PSA Gen4 4" 9mm 6" Lightweight M-Lok Railed Upper - With BCG & CH

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PSA Gen4 4" 9mm 6" Lightweight M-Lok Railed Upper - With BCG & CH


Quick Overview

It is the customer's responsibility to be aware of all applicable laws and regulations regarding the purchase and ownership of uppers with a barrel length of less than 16". Federal NFA regulations are applicable to this item.

WARNING: This product can expose you to the chemical lead, which is known to the State of California to cause cancer and reproductive harm. For more information go to (CA Health and Safety Code Section 25249.6).

SKU: 5165450851
UPC: 5165450851
MFR#: 5165450851

Barrel Length: 4"
Barrel Profile: Heavy
Barrel Steel: Chrome Moly Vanadium 
Barrel Finish: Nitride 
Chrome Lining: No
Muzzle Thread: 1/2-36
Chamber: 9mm (9x19)
Twist Rate: 1 in 10"
Barrel Extension: 9mm, Blowback
Muzzle Device: PSA Fluted Flash Can
Receiver Material: 6061 Billet T6 Aluminum
Receiver Type: Slick Side 
Handguard Type: PSA 6" Lightweight M-Lok Rail
Bolt Included: Yes 
Bolt Steel: 8620, Nitride / Heat Treated

Add To:

Barrel: 4" chrome moly vanadium steel barrel. Chambered in 9mm (9x19), with a 1/10 twist rate. The barrel is nitride treated for durability and finished off with a PSA 6" Lightweight M-Lok Rail, and a PSA Fluted Flash Can muzzle device.

Upper: Newly designed 6061 Billet T6 Aluminum slick side upper is hard coat anodized black for durability.  These upper receivers are made for us right here in the USA.

Bolt Carrier GroupGen 4 Hybrid 9mm BCG.  Nitride treated 8620 steel bolt, with an enhanced firing pin and external 5.56 style extractor. The bolt carrier group is compatible with most aftermarket fire control groups. 

Flash Can: Palmetto State Armory's new fluted flash can. This is a solid 6061 aluminum device that is designed to direct muzzle gases and the muzzle flash forward. Threaded 1/2-36 for 9mm.  Black military-style hard anodizing.   THIS DEVICE IS NOT DESIGNED TO REDUCE RECOIL, MUZZLE RISE, OR FLASH SIGNATURE. This device is designed to direct gasses and noise forward away from the shooter and enhance the weapon's appearance.

SKU: 5165450851
SKU 5165450851
Department Uppers
Brand Palmetto State Armory
Daily Deal No
Daily Deal Expires No
Unit Price N/A
Youtube Video No
Free Shipping? No
Free Shipping Qty Label No
Free Shipping Qty No
SKU: 5165450851

Questions and Answers

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Browse 28 questions Browse 28 questions and 33 answers
Is this Last round open?
TJGuns on Feb 27, 2019
BEST ANSWER: Most cases the lower design has to do with lrbho.
What is the diameter of the inside of the handguard. Greater than 1.4”?
KBrock on Apr 1, 2019
BEST ANSWER: I don’t own one, but asked a guy on a local form that was selling just the handguard to measure it and he said 1.34”. Just means I’ll be building a 1.25” Form 1 suppressor for mine. :)
Will this work with non-PSA brand 9mm lowers?
Tayler M on Apr 8, 2019
BEST ANSWER: I used it with another companies AR9 specific lower with no issue.
Any idea when this will be back in stock? I have a lonely pa9 lower that needs a mate.
Bryce C on Mar 17, 2019
BEST ANSWER: Now, I just bought one
Can this be used with a regular AR15 lower?
Juan M on Feb 27, 2019
BEST ANSWER: It is possible if you are using a 9mm magazine like MEAN Arms EndoMag 9mm pmag conversion. Most folks have a dedicated Glock or Colt magazine compatible lower receiver.
What is the ID of the handguard, want my can to go up in it? thanks
nick on Apr 9, 2019
BEST ANSWER: About 34mm give or take a mm. The Gemtech GM 9 will fit under the hand guard.
Will this work with a standard 556 buffer spring or will I need to replace the springs ?
Kirt S on Apr 8, 2019
BEST ANSWER: I have used a standard 5.56 Buffer spring set up, however i did introduce a spacer which was about 13 quarters stacked in the back of the buffer tube to prevent excess travel. Excess travel will result in slamming on the bolt catch and eventually shearing it off.
Is there enough space to use a octane suppressor? Any rail interference?
Maiwiduenwj on Mar 28, 2019
BEST ANSWER: 34mm, give or take a mm is the inner diameter. The Gemtech Gm9 is is a can that will fit under the handguard.
Can I use this on a PSA AR 9
lower? Mine is for glock mags.
George S on Apr 2, 2019
What is the recommended buffer weight to use with this 9mm upper?
Coach on Apr 28, 2019
BEST ANSWER: a heavy pistol buffer will be best for this set up. However if you have ordered a parts kit from PSA that contains a regular ar15 buffer, you can use a spacer the size of 13 quarters stacked in the back of the buffer tube to prevent excess travel.
Can a shorter M-lok rail, 3" fit on this upper?
James R on Apr 9, 2019
BEST ANSWER: anything will fit technically as long as it goes over the flash can which i would say is about 32-33mm Outer Diameter. the inner diameter of the handguard is about 34mm give or take a mm. If you get a rail that doesnt fit the barrel nut then you will have to get a barrel nut that fits that handguard.
Is there a shorter hands guard I could throw on this without changing the barrel nut?
Stephen E on Apr 20, 2019
Which silencers will fit inside this shroud?
D T on Apr 20, 2019
BEST ANSWER: Not many. The ID is ~1.35”, and most pistol cans are 1.375”. I believe the Thompson Machine Poseidon and the Gemtech GM9 are 1.25”, and the Dead Air Odessa’s 9 is 1.1” those three would work. I’m going to use a 1.25” Form 1 can with mine.
9mm NATO or 9mm Luger?
Robert H on Jun 19, 2019
BEST ANSWER: I Usee 9mm luger, the nato rounds have +p pressure, I wouldn't use nato rounds, the gun will last longer. The gun also shoots hollow points well,
Will this work with MP5 magazines?
Isaac A on May 10, 2019
BEST ANSWER: Ar9 currently only use Glock mags and Colt smg mags. Exception of Stern defense which has different mag well adapters like p320 mags, S&W mags, however i believe they do not work with PSA Uppers. This is all to my knowledge.
Will this work with a freedom ordnance FX9 lower?
Jim D on May 8, 2019
BEST ANSWER: if it is spec to milspec then it technically should. not 100% Guarantee
What type of bcg is included, is this a full auto profile like most ar15, just modified for 9mm? New to pistol caliber ar15.
Joey B on May 4, 2019
BEST ANSWER: regular 9mm bolt, not rated for full auto as full auto bolts are cut a little different i believe. This bolt should fit in any mil spec upper with a 9mm barrel.
Will this upper work with CMMG 9 ARC magazines?
Joel M on Apr 27, 2019
BEST ANSWER: Negative, CMMG arc mags are designed to be used on their cmmg banshee upper 9mm. They will not work with anything else.
What is needed to complete the build?
Chauncey S on Apr 12, 2019
BEST ANSWER: Everything that is not the complete upper. You can buy a lower build kit from psa and buy a lower receiver. However keep in mind if you do regular ar15 receiver you will need a magwell adapter to glock mags or colt mags unless you get mean arms endo mags which i dont recommend.
Can the flash can be re removed? On both the 4" and 6" to put on another device like a suppresor.
James R on Apr 9, 2019
BEST ANSWER: yes. with a 3/4 wrench i believe.
Do I need a license to purchase the flash can?
Al Z on Apr 6, 2019
BEST ANSWER: No. you can buy 1000 and no one will care.
Does this have to be used with any specific lower? I plan on using a New Frontier C9 Billet Lower
Jonnnnn on Apr 5, 2019
BEST ANSWER: i believe if it is mil spec it should work fine.
Can these uppers use a standard AR rail ?
Joshua on Mar 29, 2019
BEST ANSWER: it uses the standard 1913 rail on the top.
Any idea on when this will be back in stock?
Justin K on Sep 26, 2019
What is the overall length of this upper?
Marvin K on Sep 6, 2019
Will the PSA CUSTOM 9MM PCC 1/2X36 LINEAR COMPENSATOR for this considering the hand guard ID and length?
Stephen E on May 7, 2019
What’s the interior diameter of the ?
James O on Apr 28, 2019
BEST ANSWER: 1.35” according to an answer from Staff for the 5” long version.
Can I use a Franklin bfs trigger with this bolt?
Joe D on Apr 16, 2019


4.5 / 5.0
6 Reviews
5 Stars
4 Stars
3 Stars
2 Stars
1 Star
Trust me buy this!!!!!
This thing is so awesome. Put this together with a PX9 lower with the adjustable pistol brace. Running a red dot and man thing this is a blast to shoot. Built it for the wife but I might keep as my own. Can’t say enough great things about it.
If your on the fence buy it!!!!!
October 5, 2019
Very nice
Very nice, I have over 500 rounds through it in 2 outings no issues at all
August 23, 2019
4 months ago
Good not great. Still a lot of fun tho..
I would give a 3.5 if possible but it’s not possible. The fit between the upper and lower is the worst I’ve seen on the market and that’s the same for all the guns I bought from psa except for one. That one is still not great but just not as bad. The finish on the 9mm Glock lower was completely gone around the screws by the bolt catch. I heard they had problems with those screws coming loose. And im assuming a guy went through real fast and tightened them down with the wrong tool for the job. I put magpul mbus sights on this and when I fired it. It was shooting low.. really low. So I had to adjust the sight till I couldn’t adjust it any lower to bring the barrel up. I still don’t know if it’s low enough to bring the barrel up enough to hit where the sights are aiming. Luckily I have a red dot coming in this week. I just hope the sight has enough play in it to be accurate.
Low mbus sight
User submitted image
June 22, 2019
4 months ago
Response from Palmetto State Armory
We do apologize for that. Please contact Customer Service so we may resolve this issue.
June 24, 2019
Casey S
Couple of small issues but a decent upper for the money.
You have to take the two screws out that hold the extractor and retighten them with blue loctite right out of the box. If you dont your extractor will come loose. Mine took about 180 rounds to come loose and fly out of the upper. Since I put loctite on the screws ive shot about 700 rounds no issues.

The flash can prevents you from using the front 3 inches of mlok rail. You have to file the tabs and cut the screws of whatever youre trying to mount to get it to fit. Took about 20 minutes with a dremel and bolt cutters.

It will feed HP ammo (ive only tried fiocchi) but only out of glock brand magazines. My korean mags will only feed FMJ.
June 20, 2019
5 months ago
Does exactly what it's supposed to do. Depending on ammo playing around with a heavier buffer weight may make the gun run with less recoil.
Functions great, highly recommended, lots of fun!!!
June 10, 2019
6 months ago
Like the feel and accuracy of the upper.
I ordered 2 more for customers. Never missed fire, extracted and eject each round using a high capacity mag powdered with 28 rounds.
February 28, 2019
7 months ago

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