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Posted: 2/9/2020 7:38:37 PM EDT
This is my 12th build so know what I am doing. This is however the first time using a BCM upper. I have always used Aero uppers. This barrel will not fit into the upper. I heated the upper and cooled the barrel as well as plenty of grease. It went halfway in and that was it. I destroyed my rubber mallet, and my garden rake in order to use the handle to knock the barrel back out. I had to use a BFH after the first two smaller ones failed to even move it. I know BCM builds their uppers on the tighter side but this is fucking ridiculous. Any more tips than what I have already tried? I should have stuck with what I know to work.
(Update 19 Feb) Here she is all together and tested. Zero issues period. Once she was dialed in, all shots were landing in the white center at 50yds. This is a 200yd gun for me, so 1” groups do not matter.  RRA Lower (SBR’ed 12 years ago) BCM Upper BA Hanson Barrel BCM KMR Rail Toolcraft BCG Strike Industries CH Magpul MBUS Pro sights Magpul SL stock Magpul grip YHM 5.56 QD Suppressor (12 years old, but still holds it own with Suppressors costing 3x’s as much) Bushnell Lil P Prismatic. Nice little optic for a SBR or pistol. 
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Posted: 2/9/2020 7:41:39 PM EDT
[#1]
Yep, been there. Did you use a heat gun? Blowdryer won't get it hot enough
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Posted: 2/9/2020 7:55:53 PM EDT
[#2]
Heat it up and wack it in
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Posted: 2/9/2020 8:23:32 PM EDT
[#3]
I use a propane torch to heat the receiver threads. Put the barrel in the freezer for an hour or so.
Screw an a2 flashhider on the barrel. Upper goes between wooden blocks in the vise. I beat the barrel in with a scrap 2x4 chunk. It'll go. You probably need more heat. |
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Posted: 2/9/2020 9:10:03 PM EDT
[#4]
Handheld torch and BFH.
It will go unless something is out of spec. |
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Posted: 2/9/2020 10:07:52 PM EDT
[#5]
Quote HistoryQuoted:
It'll go. You probably need more heat. |
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Posted: 2/9/2020 10:20:56 PM EDT
[#6]
Dry ice and rubbing alcohol to cool the barrel.
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Posted: 2/9/2020 11:21:57 PM EDT
[#7]
Definitely use a heat gun.
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Posted: 2/9/2020 11:29:19 PM EDT
[#8]
Quoted:
This is my 12th build so know what I am doing. This is however the first time using a BCM upper. I have always used Aero uppers. This barrel will not fit into the upper. I heated the upper and cooled the barrel as well as plenty of grease. It went halfway in and that was it. I destroyed my rubber mallet, and my garden rake in order to use the handle to knock the barrel back out. I had to use a BFH after the first two smaller ones failed to even move it. I know BCM builds their uppers on the tighter side but this is fucking ridiculous. Any more tips than what I have already tried? I should have stuck with what I know to work. |
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Posted: 2/9/2020 11:34:25 PM EDT
[#9]
Quote HistoryQuoted: I would just use an Aero upper. No reason to buy a BCM upper if it's not a complete upper. 
You don't know what you're talking about. BCM uppers are the only thing of theirs worth buying. You can get a blem with parts for $60. Their barrels suck, and all of their other parts are overpriced. |
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Posted: 2/10/2020 12:20:46 AM EDT
[#10]
I just finished a build, BCM upper and Faxon 762x39 barrel.
She was tight, but wasn't any trouble. I cleaned the barrel extension and upper real good, then applied Aeroshell 33 grease Next I heated the upper on the kitchen stove for couple minutes, I got it half way in with hands only, then tapped in the rest of the way. When I install barrel nut I crank it on over torque and release couple times then torque to spec & time my HG If I was the OP I would apply more heat, maybe torch propane or map and beat it in, maybe heat and slow cool several time then beat in. The upper will heat faster than the barrel, point being to heat upper not so much the barrel |
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Posted: 2/10/2020 12:46:34 PM EDT
[#11]
Put the barrel in the freezer then heat the receiver up and insert the barrel.
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Posted: 2/10/2020 12:49:05 PM EDT
[#12]
Have you measured the barrel extension and the upper receiver to make sure both are in specs?
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Posted: 2/10/2020 11:48:37 PM EDT
[#13]
Call BCM and see what they say.
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Posted: 2/11/2020 10:33:46 AM EDT
[#14]
BCM uppers are thermal fit. Many quality uppers are.
 The Secret of Thermo-Fit™ |
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Posted: 2/11/2020 10:46:41 AM EDT
[#15]
Measure the I.D. of the receiver, and O.D. of the barrel extension. If the extension diameter is > .004” bigger than the receiver inside diameter, you should use a different upper or barrel.
.001-.0015” interference is about ideal. Getting over .002” interference approaches the zone of plastic deformation for the receiver. |
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Posted: 2/11/2020 7:42:57 PM EDT
[#16]
I had one like this once. Large frame Mega arms upper and a Ranier match barrel. I used some 1000 grit sandpaper wet and went a swipe at a time on the inside of the receiver until it felt like it was getting close to fitting. Don’t go through the anodizing. Then I froze the barrel and whacked it in place.
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Posted: 2/11/2020 8:26:11 PM EDT
[#17]
Quote HistoryQuoted:
BCM uppers are thermal fit. Many quality uppers are.  https://www.youtube.com/watch?v=-cOlNGxUhsk |
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Posted: 2/12/2020 11:50:53 AM EDT
[#18]
Quote HistoryQuoted:
BCM uppers are thermal fit. Many quality uppers are. https://www.youtube.com/watch?v=-cOlNGxUhsk I went to Home Depot and purchased a kit for $19. I then put the barrel in a vice and heated the receiver. The entire process took about 1.5 mins from screwing the torch on, heating the receiver for about 30 secs and pushing the receiver onto the barrel. No tapping was necessary.
Now my next issue. My BCM KMR Rail is about a 1/2 too short. The gas system is carbine length, so the gas block sticks out about a 1/4 inch  . It doesn’t look too bad and I have seen rifles with way more of the gas block exposed than mine. I may just keep it this way since I got such a great deal on the rail.
Rail mocked up. 
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Posted: 2/12/2020 12:57:09 PM EDT
[#19]
Quote HistoryQuoted: THANK YOU SO MUCH FOR THIS. I went to Home Depot and purchased a kit for $19. I then put the barrel in a vice and heated the receiver. The entire process took about 1.5 mins from screwing the torch on, heating the receiver for about 30 secs and pushing the receiver onto the barrel. No tapping was necessary.
Now my next issue. My BCM KMR Rail is about a 1/2 too short. The gas system is carbine length, so the gas block sticks out about a 1/4 inch . It doesn’t look too bad and I have seen rifles with way more of the gas block exposed than mine. I may just keep it this way since I got such a great deal on the rail.
Rail mocked up. https://i.postimg.cc/6Q3m27dh/435-A670-E-D004-4662-B075-21591-FB0-EB3-E.jpg How are you attaching the gas block? Pinned would be your best bet. At the very least i would dimple the barrel(if not already) for the set screws and use rockset |
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Posted: 2/12/2020 1:41:06 PM EDT
[#20]
It is BA Hanson barrel, so it comes pinned. I’m going to leave it as is. I don’t want the hassle of trying to sell this one and then spending more for just an extra inch.
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Posted: 2/13/2020 11:50:35 AM EDT
[#21]
It looks good. I wouldn't sweat the little bit of GB sticking out. It is very minimal.
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Posted: 2/13/2020 11:58:37 AM EDT
[#22]
Nothing wrong with a little bit of gas block showing - especially if it's pinned.
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Posted: 2/19/2020 7:20:57 PM EDT
[#23]
Update in OP.
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Posted: 2/20/2020 9:35:55 AM EDT
[#24]
Quote HistoryQuoted: If you notice JP is able to consistently offer an ideal fit between receiver and barrel extension by tightly controlling tolerances of both. Use one or the other with another manufacturers receiver or barrel and all bets are off. It is absolutely possible to buy "quality" components (JP upper with Krieger barrel etc. etc.) which are within specified tolerance ranges and end up with less than ideal fitment (receiver on upper end of acceptable, and barrel extension on lower end or vice versa). Most quality receivers will be thermal fit. It's part of the design, not because parts don't fit. |
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Posted: 2/20/2020 9:37:49 AM EDT
[#25]
Quote HistoryQuoted: THANK YOU SO MUCH FOR THIS. I went to Home Depot and purchased a kit for $19. I then put the barrel in a vice and heated the receiver. The entire process took about 1.5 mins from screwing the torch on, heating the receiver for about 30 secs and pushing the receiver onto the barrel. No tapping was necessary.
Now my next issue. My BCM KMR Rail is about a 1/2 too short. The gas system is carbine length, so the gas block sticks out about a 1/4 inch . It doesn’t look too bad and I have seen rifles with way more of the gas block exposed than mine. I may just keep it this way since I got such a great deal on the rail.
Rail mocked up. https://i.postimg.cc/6Q3m27dh/435-A670-E-D004-4662-B075-21591-FB0-EB3-E.jpg Just off the top of my head, Hodge, ZEV, BCM, SOLGW, and SIONICS uppers are thermal fit. Aero Precision uppers are not. Most people are afraid to heat up parts, but you're not really heating anything up beyond what it will experience with a high volume of fire. |
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Posted: 2/21/2020 1:44:36 AM EDT
[#26]
My BCM upper and barrel slide right in and out. The fitment is very close, but I wouldn't call it tight.
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