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

[TonyAngel]

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]

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]

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]

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

 

[TonyAngel]

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]

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]

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]

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

 

[TonyAngel]

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]

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

 

[fedupflyer]

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]

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]

Hodge AU Mod 2

 

[fedupflyer]

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]

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

Last ones I had experience with were not

 

[fedupflyer]

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]

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]

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.

 

[reelserious]

All BCM here

 

[thedude824]

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

Mine have not been

 

[thedude824]

I recently used a San Tan Tactical STT 15 receiver set and the upper was very much a thermal fit. I should also mention that I’ve had problems with some bolt carrier groups hanging up though…

 

[DemonicLemming]

Didn't know about BKings before this thread...couple uppers on the way now. Cool beans.

 

[TonyAngel]

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.

I have two lapping tools. One from Brownells and one Wheeler.

My Brownells tool is 15 years old. This particular upper was way too tight. It's not a big deal. I just prefer to go with something else for now. Having problems with two out of three was just too much.

 

[Bantam1]

Out of all the BCM uppers I have built on I only have one that needs some attention. The pocket for the charging handle latch is really shallow, .020" depth. It holds the latch but I was a little concerned once it has some wear. So I will probably mill the pocket out another .030 to be closer to all the others I measured. I have had some that were tighter than others for thermal fit. They just needed a little more heat and the barrels went in as needed. No accuracy issues or any other issues with those.

The latest one I received has their star forge mark. I haven't seen that before. It's a round recessed pocket with a raised star.

 

[WeR0206]

Out of all the BCM uppers I have built on I only have one that needs some attention. The pocket for the charging handle latch is really shallow, .020" depth. It holds the latch but I was a little concerned once it has some wear. So I will probably mill the pocket out another .030 to be closer to all the others I measured. I have had some that were tighter than others for thermal fit. They just needed a little more heat and the barrels went in as needed. No accuracy issues or any other issues with those.

The latest one I received has their star forge mark. I haven't seen that before. It's a round recessed pocket with a raised star.

I just got two blem m4 uppers from BCM recently and mine also had the star forge mark. One im keeping as a spare and the other one was mounted to a 16” criterion core barrel. I dont have a torch so I had to use a heat gun on high for about 4-5 mins before I could slide the barrel on, its rock solid though!

 

[JR1200W3]

@padom @TonyAngel

Gents, I'm curious. What is the situation that you have built 50-100 rifles of just one brand and type of receiver? Are you gunsmiths, building guns for customers? I'm sure you've built guns in other brands so you're really talking about just a portion of the ARs you've built.

 

[TahoeDust]

Mega forged upper

 

[TonyAngel]

@padom @TonyAngel

Gents, I'm curious. What is the situation that you have built 50-100 rifles of just one brand and type of receiver? Are you gunsmiths, building guns for customers? I'm sure you've built guns in other brands so you're really talking about just a portion of the ARs you've built.

I don't build anything. I assemble parts. I don't think I said that I built that many using only one brand of anything. I haven't liked any one product from any particular manufacturer enough to use it that many times.

I was just trying to point out that I've put together more than a few and understand the concept of a thermal fit what is necessary to accomplish it. I also recognize when things have gone far beyond merely being a thermal fit as it is intended.