As Issued 1944 IBM M1 Carbine

[majspud]

Sorry, thought you were referring to the "I" cut under the front sight, which all IBM barrels have and is visible on some even though the front sight is installed properly. Some IBM barrels have an additional cut aft the "I" cut.

https://www.milsurps.com/images/impo...Barrels1-1.jpg

Curious about the plain versus grooved barrel. As mine is very late production, is it a deleted milling process, early vs. late? Or are the little 'ribs' to aid in heat transfer to cool the barrel more quickly?

T

[majspud]

I'm referring to the barrel on the right.

T

[browningautorifle]

So, you mean the machining marks in the barrel? The chisels leave that because of the machine screw feed that moves the headstock along at a measured pace. It's just a matter of an extra run to remove those rings after the barrel reaches correct outside diameter...time. If that's what you're referring to...

[majspud]

Yes, that's what I meant; an extra milling step removed to speed things along.

T

[browningautorifle]

Not that it was poor machining, I even like the look. Our peacetime C7 rifles have the same machine marks.

[RASelkirk]

I get those marks on my lathe whenever the bit gets dull. Pretty sure they didn't have carbide tooling back then, could be the bit went dull or the coolant/lube flow got interrupted...

Russ

[browningautorifle]

Sometimes the angle of the chisel will effect it too.

[emmagee1917]

Used to turn drums and rotors . We'd do quicker / deeper cuts to get the right shape , then do a final pass of a shallow cut at a slower feed to smooth it up . Same thing here .
Chris

[CrossedCannons]

It also looks like the left one has been refinished. The sand has smoothed the edges some.

[Newscotlander]

C.C.N.L #371, page 16. For some barrel manufacturers, early barrels were ground smooth, later barrels were not.

OP, Nice carbine. Rear sight not original.