940 Pro Gas Pistons

[rickman]

I have a 940 Pro Tactical and I took it apart to wipe down before use. I noticed that the piston looks like the piston from a 930, i.e, it doesn't have the cutouts for gas release.The JM 940 Pro has the updated piston. Is the updated 940 gas piston available for the 940 Tactical? Also I am a bit confused as in the manual it shows two different types of piston. One with with 1 outer gas ring and the other has 2 outer gas rings. I would like to purchase the updated piston with the cutouts and the single outer ring but not sure which one for the 940 Tactical. Any ideas?

 

[waz0wski]

Not seeing the individual parts for the 940's available on their web store, probably will have to call Mossberg directly and see if they can custom order it for you - I've been able to get unlisted 930 parts this way in the past

 

[rickman]

In the 940 Tactical Owner's manual it shows two different exploded diagrams. One for the 940 Pro and one for the tactical. This piston for the Pro shows a piston with 1 outer gas ring and the Tactical diagram shows a piston with 2 gas rings. ???

 

[waz0wski]

In the 940 Tactical Owner's manual it shows two different exploded diagrams. One for the 940 Pro and one for the tactical. This piston for the Pro shows a piston with 1 outer gas ring and the Tactical diagram shows a piston with 2 gas rings. ???

The Pro does have a different piston configuration designed to vent gas/carbon and run cleaner - it's a similar to/based on the aftermarket piston that became available for the 930's years ago

 

[rickman]

Here is what I am referring to:

This is the piston from the 940 Pro Tactical:




This is the piston as shown in the 940 Pro Owner's Manual, both for the Pro and Pro Tactical:

Pro:



Pro Tactical


I contacted Mossberg support and the rep told me that the housing for the piston has two reliefs cut in it to allow the gas to escape and run cleaner. All of the photos online as well as the in the Mossberg manual shows the piston itself with the cutouts on the lip of the piston. This is supposed to be the new piston design similar to an aftermarket 930 piston that used to be available from SBE and that Mossberg apparently got the idea for the cutouts. I may be a little anal but I want to make sure I have the latest parts available for my "new" 940 Pro Tactical. The current piston looks like the older 930 piston. Maybe the reliefs cut into the current piston housing does the same thing. I don't know.

 

[Jmm14534]

Attached are pics of my SBE Precision Products cylinder for what it’s worth. I purchased the one piece seal ring from Mossberg. It’s going to be installed in my M930. I look at Mossberg’s website and they don’t seem to have cylinders for the 940 advertised. Talk to SBE and see if there piston fits in the 940???

 

[rickman]

From what I've read from the folks at Or3gun, the SBE piston will not work in the 940 plus they are sold out. I emailed Mossberg with photos and received a reply that didn't answer my question:

" Hi Rick. The owner's manual is just a general reference guide, and pictures might be dated. The pistons can go through different revisions. If the piston is functioning in the gun, then there wouldn't be any further steps to take. Thanks."

The current piston will function, that's not the issue. I want to be able to go longer beteen cleanings and if it is supposed to have the 'upgraded' piston for the 940 Pro models, I want that piston in my 940 Pro. Not happy with Mossberg's response.

 

[rickman]

I just got off the phone with Mossberg customer service. I inquired about the gas pistons for the 940 Pro and the 940 Pro Tactical. I informed him that the Owner's Manual shows two different pistons, one for the 940 (with single outer ring) and one for the 940 Tactical (with 2 outer rings). He said either piston will fit as the pistons are all the same. Hmmmm, manual shows two different types. Anyway, I asked if I could order a piston with the outer ring and he said they do not have 940 pistons in stock as they are all going into guns being built. Soooooo, if you want a piston for your 940 you will not be able to get one from Mossberg... at least not now.

 

[Jmm14534]

Rickman,
Shoot it as is until it starts to f up. You should probably get somewhere between 200 and 400 rounds. This is not bad for a semiautomatic shotgun.
Then when you have the upgrade parts available do a complete disassembly, inspection, deep cleaning and reassembly with the new upgraded parts.
Repeat the process.
You should get something better than 200 - 400 rounds. I’m going for something in the thousands for my 930 Snow Goose!

 

[AIRB0RNE6176]

Followed (& appreciated) as I have a new 940 Pro Tac that I plan to shoot the $#it out of, with cleanings around the 200-300 mark.