Mossberg JM Pro Failure To Feed

[ladysaiga]

I've already emailed Mossberg on this, and will update this thread as I hear from them.

Background: in spite of my username, I've been transitioning into tac class and using a JM Pro. I really do like it. My gun has had possibly 2-3000 rounds through it and an equal amount of dry fire in the past year. Never had an issue with it.

Yesterday, stage 1 no problem. Stage 2, one single issue. The second shot of the stage it failed to chamber the shell.

On stage three and four, I had that problem with nearly every round. I'm too new a member to post links, but for those curious my youtube channel is under my name, Rachel Bonaccorso Lindsay.

Upon cleaning and disassembly, there's not any clear issue to be seen. Gas system not clogged up, rear recoil spring looks fine.

Now, I've got a friend who's going to tell to buy a Benelli. But aside from that, what can anybody tell me to look for here?

Thanks!

Rachel

[mpom]

Has this ammo functioned well in the JM930 previously, or not?

Have you tried other ammo that has worked well in the past to determine if the problem persists?

Looked at your UT videos and it seems a round did not even make it from the mag tube out.

Have you looked at the 2 gas ports to make sure they are open?

Edited June 1, 2014 by mpom

[ladysaiga]

Yes, thanks for the reply. It was a fresh case of Rio, but the same stuff I've been using all year. My husband ran it too in our saiga, no noticeable difference from usual. The ports were open, not very dirty. I wanted to try something hotter just for kicks, but nobody had brought any I could borrow.

[alma]

I watched your video. It kind of reminds me of this:

http://youtu.be/IggfqXA-os8

As far as I can tell it is some problem with my gas system since it seems that the bolt is being pushed back far enough to eject the fired shotshell but not quite far enough to release the next one into the chamber. The gun was running fine AM and then PM it started doing this. Interestingly enough it has been 100% with slugs which also makes me think it could be a gas issue. Cleaning hasn't helped and unlike the JMs it is pretty hard to disassemble the piston on my gun to really clean it well. I actually picked up a recoil operated shotgun to use at my next match but will be coming back around to try and fix this one. My next try will be to replace the gas piston to see if that helps. Miculek just posted a video on JM maintenance and how he cleans the piston. It might be helpful.

Edited June 2, 2014 by alma

[usmc1094]

Has the side saddle always been on the gun? I have read some posts of that messing with the feeding of the 930.

[bigkyle72]

http://www.brianenos.com/forums/index.php?showtopic=192975

thy this stuff

[ladysaiga]

Hi guys, I will watch those videos during lunch, thanks. Yes the sidesaddle has been on it the whole time. I'm really puzzled by this, it's been running great. I know I'm not as solid as most of the guys I shoot with but I'm not thinking it's me, I can run the saiga fine without soft shoulder type issues, and haven't had them with this gun either. I haven't heard from Mossberg yet. Will definitely be interested in how they respond. I don't really wanna send off my gun and have to wait!

[ladysaiga]

I did see that other thread, yeah. I'm not thrilled about the idea of cutting coils, it sure oughtta run the same as it did last week if nothing's broken, right?

[usmc1094]

It should. Maybe try blowing some air from an air compressor through the gas ports to see if maybe some small stuff is stuck in there. Im just guessing here. Mine ran great for the first 700-1000 rounds then had FTE problems. I had to polish the chamber to let things work right. Cheap Winchester shells still get stuck and rip the lip of the case off. I can post a pic if you want.

Not sure if a little polishing of the chamber might help speed up your bolt enough to make a difference.

Edited June 2, 2014 by usmc1094

[GunCat]

Will the gas piston easily slip into and out of the ring under the barrel? (It needs to do so)

The piston itself is actually 3 parts, the 2 smaller rings on top will snap off so you can clean all the parts. Fouling build up underneath can cause those 2 rings to expand and let the piston hang up causing short cycling (or no cycling at all)

That is one of the areas to watch and keep clean on the 930

[ladysaiga]

It's cleaned now but yes, it did slide in and out. Was dirty but not stuck; the two ports were open as far as a probe with a little pick would confirm. Nothing fouled to an unusual degree, it only had about 200 or so rounds through it max since the previous cleaning. I'll pull it apart and take pics tonight. Am also very curious if it will shoot now that it's clean.

[alma]

As discussed

[Who Knew]

I had a similar issue. When I first bought the gun new I had already seen the Brownell's video so after only a few rounds for initial function testing I pulled the shell stop and did a little polishing. My shell stop had a small bur that would leave a little scratch on the head of ejected hulls so I basically smoothed that down with fine sandpaper and then polished with a dremel minimally. My only other modifications were a xl extended cap and welding up the lifter. The gun functioned great with factory mag spring but somehow it got twisted up so it was replaced with a Nordic cut approx 10" past end of extension. Fast foward to about 600 rounds with no problems shooting Rio, Estate, and Federal bulk with cleanings after every 200 rounds.

Last stage of a match with empty chamber start, when I charged the handle the first shell wouldn't release. After several attempts I dropped one in the port, fired it and the rest fed just fine. I finished the match with no other problems and thought it was an isolated incident. At the next match on the second stage the problem came up again so I ended up borrowing a gun for the rest of match. The gun went from running great to not releasing shells by hand cycling or live fire. After reading all the post on here I could, I tried stretching the shell release spring and changing to a new mag spring because mine had compressed a little. Although better the gun would still not cycle reliably. I ended up pulling the shell release again and polishing the tip that touches the shells really well with dremel. I also found an area at the back of the release that had been rubbing the lifter so I filed a little off that area and polished it and the area on the lifter where they were contacting. I have since shot about 80 shells with no problems and it is hand cycling fine. I still have no idea if the gun is going to be 100% but I'm going to be putting some rounds through it over the next couple of weeks for testing. If something changes I'll update

[ladysaiga]

OK guys, watched Miculek's video and one thing we have not been doing is taking the two rings off the gas piston when we clean. Now, normally we give that piston a very thorough scrub anyway and clean it with a good blast of brake clean or whatever we've got, which probably has been getting in there to some degree, and the piston felt like it was moving well but yes the rings were a little crudded up. From the sound of things that may very well have been enough to cause my malfunctions. I took some pics but don't know if i'll be allowed to attach them. Will try in a sec.

I may or may not have a chance to test fire it this weekend. I will let you know what Mossberg say to me but so far I have not gotten a response from them. If it runs after this, I'm happy. I was just getting a little steamed that it seemed to have pooped itself so soon, but it might just have been my maintenance.

Meanwhile I may have let myself agree to picking up a Benelli anyway.

[AirForce2]

Your problem most likely will not be fixed by the recoil spring in the rear stock (I had a few of the same jams you had in the first 300 rds thru the gun) and cutting down the recoil spring, using a Nordic spring appx 10-11 inch past end, and a cut down 14 inch past tube factory spring & a new full length factory spring, no help. Between 300 rds and 7-800 rds the issue grew like a weed and happened 30% of the time or more. I worked over and smoothed out all the internals including the shell stop assy also. I picked and scraped all the carbon off the piston & removed both rings and clean all the grooves to, no help. My piston moved in/out easily also. Issue compounds as the round count went up every 20 rds (from an all items cleaned & lubed start point).

The Nordic spring is much stiffer. A new Mossberg feed tube spring is cheap, but should not be installed at full length in my opinion. I think a new Mossy tube spring even w/Nordic XXL end cap should not be 19-20 inches past the tube, but more like 16 inches past and bend down the 1/8 inch of the ends down & into slightly and rounded so no wrapping in the end cap or follower.

Remember, it's not a good idea to stretch a hardened steel spring much at all because it likely will only make it weaker quicker back down to the orig spg weight or even less. If you scape out and brush out all the carbon on the piston & 2 rings inside & out and at least remove gunk/carbon and lube the piston housing the piston goes into, you should be good. If this doesn't fix it, then your in the same boat as I am, awaiting Mossberg to fix the same issue on mine. I suspect a gas system issue on yours that you can fix by cleaning. I suspect a gas system issue on mine that requires gas sys parts. Regardless of how or what they do to mine at the factory, it's being replaced by another brand as I write this. I will test it, hope it runs and leave it on a doorstep somewhere and ring the doorbell and haul ass away. I bought a gun that's been out 2 years and had every issue that can plague the JM Pro and fixed most of them which tells me the factory should have a handle on it by now and I don't think they do. No excuse for a company that's been making a not so technical semi auto & pump shotgun for years. My gun was made before Jul/Aug 2013 by the paperwork from the dealer and I bought it new Dec 2013. Good luck.

[AirForce2]

PS. If your gun won't hand cycle it's probably not a gas system issue. Likely the shell stop assembly and/or shell stop springs or the tube spring, or lifter. Steve at RAS gave me a good suggestion to removed the trigger assy & lifter out of the gun and see if it hand cycles reliably then. This may narrow down you're problem area to eliminate the lifter/trigger assy section so you can focus on the tube spring/shell stop assy. That's if the gas rings cleaning doesn't work.

[stinsonbeach]

Great thread & here's my 2 c..

When I got my first JM Pro it had FTF issues right out of the box.

Cleaned it. No help.

De-burred it. No help

Piston ran free.

Then it hit me - this won't sound like anything apropos but it cured the FTF issue. I remembered as a kid all the followers had a post on them. Desperate to try anything I ordered one from Brownells (800-100-004WB) along w/ a new mag spring. Cut the spring at 13" past & tucked under the ends like someone said above. Put the original follower on the top - ended binding.

Runs 100% since.

22" 9+1+1.

Doesn't sound like it has anything to do w/ anything. Right? ...but it "runs 100%"!!!

Edited June 3, 2014 by stinsonbeach

[ladysaiga]

Hand cycling was fine. I'm hoping it was just the rings...one thing I did was before reassembly, I gave 'em a tiny bit of Fireclean. I find that stuff really helps prevent fouling from sticking so bad. If that was my issue, I hope the synthetic lube prolongs the time between needed cleaning. I know I can't get to the range to test fire tonight. Maybe tomorrow, though.

[TitoR]

Any update, did the problem go away?

Sent from my iPad using Tapatalk

[ladysaiga]

Thanks for checking in! I haven't had a chance to test yet. I'm dying to know. I DID hear back from Mossberg on Saturday. A badly spelled three-sentence missive asking me for a mailing address and serial# so they can send me a box to send it to them. Not even an attempt at advising me, even though I attached videos and a detailed explanation of what I had already checked. I don't want to send the gun back, I want to figure it out and if any parts are needed just order the parts. Chances are, the cleaning fixed it.

Meanwhile, I didn't even think about it because I was so busy on Saturday, but I worked the HAVA family day event at Academi and Tom Taylor from Mossberg was there representing them with the guns Mossberg sent for the occasion; and until I went home that night it never crossed my mind to ask HIM for some expert advice. I didn't work the shotgun stage so my mind wasn't on it.

[muddywings]

I'll throw this out as a total noob.

I bought a 930 SPX that had been converted for 3 gun. Price was right and money was an tight. Would I prefer a Benelli or a Versamax-sure; but for the price point this got me in the game.

Took it out, ran like a top. Used it for a year now, no issues.

I decided to open the port up and in my research I found a good general practice suggestion of always having an extra spring on hand.

Bought a Nordic spring from Brownells. Trimmed it about 2 inches longer than my current one. MASSIVE feeding issues. Trimmed it down to just an inch longer. Still feeding issues. Put my original spring back in, no problems. Put it away and scratched my head. A few days latter I went back to tinker. With the new spring in, I undid the top of the mag extension and then only threaded one or two turns. 95% function rate. Threaded it all the way down, back to having problems. Trimmed the spring to be about 1/2" less than the original spring and got a 90% success rate. Trimmed it another 1/2" so now I'm a full inch-ish less than my original spring and seems to be working fine and is not overpowering the bolt release, shell stop/catch.

I haven't run it outside yet.

Don't get me wrong, I'm not knocking the nordic spring, in fact as for springs go, I would say it's a nice quality. I'm just saying it is a lot stiffer than my original one which started giving me fits. Even that much shorter, the shells are still getting thrown back into the lifter with decent force.

For the price of a spring, you might want to tinker with that.

(Sorry for the long post-work is slow...)

I throw this out there more for general consumption than maybe your issue.

Good luck though...

Edited June 9, 2014 by muddywings

[stinsonbeach]

"muddywings" et al,

See my Post # 17 - I thought it may have been irrelevant but - just threw it out as it was my experience - obviously that may have been more relevant than I ever thought.

Have an SPX & changed the follower & springs (in any shotgun change out the springs immediately - no matter what "they" say) w/ no issues as opposed to my JM Pros...anywazzz have fun tinkering & keep in mind the simple springs - do NOT be afraid to keep clipping & put another cheap-o follower on top in the extension tube. Once you get them (all shotguns!) running they are BIG-FUN & probably will run w/o another "tweak" for as long as you have'm!

Edited June 10, 2014 by stinsonbeach

[muddywings]

Stinson-

Yup sounds familiar! Haha

I was just tinkering and happy I went from problem to a solution. I mainly lurk here but thought it was worth posting somewhere to help someone when I came across this thread.

Honestly poor interweb thread etiquette as I didn't read all the posts and just threw it out there.

A follower at the top you say....interdasting! Might have to tinker more.

Happy shotgunning!!

Sent from my iPad using Tapatalk

[stinsonbeach]

"muddywings" -

Both had the same problem / solution.

Seems frivolous, but there it is.

As for the cheap-o follower up top: I was having binding w/ the spring when I snipped it & even tucking in the ends - someone above suggested that - it wouldn't solve the problem. As I changed out the follower w/ the one from Brownell's I had the stock one just lying around, so . . . I now do that w/ all my shotguns when I change out the guts.

"Keep on tinkerin'..."

Edited June 10, 2014 by stinsonbeach

[Bullittmcqueen]

The first thing to be replaced on the stock 930 should be the cheap flimsy magazine spring. I would replace it with a nordic spring. Also what you have said about keeping the piston clean is right. These guns seem to be sensitive to fouling.