In the process of building a san tan upper with a faxon 9" 300 blk barrel. Super tight fit.. So, I put grease on barrel extension and left the receiver outside in the sun a couple hours (102*degrees today). With the use of a rubber mallet i went as far as I could (pic). So, would it be ok to torque the barrel nut with the hope it would seat the barrel? Any possible issues from it being this tight?
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Gunsmithing AR Barrel Tight Fit
- Thread starter GibsonL5
- Start date
Put the barrel in the freezer over night. Tomorrow before you try to seat it heat the receiver extension a bit with a heat gun. Should slide on a lot easier.
So your saying to remove the barrel I assume? I tried to remove this even and nothing.. It wont budge, but I'm open to suggestions for removal process. I'm not sure how I could get it out without damage...?
You can use a wooden dowel from the back of the receiver and tap it out.
My only concern with the barrel nut idea is that you could possibly reach your desired torque but not have the barrel fully seated.
I guess you could torque it down a bit and remove it to make sure it went all the way down. I haven’t tried this but someone else may chime in that’s got some experience with it.
My only concern with the barrel nut idea is that you could possibly reach your desired torque but not have the barrel fully seated.
I guess you could torque it down a bit and remove it to make sure it went all the way down. I haven’t tried this but someone else may chime in that’s got some experience with it.
Tap it out as mentioned
Chill barrel and heat up receiver and rejoice in a nice Extension fit afterwords
Chill barrel and heat up receiver and rejoice in a nice Extension fit afterwords
So any issues down the road with this being extremely tight? Ive used san tan receivers on my last 3 builds with criterion barrels. They were super snug with no slop, but nothing like this faxon barrel. I've used aero uppers with faxon barrels in the past and there was slop.
Only if you consider better accuracy an “issue” haha. I like having to fit them in this way. Makes for a better finished product.
Play Ron Jeremy and just spit on it. 
A hot hair dryer has worked for me in the past.
A wimpy one will not work. Not all heat the same.
I was a tad nervous about taking a paint heat gun to my upper, so used the hair dryer and it worked.
A hot hair dryer has worked for me in the past.
A wimpy one will not work. Not all heat the same.
I was a tad nervous about taking a paint heat gun to my upper, so used the hair dryer and it worked.
Its gonna be tough to tighten it all the way down.
My bcm blem upper is a thermo fit too, stuck the barrel in the deep freeze later stuck the upper in the oven on warm for 5 minutes, got hot enough that I used an oven mitt. Took both out, smeared grease on both and smashed them together with my hands and I got about as far as you did so I smashed it on using a 2x4 to the back of the receiver with the barrel in a vice to not mar anything too much.
When that barrel goes Im just going to throw the $50 upper away with it. I dont see how I would ever get it out and it being worth my time and efforts and cussing. I wouldnt trust just torquing it on to fully seat it from where youre at, youre going to want some mechanism of thermo expansion to make it easier.
My bcm blem upper is a thermo fit too, stuck the barrel in the deep freeze later stuck the upper in the oven on warm for 5 minutes, got hot enough that I used an oven mitt. Took both out, smeared grease on both and smashed them together with my hands and I got about as far as you did so I smashed it on using a 2x4 to the back of the receiver with the barrel in a vice to not mar anything too much.
When that barrel goes Im just going to throw the $50 upper away with it. I dont see how I would ever get it out and it being worth my time and efforts and cussing. I wouldnt trust just torquing it on to fully seat it from where youre at, youre going to want some mechanism of thermo expansion to make it easier.
Just heat the receiver up A LOT with a heat gun. Don’t be afraid, it’s not going to turn into a molten pool in front of you.
I had a Aero upper and BA barrel that weren’t going to go together without help. Heated the shit out of the receiver and the barrel dropped right in. Once it cooled there was no way I could pull it out.
Torque, loosen, and then retorque the barrel nut and you’re off to the races.
I had a Aero upper and BA barrel that weren’t going to go together without help. Heated the shit out of the receiver and the barrel dropped right in. Once it cooled there was no way I could pull it out.
Torque, loosen, and then retorque the barrel nut and you’re off to the races.
I do this with every AR upper I build. You heat up the front barrel extension area of the upper receiver with a heat gun for a few minutes, then the barrel slides right in. Torque on the barrel nut. Let it cool. Done
You won't hurt the aluminum get it hot. Everyone here would be happy with the light interference fit you currently have. Put it together and try it out. If it doesnt shoot you already know it only took 3 taps to take apart.
I have one Faxon barrel...I think they're designed to be thermo-fit.
There are a couple of manufacturers of barrels and uppers that will require the process.
As a side note: I did get a ridiculously tight barrel in once using a rubber mallet and then hitting that with a 2lb sledgehammer when the option to freeze the barrel wasnt there. It worked and the barrel shoots fine...but it did eat up the mallet.
There are a couple of manufacturers of barrels and uppers that will require the process.
As a side note: I did get a ridiculously tight barrel in once using a rubber mallet and then hitting that with a 2lb sledgehammer when the option to freeze the barrel wasnt there. It worked and the barrel shoots fine...but it did eat up the mallet.
Who said anything about taking a torch to anything? Put a damn hair dryer to it until it's hot to the touch and the barrel goes right in. Geez.
Everyone that's bothered to type in a response based on empirical evidence has said heat gun or hair dryer.
Put the barrel in the freezer and put the upper in the oven at 170ºF, barrel should drop in, allow to reach room temp and assemble
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