Upper Receiver and RIS II issues

[gatordev]

Hoping someone can point me in the right direction as I haven't been able to find the right Google search terms yet...

I'm converting a stock Colt 6920 into a 6921 with a RIS II. I have all the parts, including a used RIS II I got a few months ago. Other than a few marks on the barrel nut, the RIS II is in like-new condition (including all the original parts, directions, box, etc...ie, if it's a fake, it's one hell of a fake). I unscrewed the stock barrel nut with no issues and popped off the 6920 barrel. I have a 6921 barrel ready to go, but first, when "dry fitting" the RIS II barrel nut on the Colt receiver (with or without the barrel attached), it only tightens a few turns and then stops. I stripped off the existing grease and applied some Aeroshell moly grease and the nut is threading on fine (no cross threading). Everything is smooth, it just stops way too early on the receiver, leaving about 80% of the nut threads still unthreaded.

What am I missing? The first barrel was removed using a Geissele rod and a barrel nut wrench (with some initial tapping with a hammer on the wrench to get it loose, but nothing destructive). The new barrel fits into the receiver fine, so no evidence of deformation that I can see. I'll have to look again tomorrow, but I didn't notice any damage to the barrel nut threads.

Hopefully someone can point out something obvious I'm not seeing. ...and Merry Christmas!

[UWone77]

Are you able to test the threads of the upper receiver with a different barrel nut? Or test the RIS II barrel nut on another stripped upper? It wouldn't be the first time one was out of spec. I just had this same problem with a different upper a few days ago.

[Judicator]

^ exactly. I just had and out of spec fortis charging handle, so they do sneak by quality control. Only way to find out is doing what was mentioned above.
To me sounds like the barrel nut for the RIS is fubar'd if it's new the. Out of spec or damaged threads, if it's used then damaged. IF it is damaged thread depending how bad you could crank it down and that MIGHT clean the threads out.
WARNING: whatever the weaker metal is would give first, so you could possibly damage our upper.

[UWone77]

^ exactly. I just had and out of spec fortis charging handle, so they do sneak by quality control. Only way to find out is doing what was mentioned above.
To me sounds like the barrel nut for the RIS is fubar'd if it's new the. Out of spec or damaged threads, if it's used then damaged. IF it is damaged thread depending how bad you could crank it down and that MIGHT clean the threads out.
WARNING: whatever the weaker metal is would give first, so you could possibly damage our upper.


Did they replace it for you? Sorry your prize was out of spec!

[Judicator]

Ya Paul took care of it! Pics when I receive it. Wasn't anyone's fault like I told Paul these things happen :)

[gatordev]

Are you able to test the threads of the upper receiver with a different barrel nut? Or test the RIS II barrel nut on another stripped upper? It wouldn't be the first time one was out of spec. I just had this same problem with a different upper a few days ago.

I don't have another receiver to test here, but I do have two standard barrel nuts and they screw on just fine by hand. When I try to screw on the RIS nut, I get half a turn by hand and then if I crank on it a bit, I MIGHT get another quarter turn (but probably less before I stop so I don't damage the aluminum).

I'm with Judicator at this point. I think the nut is the problem. When you run a small screwdriver through the threads, it's pretty rough, but maybe that's normal (it's my first RIS). I'm thinking it was just threaded out of spec as it seems like the pitch isn't right to keep going. The threads themselves look fine with no burs or anything.

Guess I'll shoot an email to DD today and see when they can get back to me. I may go see if Gun Gallery has a spare I could buy, but I'm guessing that will be a long shot. It's too bad...I was hoping to have this together in time to go shoot it on Friday with the new can.

[Judicator]

In my trade we save thread(clean them out) by threading it on till it's tight. Give it a small turn more then back it off and repeat if it is screwing on more. Hope you get it sorted out bud.

[gatordev]

Thanks. I started doing that last night, but to get it much farther, it was going to start taking some serious torque, which just seems a bad plan with aluminum. Hopefully DD can help out tomorrow.

[UWone77]

Thanks. I started doing that last night, but to get it much farther, it was going to start taking some serious torque, which just seems a bad plan with aluminum. Hopefully DD can help out tomorrow.

The only time starting, stopping, starting again worked was on a receiver extension. In the end I put the stock on and used it as leverage to turn it the last couple of threads. Needless to say that receiver extension is never coming off. Much like you, I tried several different receiver extensions and concluded that the lower was out of spec. I was hoping that it was just a burr in the threads.

[gatordev]

Well, I tried something new today and made some progress. I still think the threading was less than optimal compared to the videos I've found online for installing these, but I used an actual armorer's wrench instead of the cheap DD one and slowly started turning. The little extra leverage let the nut thread on smoothly, albeit with more force than "hand turning." Got it snugged down and then torqued it. Rail is installed. Hope to function test my install of the gas system tomorrow. It may turn out to be a single-shot rifle, but at least I got the rail on.

Sadly, due to all the fiddling, I didn't have enough time to get the Surefire flash hider on and let the Rockset set. For now I'll have to just sport a RA Mini XTC for it's test firing.