BKF M4 MOD-0 Upper Receiver

**Disciple** · 05-11-23, 15:42

I came across this upper receiver they claim to have a thermal fit barrel flange and good tolerances. Anybody tried one?

**JediGuy** · 05-11-23, 19:17

I’ve bought other things from them. Let us know your experience if you buy the upper.

**GH41** · 05-12-23, 03:33

Me thinks the "Thermal Fit" claim is nothing more than a marketing ploy. Ask them what barrel diameter it thermal fits to?? One size doesn't fit all.

**TMS951** · 05-12-23, 05:49

Originally Posted by GH41

Me thinks the "Thermal Fit" claim is nothing more than a marketing ploy. Ask them what barrel diameter it thermal fits to?? One size doesn't fit all.

They say exactly what they do. Undersize the hole.

There are published numbers for a size range for a barrel and a receiver. They make the recover smaller.

It’s likely to be a press fit for most barrels, maybe not the ones on the smallest side of the tolerance range range.

Honestly the answer here is for recover and battle makers to simply produce these two areas to a tighter tolerance. Like .002 instead of .005.

**markm** · 05-12-23, 09:07

I'm not a fan of that tight Upper/Barrel extension fit crap. I don't want to have to use a heat gun to take apart a weapon if needed. Just build the shit to the correct spec in the first place. #americanmediocrity

**Curlew** · 05-12-23, 11:25

The one I got last year was nice enough, but certainly didn’t need “thermal fitting”

**Stickman** · 05-13-23, 09:54

Originally Posted by markm

I'm not a fan of that tight Upper/Barrel extension fit crap. I don't want to have to use a heat gun to take apart a weapon if needed. Just build the shit to the correct spec in the first place. #americanmediocrity

I might shed a tear over our disagreement, but I would rather have a receiver with a press fit, than one where the barrel extension fits in like a Kardashian.

I do understand your spec comment, but one that takes a little effort is easy enough to take apart. If you have to, and for some reason you can't hit it with heat, you can always tap the gas block forward with something and loosen it that way.