I have a 10 round mag for .450bushmaster, but would like at least 1 smaller mag for hunting. Deer rules only allow for 3 rounds in the rifle anyways, and on a bipod, the gun rests on the magazine.
Does anyone have a 3-5 round mag for an AR-15 .450bushmaster, or where would you recommended, and why?

You can use 223/5.56 mags if you change the follower

http://www.chambertactical.com/product/ar-15-big-bore-follower/

I've read that if I do that, I also need to mill out a bit in front of the bullets nose, and adjust or cut back the feed lips. I do not happen to own a drimmel. I will attempt that method if I can not find what I want already made. Thank you.

Here is a 5 Rd.
https://www.cattailrunllc.com/450-bushmaster-magazine-5-round-93309

The fee is reasonable, and they are American made. That looks good. I am not familiar with this company, have you dealt with them before? Would you recommend doing business with them? (Always good to know if they have a track record)

No I havent. I just found them today

Midway has AR stoner brand $27
Windham weaponry has some for $32

Thank you.

These are the ones my LGS recommends. https://www.brentonusa.com/ar-hunting-bartz-brenton-magazines/

I've been using the Bushmaster brand (like TLB2 linked above) that came with my BM upper. No problems so far. That's a good price too, I might have to get a spare.

Yes, my existing mag came with my BM upper as well, but the supplier (walsh gun and tackle) has not been forthcoming with the 5 round I asked for. And after a 6 month wait, I decided to look elsewhere. The upper has worked flawlessly, just not happy with the small followup sale.

Ordered 1 from midway (stoner) . If it feeds properly, I will pick up a few more. Thanks for the responses.

Stoner mag has arrived, and loads and feeds flawlessly by hand. When I hit the range to sight in the new scope, I will be able to test it further. So far, looks like a perfect match for the original, just shorter.