I live in Ohio and according to Ohio law any magazine that holds more than 30 rds and is inserted into a weapon makes that weapon an automatic weapon.
So, I decided to convert my newly purchased 9mm C-Products 32 rd mags to 30 rd mags. I wanted to use materials that I had on hand. I used a common wooden paint mixer that you get with the purchase of a gallon of paint, golf tees and wood glue.

I first loaded the mag to full capacity then removed 2 rds. I then noted the position of follower, which was completely covering up the 32 rd window. I disassembled the mag and inserted the follower only to the position where it was covering up 32 rd window. I measured from the bottom of the mag to the bottom of the follower, which was 1.5" and cut the tees 1.5". I then lightly sanded the cut portion and sanded the cup portion of the tees. I also carved out a small cavity into the cup of the tees to hold more glue.

I then used the locking plate as a template to cut out a piece of the wood paint mixer and then lightly sanded it. I glued the tees to the wooden cutouts and let dry for 48 hrs. I reassembled the mags with the capacity limiter between the locking plate and the spring. I realized that the tickness of the paint mixer might limit the mag to 29 rds, but as it turned out, the mags hold exactly 30 rds. So far, I have about 300 rds through the mags with zero problems.
http://i45.tinypic.com/6tk0pj.jpg
http://i48.tinypic.com/2vcfjnb.jpg
http://i47.tinypic.com/mjwz88.jpg

'dog, the wonder of gun laws, one more time.  A pretty tidy fix, tho' my personal advice would be to get some twenties and keep them for any potential social use.
Does OH have a 'magazine czar' or somebody who actually checks on these things?

Never could figure out where the 32 round capacity came from in any case; I usually only load mine with 30 for easier insertion against a closed bolt.
Moon

Get caught with an illegal mag (in OH) and it is a Felony
The law actually restricts the firearm to "more than 31 rounds without reloading", unless it is .22 short, long or long-rifle (any other rimfires e.g. .22 Mag and .17 HMR are left out).  The fun part is, the magazine isn't illegal, possessing the firearm with the 'adaptor' that allows the firearm to fire more than 31 rounds without reloading (the magazine is the adaptor) is illegal.  You can get a permit from your Sheriff to possess this 'Dangerous Ordnance' though.

Please note:  I am not your lawyer.

See 2923.11 (E)

2923.17 (D) makes it a felony

I use MetalForm mags and drilled a hole in the rear 'channel' large enough for a 6-32 round headed cap screw and modded square nut.  This stops the follower at 30 rounds if drilled in the right spot.

Yep, I have a couple 25rd converted Uzi's for potential social use.
No mag czar, just want to be kosher when I'm at the range. Ya never know.

Correct, I forget to mention that rimfires are excluded.
The cap screw and modded square nut is a pretty cool idea, I'll try that with next the 32's I buy. Thanks.

NJD, is it then necessary to remove the screw to detail strip the magazine?  Since it's in the channel at the rear of the mag, I presume it doesn't interfere with the mag spring.
Is a potentially removable block considered okay under OH law?
Moon

Yes, the screw has to be removed to detail strip.  The mag spring never touches the nut, the screw is cut to be flush with the nut and a tiny amount of blue LocTite is applied. This is for a 'game playing' gun (3-gun on pistol ranges or carbine friendly USPSA type matches).



No idea, but if you pick  up one of my mags, you would have to 'modify' it to have it accept >30 rounds.  I am not your lawyer, but I feel safe enough with my modification.

Rimfires are NOT excluded.  Firearms chambered for .22 short, .22 long and .22 long-rifle are excluded.  the .22 WMR, .17 Mach2 and .17 HMR are affected by the law.



I don't know about C-Products, but as far as the MetalForm mags go, they are some seriously hard steel.  Cobalt won't get it done.  
I used a solid carbide center-cutting end mill.

Magazines can indeed be amazingly hard.  Does the hardening go all the way thru'?  How about dimpling the spot to be drilled with a Dremel and a stone, and then using the drill on the (presumably) softer metal underneath?

Moon

When I did mine, an automatic center-punch made a dimple.  The cobalt bit for a pilot hole just got hot - no cutting.  I used a fancy cutting fluid (but not flood coolant), I ruined the bit.
So I stuck it in the Bridgeport and used the solid carbide mill on it.  Hardness probably goes deep enough from both sides that it meets in the middle.

I'm still laughing!
Luckily, not my problem; as close as I come to OH is Mercer on occasion.  My earlier question about the mag limiting device being removable wasn't meant to be fault-finding.  Both of the proposed solutions here are reversible.  I was thinking about the BATF thing of having a SBR length upper in your possession, even if it isn't installed on a lower you also possess.  If the authorities don't get too chickenshit about it, that's a good thing.
Been shooting the snot out of my 9mm, and it has enough more power than the .22 to be really interesting, and cheap to reload as well.
Moon