[TightLines]

Have done some research without much luck.

When I first received my Gen 2 MPX I quickly found my light 9mm loads (4gr RD, 115 Xtreme RN*@ 1.135 OAL) would not cycle or reliably feed with Gen 1 or 2 mags but it gobbled up any and all factory loads. *Second*set of loads I increased charge until the gun would properly cycle but quickly found I was having severe feeding issues. *Increased OAL to 1.160".

Current load of 5.5gr of Unique, 115gr Xtreme plated @ 1.160" runs like a top in my single Gen 2 mag. *Put the same load in my Gen 1 mags and it's constant FTF all over again. *The rounds all jam in the same manner (picture below). *

The only other exterior spec that differs from my loads to factory is the amount of crimp and I've got my back against a wall (.377) here since I like the economics of plated bullets. *All rounds pass the plunk test.

Any insight here? *Have a handful of Gen 1 mags I picked up at a decent price and would love to get these working.

TLDR:
Gen 2 MPX cycles reloads and factory ammo perfectly out of Gen 2 mags.
Gun eats factory ammo with Gen 1 mags but severe FTF with reloads. *Rounds at 1.160" and .377" crimp.

 

[TightLines]

A little more detail.

Looks like the nose of the rounds are actually hitting the top of the barrel throat. I'm guessing this is also the cause (could be the effect) of the round not seating properly against the bolt.

See additional photos below (one shot from inside the mag well).

The rounds feed much better when hand cycled than when fired.

Only steps I have before swearing off the Gen 1 mags for reloads (all I shoot):

Try shortening up the OAL to 1.050 and try reducing crimp a hair to .376 or so.

 

[Mnolan660R]

I can't remember what coal I am running, I'm using hs-6, cci and Rem 5 1/2's, with rainier lead safe 124's.
Your pics look like the same issues I was having at first with my gen 2 mpx, running both gen mags and various ammo types and manufacturers.
After a few hundred rounds down the pipe, and letting all my mags sit full for about a week, everything runs great.

I will check what coal and crimp dia. I am running and post up tonight after work.

 

[Mnolan660R]

Here is the data that seems to work for me:
Win. Brass (mostly, but sometimes others mixed in)
Rainier lead safe 124gr pills
6.3gr hs-6
Cci #500 (have sub'd rem. 5 1/2)
Coal- 1.135
Crimp-.375 w/ lee fcd

 

[sigmpx2017]

I'll start with easy: sell the gen-1 mags on GB and move on. I have about 500 rds thru my MPX with gen-2 mags (both with the flash hider and with a GM-9) Almost no malfunctions with both factory and reloads. 115, 125 and 147 grain all work great. All loads are within the specs of Hodgdon #26. 1.13" OAL. I DID make sure to carefully adjust the crimp and make sure that each re-load fit in a case gage.

 

[dgrbr13]

I'll start with easy: sell the gen-1 mags on GB and move on. I have about 500 rds thru my MPX with gen-2 mags (both with the flash hider and with a GM-9) Almost no malfunctions with both factory and reloads. 115, 125 and 147 grain all work great. All loads are within the specs of Hodgdon #26. 1.13" OAL. I DID make sure to carefully adjust the crimp and make sure that each re-load fit in a case gage.

Where can I get that handguard?

 

[sigmpx2017]

Where can I get that handguard?

That's the OEM one mine came with.

 

[TightLines]

Here is the data that seems to work for me:
Win. Brass (mostly, but sometimes others mixed in)
Rainier lead safe 124gr pills
6.3gr hs-6
Cci #500 (have sub'd rem. 5 1/2)
Coal- 1.135
Crimp-.375 w/ lee fcd

Thanks for the info.

No issues with over crimp at .375 with the plated boolays? .377 is about as small as I go before leaving a ring on it when pulled. Over crimping caused some tumbling for me a few years ago..

 

[Mnolan660R]

I'll pull a few and see if it is leaving a ring. As far as tumbling & accuracy, they seem to be as accurate as factory win. Out of my mpx. I'll have to set my crimp a bit lighter and see if they still feed reliably.