Mossberg JM Pro light strikes, what is the cure?

[sasquatch981]

So I was at the Northwest Multigun and everything was working great except I had 2 issues with the JM Pro.

1) 4-5 light strikes over the course of the match.

2) 1 double feed where two rounds fed out of the magazine tube instead of one. I had to hold the bolt open and push the second round back into the tube and then rack the first round into the chamber.

Any ideas on how to fix the problems? Gun is totally stock except for rifle sights.

Thanks

[GunCat]

How many rounds have been fired since you last cleaned (thoroughly cleaned) the piston, rings, and the area in the mag tube ring that the piston fits in to? Build up in the piston area will keep the bolt from going into battery completely and light strikes start happening.

Look on down the page at some of the various other 930 threads, this topic and related issues are covered and ma give you more ideas,

[Thecelt]

I'm not an expert but I've read that some replace the firing pin spring (its been talked about so you can do a search). Some have stretched the spring.

Ad for the double feed (I've had one of those) you can polish the shell stop (I just did but haven't had a chance to test it). I also wonder if the mag spring is a bit stiff or long. How far passed the end of the mag tube does your spring end?

http://www.brownells.com/.aspx/lid=15831/GunTechdetail/Fixing-A-Mossberg-930-Feed-From-The-Tube-Problem?source=CJ&ch=aff&AID=6147349

This tells you how to polish the shell stop. However on the jm there is no cotter pin holding the ss pin in place. Just use a allen key and push the pin down from the top and it will pop out.

[mpom]

Weak hammer spring can cause misfires. I replaced mine with a Extra Power Ruger 10/22 hammer spring, no more light hits/misfires.

The JM DOES have that very small cotter pin described in the video.

Mark

[Thecelt]

Weak hammer spring can cause misfires. I replaced mine with a Extra Power Ruger 10/22 hammer spring, no more light hits/misfires.

The JM DOES have that very small cotter pin described in the video.

Mark

mine did not, so i assumed all the jm's didnt.

this slot is not on my gun.. not sure if that means that older guns had it or if that is a newer feature.

http://ga.brownells.com/UserDocs/email/Images/Mossy930_Photo_2_tool.jpg

Edited July 23, 2013 by Thecelt

[Thecelt]

Btw, I said firing pin spring but I believe what I recalled was the hammer spring as mpom posted up about.

Mpom, was that a direct drop in or did you have to modify it? How much stiffer is it and do you see any downside to running it?

[mpom]

I trimmed the hammer spring a bit, around a quarter inch, as I was afraid of spring binding when compressed and not letting hammer cock, but you could start with full length. Don't remember where I got the spring, but its made from thicker wire than Mossberg, still .25" OD, which allows it to fit. Harder to compress when trigger housing is out, so have to assume it hits harder. Don't see any downside. Trigger pull has not significantly changed.

Yeah, if no slot then makes sense there is no clip. My JM has the slot, so I ASSumed they all do.

Mark

Edited July 23, 2013 by mpom

[Thecelt]

Well we both ASSumed and we know how that goes. I would be curious if the stiffer hammer spring would slow down the bolt as it retracts and in turn have an effect on lower recoil rounds. Have you had any issues with lower recoiling rounds? in theory, a stiffer hammer spring should make it harder for the bolt to reset the hammer.

[mpom]

No doubt the stiffer hammer spring takes more energy to cock, but it does not seem to have any noticeable effect on function; I often run 1190 ft/sec shot shells and have had no issues. Ejects, loads and resets hammer just fine. Believe some ammo had 1145 ft/sec printed on box and that ran fine as well.

Its not like the spring is twice as strong as the factory, would guess that with wire diameter of 4 thousands difference and original at around 39 thou, we are talking about a 10% difference keeping length the same. A bit more if using a longer spring.

Mark

[Thecelt]

Good info. Thanks, I've been trying to gsin all info possible on the jm to make it as "bullet proof" as possible. I will be very happy if I can run this thing with no more than a 1% failure rate. I've even debated sending it to salient just to help ensure reliability.

[LikesToShoot]

No doubt the stiffer hammer spring takes more energy to cock, but it does not seem to have any noticeable effect on function; I often run 1190 ft/sec shot shells and have had no issues. Ejects, loads and resets hammer just fine. Believe some ammo had 1145 ft/sec printed on box and that ran fine as well.

Its not like the spring is twice as strong as the factory, would guess that with wire diameter of 4 thousands difference and original at around 39 thou, we are talking about a 10% difference keeping length the same. A bit more if using a longer spring.

Mark

Thanks for the review. Based on what you've posted I went to Wolff and ordered a pair, may need one for my 10/22 some day. I took the < $4.00 USPS shipping so it's around $15 for two springs delivered.

Thanks again!

http://www.gunsprings.com/Rifles%20%26%20Shotguns/RUGER/10-22/cID2/mID52/dID225

[mpom]

let me/us know how it works out.

Mark

[LikesToShoot]

let me/us know how it works out.

Mark

Yesterday during two rounds of trap I had one more light strike, dimpled the primer and fired on the second try. Federal Ultra ammo.

Well today in the mail my Wolff order arrived.

On my cheapo scale the wire size appears to be the same. The original spring has 18 coils and is 1.360" long with the 10/22 spring having 20 coils and is 1.740" long. I swapped it out tonight without any modification. It fit right in and the trigger pull is still right at 4 1/4 lbs, unchanged.

I might get to the range tomorrow, if not I'll be there on Friday.

[Thecelt]

thats really good info likestoshoot. ive had one light primer strike myself and it seems as if this might be a good "preventative" measure to take. my only concern would be how much extra effort it takes for the bolt to push the hammer back and if it would cause any trouble with the lighter type loads.

Edited July 30, 2013 by Thecelt

[mpom]

No problems running light loads, sample size of 1, soon to be 2, maybe more.

would be surprised if this slightly more powerful spring would soak up enough energy to impede

normal function, but anything is possible.

mark

[Thecelt]

i think we should start a thread pertaining to the jm pro and all reliability upgrades so we can track everything in one thread that help improve smooth running of this gun. im going to order 2 of these springs myself (could actually just take one out of my spare 10/22 trigger group if i really needed to).

[bpipe95]

If you are getting light strikes be 100% sure the gun is actually going all the way into battery.

Around 7k rounds mine developed a burr on the locking lug that would prevent it from locking up time to time. This would leave a light strike on the primer.

It can be hard to spot because when the hammer falls it tends to knock it the rest of the way into lock up.

This may not be your cause but it is worth looking good luck.

[LikesToShoot]

I shot 50 rounds of Fed. paper target loads, size 9, 2 3/4 dram and 10 rounds of Fed. Ultra, size 7 1/2, 3 drams tonight without any issues.

One in the chamber, nine in the tube. Timer went off and I was chucking charoal brickets in the air and blasting away. I shot this stage at a match earlier this month and still need more practice.

[Thecelt]

Good report lts.

[LikesToShoot]

Good report lts.

Thanks.

The real credit should go to Mark for pointing out the 10/22 hammer spring. That's the ticket!

Thank you Mark!

Steve

[mpom]

Glad I have something worthwhile to share!

I appreciate the fact that although many here are very competitive, they are very willing to help out fellow shooters.

Hopefully will not have to find a replacement spring for the shell stop, although with the numerous complaints of double feeding, that may become a future project...

Mark

Edited August 1, 2013 by mpom

[LikesToShoot]

Glad I have something worthwhile to share!

I appreciate the fact that although many here are very competitive, they are very willing to help out fellow shooters.

Hopefully will not have to find a replacement spring for the shell stop, although with the numerous complaints of double feeding, that may become a future project...

Mark

At least those two springs are listed and possibly available from Mossberg.

http://mossberg.com/manuals/930_935.pdf

[Thecelt]

Glad I have something worthwhile to share!

I appreciate the fact that although many here are very competitive, they are very willing to help out fellow shooters.

Hopefully will not have to find a replacement spring for the shell stop, although with the numerous complaints of double feeding, that may become a future project...

Mark

did you polish yours up yet? i have also thought about perhaps adding a second smaller spring or even a stiffer spring for this part. in the mean time i polished it up as the brownells article instructed. i have only had one double feed, but it was within the first 30 rounds i fired through the gun so i chalk it up to the gun being "tight". i still havent broken this thing in yet at only 180 rounds.

[mpom]

I polished up the front of the shell stop a few months ago and have not had any incidents of double feeds. My 930 ran fine last Sat at a match, but a couple of other 930s choked; one had multiple light hits and the other had double feeds.

Hopefully with the few mods I've done it will continue to run well. Will continue to clean and lube every few hundred rounds. Did have a gouge in the mag tube inflicted by an end of the strong spring inside the gas cylinder the piston runs in, and dremeled the offending end of spring down a bit, also months ago. Have not looked into the springs controlling the shell stop as I don't want to start messing with the balance needed for the shell stop to function as intended. However if the spring(s) take(s) a set, will have to.

Yes, its rough around the edges, but if it keeps on trucking and lasts, I will not regret buying it. Versamax sounds good, but not crazy about increased weight.

Mark

[LikesToShoot]

After another 3 boxes thru mine today that makes 210 rounds without a problem since I installed the XP 10/22 hammer spring.