Mossberg 930 JM Pro Setup/Fixes

[swhiteh3]

https://www.youtube.com/watch?v=QfqdygODl9k

[AirForce2]

Tks for the video. I do clean everything he talks about and even scrape off some of the carbon that the brass toothbrush doesn't get. Would be nice to have that shotgun/ portable toilet brush for it though. Hmmm, so I guess the consensus is not to use any oil in the piston housing or on the piston/rings except for bullet casing type dry lube huh. This sucks. I don't have much time to test it this week and won't get the new parts in before the Pikes Peak nest weekend. Gonna see what happens Wed after cleaning every thing in the gun as much as possible.

Is there something common/brand to buy to remove gun carbon besides or better than Hoppes #9 and MPro 7 cleaner.

[mpom]

As far as carbon, been using FireClean for lube and while carbon does not just fall off, it is not hard to clean with brass tooth brush looking brush. Only clean gas system every 3-400 shells.

AF2, have you checked for free motion of piston with the handguard off? Similar to what JM shows in the video, but with the barrel on the frame. Just wondering if there is any interference between the piston and mag tube. Sounds like your SG works with higher powered loads but not with lower powered ones, so wonder if there is excess friction somewhere hampering function.

Edited May 12, 2014 by mpom

[robg2008]

My setup-fix for the JM Pro was to get a Stoeger m3000. Just had to many issues and reliability problems overall with the gun. Decided to go back to an inertia gun since i have owned a m3500 before for hunting and never had a malfunction.

[AirForce2]

_{Actually this last time out, the piston & piston area was pretty dry ie...almost not lube on or around the piston/rings or the area where you insert the piston. I'm gonna hit the range after work and try it piston w/decent dose dry lube only & if issues clean and piston wet and see. I've had issues the last two times out with more than powerful enough ammo. My guess is something keeping the bolt from going back hard enough since a hand cycle works after each failed eject from mag tube. Should be related to gas system and those components.}

[Dustysa4]

Mine is a field model, converted over to somewhat resemble the JM. Having said that, I noticed that my piston assembly was not returning back under spring pressure alone. With the forend off and the bolt locked back on a CLEAN gun, you should be able to pull the piston assembly down and have the spring pop it back in place. If the bolt is dropped, it will obviously knock it in place. But ideally there shouldn't be any binding. I paid no mind to this, as the gun never malfunctioned. Later I ended up sending the gun and 2 barrels in for a different issue. Mossberg returned it with 2 new barrels and 2 pistons (before I shared 1 piston between the 2 barrels). Now the pistons snap back freely from the spring force, as they should. I believe the piston sleeve was slightly off center on both barrels, causing a slight bind. Just thought I'd share in case this is your issue.

[mwc5]

Great video, THANKS !

[TitoR]

I ran into some cycling issues with my JM Pro that i am not sure what is causing it, although i have my suspicions. The gun will cycle, eject the spent shell and the new round will get caught in the ejection port. Could this be caused by the shells I am using, ARMUSA 7/8 oz., size 8 shot? I was able to reproduce the issue by hand cycling, but after tweaking the alignment of the lifter it seems to work better. I am planning to go to the range tomorrow to verify pattern of the load/choke combo. Any suggestions on what to look for?

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[mpom]

Sounds like the round is being directed towards the ejection port rather than the chamber, by the shell lifter. If you have dummy shells, I would observe the way shells are handled by the lifter. By tweaking, I assume you bent the lifter into better alignment. Also, the sharp right edge at the chamber opening, by the extractor, can interfere with reliable chambering. Easy to fix, along with the sharp edge at the top of chamber.

[TitoR]

Mpom, i was also wondering if the 7/8 oz. load is too weak to allow the bolt to fully cycle. Thoughts?

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[cajunautoxer]

My buddy bought a JM amd had Benny Hill work on it. It wouldn't run on 1 oz and works liked a champ on 1 1/8

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[AirForce2]

Tested my 930 jm pro again today after complete tear down and meticulous cleaning, scraping, checking of "everything" except the safety latch. I scraped and cleaned every tick of carbon off the piston and both rings on the piston as well as thorough scrubbing & scraping inside the piston housing area. Removed the shell stop assy and cleaned. I left the piston & piston chamber barely oiled w/one shot dry lube and of the first 20 shells, had one not come out of the tube, and another 50 rds had at least another 5 that would not come out of the tube. Each time a hand cycle of the bolt made it function correctly as in the last 2 times out. The bolt & rails were fairly wet. After total of 100-125 rds of mixed 1200 fps, 1 1/8 oz 7.5 shot and-1300 fps, 2 3/4, 1 oz, 7.5 shot, and 6 shot loads from win super target, Remington, herters, estate all had issues sometimes with 9 in the tube, half full, or 1 or 2 in the tube. Sometimes 9 rounds straight would function fine and then another 9 rds of the same ammo failed to come past the shell stop.

The next 60 rds I did an inspection w/partial disassembly from receiver forward and wiped down primary carbon deposits and "medium heavy" oiled the piston & piston housing, and ext of tube assy & spring etc (very, very light dry lube inside mag tube), and more oil to the bolt/receiver rails and bolt housing and the gun still had issues scattered appx 5-10 times of 60-70 rds fired again. Each time after failure to come out of tube, a rack of bolt and the next shell feeds from the tube. Whatever my issue is, it's not the ammo and it doesn't get any worse if piston & components forward of the receiver are light or heavily oiled. I also went back to the OEM Mossberg mag tube spring today instead of the short Nordic spring, no help. Could not find any obvious burrs anywhere that might be causing the issue

I'm kinda stumped now after initially fixing the "double feeds" & "bolt locking open w/rds in the tube", "shells unable to feed from the mag tube" "ext tube misalignment" and having only 1 feed jam for appx 200 rds and now the primary and only issue that's flared back up is the shells won't feed out of the tube 10-20% of the time. It also didn't seem to matter if I held tight shoulder or at the hip, light grip with no shoulder behind the gun. The gun now has 6-700 rds thru it. From about round count 150-400, this gun was shooting no shit, tight shoulder, from the hip, one handed, sideways, loose gripped and just with herters target ammo & estate 1200 fps 1 1/8 oz loads. If a semi auto is dialed in correctly ie...fit (not shoulder stock fitment), dimensions, finish, springs poundage correct, the gun should function with factory common middle road loads reliably regardless of hold. When my pistols are set up correctly they should fire strong, weak, both hands, woman or man shooting it. I shot a guys 22 inch FN/Win X something at the range today and the same exact loads from my shotgun thumped much harder than his gas gun and he said the same. My earlier post that my Mossberg seemed very stout recoiling is likely true since my 26-28 double barrel 12 ga kicks equal or less with same loads and it's a way lighter gun.

I'm going to try to polish the shell stop again, more on the side that faces back towards the bolt and try again tomorrow. If this doesn't work, I'm kinda stuck at the Pikes Peak Challenge this Sat. I have some parts on order for the Mossberg but won't be here until next week. If the new shoulder stock recoil spring, mag tube spring, and shell stop assy I ordered don't fix it, I'll give the factory one shot at it before I can it. Hope not since I put a lot of effort and time trying to make a crappy gun into a good shotgun. Sucks that I've only shot a shotgun for 2.5 months ever and I feel I know as much as half the tech dept at Mossberg on this gun. Sad thing is some run great out of the box and some suck like a coin flip. This guns been out for 2-3 years and still their iffy. Out of the box to date have had I think every possible malfunction listed online in forums except the light primer strikes & that's because I replaced the hammer spring before even fired it.

[mpom]

No expert here, but have you cleaned up the front of the shell stop? the piece that stops a shell from coming onto the lifter? Someone mentioned that it should have a semicircular shape, with the edge towards the center of the mag tube reshaped like a crescent. mine was a straight edge and the recommendation was to cut the middle away, so the shell rim is released with a bit less movement of the shell stop needed. Polishing the front and back of the front end of the shell stop helps make mine easier to load as well.

No harm in doing this mod, as long as you dont remove too much material from vertical edge of front of shell stop, to the point shells pop out of mag tube before they are supposed to.

maybe The Man from RAS has an insight into your problem.

Tito, never shot 7/8 oz shotshells, so dont know if they work, however 7/8 oz slugs are 100% in my 930JM. Not sure if there is a velocity difference.

[Tuflehundon]

Check the spring plunger (not sure of it's name) that is in the stock with the recoil spring. Buddy of mine had tons of issues with his 930 and replaced tons of parts. He was getting ready to sell it when a gunsmith we know checked his gun out and noticed the the plunger had a crack in it and had rough edges. This was causing his bolt to not move freely or sluggishly. he replaced the part and they did a test fire and it seemed to work fine. We are going to the range tonight to run some more rounds through it and see if it fixed his issue.

It's one of those parts that I would not have even known to look at. I plan to take mine apart and double check that it's in good condition to.

Here is a pic of the new part. Not sure of he has pics of the damaged one.

Edit: Just looked at a pic he texted me of his old plunger compared to the new one above which he got from Mossberg. The old one in his gun did not have the beveled edge you can see in the pic. Mine is like his new one, but mine is a newer gun than his. Wonder if this was one of the fixes they implemented?

Edited May 15, 2014 by Tuflehundon

[JonF]

No expert here, but have you cleaned up the front of the shell stop? the piece that stops a shell from coming onto the lifter? Someone mentioned that it should have a semicircular shape, with the edge towards the center of the mag tube reshaped like a crescent. mine was a straight edge and the recommendation was to cut the middle away, so the shell rim is released with a bit less movement of the shell stop needed. Polishing the front and back of the front end of the shell stop helps make mine easier to load as well.

No harm in doing this mod, as long as you dont remove too much material from vertical edge of front of shell stop, to the point shells pop out of mag tube before they are supposed to.

maybe The Man from RAS has an insight into your problem.

Tito, never shot 7/8 oz shotshells, so dont know if they work, however 7/8 oz slugs are 100% in my 930JM. Not sure if there is a velocity difference.

I have a new 930 JM with very little rounds through it and right away had the problem with shells not releasing when the tube was full. Took as little as 5 shells for this problem to rear its head. Breaking the sharp lip edge and side corners with a fine file, then doing the polish job with a series of 600, 1000 and 2000 grit wet/dry was all it took to get this running smoothly.

Not sure about reshaping it in the crescent form though. The tip of the stop is flat, not curved, to begin with so there's not much material you could remove on the relatively thin tip that actually contacts the head of the shell. Removing material there would be removing actual bearing surface thus increasing the pressure on the remaining points (though it could reduce friction/sticktion subsequently as well).

[mpom]

Probably did not explain myself clearly.

I left the face contacting the shell rim flat, but cut a radius in the "vertical" edge, to mimic the radius in the shell rim, so when shell stop moves aside in order to release a shell, contact is lost all at once. Just took out a bit of the center of the vertical edge with a 1/2" round drum in my dremel.

[AirForce2]

I got the parts from mossberg yesterday ie...new shell stop assy, rear stock recoil spring, tube spring.

The gun was cleaned immensely prior. First 19 rds had one failure, live shell did not release from tube (empty ejected and bolt closed with no shell). Next 30 rds had 10-15% of the exact same I've been fighting lately.

Swapped out the rear recoil spring in the stock w/new (I had cut 9 coils off to see if 1100-1150 fps loads would feed). Shot 50 rds Still had the same exact failure to feed from tube and bolt closes on empty chamber (happens on biggining, middle, last shot of loaded tube).

Swapped out the shell stop assembly. Now immediately inherited another malfunction that I had when gun was new (gun locks bolt open before tube is empty) as well as the shells not feeding out of the tube and closed bolt.

I retweeked the front shell stop at the range enough to round the top & bottom corners of the forward shell stop (sits on the back of live shells in tube). I left the flat face flat and curled the leading edge since the shell stop doesn't come straight back and swings back at an angle. No help.

I tried swapping my old front shell stop half to the new rear shell stop assy, no help. I swapped the new front shell stop half to my old shell stop rear half, no help.

Ohh yeah, I found the problem doesn't get any better or worse with a light dry lube on the piston & in piston housing & on the tube & components riding on tube below the piston. The problem is the same if I majorly clean & wet lube with a lot of synthetic tranny fluid. Problem seems same on dirty or clean gun ie..between 1-70 rds.

I did not replace the tube spring, because if I remember right a full length mossy tube spring had to much pressure and mine is about 13-14 inches past the tube end cap now. I thought to much tube spring might cause the bolt locking back when not empty or double feeds but can't remember. I shot 250 rds the last few days and I'm stumped and know I'll have problems at the Pikes Peak this weekend. The only part I hanven't removed is the safety assy & the little tube mentioned in prev post that goes into the stock recoil spring tube. What size is most people cutting their stock mossy shell tube spring down to or are you putting the whole thing in? I'm on squad 6 at the Pike Peak Shotgun Challenge tomorrow if you have the "miracle" fix.

Tks for the help

Billy

Edited May 16, 2014 by AirForce2

[mpom]

FWIW, with the +2 cap, running full length factory mag spring.

Sorry i don't have enough experience to offer any help...

Why not call up Steve @ RAS? Doubt he would mind and you have nothing to lose.

[Kevin G.]

Not sure if you've looked, but the area on the bottom, side of the bolt that rides the frame rails had a small burr and was causing the same failure mode. Once I found it and filed it away everything has been running fine. Hope you get it figured out.

[AirForce2]

_{Do you guys think Mossberg will pay for shipping ie..(return auth) or make me ship on my dime?}

_{I bought the gun in late Dec and didn't shoot it until mid Feb for the first time. I had problems from the start and tried to fix on my own and just recently orderend $40 in parts from mossberg and still issues. I did all of the polishing of the guts, bolt, stock cut & fit, tube junction, sights before I shot it almost. Then in Feb did the shell stop work and from what little pics & instructions found online like Brownells pics it seemed I cured most of the problems that can come with the JM Pro, but they were short lived.}

_{One thing I noticed when installed the brand new shell stop assy, is the rear half seems to stick out way more than my orig one (hence the reason I'm sure the bolt gets locked open when shells are still in the tube. This seems to the the area that caused this with the orig shell stop assy. This one has to much to just round off a little. If you hold the gun upside down you will see the lifter should clear the shell stop assy flat section if you push the lifter into the gun when loaded one in the chamber and only a few shells in the tube. Someone send me a pic of your shell stop mods and I can compare it to mine, but I'm pretty sure mine is good on both shell assy's.}

[Dustysa4]

Mossberg would only pay to ship it back in my experience. Fortunately, the sporting good store I bought it from paid to ship it to Mossberg.

[AirForce2]

Has anyone looked at the rear most portion of the shell stop as a dummy round is fed from the tube, the shell feeds out of the tube back over the elevator and as shell goes rearward it slide along the inside flat of the shell stop assembly and disengages the shell stop out from under the elevator to be fed upwards to chamber? Easier w/everything except the tube off the gun and everything in the receiver w/flashlight. My rear shell stop (rear slotted/extractor section) bumps into the ejection side of the front most portion of the trigger group. I assume the shell rides back and stops at this point and by that time has moved the rear portion of the shell stop into the side to release the elevator then kicks the shell upward. I'm not sure if this is a bad thing for the rear hook to hit the side of the trigger housing area or not. Thoughts?

I've double checked and all parts in this gun have been deburred/smoothed and recontoured the shell stop forward hook (front area). My friends in the day called me the dremel king and with the soft multi size & shaped polishing heads can do wonders if an area is not 90 degrees then I use a file. I do all of my feed ramps, resurface, shape, mirror finish with these. Find them on amazon in an orange box "54 pc universal rotary assorted grit rubber polish accessory kit for dremel"

[mpom]

Fortunately have not had to analyze this portion of the 930, but would bet that Steve at RAS is familiar with it! Seems very willing to share info in the forums. If I had this issue, I would call him up. 270-348-3262

After all, the brain trust here is not getting it done ;-)

[AirForce2]

What company is this guy Steve working for and what does RAS stand for. tks

Let's just say I've never wanted to discontinue a match before, but being it was my first shotgun match and so many malfunctions today, I felt it better to bow out after 8 of the 10 stages at the Pikes Peak Shotgun Challenge with the malfunction #'s growing each stage and was worried that I'd do something dangerous. Great fun match. I'd say out of an avg stage count of 20 rds fired, I had anywhere from 2-6 rds per stage that would just go click on an empty chamber and have to hand rack. The only malfunction free stage was my first one of the day. You watch a lot of clay pigeons go by with all the activated targets thrown and gun malfunctions in between shots and keeping up with reloading let me tell ya. That spinning target you gotta hit and make it swing over is not cool either when every other shot requires hand rack.

Funny, out of our 10-12 person squad at least 3 had a JM Pro, maybe 4, one was a Flannigan, still 930 pro'ish and out of all the people that had gun issues Mossberg was 1st Place in that dept in our squad. I took top malfunction honors. The last stage the RO said he'd seen a "whole lot" of mossbergs having issues today. One guy had a versamax and had probs on multiple stages, but don't know his gun or habits ie...new gun, ammo, etc

I will let you guys know in a month or 2 when I get my gun back from Mossberg (if they will work on it) since I've 3 gun mod'd it quite a bit. My money's on it being a gas system piston or piston housing issue. Thanks for the suggestions

[mpom]

RAS stands for Rose Actions Sports. Steve Rose is the guy, goes by Gun Cat. No personal experience, but seems very willing to share his knowledge of shotguns, from reading his posts. Probably more likely to be of help than Mossberg, and a phone call is cheaper than shipping, which is always an option after the call!

Feel bad for you, as I would be pretty pissed, having put in the work you did, and then having frequent malfunctions.

Can see why people have been washing their hands of JM930s of late.

Hope you get it straightened out soon, whether its the gas system or shell release, or something else.

Edited May 18, 2014 by mpom