I have an apparently new magazine, which will not accept cartridges. One cartridge will go in, and the follower holds it upright in the proper position. The second round goes in, but then that first round seems to hang up in the magazine body. More rounds can go in, to a point, but the magazine spring cannot push the cartridges through the body towards the feeding position. The cartridges are held hostage by the sidewalls of the magazine.

I have inspected the follower and spring position carefully. These match other magazines I have. I have tried both Speer Gold Dot and Sig FMJ ammo. I have verified the ammo works in three other magazines that I have (the 8-hole 7-round P239).

The question is -- is this magazine fixable? I may have to send it to Sig for commentary, I guess.

Have you disassembled the magazine to inspect and clean the innards?

It is new. I disassembled it to inspect follower, baseplate, spring position, etc.

I got that it is a new magazine, however, it wasn't clear that you disassembled it. It sounds like the tube may be pinched. Will the follower drop free through the empty tube? If not, and absent any burrs, I would fashion a way to spread the tube sides apart until the follower moves freely.

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Originally posted by 4MUL8R:
It is new. I disassembled it to inspect follower, baseplate, spring position, etc.

Are you sure you reassembled the spring in the correct orientation?

With these magazines it is nearly impossible to misassemble. The magazine spring is attached to the magazine interior baseplate, which is what holds the plastic baseplate on. Having several magazines on hand, it is fairly simple to compare and evaluate the bad magazine. This morning, I disassembled the magazine and tried to slide a cartridge in from the base. It slid all the way to the magazine catch notches. At that point, the round would not move. I could push it all the way to the feed lip area, but clearly it was bound up on the major diameter of the case. The magazine seems to be too narrow from that point upwards towards the feed lips.

Almost sounds like you have a 239/9mm magazine body.
How does the OD compare to the 239/357 mags?

The 239/40-357 mags won't fit in the 239/9mm frame so the OD may show a considerable difference if its a 239/9mm body.

The outside width of the offending magazine is 0.500, while a magazine that works is 0.510. This was measured at several of the seven-round witness holes.

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Almost sounds like you have a 239/9mm magazine body.

If that were the case, I am surprised that the cartridges would even go halfway up the tube.

It has seven witness holes, is marked 357 Sig, and is nearly the same width as a functional magazine having the same marking. I am bemused by the slight difference in width and interior jamming.

Sig won't do anything to correct it. I already asked. They just buy and resell magazines.

What have you got to lose? As I suggested above, try to spread the tube open. Working from the bottom, push a dummy round up the tube and see if it opens up.

I will try to find a brass rod at work and have it machined to 0.430 diameter and 0.600 long. I don't think a hollow cartridge will have sufficient strength to move the steel outward.

Expanding (sorry) on the idea of using a brass rod, you might also consider just ripping a suitable piece of wood on a table saw. Taper one end a little, stick the other end in a vise. The wood has only to fit closely.

Fold a bit of cloth (preferably oiled) over top of stick and push mag down. Remove, add another layer of cloth, repeat. Try in gun for fit at regular intervals. You can substitute plastic for rag - whatever works.

If removal from expander jig becomes difficult, cut a suitable notch in a plywood scrap ahead of time. Insert in between vise and mag to pry it up. Notched wood might also be used to push mag downwards on mag's base edges so as to avoid any risk of damaging feed lips.

Now we are talking! I will find 7/16 oak and saw to 0.6 wide. Then belt sand taper. Then cloth. Thanks.

I love ambition more than most. but we are talking a $20 magazine that is a consumable part.

It retails for double that. Discontinued item also.

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Originally posted by 4MUL8R:
It retails for double that.

Not at the moment.
https://gunmagwarehouse.com/si...-round-magazine.html

I've used 40 S&W magazines with 357 Sig in my P239 for 100's of rounds. It doesn't fix your problem magazine but a FYI if you didn't already know. I also have a 9mm conversion barrel and they also feed from the 40 S&W without problem. You get about 1 more 9mm round than 40 in the magazine. Again 100s of rounds without problem.

I did buy one 9mm mag when I first bought the conversion barrel just in case but the 40 mags work just fine.