My 2nd review of the Primary Weapons piston conversion

AR/M4 AR General Discussion
1

My 2nd review of the Primary Weapons piston conversion.

Here’s my initial review: https://www.m4carbine.net/showthread.php?t=10834

Friday I received my Colt 6920 upper back from Primary Weapons Systems. I had the newest version of their piston conversion installed on my upper. I like this system even better than the first. Yesterday I fired 300 rounds of a mix of American Eagle 55gr, Federal XM193 and PMC Bronze. I used 10 PMAGs and had no problems. I lubed it up with Militec-1 but not nearly as wet as I do a standard gas ARs. I didn’t even have to change a thing on my Aimpoint M4. It was still zeroed deadnuts on at 50yds. The biggest thing I noticed is that the rifle now shoots ‘softer’. Softer meaning the recoil doesn’t feel like an AR with a harder smack to the shoulder as it was prior to this newest version (the older system had the typical piston AR feel). It now feels more like a standard direct impingement AR but with less muzzle lift, it still feels different than a standard AR as all piston guns do. Compared to my 12.5" SBR that I shot right along with this Colt, the piston converted Colt recoils harder (not by much) but with roughly 1/2 of the muzzle lift during recoil. This rifle recoils very flat very much like if one were using a muzzle brake or muzzle comp on a 16" CAR length standard AR15. This in my opinion is very impressive especially while using a standard Colt A2 flash hider. This newest system has a standard setting (0 is facing up on gas block cap) and a supressed setting (- facing up on gas block cap). On the supressed setting the cap is rotated so that the (-) setting is facing up and is visible. This works a little differently than it previously did. Instead of venting the excess gas out of the gas block for supressed use it now restricts the amount of gas coming into the gas block which in turn should be quieter while running a supressor and should be really nice while running full auto supressed as it should run a nice consistent RPM.

My AAC Blackout is on backorder but I do plan to install it and test it on this upper with my AAC M42000 Mod 07 supressor.

Upper: Colt 6920 upper with a Daniel Defense 9.5 FSB Lite Rail, Colt M16 carrier, BCM bolt, cam pin and firing pin, PRI Gas Buster charging handle, YHM 45 degree mount with VLTOR ring and Surefire G2 light.

Lower: 6721 lower w/Colt match hammer with SAW ‘blue’ hammer spring & KNS pins, VLTOR E-MOD stock w/H2 buffer and standard rate chrome silicon spring, Tangdown grip, Magpul triggerguard.

Sights/optics: front iron sight is a LMT MRP front sight with bobbed off large knob and KNS front sight post, LaRue rear BUIS, Aimpoint M4 w/LaRue mount.


standard setting:

supressor setting:

2

Nice gun, nice review and very interesting descriptions of the recoil characteristics.

3

gotm4, very interesting - thanks for posting. now you got me curious as to how my PWS midlength will feel when i get it back with the gen 2 conversion. when i had it with the gen 1 system, i shot it side-by-side with a carbine length gen 1 PWS conversion, and the impulse was noticeably softer - i couldn’t tell the difference between my mid and a carbine DI gun. i’m hoping i’ll feel a similar reduction from gen 1 to gen 2 - that’d be sweet!

4

Is the gas block pinned or held on by set screws?

5

good review.keep us posted.

6

Thanks for the review gotM4. Do you have any idea what the approximate turn around time is for a conversion?

7

i am real excited about this kit.
i hope to get my upper sent out this week.

8

the gen 2 is set screwed, but the screws go into the barrel as deep as taper pins would, from what todd at pws has told me.

9

Mine took about a month.

10

I wish they had a low-profile piston gas block that would fit under an existing rail. If they did I would definitely be interested in it. Maybe there is something about the design of a piston system that physically won’t allow for it.

11

i think that is exactly it…seems like the dimensions of the valve would not allow for it.

12

I thought you were just taking pictures of my new table!

13

I was, you should be a carpenter. :stuck_out_tongue:

14

personally i do NOT like long op-rods, they may be OK, but i see a tendency for bending in a full auto rifle…, of course that is just my OPINION :smiley:

otherwise very nice looking rifle, if you ARe satisfied, that is all that matters

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got back my Gen II PWS midlength today - looking forward to getting some rounds through it.

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Sending mine out today.

17

VERY interesting design…

I’d really like to hear about the suppressed rifle on the “suppressor” setting…

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Thanks for posting this info gotm4. Very interesting, as I was totally unaware of this system until just recently. The only one other piston conversion kit like this, which I was aware of, is the ARES conversion system. I know our fellow forum member Seth ?? -somebody did a review on it a while back, and IIRC, he had no problems with it.
Anyhow, a few questions come to mind:

  1. What is the cost of this system, for a converted Colt 6920 upper?

  2. What piston system is this one most similar to? LWRC? HK? POF? LMT? ARES? MASADA? Bushmaster System? etc, etc.???

  3. Is that a DD LITE Rail on the above pictured Colt? If so, it’s NOT the 7.0, but rather a little longer, correct?

  4. What is the difference between the Gen I and Gen II version you now have?

I am having slight problems with the pages of this forum loading tonight. I still cannot view your other previous review of the Gen I system. Look forward to doing so though.

19

Just looking at the system it appears to be a long stroke gas system.

Closest relative…the AK system.

Just about every other AR piston system uses a separate piston and bolt carrier, known as a short gas system or “tappet” system, like a FAL, AR-18, HK G36, vz-58, or SKS.

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pros and cons of short vs long system?