940 JM Pro Field recoil return spring

[talon99]

I have a two year old Mossberg 940 JM Pro Field shotgun. I have been overall happy with it, but as others have found out, it can be finicky with lighter target loads.

I've installed the OR3GUN Competition Spring Plunger (CSP) and the Quick-Adjust Spring Retainer (ASR) with the recommended target load setting. It has helped, but is still only about 80-85% reliability with using 1200 fps with 1 1/8 oz loads from Federal and Winchester. It usually will not cycle 1145 fps loads from Federal Top Gun at all, but will cycle similar loads from Winchester and Remington Gun Club sometimes.

I've tried two boxes of Black Cloud steel waterfowl loads during initial break in as recommended by Mossberg. 100% reliability even with five straight rapid fire shots.

Would getting and shortening up a replacement return spring seem like something to try? I noticed that Mesa Tactical makes a stock shortening kit which includes a shortened spring for the shorter return spring tube.

https://mesatactical.com/products/buttstock-shortening-kit-for-moss-930.html

I'm looking to get high reliability (optimally 100 %, but 95%) with using standard target loads (1200 fps or so.)

Thanks for any help in advance.

 

[Bobster]

You might have to put more rounds through it--ie: "break-in". What does the manual say?

 

[talon99]

I've got at least 600-800 rounds through it by now, with a general cleaning after each session of 25-75 rounds and I detail clean the gas system every other session. I've done the OR3GUN recommendations of filing the sharp ends of the return spring. I have the gas piston with the two external rings and this has been disassembled and thoroughly cleaned twice.

The Mossberg manual mentions nothing about a break-in period. I've called them and they recommended the heavy loads to work the system.

Maybe more rounds will help; just seems like it's not improving much by shooting.

Thanks for the help!

 

[Jmm14534]

talon99,
Can you describe what happens when you experience this malfunction? Start at the point you disengage the safety to make ready to fire.