Cutting down an M4 barrel to 10.3"?

Semper Noctem · Mar 15, 2014

So, I've got a BCM upper that runs like a raped ape. It has an 16" m4 profile barrel and a 10" rail. I'm thinking about turning this into an sbr upper similar to a mk18.

My question is, can this barrel be cut and threaded so its flush with the handgaurd? Or, does the barrel profile not have enough metal to cut to 10.3" and thread properly?

Thanks for the help!

iH8DemLibz · Mar 15, 2014

If the undercut is more that .500 inches in diameter, then yes you can have it turned and cut 1/2-28 threads on it.

I would be more concerned about the lack of back pressure to operate the bolt. Less bore=less pressure/gas.

You will need to open up your gas port in the barrel to compensate for less gas.

I'm assuming you have your stamp.

This is just advice and my opinion. Do what you want.

fa18hooker · Mar 15, 2014

Gas system will not work correctly, unless you plug & rebore the gas hole to a shorty configuration...

jimbobborg · Mar 15, 2014

Why don't you get a longer rail setup? It'll cost the same as cutting and pinning the muzzle device and you won't have to deal with the weirdness from trying to figure out the gas system. Get a barrel designed to be that short and stick the rail on that upper on to the new one.

Cutting down an M4 barrel to 10.3"?

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