Turning an M4 into an M16

[Ogre]

I'm wondering if I could slap a KWA M16 outer and inner barrel on my KM4 to convert it to a M16 or if the process would be more complicated than that?

[Gimpalong]

Hey Ogre,

If your KWA is the basic M4A1 model, you should be able to remove the 14.5" barrel, handguard/ris, handguard cap, FSP, and delta ring assembly from the receiver. You can then take a 20" M16 barrel, scavenge the parts you need off the old 14.5" barrel and reassemble everything. Obviously, you'll need a new handguard to fit the longer barrel, but everything else is interchangeable.

I've done this a bunch of times with my G&P rifles and it's almost always a straight swap.

[Maverick]

You should be able to do it straight as described, but personally I wouldnt run the 363mm inner barrel when the m16 uses a 509mm. Theoretically it should work, but I would swap it. Then you run into the system being undervolumed if they use a ported cylinder in the gearbox. It will work, but you should change the cylinder to a full cylinder for optimum performance.

[MayhemXXXFrosty (AndrewMp5k)]

Since your M4 gearbox most likely has a ported cylinder (holes in the cylinder, though some have non-ported cylinders depending on brand even for standard M4's) thus you should keep your inner barrel the same even though your M16 outer barrel can now house a 509mm barrel. Running a ported cylinder with an inner barrel above 363mm is not advised because of undervoluming. If you want to run the 509mm barrel I would swap to a non-ported cylinder. Theoretically though unless your 509mm barrel is a better barrel (like say a 6.03 instead of a 6.05) or a good brand like Prometheus where quality is better, there isn't a real point in upgrading inner barrel length. Correcting other things like a good bucking or IR/R-hopping would be better.

[Gimpalong]

I regularly run a 10.5" inner barrel in a 14.5" outer, so a 14.5" inner in a 20" outer probably won't cause any issue.

If you find that your BBs are hitting the inside of your outer barrel or your flash-hider then switching up to a 509mm barrel will solve the problem. That said, it may also be indicative of other issues as your BBs should not be deviating so much within the space of 6" that they hit the inside of the barrel or flash-hider.

[Maverick]

At the very least, I would shim the inner barrel within the outer so that it is centered for sure. Especially with that floating barrel group in the KWA, not sure how all the alignments are going to stack up.

[Ogre]

After a quick google search it seems like most KWA 2GX gearboxes have un-ported cylinders so I should be fine.

Main reason why I want to switch it over to an M16 is everyone seems to have an M4 so I want to be a little different yet still keep that mag compatibility, as well as just giving myself an excuse to upgrade things I don't need to. Besides, I'm a big man and I want a big gun