I'm planning on picking up one of the piston conversion kits from Adam's Arms soon to build an upper for my Colt Piston Carbine lower and have a couple questions.

Basically the upper will consist of a Colt M4 upper, 16" Colt barrel with carbine gas, Colt 556 bolt, hopefully a Gen 3 Midwest Industries rail and obviously the AA piston kit. The lower will be standard other than a Geissele Super 42 H buffer and spring.

I've read that the gas port may need to be opened up after installing this kit, how common is this? I can do it myself and realize I'll probably just have to test fire the gun to find out for certain. Maybe a standard weight buffer and weaker stock spring is better to start with?

Does the gas block fit under most of the popular handguards people use? I tend to prefer a longer handguard leaving a couple inches of the barrel exposed and would like to run the 12" or 15" Midwest Industries gen 3 mlok rail. They seem to have pretty good clearance although I've only used lo-pro blocks with them.

Lastly, is there a better piston kit I can buy for under $500? I would prefer to just buy the matching Colt 6940P upper but we all know how uncommon and grossly expensive they are so a kit is my only option at this time (I already have a spare stripped upper and bolt so I dont want to buy a complete upper from Adam's Arms or whatever).

The AA P-series piston conversion kit is not plug-&-play with the MI Gen 3 FF HG.

The AA piston kit presumes the use of the toothed USGI barrel nut and uses the teeth at the front of the barrel nut to support the op rod spring cup.  The USGI barrel nut is .850" tall.  The MI G3 barrel nut is about 1.165" tall and compresses the op rod spring too much and limits op rod travel, and doesn't have teeth at the .850" dimension.  metal cutting and grinding would be required at this end to provide the correct dimensional environment for the AA op rod.

The AA P-series gas block will not fit inside the MI Gen 3 without some judicious metal contour reprofiling of the GB.  could be done with a Dremel.

Supposedly they are better now.....

mine is dumped in the gun closet as a fuck this pos  kinda thing

Man that sucks, I didn't think the barrel nut would matter. I havent found a one piece free float mlok rail that uses the standard nut that I like yet. I've used the 2 piece free float Midwest Industries rail and did like it for its use behind a front sight block. Even if I find a rail I like that uses the standard nut it sounds like ill have to get crafty with the belt sander and dremel if I want a long one. Nothing can ever be easy can it

What about the SA kit? Seems like itll at least fit under the handguard and is priced similar, but I assume the barrel nut issue will remain. Anyone use this one?

It looks like to me that the SA kit would work with any barrel nut that accommodates a DI gas tube.  the spring for the op rod seems to be contained internal to the gas block assy, so you don't have an op rod spring cup resting against the barrel nut.  if that's the case, then it's just a matter of making sure the gas block fits within the intended rail.  I might have to try one on my next build, one of these days.

See the piston system handguard compatibility thread. It will answer your questions about fit with both the Adams arms and superlative kits.

I've pretty much decided on giving the Superlative Arms kit a try. I like the adjustable gas block, the fact it has a clamp on option and can be used with the Midwest Industries barrel nut. I dont think I'll be able to use a 15" MI G3 rail but their 12" or 15" Suppressor Ready rail should have plenty of room to slide right over everything and keep it clean looking.

I happen to be a fan of Adams arms. Recently switched to superlative. Superlative is the superior design simply because of the way the op rod is designed. Phil and the rest of the crew at Adams are phenomenal though. both are great options.

I used an older (fat) midwest quad rail on my 7.62x39 rifle. Yes the barrel nut did not allow for their piston and spring to work.
So I simply measured the standard barrel nut (the one AA designed the kit for) then the midwest barrel nut.
Then subtract the GI nut dim from the MI nut dim. This number is the amount you must "set" the spring shoulder on the piston rod back for normal operation.
Done. Enjoy!!
P.S. that piston is hard as hell. Do the mod in a lathe with a new carbide bit and all is well.

I am looking for handgaurd options for a 7.5" build. As we all know there is not allot that will work due to compatibility. Had a conversation via email with AA and was sent the following images as well. Looking for a 6.5" ish handgaurd that will work. Anyway I hope some of this helps.

Attached File


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"This brings me to barrel mods that are needed with some of the rails. You will see that some of the rails say that there is a modification needed to the barrel nut in order for them to fit correctly. This is done by cutting a “channel” or “seat” into the barrel nut itself, you would want to install it and time the barrel nut first. Then measure from the receiver towards the muzzle .85 inches. and make your mark on the barrel nut. This way the Drive rod bushing can sit properly and allow the approximately ½ inch of travel needed for the drive rod. the diagram attached shows an example of this mod. "