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Hello, just received my MPX SBR and Octane 45HD I have been waiting on. Original plan was to order the shorter 4.5" barrel once I received the gun so the octane would be under the handguard. After reading on the forums it looks like that is not the best way to go and I have researched what others have done and who to send the 8" to and have it cut down. Took the new toy to the shop today to remove the barrel. The first screw/nut came loose without a hitch. The second just spins as others have stated in other threads. I did not want to post in some of the other older threads because I didn't want it to get lost in the shuffle and see if someone has figured out a better way yet that I have not read about. I tried applying heat to loosen the loc-tite with no luck. Put a large flat blade screwdriver in the hand guard groove to apply pressure with no luck before and after heat. Even tried my mini impact with pressure on the blown out rail slot. This is a **** poor design I must say. Anyone have any other ideas before I call Sig tomorrow? I am seriously bent at the moment as I have not shot a round through this thing. Thanks for allowing me to vent. :D
 

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I can't believe that nobody has a fix for this. I have read a few posts where people end up with the nuts turning in the receiver and I don't recall anyone that had a solution. I hold my breath every time I tightened mine.
 

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I have a MCX, and I'm not sure if it's barrel assembly is exactly the same as your MPX. I've removed/installed this rifle's a bunch and have some experience with 'stuck' barrels.

At least, after the 1st few hundred rounds, the barrel was hard to remove. In that case, I backed out both T27 barrel screws on the right side. These screws are retained in a spring loaded flange and will spin freely once they are fully backed out. The barrel wouldn't pull straight out though, and the manual says it's important not to put lateral pressure trying to wiggle the barrel as that may damage the barrel extension.

SIG suggested inserting a wooden dowel into the upper receiver against the barrel extension and knock the barrel straight out with a hammer. I know this sounds weird, but it actually worked!

Since then, I've smeared a very small dab of a copper based high temp anti-seize lube on the barrel extension when installing the barrel. The barrel now easily slides out with no drama!

Hope this helps

Cheers
 

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Right, these high temp lubes are used on turbo, cylinder heads & exhaust manifold bolt threads, so auto parts shops usually carry them. Or, like almost everything, just order some on Amazon

https://www.amazon.com/Versachem-13...=1492875281&sr=1-2&keywords=copper+anti+seize

I now use this stuff on all my barrel parts. It's great on muzzle devices too. It's just as secure as Rocksett, but much easier to change out flash hiders & brakes. Also, works on those loud, annoying kitchen oven door hinges...

Cheers
 
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