Quoted: Quoted: I need to buy some more mags for my carbine.  I have one 30 rounder that seems to fail quite a bit.  Is that common with .30 high caps? What is your preference? I would go with usgi 15rd. mags. But if you do want to use 30's, replace your mag. catch with a type IV (4) mag. catch It was designed with an arm on the left side to add support for the 30rd. mag. It was an upgrade for the m2. It is marked M with a line under the M.

+1000.  Even good, GI 30-rd mags will malf without the Type IV catch installed.  Of course, 15-rd mags can still be used with the new catch installed.

As far as Carbine mags go, don't be one bit surprised if the mag spring is worn out or even weakened by rust pitting.  Almost any Carbine mag can benefit from a good, new spring, and that goes double for the 30-rd versions whose springs seem to be especially problematic.  Some of these mags are 60+ years old and have seen some hard use.

Quoted: Two questions: 1. How do you recognize a genuine GI M1 Carbine Magazine? What marking etc do you look for? 2. Can anyone recommend a good source of springs followers, floor plates etc, for M1 Carbine Magazine rebuild?

To answer a part of your question, Wolff makes the springs, and you can get them there or from most vendors such as Midway and Brownell's.

As a side note, the 30-rd mag had a follower that held the bolt open on last shot, while the 15-rd mag's follower was tapered at the rear of the cartridge-shaped "hump" stamped into the follower.  They can be interchanged, but I suggest you standardize on one or the other.

I had no problems with my 30-rd mags in my nice Inland Carbine, since it had the later mag-catch, and since I had dis-assembled and cleaned the genuine GI 30-rd mags.  I just threw away the old springs and replaced them with new ones.  Eventually did the same with my 15-rd mags, and in both instances the springs were almost always so worn that you could see portions of the sides of the springs actually removed by wearing on the insides of the mag bodies.

The magazine is usually the weak link in most semi-auto firearms, and the weakest link is usually the spring.  It is a testament to the original overbuilding of the OEM springs that most seem to work even now after 60+ years.

If you ever will need to rely on your Carbine for a life-and-death situation, then just bite the bullet and toss the old springs.  If the mags are New Old Stock, and old but unused, that is one thing.  Otherwise, just toss the old, worn ones.  Simple as that.

I might point out that soon after we are subjected to a President Obama, there will be many parts for our toys that will become unavailable.  Time to think ahead, folks.

I've got a box of USGI 15-round magazines that have never failed me yet. Didn't know the .gov even made 30-round magazines.