I ordered this 10 rounder so I can shoot the thing off the bench when sighting in an optic.
Problem is that the bolt won't close over the mag.
The 32 round Brownells mag has been flawless & the gun runs both steel & brass cased ammo without  hitch.
The mag catch slot is correct & both mags sit at the same height in the lower.

The slot in the back of the ASC mag seems tighter/narrower than the Brownell mag but the lips line up with my bolt when disassembled.
Bought a Spinta blem bolt.

Mag Link
Any ideas on how to modify the mag to work properly? Should I get something else?

See this post about working mags down.  The mag probably needs to be shaved down in a few places



This Link

Thanks for the link.
Seems this may solve my issue.

It will solve your issue - it solved mine.

It's something to do with the mag clips of the ASC magazine. I've heard that if you file them that it will open them up to where the bolt will close but in my opinion all the ASC 9mm magazines are garbage.

You would think ACS would have fixed the problems by now.

Looked at this link to get an idea on a way to fix my ASC magazine problems, using a KAK bottom install 9mm adapter, my magazines do not have a problem with the follower hitting the feed ramp on the adapter like the ones in the link. The last round hold open did not work and last round in the magazine nosed up and jammed the bullet nose into the rear of the barrel flange above the barrel chamber. Disassembled the magazines and filed and sandpapered some material on the left side of the plastic follower for more upward push of the follower, that in turn raised the last round hold open lever upward, now the last round hold open works.

The last round jam fixed by sanding down the follower upward slant on the ejection port side. Sanded until the last single round fed nicely into the chamber, polished up the followers when done, ASC mags work like a champ now. Took me about 10 minutes per magazine to modify them. Contacted ASC about my magazine issues and they offered to have them returned to them at there expense but replacement magazines would still have the same issue I bet as it is the way the follower is made

When I ran into the issue with ASC magazines, I did a lot of research trying to figure out what the problem was.

From what I've learned, there's little standardization with 9mm ARs.  Some bolts (like mine) were based upon the original Colt 9mm AR specs.  Those specs were also based on using modified Uzi magazines, which had a wider gap between the feed lips.  Apparently, ASC and its predecessor C-Products used a different spec for their magazines, so that explains why my bolt was catching on the feed lips.  If your bolt is built to another spec, it may work fine with ASC magazines.

Personally, I wish that 9mm AR manufacturers would standardize across the board, but I don't see any chance of that happening.

There was also a recent post - IIRC, last 30-60 days, where we discussed the issues with ASC magazines and what to do to solve them.

Lucky! One of mine became a 9mm lower block for my vise.  

Have eight 32rd ASC mags and two 20 rounders.  I paid around $12.00 each for them when J&G had a sale on them a couple of years ago. Never had a problem, they run just as good as the $50.00 original Colt mag I have .

They do seem to vary. I ordered three 30s and two 20s a year or so ago when I built my 9. All the 20s & 30s had very thick finish, powder coat maybe, on the feed lips that I wore off by running the bolt 4-5 times. After that fine.

Fast forward to a month ago and I ordered two more 30s and a 20 and they all were a flawless fit from the get go. Finish seems different though, more like that basic gi grey dry lube new ar mags have, less like the thick powder coat finish the other ones had.

But hell, a full stainless magazine for an average of what $15-$18. Can't beat 'em IMO. But I am running a designated lower which the ASCs seem to be more reliable with.

Make sure the springs are in them correctly.   If they are in wrong, the follower will be tipped up.   Had that problem with 2 mags.