やはりリップなんかもいじらんとアカンぽい

https://www.thefirearmblog.com/blog/2016/06/28/review-ar57-the-poormans-p90/

>Some of you may be asking: “Why do you have a PMAG inserted into the AR57?”.
It is actually a brass catcher. Just like the P90, the AR57 ejects the spent brass downwards.
You do not need to use an AR magazine but it is nice to use as a brass catcher.
Only problem is that you need to permanently modify the magazine.

You need to remove the follower and spring from the magazine so that the empty brass can fall into the mag body.
You also need to chop off the feed lips so the magazine can insert properly and engage with the magazine catch.
Since the rounded feed lips are removed, you need to depress the magazine release button to insert the modified brass catching mag.
Otherwise the edge of the magazine will hit the magazine catch and you can’t insert it further.