Colt M4 Carbine Dissipator Build

[jbjh]

Also, do you have to use a rail or would the distance you chose also be able to use a set of round handguards?

Lastly, where could you get an upper built like this?

Original Dissy's were rifle-length gas and 16" barrels. Round handguards were the norm.

As for where to get one built, I'm sure ADCO could help (I'm sure there's others).

[n4p226r]

Adco said the only way it would work with a barrel that was .730 would be to turn it down to .625 and use that size front post. Not very cost effective but I bet it would work great.

[Iraqgunz]

This particular barrel was just under .750 in that position and pinning it wasn't an issue. We later did another run of SIONICS barrels with the .750 continuous profile for people that wanted to build a Dissy.

You have to pin the FSB in the rifle position to do so you need the correct jig.

Not sure where you could get this done. Your biggest issue is getting a proper profile barrel to correctly pin the FSB. After that it is pretty gravy. I built another such upper with one of our barrels, and then used a KAC RAS.

I know I'm bumping an ancient thread but since this seems like the right way to do it I have a question.


So I assume the gas block is .750 but the barrel at that point is something like .730. Is that correct? We're there any issues pinning to the barrel with it being undersized? If really like to do this with as many colt specific parts as possible.

Also, do you have to use a rail or would the distance you chose also be able to use a set of round handguards?

Lastly, where could you get an upper built like this?

[advntrjnky]

You could also ream the I.D. of a .625 FSB to match the barrel O.D. That way you could match it to what ever the actual is .740", .730", .735", etc. You can get cheap adjustable hand reamers from various sources. I bought a set to do just that, but ended up tapping the hole under the sling swivel for a set screw. I then cut a strip of .010" shim stock to fit about 2/3 around the diameter of the barrel. That filled out the .730" barrel diameter to match the .750FSB, and also allowed the set screw to tighten/ center the FSB against the barrel. I used a torqued/ aligned A2 HG to set the distance, and tightened the set screw. Center the rear sight, shoot to confirm mechanical zero, adjust as needed, and then drill the front band of the FSB to pin permanent. You can leave the set screw or pull it and install a second pin in the FSB.

advntrjnky


advntrjnky

Adco said the only way it would work with a barrel that was .730 would be to turn it down to .625 and use that size front post. Not very cost effective but I bet it would work great.