Going to go deer hunting this coming winter, and built a 450bm to do so. I have an epic ass-ton of USGI 20rd magazines, and I'd like to find a limiter I can insert into the magazine to make it legal to hunt with. (Ohio is 3rounds total). Does such a thing exist?

Nevermind. I figured it out.

1/4 wooden rod cut to required length

What did you find out?

I was under the impression that mag blockers were now unnecessary but DO NOT have more than 3 rds in a firearm.

Not needed, the law is that you can't have more than 3 rounds in the gun, but you do not need to have a physical limitation in magazines capable of holding more than that.

Correct, they're not needed.

Back when I built my 450, converting USGI 20rd mags with followers designed for single stack didn't seem to work as well as running 450BM specific mags. The feed lips are different IIRC. Maybe things have changed, as that was several years ago.

I run ASC .450BM 5rd mags (same size as a USGI 5.56 20rd) and just load three. Franklin Armory did extensive mag testing for the .450BM and the ASC were the most reliable. I have used mine since legal in Ohio, annual zero checks, and a few range trips for fun - 100% flawless.

Basically what he said already. But I also found stl files for 3d printed followers, so I'm going to try using those before I go out and buy 450bm magazines.

When I needed to block a 20 rounder to limit it to 5 for hunting in a particular state, LEGO was my friend.  Just start snapping blocks together until you achieve the correct capacity.  Worked great.