I just got a couple of the new brownells 30 rd. mags.  The only problem seems to be that the square hole that is cut in the mag for the mag catch doesn't quite line up with the catch on my gun.  Now I know that I have an Oly arms and I'm starting to see that the quality isn't as good as it could be. ( I will be looking for a bushmaster or rra soon ) My question is , can I just open the hole on the mags up a bit with a dremmel tool so it will catch ?  thanks

I would suggest a small needle file, if you are intent on modifying your mag.  Make sure of how much and where you need to make the mod.  Use a felt tip marker (almost any color will do) to see where the catch is contacting the mag and where it isn't.  Then use the file.  Dremels are great, but I have seen more firearms of all kinds ruined by folks with out a Dremel license. Way too fast for the task at hand.

Do you think it would be better to file the mag catch instead ?   thanks

Quoted: I have an Oly arms and I'm starting to see that the quality isn't as good as it could be.

Get yourself a new lower.  I shot with a guy who had an OLY so out of spec that the mag catch caught the bolt CARRIER instead of the bolt on an empty mag.

I wouldn't go modifying good gear to function in a crappy lower.  Just My Opinion.

Quoted: Do you think it would be better to file the mag catch instead ?   thanks

It depends on how well other mags work and what brand they are. In this case, it appears that it is probably the mag, if your other mags work. The first rule of gunsmithing is to always mod the least expensive part.  The second is if the first rule is a toss up, to mod whichever part is easier to replace.  IMHO, I would suggest you try a bunch of other mags (from friends, folks at the range, etc.) first. That should narrow it down as to mag or mag catch.  A non-ambi mag catch is not that expensive and is easy to replace. But, if it is a QC issue as pointed out, then the slot for the mag catch may be out of spec.

I have no experience with Oly Arms so I will not comment.

Quoted: Quoted: I have an Oly arms and I'm starting to see that the quality isn't as good as it could be. Get yourself a new lower.  I shot with a guy who had an OLY so out of spec that the mag catch caught the bolt CARRIER instead of the bolt on an empty mag. I wouldn't go modifying good gear to function in a crappy lower.  Just My Opinion.

Mag catch or bolt catch?  That would have to be one hell of an out of spec lower if the mag catch was making any kind of contact with either the bolt or the bolt carrier.

Bolt catch, Indeed!