What upper receivers are you guys using to get a good thermal fit?

TonyAngel · 2025-04-11T15:55:10-0400

Until recently, my goto stripped upper receiver was the BCM blems. A while back, I ordered half a dozen of them. They all worked fine for various rigs and provided a good thermal fit. When I ran out, I ordered 3 more.

Of those 3, two were unusable. One was so tight that I couldn't even get the lapping jig in, much less the barrel, even with liberal use of a torch. Once I got things together, it shot like crap. Gotta imagine there was a whole lot of stress.

On the other, the charging handle, no matter which I used, kept reciprocating.

So, what else is being used to get a good thermal fit?

USK308 · 2025-04-11T16:04:48-0400

My original 300 blackout pepper is a spikes tactical M4 upper; my new upper to add to my collection with an 8.2 inch Roscoe manufacturing barrel is an aero precision upper. The aero precision upper is actually a little bit better fit to the Spikes Tactical lower than the Spikes Tactical m4 upper.

DOB161 · 2025-04-11T16:13:00-0400

Centurion and BKings offer advertised thermal fit uppers. I like the Zev/Solgw/Icon stuff but they aren’t a thermal fit. Generally advertised as a slip or resistance fit. However barrel extension size always has a say.

Ronin22 · 2025-04-11T16:25:20-0400

Thermal fit isn’t always necessary. Lots of times it’s not. I do mean lots of times.

TonyAngel · 2025-04-11T16:27:48-0400

DOB161 said:
Centurion and BKings offer advertised thermal fit uppers. I like the Zev/Solgw/Icon stuff but they aren’t a thermal fit. Generally advertised as a slip or resistance fit. However barrel extension size always has a say.

Thanks for the heads up. I'm inclined t go with Centurion, but man, the BKing is half the price. Now I'm on the fence. I'd like to stock up and don't want to buy a bunch at first. Maybe I'll get one of each.

padom · 2025-04-11T17:07:56-0400

I've used at least 100 BCM demo uppers and just got 5 more last month. I've never had a single issue with any of them, run great.

I also never heard of a stripped upper receiver shooting like crap.. I'd look elsewhere on the cause...

TonyAngel · 2025-04-11T17:19:05-0400

padom said:
I've used at least 100 BCM demo uppers and just got 5 more last month. I've never had a single issue with any of them, run great.

I also never heard of a stripped upper receiver shooting like crap.. I'd look elsewhere on the cause...

Oh, I hear you. I must have used over 50 BCM uppers, but my last experience left me wondering.

As for an upper affecting accuracy, all I did was replace the upper with the last of the BCM uppers I had and everything was as it should be. I dont think you're getting the gist of what I was saying about how tight it was. I mean, it was really, really tight. As I said, it could have been due to induced stress.

TonyTheTiger · 2025-04-11T17:20:46-0400

BKings has been thermal fit for me. Can't remember exactly which model, but they specify on their website.

TonyAngel · 2025-04-11T17:35:47-0400

TonyTheTiger said:
BKings has been thermal fit for me. Can't remember exactly which model, but they specify on their website.

Yep, the Mod 0. There's a sale on right now too.

Centurions are out of stock, so decision made.

B Man · 2025-04-11T19:57:59-0400

Bking mod 0 forged or GGP for billet. I use all GGP stuff now days for my lighter rigs.

fedupflyer · 2025-04-11T20:21:30-0400

I currently use Centurion uppers for a nice tight fit.
Take about 30 secs with a torch and a final tap with a dead blow hammer for a nice tight sit.
Just built one that shots 0.6 MOA with FGM 77g. Maybe tighter with handloads.

I stopped using BCM uppers after the last couple were very sloppy and could force in by hand.

Unfortunately Centurion has changed their lowers and are no longer mil-spec. The have added some sort of strengthing material to the front side of the mag well.

WeR0206 · 2025-04-11T20:47:53-0400

fedupflyer said:
I currently use Centurion uppers for a nice tight fit.
Take about 30 secs with a torch and a final tap with a dead blow hammer for a nice tight sit.
Just built one that shots 0.6 MOA with FGM 77g. Maybe tighter with handloads.

I stopped using BCM uppers after the last couple were very sloppy and could force in by hand.

Unfortunately Centurion has changed their lowers and are no longer mil-spec. The have added some sort of strengthing material to the front side of the mag well.

Do you happen to know if the forged vltor MUR upper is still a thermofit?

Milspec Longhorn · 2025-04-11T21:11:42-0400

Hodge AU Mod 2

fedupflyer · 2025-04-11T21:22:34-0400

WeR0206 said:
Do you happen to know if the forged vltor MUR upper is still a thermofit?

Sorry, I do not have first hand knowledge.

B Man · 2025-04-11T21:47:24-0400

WeR0206 said:
Do you happen to know if the forged vltor MUR upper is still a thermofit?

Last ones I had experience with were not

fedupflyer · 2025-04-12T00:12:02-0400

Just don't buy that Aero precision junk.
Sloppy fit on both small and large frame AR patterns.
I still don't know why folks think the are so great.

bfoosh006 · 2025-04-12T07:41:28-0400

What brand is your lapping tool ?
I memory serves me... the Brownell's lapping tool fit my BCM uppers.... The PTG's would not fit the BCM's

That said... All my SOLGW stripped uppers are thermal fit... however they are all a few years old production.
The SOLGW uppers all have a snugger fit on ( between the upper and lower ) on various brand lowers.

From very snug on a BCM lower, ( have to slap it apart ) to much better on a PSA lower.

Gtscotty · 2025-04-12T14:58:48-0400

Thanks for the heads up on BKings Mod 0 being thermal fit, have one and one of their 13" handguards on the way for my next build.

What upper receivers are you guys using to get a good thermal fit?

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