[Tackleberry1]

I have seen it but with 5.56 MM fired through an M249

My question with your S70 would be if it happens with all of your magazines?

I suspect you may have an older mag that sits a bit to deep in the mag well and your fired, and very hot spent casing is being drug along the leading edge of the top round in your mag producing the deformed casing in your picture.

So... Are you seeing it with all your mags? Or just one?

If ^^THIS^^ is the case, you will notice much more deformation on the first few rounds fired and it will get less severe as the mag runs empty due to the reduced "up force" on the leading round in the mag.

Tack

 

[Tackleberry1]

I have only one mag. So I don't know. Can I adjust the lips on the mag or just a few new ones?

Lips can be adjusted but reliability trumps dented brass... And I dont think adjusting the lips would solve the problem... Which... Unless you reload, really isn't a problem, as much as it's a "curiosity".

Personally, I've had great luck with Wilson Combat 8 round mags and run them in all my 1911's.

Several other "slab siders" here swear by both Chip Mcormic and Tripp 1911 Mags.

I'd say to pick up a couple of new mags and see if it eleviates the problem.

Tack