I recently built an AR-15,  14.5" carbine, and it's failing to strip rounds from the magazine almost every time.  When I rack it, it will strip and feed a round correctly.  If it's the only round in the magazine, the bolt will be held back correctly after it's fired.  If I have a magazine with more than one round, it will almost always fire the round, and drag across the next cartridge leaving a nice scratch along it, without stripping it from the magazine.

I assumed it was just a magazine issue, so I tried 2 other magazines but the results were the same.

I am using the standard carbine buffer (2.9oz).  

I am thinking I should try an H2 buffer, perhaps it's cycling too fast? I am shooting 52gr varmint.  I did order an H2 buffer, it's cheap and worth a try.

Plan B, all of my magazines are used, perhaps the are all bad.  I find this unlikely but anything is possible.  I don't have another AR to try them in at the moment.

Opinions?

Thanks gentlemen.

Just disassembled the mags and they are all dry.. cleaned them an lubed them, maybe this is a contributing factor?

Low power reloads?

Clean your mags again and strip all of the lube from them.  Never lube a mag.  Wolff sells stronger springs if that ends up being the problem.  Try a heavier buffer first.  And yes your bolt is running too fast for your mags to keep up.  That's why you're getting the scratches, mag is pushing the round up after the bolt has already passed over the base of the cartridge.  

Should've got an H3, you can cannibalize it and your standard to make an H1 and H2 as well to see what runs best.  The H2 will likely be heavy enough though, if it's too heavy replace one of the tungsten weights in it with one of the steel ones from your standard.

Nope commercial

Thanks fellas, sounds like I am on the right track aside from spraying the mags with lube.  Sounds like I need either a heavier buffer, or new mag springs, or both.

The mags are USGI mags, but I got them in a "bargain" box at a local shop... probably a hundred aluminum mags in there.    Thinking back that was dumb, they are probably ALL bad and that is why they are in that bin.

Unless the feed lips are seriously out of spec or the welds are broken, USGI mags are easy enough to rebuild.

They look fine, and mag springs seem ok. I'll try the heavier buffer and see if it helps with the same mags.

Check your gas system, including gas key on the carrier.

gas key looks good, tight and staked

Also, separate the upper from the lower, break down the bolt carrier group, and insert the stripped carrier into the upper to check gas tube and carrier key alignment. When I built my 14.5"; when I first installed my gas tube I realized the tube was not centered by doing what I describe above. The carrier was barely catching the edge of the gas tube. I straightened the tube by adjusting the tightness of my barrel nut. The TM also says you can tweak it inside of the upper to get it straight. I also noticed a wear pattern on the tip of the gas tube where the carrier was catching it.

Or it's overgassed and cycling too fast.  Which is more likely when multiple mags are having the same issue.

+1.
I have a noveske afghan that was doing something similar except the round was jamming with a partial feed. I went to a DD h buffer and never had the problem again.

Thank you all for your advice.

New buffer on the way. Will let you know the result.

Thanks

Those who suggested the heavier buffer were correct.

Rifle functions perfectly now with the H buffer and the same magazines. 100 rounds no issues.

Carbine buffer goes in my misc junk bin.

Thanks fellas.

I'd suggest an H2.  The original carbine buffer isn't fit to work in ANY gun.  I remember in the old days thinking these guys and there H2 and H3 buffers were nuts.

But now we know that an H2 buffer most closely mimmicks the DESIREABLE characteristics of the Rifle buffer system.  Now depending on the make of your barrel, and it's gas port size, it may run even better with an H3.

With the A5 system, we now can have our cake an eat it too... but if you didn't feel like changing REs and finding an A5 buffer, the H2 is the starting point.