I have 3 identical 30 Carbine rifles.
All 3 have extraction problems, one worse than the others.
One has what seems to be a chamber that is very oversize. Fired brass comes out with a bulge on one side near base and unfired new round seems to wobble a lot when seated.
Other 2 rifles are better, but the unfired rounds also wobble a little when seated.
I don't think there is any question that the first rifle needs to be rechambered, but am unsure about the other 2. Since all 3 rifles are in excellent condition, I believe that the oversize chambrs were incorrectly done when they were made. I have read that one or two "smiths" that had gotten one of these had to rechamber to fix the same type extraction problem.
Any thoughts.
Also, can someone give me an estimate to set back the barrels and rechamber the 3 rifles. As mentioned, they are all identical (Marlin model 62 Levermatics).

Obviously I am not familiar with your guns, so I won't comment on them.

What does immediately come to mind is that I doubt if all three of your rifles have oversized chambers. So, I'll ask these questions:

1. Are your sure your ammo brass isn't less than factory brass dimensions of the era when your rifles were made?

2. Have you measured the diameter of any loaded round factory brass (at the base), and compared that measurement with the dimensions after the brass is fired?

If the difference is significant (.004" or more) have you tried measuring the base diameter of different brands of .30 carbine brass available on the market? It might be there is a brand out there a lot closer to the dimensions of your chambers.

I only mention those questions for two reasons. I know a lot of brass cases now made by American factories or available in America are significantly smaller than original brass of certain chamberings...the 6.5 Japanese and 6.5 Swede immediately come to mind as examples. Also, I have bought .30 carbine ammo made in China (PRC, that is) which were both very undersized and very hotly loaded...to the point where it blew the primer out of the case about every other round. (Of course, I didn't have to worry about reloading THAT brass...the primer pockets were too expanded to consider reloading even the ones which had not shed their primers on firing.

Properly sized and finished chambers are certainly important to facilitate extraction. I charge $100 to set back a Remington-type (no extractor cut) and $140 for Winchester-type with extractor cut.

Just how for do you have to set back a (basically) straight wall chamber to in order to reduce the base diameter by .004=.006?

Your looking at either replacement barrels, or possibly reaming the chamber oversize than having a sleeve "heat shrunk" in before re-reaming the chamber (say a piece of 1/2 drill rod with a .0005 to .0007 interference fit).

Not a gunsmith, but a machine builder

new barrel would be your best bet if the chambers are that bad, I've seen the sleeves cause problems with the semi autos if you shoot a bit and the barrel gets warm

joe

www.gunmaker.biz

The ammo I checked is 1960s USGI, Aguilla recent production and Federal commercial. All are the same and exhibit chamber looseness.

I hadn't thought about that cartridge being streight wall. That would throw a monkey wrench into the works. here are the dimensions.
Neck diameter (0.331 in)
Base diameter (0.354 in)
Rim diameter (0.360 in)
Case length (1.290 in)
That indicates just a hair under .018 per inch.
If the barrel threads are 1-10, then cutting two turns would probably yield enough to properly rechamber. And Yes, there are 2 extractor cuts, one on each side.