Over the years I have bought a few stripped lowers and assembled them but I always just bought and attached complete uppers. I have never messed with taking apart or building an upper.

I have a factory built Wilson combat 8” barrel 300 HAM’r pistol. I want to put a longer 300 HAMr barrel on it. Not sure if I want to keep it a pistol and put an 11.3” or go to 16” and make it a rifle. Long story short I bought it as a bedside gun but now want to make it my dedicated nighttime hog rifle with a thermal and the 8” barrel has a goofy twist rate and is so short I can’t get it to shoot good.

Wilson has the barrels for $250. Is it pretty straightforward changing them out? Would I need to change anything else?

Verify empty chamber first, of course.

You'll need a vise block, if you don't already have one. It goes in the mag well, and you clamp that into a machinist vise. Take the forearm off. Remove the gas block and gas tube. And you'll need an armoror's wrench to break loose the barrel nut. Once the nut is off, the barrel slides out of the upper. Put the new barrel in the upper, screw the nut on, and torque it to spec. Armoror's wrenches have a 1/2' square drive to accept a torque wrench. If you don't have a torque wrench, get the nut as tight as you can with just the armoror's wrench.

With the proper tools, it takes a little over 5 minutes. Without the proper tools it is very difficult.

If the 8" barrel is using a pistol-length gas tube you may need a new one to match the 11.3 " or 16" barrel (ie carbine, or mid-length?).

If the upper has a free-float hand-guard, the barrel nut may just need an open-end wrench to remove or install.

If going from 8" to 16", you may want a longer hand-guard too.

If you're looking to squeeze out some accuracy, bedding the barrel extension in the upper receiver with something like Loctite 620 is also a thing. I've done it both with and without bedding, and the bedded receiver was astonishingly more accurate. YMMV.

+1!!!

Sewer Rat, If you are in the North Dallas Area, and you don't have the vice block or the Armoror's wrench, I'd be happy to let you borrow mine. Yes, it is very easy with the proper tools.