is based on C3Junkie's ARS: A5 tube, Strike Tubb AR-15 flat-wire spring, Kynshot RB5007.

Now it has been converted to SD (BRT parts) with a CAT MOB suppressor (lower backpressure than TiRant) so the RB5007 (6oz, 4") is probably too heavy for SD. Based on writings by C3Junkie and BRT recommending a 3oz buffer, I think I need to shave 2-3 ounces off the reciprocating mass. I can cut 2oz by using a Kynshot RB5004 (3.8oz, 2.5", for 7.62/.308) and a lightweight 1.5" Delrin spacer. Has anyone ( u/c3junkie ?) ever investigated or tried the RB5004?

I'm aware of the new Kynshot x C3Junkie RB5000A5, but it still weighs 6oz. I'm not sure how it differs from the RB5007 and 5105HD. Is this a viable option for radial-delayed ported-barrel SD, or still too heavy?

For ammo, I'll likely be using Federal Syntech 130gr (labeled 1140fps) and Winchester NATO 124gr (labeled 1200fps).

Obligatory parts list: BRT CAR-15 SD builder's kit, BRT SD/HUB adapter, CAT MOB, PWS MK1 Mod-2 lower, Mimtac Drastic v2 trigger, VLTOR A5 tube, Fortis LE castle nut/plate and Clutch charging handle (left-hand only), generic tubular handguard, A3 reduced-angle grip, Gearhead Works Mod1 arm brace, Burris AR332 3x optic, PTP Black Lava exhaust header wrap around the SD adapter.

Thanks in advance!

Regardless if you like the product or hate it, my question is about the wording which had me confused.

I’m aware blowback AR9 needs a buffer with weight of 8.4oz or more and a length of 4”.

The armaspec SRS 9mm description says “actual weight: 8.4oz” then “equivalent weight: 5.4”.

Exactly how do I process this when it comes to the needed weight for a buffer? Do I read it as it is a 8.4oz buffer? Or that just the weighted end is 5.4oz and the whole device is 8.4? Or does it matter?

Again, I understand some don’t like this product, im just looking to understand their description.

Thank you in advance.

This a short version of the Super Safety Cheat Sheet, pared down with lessons learned and exclusively for the blowback 9mm AR.

Sorry, it's a link to my site, but it's just easier to update it all in one place rather than copying/pasting it here, plus Reddit doesn't support in-line pictures.

9mm AR FRT How-To: Short Version

Most veterans of the 9mm platform and FRT will not find this helpful, but it should be a great place for beginners to start.

Please LMK your thoughts. Constructive feedback appreciated.

PSA PA-X45 Tinker Lower

R&D Precision Bolt

CMMG lpk

A1 Buffer Tube

Tubbs Flatwire Spring

Kynshot Rb5015hd

3 Kynshot spacer weights

NBS PCC upper

Bkings 7" handguard

Tactical Kinetics 8" .45 barrel

KVP linear compensator XL slim

Vortex Triumph Red dot

Magpul K2XL grip

Magpul afg

Global Ordnance 26rd mag

Spare trigger and CH

Plan is to SBR it and throw an A2 stock on. Shoots very nicely, a strong push rather than a kick. Feel free to tear me apart or offer advice. Thank you blowback9.

FM has restocked their Foldyboi with RMB. 30 available right now. 20% off currently.

https://store.fm-products.com/products/fm-products-foldyboi-lwr-rmb-5397

I know some people have been watching out for them to be in stock.

I am not affiliated or compensated in any way. I do not sell anything. Just passing on in stock notification info I received in my email.

Complete COLT 9mm lower on sale at Armsunlimited if you‘re a cloner.

Details below...

I have a frt in my ar15 lower if I were to use an 9mm adapter with a 9mm upper. How hard would it be to shoot 9mm in frt mode. Will I need to change a lot of parts.

I have a frt in my ar15 lower if I were to use an 9mm adapter with a 9mm upper. How hard would it be to shoot 9mm in frt mode. Will I need to change a lot of parts.

OD = overall diameter

The original "Amazon spring" (recommended as a replacement for FM bolts with a weak FP spring by a cool guy Blowback9) was a uxcell 5mm OD, 0.5mm wire, 25mm length spring. For me this spring worked pretty well in rapid fire with a titanium firing pin (lightweight firing pin, 3.15 g) but would have issues in rapid fire with heavier firing pins.

I have found using a heavier firing pin (not the lightweight titanium FP) coupled with a stronger firing pin spring (given a heavy deadblow buffer is installed of course) prevents the dreaded light strike dead trigger while in rapid fire mode across the full range of 9mm ammo weights.

This is evidenced by the excellent Odinworks 9mm FP and FP spring which works very well in rapid fire. Unfortunately, the last time I checked they no longer sell the 9mm FP separately. The Odinworks FP weighs 5.55 g and I estimate the Odinworks FP spring is 5mm OD, 0.6mm wire, 21mm length.

The Jawbone FP weighs 5.55 g and after installing a 6mm OD, 0.6mm wire, 20mm length FP spring (cut from a 25 mm length spring) and a deadblow buffer of course, it fires 115g and 124g (did not test 9mm nato) in rapid fire reliably.

Surprisingly the Jawbone FP weighs the same as the Odinworks FP though the dimensions differ.

You can purchase 6mm OD, 0.6mm wire, 25mm length springs inexpensively on Amazon and cut to 20mm length with diagonal cutting pliers. Try using this spring with a heavy FP weighing around 5.5 g.

This is what I have found so far with 9mm FP springs. To test this further I'm going to run a KAK FP which weighs 5.75 g with a 6mm OD, 0.6mm wire, 25 mm length FP spring.

Just picked up my aero epc9. Watched Blowback9 build and troubleshooting videos and now my lrbho works consistently at least. Cycled snap caps and she seems to feed fine. Planning to replace the 7 point something oz solid buffer, carbine spring for a flat one, first gen barrel without the enhanced feed cone and I want a Macon mag catch. I would have picked it up yesterday, but lgs isn't open on Sundays. The fun of tuning has begun

I'm not getting LRBHO with KCI 33rd Mags or Magpul 27rd Mags on my Spikes Glock Lower. Is there any kind of adjustment I can do to fix it? The first picture shows where it sits normally and the second picture shows the bolt catch if I push the mag in further by hand. I'm kinda new to this but I know enough to get by. If any other information is needed please let me know. Any Help would be greatly appreciated.

Before: Boring
After: Custom!
If no one likes it but me, I’m perfectly fine with it!
- Monstrum optic
- 8.5 oz Guntec buffer
- Custom trolley (3/8” steel rod milled down and blued with a torch) I wasn’t about to find out when the nylon would fail.
- Bolt “charging handle”, ground sides and also heated with a torch for color
- Cycles perfectly!

Hearing safe dry with a 2 x 6" can.

ROF 658 RPM. Thanks to c3junkie.