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Discussion Starter #1 (Edited)
Also posted over at AR15.com, but so far no response, so might as well cast a wider net...

I've got a Radical Firearms 8.5" complete upper in 300BLK, and a SilencerCo Omega sitting on a shelf at the local FFL. The local dealer let me take all of the other goodies in the box except the can, so I'm trying to install the SiCo muzzle break, and get it timed correctly.

SiCo was kind enough to provide a shim kit, which I understand how to use, but am running up against a problem of the shoulder on the barrel being too small (and slightly angled or rounded?) for the shims. The result is that when I figured out the correct shim combination and tried to tighten them down snug (I think the manual suggests ~30 foot pounds), the shims are warping and rounding around the shoulder, instead of seating against a flat surface, as the shoulder doesn't seem to provide one. Not only does this end up looking pretty ugly, but it provides no confidence in the muzzle device being seated flush, to avoid baffle strikes. It's like my shims are turning into crush washers.

Just to be clear, the Inner Diameter (ID) of the shims fits around the threads just right. The Outer Diameter (OD) of the shims is wider than the barrel before the threads, which is annoying and ugly, but not the main problem. The real problem seems to be that the shoulder of the barrel is very skinny and doesn't seem to be flat. Pictures below.

What are some good options? Am I missing something, here?





 

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You're right. That doesn't look like a very sharp corner where the threads end.

Please explain what you mean by "timing" the suppressor. I thought the thing was basically a tube with baffles in it. Why would it have to be set in one specific position, relative to... what?
 

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I see a couple problems. First there is almost no shoulder for the shim to butt against. The second is there appears to be a taper at the tangent of the thread/shoulder. Normally that type of thread would be undercut with a radius to at least the minor thread diameter.
 

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Discussion Starter #5
Please explain what you mean by "timing" the suppressor. I thought the thing was basically a tube with baffles in it. Why would it have to be set in one specific position, relative to... what?
Well, I guess some people would argue "indexed" is a better word, but regardless, it's the muzzle break, not the silencer, that needs to be oriented correctly. The SiCo muzzle break has left/right holes that you would want indexed.

Sorry, I kinda ditched this thread, but followed up on much more detail over on 300blktalk. Check it out if you want, but the short version is, I used the SiCo flash hider instead, to avoid any indexing anyway, and bought a barrel guide rod that confirmed concentricity, so would I have preferred a barrel with a better looking shoulder? Yeah. But this one is entirely functional.
 

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I install shim washers everyweek using Surefire shim kit for our issued SOCOM suppressers/SF4P flash hinders. If the barrel shoulder isn't square you're going to have problems as your running into. I would call the Radical Arms or the barrel maker to get that shoulder squared. Sorry, I missed your post on ARFcom, as I post there under the same log in.


CD
 

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Like Combat Driver said. You are going to need to get the barrel shoulder square or get a tapered shim to fit. The shim is so thin it will be distorting at 30 in#.

That type of shoulder is often used on non-binding threads to get some friction hold after take-up.
 

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Discussion Starter #8
Thanks for the help, everyone. I really don't mean to seem ungrateful, but since this has all been covered in the other forum's thread I started--emails between me and RF, all the potential options, and what I've done since then--I think it would be valuable for any future readers to head over to that thread (linked here, again) for all the specifics. Much easier than trying to re-tell it all.

Thanks, guys!
 
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