I have for sale a threaded 4.5" barrel with gas block assembly made by In Lead We Trust. From their website:

"Our proven 4140 hard-melonite barrel, pre-installed/pinned in an Ordnance steel hardened gas-block. All gas-block dimensions are machined within 0.0005", to correct specification, and hardened."

I had this installed in my MPX coupled with an Omega 9K suppressor. It looked awesome and ran 100% with no issues at all. My only problem was that my boys and I were shooting the MPX so much at the range, the heat of the suppressor under the hand guard was becoming an issue. I decided to go with function over aesthetics, went back to my original 8" barrel, and moved the suppressor forward of the hand guard. My 4.5" barrel probably has 1500 rounds through it. A brand new barrel will run you $330, will sell this one for $210 shipped. I accept PayPal and have positive feedback on the forum. Feel free to PM me with questions.

Jake
MPX with 4.5 barrel.jpg
ILWT Barrel.jpg