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Who Makes Thermal Fit Stripped Uppers?

J

JS8588

Ballistic Hipster
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Apr 7, 2020
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I haven't found a comprehensive list anywhere of known manufacturers of tight/thermal barrel fit stripped uppers yet, so this seemed to be a good thread to start on a Covid Quarantine Sunday.

For the purposes of this thread, let's say uppers that may not have needed thermal fitting per se but a rubber mallet & strong words did the trick also count.

I'll start with those I have firsthand experience/knowledge of.

San Tan Pillar Billet
Rise Armament Ripper
Mega/Zev
Grey Ghost Precision
BCM MK2
Precision Firearms Billet
Lantac Billet
JP Enterprises

That's all I've got. What's the experience of the rest of the Hide?
 
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how Can you tell they are thermal fit? Some of them don’t specifically say. Do you know about Noveske Or Vseven?
 
My limited experience with Noveske indicates they may be tight. Gen 1 forged set is what I have. Could be what DD uses for barrel extensions. Rainier Arms logo uppers are or were Mega/Zev made. The forged uppers are money.
 
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Barrel extensions have tolerances. If you get one on the small side, it might slide right into an upper whereas an extension on the upper end will need some coaxing. Then there are also companies (like Lija) who use oversized extensions and need to be pressed into more uppers than others barrels.
 
JP uppers are standard dimensions. It's the barrel extensions that are oversized. Bat Machine Company makes them in various sizes IIRC.

I recently had a barrel done by White Oak and specified a +0.001" barrel extension. Wouldn't go together without heating the receiver, and wouldn't come out after it cooled. Super easy.
 
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You can get extensions in .98, .99 and 1.0 and I suspect some of the cheap brands are even smaller.
 
BCM uppers are not thermal fit (none of the ones I’ve used or taken apart were) and the upper to lower fit with them are usually shit.

Using a high quality thick walled upper is far more important. You can bed the extension and accomplish the same thing. Bedding it will be “thermal fit” essentially because you’ll have to heat it up a good bit to get it back apart. Bedding also fills any and all voids in the extension or the receiver. Most good receivers and barrels are going to be max .002” clearance which fits beautifully. The Forward Controls Design receiver and Proof barrel SPR upper I put together a few months back had .0005” clearance... fit like a custom tailored suit doesn’t get any better than that. Yes I still bedded it and it’s a hammer.
 
I've put together BCM receivers with Dawson and ARP barrels and both were thermal fit. Also had to use a rubber mallet to get the extension in the last 1/4". Experiences vary slightly. Building on a CMT set now which I hear requires heat, but haven't assembled it yet.

Edited to clarify. Uppers were already more snug fitting without heat than the VLTOR MUR uppers I've assembled.
 
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IndustrialHalo said:
I've put together BCM receivers with Dawson and ARP barrels and both were thermal fit to get the extension in the last 1/4". Experiences vary slightly. Building on a CMT set now which I hear requires heat, but haven't assembled it yet.
Click to expand...

If it was tight in the last 1/4” then you had a tapered part somewhere. Far from ideal.
 
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Hmmm, I’ve used 4+ BCM uppers and the only barrel that wasn’t a thermal fit was a single LaRue barrel. The uppers even come with paperwork stating that the receiver extension is undersized and will likely require heat for barrel installation.
 
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srt-4_uk said:
Wouldnt you need to know what diameter barrel extension was used to know if you needed to thermal fit an upper?
Click to expand...

No. You can theoretically make any receiver a thermal fit by buying an oversized barrel extension. 99.5% of AR builders/owners will never get THAT into the weeds (I'm part of that 99.5%. I buy barrels "off the shelf").
 
JS8588 said:
No. You can theoretically make any receiver a thermal fit by buying an oversized barrel extension. 99.5% of AR builders/owners will never get THAT into the weeds (I'm part of that 99.5%. I buy barrels "off the shelf").
Click to expand...
Oversized extensions are used on quite a few off the shelf barrels and most dont realize it. Even an extension on the high end of the tolerance would be a tighter fit on the same upper than one on the low end. I'm just saying you cant do the math with half an equation. Knowing the OD of the extension or even better, measuring the ID of the upper makes for a much clearer picture. Like how some people in this thread thermal fit BCM uppers and others didnt need to.

It's a good idea though. Most people arent going to tear down their builds to measure. It would be nice if MFGs would tell you dimensions.
 
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Well the last barrel I had made (Black Hole/Columbia River) I requested an oversize extension for an always loose Vltor upper. Black Hole was out and couldn't get any more I was told.
Black Hole uses Bat extensions and the oversized option is no longer listed by them.
I then asked them to mic a bunch they had and pick the biggest they had...........still loose as a $10 Hooker in the Vltor. It got loctite 620 with SF7649 primer and .001 stainless steel shim stock on top 1/3rd of extension as did the other Vltor I built on with a Faxon barrel (shim stock went 2/3rds around that one).

If someone has a verifiable source for oversize extensions please post it here.

I just ordered 2 x BCM blem thermal fit uppers for $127.00 & free shipping. 1 is slated for a 350 legend getting ready to go together.
BCM is the only upper I've ever seen that puts it in print that it's undersized and will require heat to assemble.

Again if someone has a verified source for undersized uppers post it here.

I'll start.

There are 1020 reviews for the "Blem" thermal BCM uppers and it's 5 star.
1587439899768.png


1587439653622.png


BCM now has a MK2 that is bad ass. It is undersized on the receiver extension (thermal fit) and thickened up around receiver extension & charging port area. They sold out fast. If they ever come back in stock I will be buying them!
 
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JS8588 said:
Edited OP to reflect BCM -may- be specific only to the MK2 upper. (y)
Click to expand...

It’s not. I tried 2 Rainier Arms, 2 White Oak, a CLE Krieger and a Bear Creek in 2 regular BCM’s tonight and none would slide in. Conversely, I was able to get them to slide into a DSG Mil-spec forged upper without issue.

I don’t have the notes with me, but all of the extensions were in the 0.993-1.00 range.
 
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^^^^ This.

What I was saying is that Both the std. BCM M4 & the new MK2 are thermal fit.......... I don't know for a fact any others that are, possibly some JP's (not confirmed).

extension spec is .998-.9987 Bat's is advertised at .999 & so is WOA .999 (the extension on my last custom from BHW was a BAT and measured .9986)
Bat used to offer 1.000 (+.001) extensions (not any more) & the WOA competition extension is a bastard child with a different thread pitch. CLE will not use the WOA extension from what I've been told.

Upper extension bore i.d. spec is .999 - 1.001 & none of the std uppers I have measured have been below 1.000 average is more like 1.0005

So without a thermal fit upper & using a BAT .999 ext + 1.0005 = .0015 slip fit. I've had .0014 - .0018 on the last 4 I've put together.
Those dimensions are measured with top of the line Mitutoyo .0001 mic's not harbor freight junk.
 
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I have used several PSA PA10 uppers that were tight as anything I have ever used, to the point, oven, action rod, rawhide mallet and sweat to seat a barrel. Their small frame stuff was all over the map. The two rebarreled PA10 rifles using Faxon Big Gunner barrels are as accurate as anything I own, bolt or S/A.

I used a BCM Mk4 to remount a PSA 22lr upper, that thing is a laser to 50yds with premium ammo. The original upper receiver was loose and out of spec, so much so you could wiggle the barrel with the nut torqued and change POI.

Most of the Aero uppers I have are snug depending on the barrel used, but nothing like the BCM.
 
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Cornerstonearmory said:
It would be worth it. They are sick. That rifle is so solid.
Click to expand...
I sniffed around the internet for them, but as everything else good, I just need to get in line cause I couldn't find any. Even emailed BCM they said they are allocating all MK2 uppers to their own builds until they have a over supply of them. Might be a while till they are back in stock.
...
 
longshot2000 said:
Strike BCM. They are pretty common mil spec, not tight. Knights is always tight. It is like other said, the secret it usually with the barrel extension.
Click to expand...

I've used 5 or 6 BCM uppers and assembled a few more (most were bought as their "blems", all were bought as stripped uppers), and ALL of them required heating to install and were very tight/solid fits. I buy BCM uppers specifically because they are thermo fit uppers with standard barrel extensions.
 
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Orphanedcowboy said:
I have used several PSA PA10 uppers that were tight as anything I have ever used, to the point, oven, action rod, rawhide mallet and sweat to seat a barrel. Their small frame stuff was all over the map. The two rebarreled PA10 rifles using Faxon Big Gunner barrels are as accurate as anything I own, bolt or S/A.

I used a BCM Mk4 to remount a PSA 22lr upper, that thing is a laser to 50yds with premium ammo. The original upper receiver was loose and out of spec, so much so you could wiggle the barrel with the nut torqued and change POI.

Most of the Aero uppers I have are snug depending on the barrel used, but nothing like the BCM.
Click to expand...

Interesting on the PA10. Mine is a pretty standard loose sliding fit, but it's a gen 1 rifle. Were yours the gen 2 versions?
 
Yondering said:
I've used 5 or 6 BCM uppers and assembled a few more (most were bought as their "blems", all were bought as stripped uppers), and ALL of them required heating to install and were very tight/solid fits. I buy BCM uppers specifically because they are thermo fit uppers with standard barrel extensions.
Click to expand...
I’m the same - about the same number of uppers because they’re not expensive and they’re thermofit..
I had to modify my lapping tool to fit the BCM uppers.
They‘re my “Go To” M4 type forged upper.
 
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Interesting comments about the BCM's... all mine are older bought, and were / are gonna be thermal fit tight.

I placed numerous brand barrels ( RE's ) into them and all were snug and not gonna slide in. ( Barrels, LaRure, DD, FN, PSA, Criterion, Faxon, Rem Defense... etc ad nauseam. )

My Rainer Arms uppers ( Large frame and small ) are a good example of using Loctite to fill voids in the fit. Great uppers just "cut" funny.

My PSA's have been ( large frame and small ) loose enough fit to make Loctiting them in "prudent", IMHO... not crazy loose, but slip in place loose.

As mentioned earlier... the SOLGW uppers are great fit everywhere, upper to various powers, parts kits and barrel fit ( thermal needed )
 
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Last build I did was a ADM billet and a rosco Nitrided 11.5 barrel. I had to freeze the barrel and heat up the upper. I had to use a rubber mallet to get it all the way seated. It was a tight fit.
 
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Kadams1563 said:
Last build I did was a ADM billet and a rosco Nitrided 11.5 barrel. I had to freeze the barrel and heat up the upper. I had to use a rubber mallet to get it all the way seated. It was a tight fit.
Click to expand...

Odd question about that ADM upper. Set screw or roll pin to secure the forward assist?
 
longshot2000 said:
Strike BCM. They are pretty common mil spec, not tight. Knights is always tight. It is like other said, the secret it usually with the barrel extension.
Click to expand...
BCM makes dimensionally, the best machined forged uppers that you can buy. You can always bed the extension but not having to face the receiver and knowing everything is dimensionally correct.

They are a fantastic base for any build. There was a time when BCM was rejecting 60% of their uppers becuase they were not built to spec. They changed machine shops a few times until they found one that could consistently deliver. Most companies mentioned here could give two shits and will sell anything that comes through the loading dock. Some companies care, some don't. Some don't even know the difference.
 
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After doing some poking around it looks like we can add Gibbz side chargers to this list.
 
Anyone have experience with the Wilson billet upper?
They say the bolt raceway is undersized (interesting), but don't say anything about barrel extension.
 
CrabsandFootball said:
BCM makes dimensionally, the best machined forged uppers that you can buy. You can always bed the extension but not having to face the receiver and knowing everything is dimensionally correct.

They are a fantastic base for any build. There was a time when BCM was rejecting 60% of their uppers becuase they were not built to spec. They changed machine shops a few times until they found one that could consistently deliver. Most companies mentioned here could give two shits and will sell anything that comes through the loading dock. Some companies care, some don't. Some don't even know the difference.
Click to expand...

Not looking to start an argument at all... but my older ones showed just as much unevenness at the receiver face as any other upper.

I suspect, the unevenness is from anodizing ... not from milling machines being off.
 
CrabsandFootball said:
Wilson parts are gtg, very well made.
Click to expand...
I have no doubt they are GTG , should have been more specific.

To OP's point, I'd like to know if anyone can confirm billet Wilson's are thermal fit on the barrel extension? Doesn't say in their description.

The Wilson billets are the only ones I've seen that are undersized on the bolt carrier raceway.
 
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