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Posted: 3/24/2009 6:40:53 PM EDT
I know this sound strange but I have an FNMI 20 barrel that has a front hand guard cup that is moving WAY too much. Never seen one move so much that with the handguards on it. I am getting 3/32" of movement. Rather than removing the FSB would a small MIG tack weld on the inside or silver solder the cup to the barrel work? I know it does not affect function but it's driving me nuts.
Link Posted: 3/24/2009 6:55:43 PM EDT
Welding a loose handguard cap seems a tad extreme.
Link Posted: 3/24/2009 7:14:04 PM EDT
It move too much, but I hear you. Either way I am going to have it done. Got the barrel at a good price.
Link Posted: 3/27/2009 5:56:28 PM EDT
Might seem as if the tapper pin grooves are mis-located. Probably because the gas tube hole is also in the wrong spot.
Or the abutment for the end cap is mis-located. May be why you got such a deal.
Link Posted: 3/27/2009 6:17:40 PM EDT
Why is removing the FSB such a big deal? Do you have the right pin punch, hammer and a way of holding the barrel secure?

Removing the FSB and shimming your hand guard cap with an appropriate washer would be much, much, much better than tacking it with a MIG welder - even if the barrel is cheap.

I am not an expert on the metallurgy of 4140 or 4150 steel, but I would be afraid that the metal discontinuity, untempered martensite in the HAZ (heat affected zone), and stress in the steel from weld shrinkage could conceivably start a crack after so many rounds fired.

On the other hand, it might turn out just fine - but why would you really want to do this?
Link Posted: 3/27/2009 11:50:04 PM EDT
Something along the line of JB Weld or a good high temp epoxy may be a better fix.
Link Posted: 3/28/2009 9:47:50 PM EDT
Thanks for the tips.

The Gas tube lines up fine the FSB is timed perfectly on the barrel. Not sure what's up with the handguard cap but I will try the other options.
Link Posted: 3/29/2009 12:33:40 AM EDT
[Last Edit: 3/29/2009 12:21:38 PM EDT by mjcarter]
Originally Posted By titan7:
Thanks for the tips.

The Gas tube lines up fine the FSB is timed perfectly on the barrel. Not sure what's up with the handguard cap but I will try the other options.


Most likely the barrel diameter is undercut where the handguard caps rests. I have personally taken an FNMI 20" barrel apart that had the same problem as yours. We used a thin o-ring in there and put it back together. Tightened it right up, but I think it was a reject barrel and somehow ended up at a gun show. Even with the loose cap, I'd still like to have one for myself. Buddy only paid $100 for it. All it needed was handguards.

Link Posted: 3/29/2009 2:34:31 AM EDT
Is it front to back movement, side to side, or rotation? If front to back, use a hose clamp.
Link Posted: 3/29/2009 11:27:47 AM EDT
Link Posted: 3/29/2009 12:22:26 PM EDT
[Last Edit: 3/31/2009 1:49:57 AM EDT by mjcarter]
double tap
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