Thermal fitting a receiver that isn't thermal fit? I had an idea

[KCode]

So if thermal fit receivers are good then shouldn't this idea be just as good for a receiver that isn't?

If a barrel can slide into an upper with little force, it isn't thermal fit. And if you cannot place a (just example) .0005 shim between the receiver and barrel...Following the same logic as thermal fit, why wouldn't you just heat up the receiver and place the .0005 shim on the barrel and then install the barrel/let it cool? Maybe even apply 620 too...

I'm sure I'm wrong for some reason but it was an idea I had.

 

[6.5SH]

So if thermal fit receivers are good then shouldn't this idea be just as good for a receiver that isn't?

If a barrel can slide into an upper with little force, it isn't thermal fit. And if you cannot place a (just example) .0005 shim between the receiver and barrel...Following the same logic as thermal fit, why wouldn't you just heat up the receiver and place the .0005 shim on the barrel and then install the barrel/let it cool? Maybe even apply 620 too...

I'm sure I'm wrong for some reason but it was an idea I had.

You can. You'll have an easier time assembling if you loctite the shim onto the extension first. Use some painters tape and a rubber band to hold it together while it sets up.

 

[Redlion]

You can certainly do that.

 

[B Man]

Thats exactly how I’ve done every upper that wasn’t thermal fit.

 

[Cascade Hemi]

So if thermal fit receivers are good then shouldn't this idea be just as good for a receiver that isn't?

If a barrel can slide into an upper with little force, it isn't thermal fit. And if you cannot place a (just example) .0005 shim between the receiver and barrel...Following the same logic as thermal fit, why wouldn't you just heat up the receiver and place the .0005 shim on the barrel and then install the barrel/let it cool? Maybe even apply 620 too...

I'm sure I'm wrong for some reason but it was an idea I had.

620 has a relatively short working time and cures with heat. If you heat the receiver up enough to expand for a thermal fit and then apply 620 you will glue the barrel half way in/out.

 

[Darryle]

You can also use 3m electrical tape pulled tight around the shim after gluing to get the shim as tight as possible on the barrel extension.

Other electrical tapes may work, but I know 3m has quite a bit of elasticity when stretched.

 

[KCode]

620 has a relatively short working time and cures with heat. If you heat the receiver up enough to expand for a thermal fit and then apply 620 you will glue the barrel half way in/out.

How? I'm not understanding this.

 

[Cascade Hemi]

How? I'm not understanding this.

How do you plan to shove a shimmed barrel covered in glue that dries with heat into a hot thermal fit receiver without the glue drying instantly before the barrel is all of the way in?

 

[KCode]

How do you plan to shove a shimmed barrel covered in glue that dries with heat into a hot thermal fit receiver without the glue drying instantly before the barrel is all of the way in?

Why do you think 620 dries instantly with heat?

 

[Cascade Hemi]

Why do you think 620 dries instantly with heat?

Because it does and I have experience doing exactly what you suggested. It doesn't work and you get the barrel stuck half way in the receiver.

 

[supercorndogs]

I have thermal fit and glued three together with 609. Stuck one half way and had to heat it up and drive it out, clean it up and start over. With the heat the loctite sets very fast where it drips out. You have to wipe it rite away or it hardens and you have to pick or chip it off.

Last thermal fit I did stuck half way while test fitting to make sure it was hot enough. I tapped it in and forgot the loctite.

 

[fedupflyer]

I have thermal fit and glued three together with 609. Stuck one half way and had drive it out, clean it up and start over. Wit the heat the loctite sets very fast where it drips out. You have to wipe it rite away or it hardens and you have to pick or chip it off.

Last thermal fit I did stuck half way while test fitting to make sure it was hot enough. I tapped it in and forgot the loctite.

I did something similar the first time I used green loctite on a thermal fit upper. I did not get the upper hot enough with my heat gun and got the barrel stuck about 2/3 the way in.
It was a pain to remove and start over.

 

[ArmchairOperator]

Depending on the amount of clearance, you can just use green loctite to “bed” the extension to the receiver. There are a couple different grades of green that are designed for different amounts of clearance. Works really good and is way easier than trying to use shims.

 

[hlee]

Glue the shim to the barrel extension. Assemble with receiver once cured…

 

[fedupflyer]

Depending on the amount of clearance, you can just use green loctite to “bed” the extension to the receiver. There are a couple different grades of green that are designed for different amounts of clearance. Works really good and is way easier than trying to use shims.

Nope, just gluing the barrel wont help. Tried it
If you don't have a receiver that requires thermal mating its almost pointless to just lather some green loctite on the barrel extension.
Shimming first, then gluing is the second step.

 

[supercorndogs]

Glue the shim to the barrel extension. Assemble with receiver once cured…

Green expands when it cures.

I would rather glue than thermal fit anymore. I did my last 4 or 5 with thermal fit recivers from BCM. I think all but one is glued with green 609. Probably my best shooter is not thermal fit or shimmed. Just glued into an ar stoner billet receiver.

 

[Cascade Hemi]

I've had good luck bedding without thermal fit using Indian Head.

 

[ArmchairOperator]

Nope, just gluing the barrel wont help. Tried it
If you don't have a receiver that requires thermal mating its almost pointless to just lather some green loctite on the barrel extension.
Shimming first, then gluing is the second step.

I disagree. You’re right that it won’t work if the clearance is too much, but if you are within the parameters of the green loctite, it works. That’s actually what it’s designed to do. Not the green 200 series thread locker, it’s the green retaining compound, 600 series. Shimming works but I’m not a fan of jamming metal in there. Truthfully, I’ve gotten away from either. If it’s thermal fit cool, if not I just let it fly. The amount of pressure created by the barrel nut will lock it from moving. I think you can build just as accurate and precise of a rifle thermal fit as not thermal fit, but that’s just my opinion.