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.

 

[Gtscotty]

@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.

"Gents, would you say you're 'in the business' of building these 50-100 rifles... In a manner of speaking"

 

[JR1200W3]

"Gents, would you say your 'in the business' of building these 50-100 rifles... In a manner of speaking"

View attachment 8665244

Meh, whatever nerd.

Unless you're a gunsmith I have a hard time believing you have 200 ARs in your safe that you built. I can't even envision 20 different configurations of an AR that need thermally fit barrels. So maybe you're building them for friends? 80 friends that you just helped into their first AR? Also hard to believe. Even as a gunsmith it would take a long time to build a resume of AR builds off just one brand and model of AR upper.

I just thought I'd pull the string and see where it led.

 

[padom]

Meh, whatever nerd.

Unless you're a gunsmith I have a hard time believing you have 200 ARs in your safe that you built. I can't even envision 20 different configurations of an AR that need thermally fit barrels. So maybe you're building them for friends? 80 friends that you just helped into their first AR? Also hard to believe. Even as a gunsmith it would take a long time to build a resume of AR builds off just one brand and model of AR upper.

I just thought I'd pull the string and see where it led.

Sounds look a poors post...

 

[JR1200W3]

Sounds look a poors post...

That's one way to avoid the question

 

[Ronin22]

Thermal fitting is a premeditated event. You are going to select an extension that’s big. Rarely do you get one where you are surprised it needs it. So, the majority of extensions are pretty slip fit. Cerakoted uppers add some reduction in fitment. The barrel nut selected does the job. But then if it shoots like shit, you shim or loctite the extension. Then 97% of the time after doing that, it still shoots like shit. So it’s all about barrel quality, not how tight it fits in the receiver.

 

[1911hombre]

Thermal fitting is a premeditated event. You are going to select an extension that’s big. Rarely do you get one where you are surprised it needs it. So, the majority of extensions are pretty slip fit. Cerakoted uppers add some reduction in fitment. The barrel nut selected does the job. But then if it shoots like shit, you shim or loctite the extension. Then 97% of the time after doing that, it still shoots like shit. So it’s all about barrel quality, not how tight it fits in the receiver.

This^^^^^^^^^. I use the green loctite. Thermal fit obsession belongs with snipe hunting and Bigfoot chasing. Oh, and crop circles.

 

[MK20]

Snipe hunting is real.

 

[Gtscotty]

This^^^^^^^^^. I use the green loctite. Thermal fit obsession belongs with snipe hunting and Bigfoot chasing. Oh, and crop circles.

So thermal fit is snipe hunting, but green loctite is worth doing? That doesn't really make sense to me? I don't see any benefit to leaving a loose fit between the extension and the receiver cylindrical surfaces, so I use 620 to bed or a thermal fit. Thermal fit is easy if you have a receiver meant for it and is a little less messy than 620, especially if you ever have to pull the barrel, other than that, there isn't much difference in difficulty or result that I've seen. If I'm going to the effort to buy a decent barrel and assemble an accurate upper, both fall into the category of "why not do it?".

 

[Ronin22]

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.

That's never been my experience. Even if the rear lug is short, the lowers have a nylon tipped grub screw that needs but decimal inches to tighten.

 

[dms416]

@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.

You reminded me of the dark days where Colt uppers were the safe bet but for some it wasn't just enough to build on a Colt upper... is it a "keyhole", "AF", "square", Diemaco, or whatever-the-fuck.

 

[TonyAngel]

Wow, all I asked for was some recommendations for upper receiver options. The only reason I mentioned my experience with BCM was so I wouldn't get 20 recommendations for BCM.

No, I do not have 200 uppers sitting in a safe, but I have been assembling uppers for over 30 years. So, yeah, I've put a lot of them together.

 

[Ronin22]

Wow, all I asked for was some recommendations for upper receiver options. The only reason I mentioned my experience with BCM was so I wouldn't get 20 recommendations for BCM.

No, I do not have 200 uppers sitting in a safe, but I have been assembling uppers for over 30 years. So, yeah, I've put a lot of them together.

At least now you know you’ve been doing it wrong all this time!

I had to thermal fit some WOA barrels. And smack the muzzle end with a rubber mallet. Did they shoot better. Nope.

 

[1911hombre]

Snipe hunting is real.

Only if they're thermal fit!

 

[fedupflyer]

That's never been my experience. Even if the rear lug is short, the lowers have a nylon tipped grub screw that needs but decimal inches to tighten.

Not talking about the upper to lower fitment. That is easily remedied by using an Accuwedge or a shim, if it bothers you.
I am talking about barrel extension to upper fit.

 

[6.5SH]

Not talking about the upper to lower fitment. That is easily remedied by using an Accuwedge or a shim, if it bothers you.

Or a hot glue gun and make your own custom fit Accuwedge.

 

[TonyAngel]

At least now you know you’ve been doing it wrong all this time!

I had to thermal fit some WOA barrels. And smack the muzzle end with a rubber mallet. Did they shoot better. Nope.

If I have a choice between a thermal fit and not having a thermal fit, I'll go with the thermal fit, just because it seems like it should be better.

I don't typically assemble an AR upper with bench rest accuracy in mind, but I’ve never seen a situation where I've taken a rig with a barrel that shoots 2.5 MOA, removed the barrel to re-install it into a thermal fit receiver and have it magically turn into a sub MOA shooter.

At this point, I think I'd prefer to have a fit that is a good slip fit or slightly loose, than a fit that is overly tight. At least with the looser fit, you can make up for it with some loctite 620 or 680. I mean, what do you do with an overly tight fit?

What I would consider overly tight is when you have to heat the receiver to over 350 degrees, just so you can get the extension started so you can pound the barrel in with a mallet. I imagine that under that circumstance the receiver has to be under stress that would cause some shifting when the rig heats up under fire.

What I'm saying is just a guess, but is based on my experience of going from an overly tight fit to a more loose fit resulting in much improved accuracy.

 

[Shoots 700's]

Sorry, I do not have first hand knowledge.

My last 2 were

 

[sheepdog697]

I came to say BCM.

I know JP uppers are thermal fit, but nowhere near price point you were paying for the bcm uppers...

 

[fedupflyer]

Thermal fitting is a premeditated event. You are going to select an extension that’s big. Rarely do you get one where you are surprised it needs it. So, the majority of extensions are pretty slip fit. Cerakoted uppers add some reduction in fitment. The barrel nut selected does the job. But then if it shoots like shit, you shim or loctite the extension. Then 97% of the time after doing that, it still shoots like shit. So it’s all about barrel quality, not how tight it fits in the receiver.

If you have a shitty barrel its gonna shoot like shit.
Just slathering green loctite on the barrel extension won't magically cure the problem with a sloppy receiver to barrel extension fit.
There is a little knowledge involved.
If you have a high quality barrel and a sloppy fitting upper, you are not getting the most out of the barrel.

Just about anyone can put together an AR but putting one together well requires some knowledge and experience.

I took a "sloppy" upper receiver with a quality barrel that would shoot around 1.2 to 1.4 MOA and did some fitment with shims and loctite and it now shoots just under 0.8 MOA