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What the %#$& Happened?

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Well, I finally decided to give the Colt/Umarex M4 a good cleaning. I removed the Umarex "fake suppressor" that I have on there, and pulled out the "guts" along with barrel (if you can call it that), and gave the innards a good spray-down and lube. After reassembly, I drew a bead on an unsuspecting varmint (squirrel) in my yard, and I MISSED HIM! BY A MILE.......! So I put up a target, 30 yards away, and could barely hit the paper! I was shooting a good three inches low, and a tad to the right. I verified with the laser, open sights, and scope, all shooting low to the right. After re-zeroing all three sights, I'm back to good groups, just like normal. Now I gotta wonder: WHAT HAPPENED? You mean I can't disassemble this rifle, and clean it without having to sight it in AGAIN? Never happened before! I've got index marks on the barrel and suppressor to keep the tension right. I just can't figure it out. The more I deal with this "tensioned barrel" the less I like it.........any ideas???

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Can't say regarding yours, but here is why I quit using the fake can. All of the Colt barrel attachments, (fake can, flash hider, ect),  have an o-ring that assists in centering the barrel in the attachment. If the o-ring breaks, point of impact will change every time you loosen / tighten the attachment. Check out the picture of the inside of my fake can. At least my o-ring is still there..... If it is missing it can be hard to figure that out. Plus, the OEM o-ring is a flimsy little thing - I milled out the flash hider a bit and put an oversize o-ring on it, and have not had any further issues.


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Thanks, TM. I believe You have "hit the nail on the head". I have been able to disassemble my fake suppressor, and discovered the o-ring, while not broken, was somewhat distorted, and appeared some form of "debris" had gotten between o-ring, barrel, and can. I swapped the o-ring from the original flash-hider, cleaned the areas of contact VERY thoroughly, and re-assembled. Everything is pretty much back to normal now! It's a shame these things weren't designed with a "cone/reverse-cone"  setup which would center precisely, without the use of a piece of RUBBER! Just a bad design, methinks...  By the way, the "can" can be easily disassembled by heating the muzzle end with a propane torch and using the tool that came with it to unscrew it. Very necessary in this case. Has anyone discovered an over-the-counter o-ring that will work?

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