My MPX must have been in stock for a while because although it is a Gen 2 gun, the mag has a black follower, which I understand identifies it as a Gen 1 magazine. The mag feeds fine, but the gun will not hold-open on empty. I wondering if this is a mag issue or some other problem. Right now I don't have a G2 mag to test this.

It might be a mag problem. Hard to diagnose if you don't have another mag. I have been running 20 and 30 round gen1 mags in my gen2 with no problems.

Gen 1 magazines in a Gen 2 MPX should not be causing LRBHO issues. It may be that particular magazine, it should not be Gen 1 magazines in general.

The major difference between Gen 1 and Gen 2 magazines was the feedlip design. This should not be affecting your LRBHO function.

Since you do not have a Gen 2 magazine, I am wondering if there might be something wrong with your bold-hold-open mechanism, but without additional mags to isolate the failing component, I can't say more.

i had this issue with geco 115 and winchester white box 115. They did not have enough umph. i put 124's and 147's and the problem went away.

How many rounds through yours. After about 500 the whole thing comes together nicely.

quote:

Originally posted by DSgrouse:
i had this issue with geco 115 and winchester white box 115. They did not have enough umph. i put 124's and 147's and the problem went away.

How many rounds through yours. After about 500 the whole thing comes together nicely.

120 rounds. 50 were 124g Federal subsonic, the rest were homebrew -- 124g Berryn traveling at about 1070fps from a G34. I will try something hotter.

DSgrouse, you got it right. I ran some +P and NATO rounds thru the gun with zero issues. It held open fine with G1 & G2 mags.

NATO 124 Winchester or Winchester Ranger is just perfect. I have used lots of different HP high end stuff with no problems. Also, some 115gr IMI high end is just fine also.

when I bought the gen 1 mags for my gen 2 MPX, I was told they would work fine. They have.

Wet BCG also helps.