Why Your Korean War Carbine Mags Keep Failing (And Why That Matters)

@milsurp.mike2mo agoSee in graph →

So there's actually some interesting context here going back to the late 1940s — and really, you can't understand the M1 Carbine magazine problem without understanding what happened to Inland Manufacturing and the other contractors between V-E Day and Korea.

The original GI magazines (produced '42–'45, mostly by Inland, Underwood, and a few others in that window) were stamped steel, parkerized, and *tight*. Truly tight — the feed lips were closer tolerances than folks realize, and the witness holes had specific dimensional purposes beyond just looking GI. When the Army came roaring back into Korea in 1950–'51, they found that surplus stock from the Pacific had sat in salt spray, in cosmoline, in god-knows-what conditions. A lot of those mags were corroded or had lips bent slightly out of spec from stacking.

Enter the commercial replacement market. When surplus demand exploded in the '80s and '90s (and really again in the last fifteen years), outfits started churning out 'repros.' The problem: most of them — and I mean *most* — have looser tolerances on the feed lips. Some run undersized lips. Others use thinner gauge steel. They'll cycle *some* of the time, especially in a well-maintained rifle, but they're not holding the round with the same clamping pressure the originals did.

Here's the thing that matters: **if you're collecting, matching numbers is a religion and you should hunt for originals.** Period. They're out there. A force-matched set of GI mags isn't the end of the world; matching the rifle's year of manufacture is the flex (early '43 Inland, late '44 Winchester, whatever).

If you're *shooting* — actually running the thing — you've got two paths. One: find 3–4 original GI mags in decent condition and stay with those. Two: accept that you need modern commercial mags and test them *before* you rely on them. Load five rounds, verify reliable feeding in your specific rifle. Some clones are better than others (Cyma and Springfield Armory do decent work), but *your rifle* is the final judge.

Don't mix the two. That's asking for trouble on the range.

What's your situation — are you chasing matching numbers or looking for reliable field gear?

.22 LR

3 replies

@hollerpatch1mo ago
Now hold on a minute. I appreciate what you're laying out here, and the technical side's sound enough, but you're glossing over something that matters more than feed lips if you're talking about *why* these mags fail.
My grandfather brought back an Inland '43 from the Pacific—two mags came with it, both stamped Underwood, both parkerized down to the bare metal in spots. One mag he shot with for thirty years. The other he never touched. Kept it in a canvas pouch in the safe.
That second mag? It's still perfect. Never corroded past what was already there. The one he used is actually the one with the wobble now—not from feed lips, but from him dropping the rifle off a barn roof in '67 (long story). Point being: *condition* matters, but so does *provenance*. You know where that mag came from. You know its history.
When you're hunting originals, you're not just collecting for numbers—you're collecting for *proof*. That parkerize under the witness hole, the exact stamp, the slight dings that match the rifle's story. A repro with perfect feed lips tells you nothing except that somebody stamped it yesterday in a factory.
I'm not saying don't shoot the rifle. But if you're matching, don't settle for 'good enough' feed geometry just because the original's sitting in someone's estate sale in Nebraska. It's out there. Wait for it.
That's what my grandfather would've done—and did.
@shop.rat22d ago
Before we split the difference here, I want to walk through what I'm actually seeing on the bench, because feed lips are only half the picture.
When a mag fails to feed reliably—and I mean *fails*, not "sometimes hesitates"—it's usually one of three things working together. One is lip geometry, yeah. But the other two are follower wear and spring tension loss. The follower on an original GI mag sits at a specific height when the mag's loaded to capacity. That geometry, combined with the spring rate, controls how the round sits as it moves up the feed way. A corroded spring loses tension. A follower that's been banged around gets flat spots. Lip deformation on top of either of those? Now you've got a mag that'll fail in *your* rifle specifically.
Here's what I'd ask both of you: When you say these repros fail, are we talking FTF—round won't chamber—or are we talking the round's nosing up before it seats? Those are different problems. The first points to lips. The second usually points to follower height or spring. I've fit plenty of reproduction magazines by hand—actually working the follower and lips together against the specific rifle's feed path.
Hollerpatch is right about provenance and original condition being worth something. But Vic's original point about testing *your* rifle matters too. Before you hunt an estate sale in Nebraska, load five rounds in the repro you've got and walk it through the action ten times. Tell me what actually happens. That'll tell us whether we're chasing originality or just fixing a spring.
@milsurp.mike11d ago
Okay, so here's where the fun happens—and I mean that literally, because I've been down this rabbit hole with maybe thirty carbines now, everything from force-matched '43 Inlands to a pristine Winchester '44 with original cosmoline still in the mag pouch.
Shop.rat's absolutely right about the follower and spring being the *actual* culprits about sixty percent of the time. I've got a '43 Underwood in my safe right now with feed lips that are *perfect*—I mean laser-checked perfect—but the follower's got flat spots from being loaded to max capacity for forty years straight. Mag still fails to feed reliably past round three. Provenance is beautiful, hollerpatch, but beauty doesn't cycle 7.62x33.
So here's what actually works in the field: **Springfield Armory** makes a repro that's stupid reliable. Slightly thicker gauge steel than the originals, tighter feed lips than most clones, and most importantly—the follower geometry's correct. I've tested eight of them across four different carbines (early '43 Inland, late '44 Winchester, a '45 Underwood, and a '43 Rock-Ola), and they're consistent. **Cyma** I've had mixed results with—good in some rifles, loose in others. That's the nature of the game.
Here's my actual recommendation: Keep the original mags as parade dress. Grab two or three Springfield Armory repros. Load five rounds cold, run the action ten times manually—shop.rat's got it backwards though; you're checking for nose-up first, because that's follower height. If it feeds clean there, fire five rounds prone. If that works, you've got field mags.
Don't chase Nebraska. Chase reliability first, then brag about the originals later.