Using .40 mags for 9mm for more capacity illegal?

[chrisf]

I have a sigma chambered in .40 as well as a 9mm m&pc. I played around one day and loaded 14 rounds of 9mm in the .40 magazine and it worked and functioned in my m&p9c. I was wondering, Is this illegal? As this wouldn't be a manufactured hi cap magazine? If it does, Im going to order some .40 magazines with the grip extension for home defense backup. So before I do this, I want to make sure the legalities of it. Thanks in advance.

[Exposed]

I-lle-gal.

[chrisf]

I-lle-gal.

I figured that. Ive been getting missed signals from people some yay some nay.

[Exposed]

Remember. Any magazine purchased/sold/imported after 2000 in ca was made to hold 10 rounds. Now, If you had mags before 2000 that hold more than 10 rounds and they need fixing, you can legally rebuild them. Or, If you came across an abandoned magazine at the range that holds more than 10 rounds, it's yours to keep. Other than this 2 scenarios, keep your 10 round mags at 10 rounds. Using .40 mags in a 9mm pistol can be interpreted as "construction ". I wouldn't play with it personally.

[Librarian]

No, NOT illegal.

No law covers the USE of magazines this way; if the owner/user has not modified the mag it's legal to use. The visuals are better if you actually own a gun in the same caliber as the magazine, but no law says you can't buy mags for guns you do not own.

[Briancnelson]

Not illegal so long as you don't have to modify the magazine so that it won't fire in the gun it was intended for, is my understanding of the Cal. DOJ position on that one.

In other words, if you can insert it into the other gun unmodified, and fire 9mm in it, then put it back in the .40 and fire .40 out of it, you should be ok.

As a former Sigma and current M&P owner however, I'm somewhat surprised to hear you can shoot the magazines from one in the other. I'm pretty sure my Sigma mags wouldn't have fit in my M&P just from looking at them, but I never actually tried, so that's not from direct experience.

[9mmepiphany]

I concur with Librarian.

If it is in a legal configuration for it's original intent, but it will hold and feed another cartridge, it's just a Plus. You cannot modify it from it's original specs to feed the smaller cartidges...such as:
1. adjusting feed lips to hold the 9mm
2. changing follower from the .40 one to the 9mm one

I did not know about the Sigma/M&P interchangeability (I have plenty of full cap M&P mags), but a couple of notable guns which will feed the smaller cartridge without modifications are:

1. Beretta 96 uses the same magazine bodies as the pre-ban 92...make sure you get the 10rd bodies, not the 11rd ones

2. H&K M10 uses the same magazine body as the M13...a little pricey, but legal to purchase

[Z28]

Interesting, does anyone know if this also works with glocks?

[chrisf]

Yeah it definitely works. I've never fired it because I was worried about the legalities of it. But I did full.it with 14 rounds of snap caps and manipulated the slide for all 14 and it cycles perfectly.

[Turo]

Interesting, does anyone know if this also works with glocks?

My .40 mags will hold their capacity + 1 or 2 rounds of 9mm, but on most mags the feed lips are too far apart to hold the top round in when there's more than 6 or 7 rounds loaded. If I had a conversion barrel, I'd try my .40 mags to see if they functioned, but I don't so I haven't.

On the average, most .40 magazines will hold 9mm ammo, some may even feed it, and they'll hold more 9mm than .40.

[paul0660]

On the average, most .40 magazines will hold 9mm ammo, some may even feed it, and they'll hold more 9mm than .40.

"

CZ's also have this "issue".

Hopefully the lawmakers will burn the midnight oil and fix this.

NOT.

[IrishPirate]

not illegal as long as you don't modify the magizine somehow. 10rd .50beowulf mags hold 30rds of .223 and some people find that they feed just fine in their guns. There's nothing illegal about jamming the wrong rounds in a magazine....if they just so happen to feed, then that's just a lucky coincidence.

my glock .40 mags will hold 9mm, but not perfectly...i'll test out their reliability when i get my conversion barrel.

[repubconserv]

It is legal to use 10 rd .40 mags with 9mm ammo. The mag was designed for 40 cal. So using 9mm does not make it a hi-cap magazine. (meaning it can only ever hold ten or less of 40)

[paul0660]

A large capacity
magazine is defined as any ammunition feeding device with the capacity to accept more than
ten rounds

It doesn't say designed to. Have your ducks in a row if you have stuffed more than 10 nines in a .40 mag.

[lilro]

It doesn't say designed to. Have your ducks in a row if you have stuffed more than 10 nines in a .40 mag.

I think designed is implied. Otherwise any 10rd magazine larger than .22 would be illegal.