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Discussion Starter · #1 ·
So, I've just recently realized that my upper with a Geissele SMR installed is not compatible with my lower, which is a non-416 lower. Unfortunately, I learned this the hard way and I think I ruined my locking bolt because I'm an idiot. Praying I didn't ruin the threads on the handguard itself, but I'll know tomorrow when I get a new screw.


Anyway, I've seen some posts and pictures of people who have had to modify their SMR to fit their lower by shaving off a rear portion of the handguard, near where it touches the front takedown pin. Does anyone have any experience or guidance with this? As blasphemous as it feels, I think I'm left with no choice but to modify one of my SMRs and I'm hoping I can go into this with a battle plan, as opposed to just hackin away at it.

When I was attempting to put my upper and lower together, it seemed as if the handguard was only a hair too close to the front of the lower. Is a cut as drastic as the one in the picture above needed, or can I just sand the corner of the handguard down a tad?
 

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didn't realize this was a problem for others too. I dremeled it down a bit. Esthetics look fine. Funny, the HK hand guards fit just fine.
 

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Discussion Starter · #3 ·
didn't realize this was a problem for others too. I dremeled it down a bit. Esthetics look fine. Funny, the HK hand guards fit just fine.
After you shaved yours down did you cover/coat the exposed metal in anything? I never coated my gas block after I cut the sling loops off and it’s been fine for the past few months.
 

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After you shaved yours down did you cover/coat the exposed metal in anything? I never coated my gas block after I cut the sling loops off and it’s been fine for the past few months.
No, I can’t really tell when it’s installed unless I give it a close examination. It’s aluminum, I can’t imagine not being coated will hurt it. YMMV
 

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My lower was an LMT. The hand guard fit, but couldn’t pivot the upper on the pivot pin until I dremeled the hand guard a bit. It was a really tight fit.
 

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Discussion Starter · #8 ·
Any pics? I have a SMR on a MR556 upper sitting on a Colt lower without any issues.
Visually, it looks like it should fit and is only ever-so-slightly off, so pictures really wouldn't do much justice, unfortunately. I also ruined my locking bolt trying to lock it like an idiot, so I can't really put it back together at the moment lol.
 
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