That's how I ended up with one. Figured at that price I couldn't lose. It absolutely required a frozen barrel and heated receiver to make the magic happen.
Who Makes Thermal Fit Stripped Uppers?
- Thread starter JS8588
- Start date
Very much a thermal fit upper.
BKF M4 MOD-0 Stripped Upper Receiver - Black (Light T-Marks)
BKF M4 MOD-0 Stripped Upper Receiver - Black (Light T-Marks)bkingsfirearms.com
Very much thermal and priced right. Ordered one for a friend based on your opinion and it took heat and ice. Appreciate it
Glad it did the trick. The one I have happens to be a laser. Not saying it's the receiver, but it can't be hurting.
Good to hear!
This is a hunting and range set up for his son. 20” WC 6.5 Grendel barrel. Know soon I’m sure, it’s all together now.
I’d use another for a quality felt lightweight thermal upper though
Yeah I've got 4 or 5 of those now (I think from your recommendation here IIRC), they've all been a strong thermal fit and shoot really well when matched with good barrels.
To clarify for anyone buying these though, their standard uppers are not thermal fit, but the "Mod 0" are. It's in their descriptions on the website too, for reference.
Always happy to help other people spend their money!
Negative Ghost Rider....
JP Thermo Fit Receivers are under sized, and thier small frame barrel extensions are standard .98 IIRC..
You can deal with this one of three ways, you can order receivers that are undersized, have a custom barrel made with a oversized barrel extension or you can go hillbilly Locktite..
My current .223 that I just finished utilizes the JP Thermo fit Receiver, and the the White Oak Competition Barrel exstenion.. she's definitely the most ridged upper I've ever built.
My current .223 that I just finished utilizes the JP Thermo fit Receiver, and the the White Oak Competition Barrel exstenion.. she's definitely the most ridged upper I've ever built.
It's. 998... if someone is making .98 on purpose I want to know. That would NOT be a thermal fit. It would be a broken receiver with any standard barrel.
The spec is -
BARREL- 0.998 TO 0.9995
Reviever- 0.999 to 1.000
The spec is -
BARREL- 0.998 TO 0.9995
Reviever- 0.999 to 1.000
The socket on the upper is intentionally undersized, that's the intent of a thermal fit. An example is linked in post #103:
"The Inside Diameter for the barrel extension is slightly undersized for a tighter fit to the barrel and will produce a more accurate rifle. Please note: you may need to use a heat gun or hair dryer to warm up threaded bore of receiver and freeze your barrel if your barrel extension is too tight."
bought a couple BCM uppers for the 'extra' Proof stainless barrel I'd forgotten ordering
Better to have one too many than one too few since VA's legislature is mostly leftist gun-grabbing morons now
M
Better to have one too many than one too few since VA's legislature is mostly leftist gun-grabbing morons now
M
Yes. But it's a big difference between a .002 thermal fit and a .020 broken upper. That is so far out of a forced fit it's not possible. Numbers matter. Multiple people claimed a .98 receiver. It would be .998.
The -0.0005 difference between the receiver ID and the barrel OD is the thermal fit.
In prespective a FN5 forced fit would have 0.0033" MAX interference.
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JP is an interesting situation for thermofit all the higher end JP stripped uppers are Thermo.
If you buy a JP-15™ Stripped Forged Upper Receiver it's not thermofit.
If you buy a JP-15 assembled upper or rifle it is thermofit. I believe they have a different upper they sell at retail that is not used for the builds.
That may be something WOA used to do but not anymore. I recently emailed them asking this question and Jane replied by telling me they are all mil-spec and they do not offer alternate sizing.
The last couple of BCM uppers I bought (retail) were not exactly thermofit.
The barrel extension goes about 2/3 - 3/4 the way in before it starts to get snug and with a little effort I can push it all the way in.
Not real happy with their uppers anymore.
Not as bad as the Aero Precision AR-10 upper I have.
Needs 0.001 shim to make it tight. Almost like a hot dog down a hallway without shims.
The barrel extension goes about 2/3 - 3/4 the way in before it starts to get snug and with a little effort I can push it all the way in.
Not real happy with their uppers anymore.
Not as bad as the Aero Precision AR-10 upper I have.
Needs 0.001 shim to make it tight. Almost like a hot dog down a hallway without shims.
I've been using B. King's thermofit uppers lately with great results.
I just built my 6 ARC upper with a BCM demo upper and had to heat it up to go in also just like all the ones before it.
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I just built out a B. Kings M5 Mod-0 large frame upper. Extension is -.004 under an Aero. Fits their M5 Mod - 0 lower like a glove.
Forgot to point out in this earlier comment - B Kings sells both mil-spec and thermofit "Mod-0" uppers. Gotta look at the description to understand what you're getting.
I have emailed several manufacturers of thiccc billet uppers that have forward assists and are in stock as of today, that's just my preference.
So far these are the ones that have replied and I'll try to update when the others do as well.
I know there are many other uppers that are thermal fit (BCM, Centurion, etc.), but I'm looking for the thickest upper that is thiccc all the way to the threads, with a forward assist.
So far these are the ones that have replied and I'll try to update when the others do as well.
| Brand | Product | Price | Thermal Fit? |
| Stubborn Mule | Octagonal | 320 | Not Thermal Fit, per email reply |
| Grendel Hunter | Billet | 159.99 | Not Thermal Fit, per email reply |
| 360 Precision | HD Billet | 230 | emailed |
| Juggernaut | Billet | 174 | Not Thermal Fit, per email reply |
| YHM | Billet YHM-110-Billet | 196.95 | Not Thermal Fit, per email reply |
| Toxic Arms | Billet | 99 | emailed |
| San Tan | Pillar Billet | 209 | Thermal Fit, per email reply |
| Rogue Ops | RO21 billet | 205 | Not Thermal Fit, but tight, per email reply |
| GunTec | Billet | 139.95 | emailed |
| Oregon Rifleworks | Billet | 249.99 | emailed |
| B King Firearms | Billet series stripped | 99.95 | emailed |
I know there are many other uppers that are thermal fit (BCM, Centurion, etc.), but I'm looking for the thickest upper that is thiccc all the way to the threads, with a forward assist.
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Add Cross Machine Tool to your list.
I don't really know how much thicker they are than BCM, but they are very nice uppers & IMHO, are lightly thermal fit (as is SanTan), compared to BCM, which is very tightly thermal fit.
CMT Upper
I don't really know how much thicker they are than BCM, but they are very nice uppers & IMHO, are lightly thermal fit (as is SanTan), compared to BCM, which is very tightly thermal fit.
CMT Upper
Good work. I've considered posting a new thread for the current year, but hell, let's keep this one going.
VKTR
Mitchell Defense
Munitionworks
Icon Defense
All thermal fit.
Yeah I have one with a Craddock RTR and it was thermo as well. I like it so far. The whole length of the body runs tight, I had to use a bev block to torque my barrel nut bc the URR wouldn’t fit into it.
Rooftop has 25 Broadsword M89 uppers in stock now if anyone was eyeing one:
www.rooftopdefense.com
Sons of Liberty Gun Works AR/M4 Stripped Broadsword Upper Receiver | Rooftop Defense
Buy Sons of Liberty Gun Works AR/M4 Stripped Broadsword Upper Receiver | Sons of Liberty's flagship stripped upper made for use with their Drivelock rails.
www.rooftopdefense.com
So I’ve got a factory built BCM 16” MK2 upper that I’m going to yank the barrel and install a SOLGW 18” SPR barrel. I’ve never tried to disassemble a BCM upper but have always heard it’s a bitch. How much heat and ass pain is expected to be needed to pull the rail and barrel? Not sure what the SOLGW barrel extension mics at.
Only thing close I’ve done is install a MCMR rail on another rifle and all I had handy in a pinch was a hair dryer lol and it took a lot of persuasion just getting the rail on. At least I have a heat gun this time.
Only thing close I’ve done is install a MCMR rail on another rifle and all I had handy in a pinch was a hair dryer lol and it took a lot of persuasion just getting the rail on. At least I have a heat gun this time.
I have a 1200 watt heat gun and I use it on high for about 60-90 secs to install a barrel and about 90-120 secs to remove a barrel from thermofit uppers (along with a rubber mallet and 1" diameter wooden dial rod). You can do the same for removing the bcm rail
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Can't remember if I posted this or not but Geissele uppers aren't thermal fit. I switched out a VSeven upper to a Geissele as I "needed" ODG and it was not thermal fit. With that said, accuracy didn't drop off one bit.
Updated
I worded my email inquiry to be non-bias in regards to the thermal fit, I wanted it to be neutral like I wasn't looking for or against thermal fit. Nearly all of the 'not thermal fit' replies have a sense of negativity towards thermal fit. I wonder why that is?
| Brand | Product | Price | Thermal Fit? |
| Stubborn Mule | Octagonal | 320 | Not Thermal Fit, per email reply |
| Grendel Hunter | Billet | 159.99 | Not Thermal Fit, per email reply |
| 360 Precision | HD Billet | 230 | Not Thermal Fit, per email reply |
| Juggernaut | Billet | 174 | Not Thermal Fit, per email reply |
| YHM | Billet YHM-110-Billet | 196.95 | Not Thermal Fit, per email reply |
| Toxic Arms | Billet | 99 | emailed |
| San Tan | Pillar Billet | 209 | Thermal Fit, per email reply |
| Rogue Ops | RO21 billet | 205 | Not Thermal Fit, but tight, per email reply |
| GunTec | Billet | 139.95 | emailed |
| Oregon Rifleworks | Billet | 249.99 | Not Thermal Fit, per email reply |
| B King Firearms | Billet series stripped | 99.95 | emailed |
I worded my email inquiry to be non-bias in regards to the thermal fit, I wanted it to be neutral like I wasn't looking for or against thermal fit. Nearly all of the 'not thermal fit' replies have a sense of negativity towards thermal fit. I wonder why that is?
I'm guessing most manufactures/resellers are avoiding the thermofit b/c they are probably more likely to be complained about/returned by ignorant customers who don't realize the barrel isn't supposed to slide right in.
Here's my updated list of thermofit billet stripped uppers (I don't have the same requirements you're looking for though re: beefy near the threads, on my list the one that seems to check that box would maybe be the Broadsword 89 upper)
- San Tan Tactical Billet Upper ($175) (thermofit)
- Centurion C4 Billet Upper ($190) (thermofit)
- SOLGW Broadsword 89 Billet Upper ($313) (thermofit)
- Lantac Upper Advanced Receiver (billet) ($175) (thermofit)
- CMT Ultra Precision Billet Upper (UPUR-1) ($200) (thermofit)
- Icon Defense Ambi Billet Upper ($230)
- Precision Firearms 1000 PF Billet Mod 1 ($225)
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I know these are both older posts, but just for info on my 2x 2012 vintage JP SCR11s that I purchased new as complete rifles, even though they were advertised as having thermo fit uppers, were actually standard diameter slip fit uppers paired with standard diameter extensions with shims... I found this out a few weeks ago when changing handguards.
One of them was indeed thermofit with a 0.002 shim producing a 0.0015 interference fit according to my mic and dial bore gauge, and the other one had a 0.001 shim which actually yielded a 0.0004 slip fit (the barrel lightly tapped out without any heat.) JP did not use any retaining compound, only the shims... Totally unexpected seeing the shims fall out during disassembly.
I ended up cutting new 0.002 stainless shims for both and thermo fit them giving 0.0015 interference fit on both. Trying to hang onto a frozen barrel and shim and then using your fingers to guide the shim and barrel into an upper you just heated up without scorching your fingertips or balling up the shim is fun. Wish both those uppers were undersized as JP claimed they were. Maybe shims are just how they built them back around 2012, or maybe they accidentally ran a batch of uppers with a standard diameter bore and decided to use shims rather than scrap them?
Either way, good info in this thread as I'm getting ready to build another upper or two and want to go thermal fit on them.
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