74 Barrel Issue

[762x40]

Okay I ran into my first problem populating a barrel. While measuring the inner portion of rsb that makes contact with the barrel I found it to measure 0.689, while the barrel portion is between 0.676 - 0.679. I attached a picture so you could see how off it is.

Any suggestions? New rsb with tighter tolerances? New Barrel?

Any help will be greatly appreciated, thanks.

[ott1]

That part of the barrel for the RSB seems way undersize. It should measure .690+-0.02.

[baker1184]

Knurle the barrel?

[762x40]

That part of the barrel for the RSB being way undersized. Is it rare or even fixable?

[762x40]

Knurle the barrel?

I'm new to knurling, will Knurleing the barrel work for the amount of space that I currently have on the barrel?

[ar15barrels]

I'm new to knurling, will Knurleing the barrel work for the amount of space that I currently have on the barrel?

Straight knurling can give you an effective increase in diameter of 0.010".
You need 0.020" or more.
You could get that with some deep knurling, but it will collapse during pressing and will not be as solid as a proper diameter barrel.

I would look for another barrel.

[ott1]

Might it be possible to sleeve that part of the barrel and turn it down to size?

[ar15barrels]

Might it be possible to sleeve that part of the barrel and turn it down to size?

Yes.

[kcstott]

Might it be possible to sleeve that part of the barrel and turn it down to size?

That would be my suggestion

[Dan FS71]

Straight knurling can give you an effective increase in diameter of 0.010".
You need 0.020" or more.
.

rsb 0.689, barrel is between 0.676 - 0.679. .

If he went 20 or more he'd have a press fit of 10thou... This is a machanical impossibility.

You need about 11 - 12 thous. Knurling will do the job. If you have a lathe, or have it done this is easily in the range of fixable via knurling. Pressing onto a knurl will typ. 'smear' the metal or gall which will create an even tighter fit then when you started.

[ott1]

There you go OP, sleeve the barrel and turn it down. Once it's drilled and pinned, the rsb is not going to go anywhere.

[Dan FS71]

Highly doubt sleeving will work at this thickness (thin-ness). Your working with about 10 thou or 5 thou thick sleeve (about the thickness of 2 1/2 human hairs)

To cut that precisely you will need a tool post grinder, to not tear the sleeve. Even if you make the sleeve and it doesn't split once you get it down that far... When you go to press the rsb on it will just wrinkle that sleeve up like a piece of tin foil.

If your bound to sleeve it turn the barrel rsb journel down some too so the sleeve is thicker and has a chance.

Hope this saves some headaches.

[ar15barrels]

Highly doubt sleeving will work at this thickness (thin-ness). Your working with about 10 thou or 5 thou thick sleeve (about the thickness of 2 1/2 human hairs)

To cut that precisely you will need a tool post grinder, to not tear the sleeve. Even if you make the sleeve and it doesn't split once you get it down that far... When you go to press the rsb on it will just wrinkle that sleeve up like a piece of tin foil.

If your bound to sleeve it turn the barrel rsb journel down some too so the sleeve is thicker and has a chance.

Hope this saves some headaches.

I agree that you don't want the sleeve to be so thin as it would not survive being pressed back into the trunion.
Obviously, you would turn the barrel down before fitting the sleeve so that you can get the sleeve to 0.025" or more.
Also, the sleeve should be soldered on to the barrel before you machine it back down to size.

[Paulie Lugnuts]

Might be cheaper to buy another barrel.

[762x40]

Thanks for all the help guys.