Mossberg JM Pro light strikes, what is the cure?

[Triggerbender]

I see the 10/22 spring seems to be working for you guys. Going to order some.

Is there any increase in lock time? The Mossy has the slowest hammer fall of any shot gun I have ever owned.

Would be nice to step it up.

Thanks

[LikesToShoot]

I see the 10/22 spring seems to be working for you guys. Going to order some.

Is there any increase in lock time? The Mossy has the slowest hammer fall of any shot gun I have ever owned.

Would be nice to step it up.

Thanks

I can't tell any difference compared to the stock spring but I probably don't have the experience to tell the difference.

After three more boxes thru it the other day I took it down for a good cleaning, man this thing was dirty. The piston and rings were sticking really bad and the tube was carboned up. I cleaned everything really well and applied some Fire Clean to see if that helps with future clean up. I did not see any signs of hammer peening or mushrooming of the firing pin.

I had a match today so I went to the range yesterday and ran two boxes thru it to make sure all was good, then shot about five more boxes today while letting another guy borrow it for two stages. He REALLY liked how it ran and loaded.

For me this issue is resolved, it was the hammer spring causing my light strikes.

[Triggerbender]

Sounds good I am considering putting the 10/22 spring in minus the cocking indicator shortening the stack a little and an ever so much lightening the load possibly speeding up the hammer a mini micro second .

I have never used it and probably could not retrain my brain anyway after all my years of shooting scatterguns.

I polished the snot out of my tube, piston and follower, after 300ish rounds all became sticky or sluggish causing issue.

Hopefully this will get some more swat on the primer.

Thanks.

[mpom]

I see the 10/22 spring seems to be working for you guys. Going to order some.

Is there any increase in lock time? The Mossy has the slowest hammer fall of any shot gun I have ever owned.

Would be nice to step it up.

Thanks

just a guess, but if the premise is that the 10/22 spring is stronger than oem hammer spring then energy imparted to hammer is greater than oem spring, and if hammer mass remaims constant then hammer velocity has to be greater, using energy =mvsquared, divided by 2

mark

Edited August 11, 2013 by mpom

[LikesToShoot]

Sounds good I am considering putting the 10/22 spring in minus the cocking indicator shortening the stack a little and an ever so much lightening the load possibly speeding up the hammer a mini micro second .

Go for it, and please let us know what you come up with. I was looking for a "fix" to a problem and Mark came up with a great idea. IIRC, he cut a couple coils off on his but I went for "easy" and just stuck the whole spring in.

[Triggerbender]

I see the 10/22 spring seems to be working for you guys. Going to order some.

Is there any increase in lock time? The Mossy has the slowest hammer fall of any shot gun I have ever owned.

Would be nice to step it up.

Thanks

just a guess, but if the premise is that the 10/22 spring is stronger than oem hammer spring then energy imparted to hammer is greater than oem spring, and if hammer mass remaims constant then hammer velocity has to be greater, using energy =mvsquared, divided by 2

mark

I agree, I am looking to get a little more velocity with the lighter mass, as little as would be removed leaving the cocking indicator out?

It's the racer in me that makes me go for everything I can get, one thing I do know is when you can't make any more HP you start making it lighter to get from point A to point B faster.

I am also looking for close to factory spring height as I can get without losing any spring. Would not hurt my feelings if it pushed the hammer that little extra farther like the other SGs I have.

Starting to have my doubts but maybe there is a reason Mossy used such a short spring to start with, although I have never had an auto or pump that left the hammer flop loose like the Mossy after it has been released, Remington, Winchester, Beretta or S&W Super Skeet none of them.

You trimmed your spring and LTS left his stock with all the factory parts reinstalled, I will be somewhere in between leaving the cocking indicator out, as far as spring height.

Thanks again for coming up with the spring.

I still have a hard time with Wolff not being able to come up with something for this .

[mpom]

Would not worry about hammer flopping around, as that cannot happen in SG, since back of bolt/firing pin stops forward hammer travel. If you look inside, hammer can only go to vertical position. I did not try full length 10/22 spring as my particular spring was made of slightly thicker wire than the one LTS has, so figured I had gained velocity with factory length, but if it works full length, then go for it, as we are trying to maximize hammer force! Suspect aluminum cocking indicator weighs very little so not likely to impact hammer velocity a measurable amount, but lighter is lighter, and the cap should keep spring from rubbing sides of channel. Would be concerned if you lend your SG to someone who has an AD and then turns around and blames it on the lack of cocking indicator.

Mark

[Triggerbender]

Would not worry about hammer flopping around, as that cannot happen in SG, since back of bolt/firing pin stops forward hammer travel. If you look inside, hammer can only go to vertical position. I did not try full length 10/22 spring as my particular spring was made of slightly thicker wire than the one LTS has, so figured I had gained velocity with factory length, but if it works full length, then go for it, as we are trying to maximize hammer force! Suspect aluminum cocking indicator weighs very little so not likely to impact hammer velocity a measurable amount, but lighter is lighter, and the cap should keep spring from rubbing sides of channel. Would be concerned if you lend your SG to someone who has an AD and then turns around and blames it on the lack of cocking indicator.

Mark

I'm with you, in reality I doubt the cocking indicator would have any effect other than making the spring height slightly shorter with its removal

Again, I still go for everything I can get, just me.

I have loaned the gun to seasoned shotgun shooters I'm talking 10/15k shells a year guys and one guy asked what the "little button" in the triggerguard was and all others did not even know it was there.

A 930 owner should know but not many around here and the way they have started to fail probably not going to be many more.

IMHO, if you have an AD because of no cocking indicator you probably should look into another sport. But that is a whole other can of worms.

Keep the reports coming on the success or not of this fix.

Thanks

[mikeAZ]

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.

exactly what happen to my shooting buddy's JM 930.

[LikesToShoot]

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.

exactly what happen to my shooting buddy's JM 930.

Any idea on how many rounds through his? Did he just file it off? Does he still have the gun?

Thanks, I'll keep my eye's open for this during clean up time.

[Triggerbender]

Got my 10/22 Xtra power spring.

The coils are smaller than the original, .039 for the Wolff vs. .042 for the Mossy.

It is longer as reported and I am going to shoot for a while and measure it to see if it takes a set or gets shorter.

Put it in without the cocking indicator and the 1 washer I used to shim the original spring, feels harder to compress with the SWAG thumb test.

The hammer bottoms out in the trigger assembly before the coils bind both with the new spring and the old spring with washer and cocking indicator.

I can not detect an increase in hammer speed old vs. new, was hoping to speed it up.

Hopefully the new spring with the added coils along with the different pitch on the coils will give the hammer a better follow through to the primer.

I am going to have to load up some shells with the hardest shotgun primer I know of (Wolf) and shoot to see if the impact prints the same or better on the primer than it did stock.

In the past the Mossy shot them with very little deformation of the primer just a small peck mark vs. the normal crater in a fired primer, so little in fact I was surprised the shells fired but they all did, where as all the rest of my shotguns made a normal looking fired primer with the Wolf brand.

Will try to get out and do some testing next week and see what happens.

[Keeganxt]

I read this thread while I was waiting for delivery of my JM. I ordered the springs (2 pack) and finally got a chance to shoot today. While I wasn't looking at primer impact, I did not notice any adverse effect from running this spring. My only note is you do have to compress it a little bit before the hammer will return to its normal range of motion after install.

[Triggerbender]

I read this thread while I was waiting for delivery of my JM. I ordered the springs (2 pack) and finally got a chance to shoot today. While I wasn't looking at primer impact, I did not notice any adverse effect from running this spring. My only note is you do have to compress it a little bit before the hammer will return to its normal range of motion after install.

Did you reinstall the cocking indicator with the new spring?

[Keeganxt]

Yes I did

[rangerguy]

I ran mine in 2 matches yasterday and today with the new 10/22 spring and no light strikes for me. I think we gots a winner here.

[dickwholliday]

Posted Today, 10:38 AM

when my 930 was new i had the light strike issue but cleaning the rings seemed to have cured that problem.....mine has been shot a bunch.....recently however it seemed like every outing i'd have some sort of malfunction......

i really didn't take time to analyze it, but a couple of times it seemed like it did't cock the hammer because when id pull the trigger for the second shot it felt like the hammer had already fallen or just didn't cock for whatever reason....not sure if that was what had happed or not....if it ever happens again you can bet i'll stop and figure it out.....

another of the malfunctions was a light strike...it had marked the primer...i reloaded the shell and it fired.....

i replaced the hammer spring with the extra power Ruger one from Wolf and all the malfunctions seem to be gone....you can tell from the sound that it is obviously dropping the hammer with a lot more force....because this past weekend i shot it 75 times and the only thing out of the ordinary was that it failed to lock back after the last shot onone occasion....D I C K

[rtp]

Are you guys trimming the Wolff springs or leaving them the longer length?

I've got a pair on order for 'backup parts,' but I've seen some saying they run full length, others not - is there a general consensus now, or has someone compared a new MB spring pressure rate vs untrimmed/trimmed Wolff?

[mpom]

If the hammer cocks with a full length spring, then go with it, as the goal is to increase the hammer force. If the added spring length causes interference issues, then I would trim it a coil at a time until its resolved.

Mark

[rtp]

Thanks, Mark.

Any consensus on round count to start being concerned with the OE spring?

In other words, does it happen reasonably reliably at some range of rounds/use, or just 'whenever it happens,' time for a new spring?

It seems like the latter, but maybe someone knows more..

[LikesToShoot]

Thanks, Mark.

Any consensus on round count to start being concerned with the OE spring?

In other words, does it happen reasonably reliably at some range of rounds/use, or just 'whenever it happens,' time for a new spring?

It seems like the latter, but maybe someone knows more..

Mine was weak at some point over 2K. If you store the gun with the bolt locked back that would have the hammer cocked and the spring compressed. IMHO not the way the gun should be stored.

[mpom]

My misfires were very rare, but first one occurred pretty early, maybe 3-400 rounds through the gun. Since this is a weak point with the JM930, why not just practice preventative maintenance and do something to help reduce the likelihood?

Said help, not simply eliminate, as it seems others have had misfires from dirty piston rings and burrs on locking lug, not just weak firing pin strike.

Mark

[Triggerbender]

Mine started also after 2k thru it, piston cleaning is a must, cleaning the mag tube and follower also for fail to feed and jam. All have been polished with no mercy.

Anyone else have their trigger assembly fit loose in the receiver ? Mine seems to be more side to side than for and aft but still sloppy.

I would think this would also absorb some of the hammer strike, not delivering it to the primer when the assembly moves rearward.

Anyone look into a fix for this, all my other autos are a tight fit and take pretty good force to remove and install for maintaining them.

[mpom]

Had the same issue with loose trigger assembly. Ended up JB welding small pieces of Feeler Gauge stock to assembly. Play gone.

Posted a couple of pictures in one of the long JM930 threads.

Mark

[rtp]

I think they've all got the side to side play, my newish (built in 2013) certainly does. It doesn't seem to be 'a lot,' but enough to feel wiggling it side to side by hand; less so with a round chambered.

I'm unsure if there is any actual effect on shooting, though it seems on the loose side.

Edited August 26, 2013 by rtp

[Keeganxt]

I think they've all got the side to side play, my newish (built in 2013) certainly does. It doesn't seem to be 'a lot,' but enough to feel wiggling it side to side by hand; less so with a round chambered.

I'm unsure if there is any actual effect on shooting, though it seems on the loose side.

Same here, gun is 3 weeks old.