mpom

I would cycle the bolt slowly with the gun upside down, and look at the shell stop and rim of cartridge to see if shell stop retracts enough to let rim pass as bolt is retracted fully. Would compare movement of shell stop between the Remington and Federal brass. Is the Remington rim larger/wider than the Federal? See if pushing shell stop away from rim allows rim to pass. Perhaps front of shell stop, facing rim is rough and hanging on to rim, or part of shell stop blocking rim is too long and will not get out of way of rim. Shortening a tiny bit and polishing the end of that hook might be needed. Looks like a MIM casting that needs a little smoothing. Fine sandpaper on a flat file or a cratex on a dremel applied carefully should not hurt it, and has not hurt mine. I put a radius into the hook of the stop to match the curve of a shell rim. If section of shell stop contacting rim is smooth and flat with no burrs and mag spring not overly powerful, cannot understand how the Remington brass is getting dented, unless its unusually soft. Possible its ammo related, but I have cycled my dummy Brownell rounds dozens of times each without any issues, and ejected live ammo shows no signs of denting the rim. Its possible the vibrations and recoil induced by live fire may allow proper feeding from the mag tube, but yes, the shotgun should still be capable of hand cycling, if only to unload it. After all that, since Federal ammo has no issues even after 30 cycles, simplest thing is to stay away from the flavor of Remington that is having issues.

have you tried running the oem mag tube spring?

If not going into battery, then there should not be a firing pin indentation in primer, correct? When I had my misfires I clearly had indents in primers. I have to apologize for sending people on a wild goose chase, looking for a stronger hammer spring at local hardware stores. Yes, I did get some springs there but for a different project. Believe the stronger spring I use which eliminated the misfires came from my collection of various gun related springs. Looking the stash over, 1911 and Hi Power main springs are too large in diameter, but Ruger 1022 hammer spring is a perfect fit at .25" OD. According to my caliper the Mossberg spring wire diameter is .043" and my spare 1022 spring is .044", and a bit longer at 1.5" vs 1.3" for the Mossberg. Looked at aftermarket Extra Power Ruger 1022 hammer springs and Wolff makes one, SKU #166803, for around $7.50. A 10 pack goes for $30, so pretty reasonable if this works. Wolff is currently closed so could not ask their tech dept what wire dia. they use in the EP one. Again, sorry for the misinformation and hope this new info is useful

LTS, sounds like the replacement spring @ .032" is not as strong as the factory, and may not supply sufficient force to hammer, even if longer.

400 round match? Where do you get your ammo from, as I would like to score some! Hope a bit longer spring does the trick. Would make sure the firing pin is clean and moves freely.

Unfortunately I do not have the part # of the spring I picked up at a local hardware store. Yes, the cocking indicator fits inside the spring. I would bring the old spring with you when looking for a replacement, and would look check out other HW stores, maybe True Value? If necessary, can order something from internet, such as http://www.springsfast.com/part_detail_compression.php?part=4039&PHPSESSID=70e45b383b04db2540d5b00ae420637b Yes, you have to buy a minimum of 6, but at $.42 each, your can spread the love!

the shell stop looks like a casting, with none to minimal machining, so pretty rough. polished mine as well for smoother function, also broke edge on side facing thumb pushing shells in, and corners. matches the welded up lifter in being digit friendly!

Before I changed out the spring I tried "preloading" the existing spring with a couple of small washers. I could only stuff one, as 2 would cause spring bind. Measured the spring plus one washer, about a 1/16 thick and trimmed new spring. Can always just trim longer, say 1/8" or more and modify as needed till you can cock hammer, cut off a bit more for insurance and call it good. Went with new spring because adding spring compression with washer did not solve problem of misfires. Nice thing is trigger pull did not change significantly with new spring; still about 4.5 lbs.

Brain fart! Meant to say hammer spring!

Had issue similar to OP; replaced hammer spring with one I found at Ace Hardware, trimmed to max length and no failure to ignite since, at least 300 rounds. Would be nice if Wolff made a stronger spring, but the Ace spring is going strong so far. Believe wire diameter is a bit larger. A shame Mossberg did not get this right, but an easy fix.

Is the shell rim which is 1/8" inside tube not actually stopped by the shell stop?

NOT a gun guru, but have my opinions. Your original bolt and barrel from BCM most likely had the headspace checked during assembly. Sounds like this is not something you have done with the new components. You are probably OK, but to be sure, you can have a reputable gunsmith check the headspace, or get the gauges and do it yourself. If you have the time and want the education, check out M4Carbine.net and search under checking headspace. Would think you are not under minimum HS or you would not be able to chamber factory ammo as easily as you describe.

Damn that sucker is hard! Wonder if that is a sign the internal parts are also made to last! Could try annealing it; heat to dull red and allow to cool slowly. No expert here, but that might soften it a bit. Will probably ruin the blue/black finish. Not a problem if its covered up by large piece of plastic.

Don't have a range that will allow me to fire the drill, so next best thing- set up one third size targets at fifteen feet, and dry fired the drill to various par times. Used a laser device to check poi. Started out at about 8 seconds and after about 20 minutes, was down to around 6.5 to 7 with an occasional C. Definitely noticed that moving the eyes to the next target was a limiting factor in overall speed. On the faster runs it seemed as if the gun wan not actually stopping on each target, but just slowing down for the shot while still moving. Weird, as I have never experienced this in live fire. Thanks all, Mark

thanks. will leave the lm choke in place for sat match which has a 75 yard slug target. may experiment with various chokes to see if accuracy varies. with a single front bead i need all the accuracy i can get! may place a drop of paint on rib for a mid rib reference.

As long as slugs are brought into the discussion, is there an optimum choke for shooting slugs, such as fiocchi reduced recoil ? i have read that full chokes are likely to cause poor accuracy due to deformation of slug but wonder if a light modified is best as a rule of thumb. Was going to try modified choke yesterday in comparison to light modified but ran out of slugs.

Would expect springs to wear out or fail with that many cycles, but what other parts have failed or broken off? Curious so I can be prepared and avoid some of your misfortunes. Thanks for the hard gained insights, particularly keeping the piston and mag tube clean.

Is the back of the bolt release flat or recessed? Interested in doing this mod, just wondering if 4-40 machine screw is strong enough compared to 6-40 or 6-32. JKW, where did you find that 6-32 button cap screw? Thanks, Mark

How about filling the hollow button with JB Weld or Marine Tex for the screw threads to grab, or embed a small nut for the screw? Will consider this mod if it holds up. Mark

Shooting high with slugs seems to be par for this model. Would guess the design was not vetted with enough (any) slugs to discover this. Easily fixed with a higher front sight base or a stout tree/trailer hitch. Granted, should not be happening, but not enough of an issue for me to sell mine. Just replaced the front sight base, tru glo 950 and its dead on at 100 yards. Mark

Sounds like problems occur through out manufacture years, which may have started in 2011. Would assume its due to poor quality control in parts meeting specs rather than crap design, as crap design would affect all jm930s. still clinging to my 1 year old jm930, which other than a couple of failure to set off primers, has run well with light and heavy loads. A stronger firing pin spring, found at a local Ace and trimmed to length solved the problem, which is not uncommon as i saw it happen to another jm930 last month. mark

is the mag tube spring original mossberg or more likely Nordic? I ended up cutting my Nordic spring to about 10" also, with no issues (yet). Mark

How is the longer end cap weaker than the shorter end cap? Mark

FWIW, Jerry Miculek and Lena, his daughter put on a youtube video concerning the JM930. In it he claims he has shot a ton of ammo through his externally modified 930s over the last few years, so unless he is just shilling for Mossberg, it appears to be a sturdy platform. Not as sleek and sexy as a Euro shotgun but capable of good performance in the hands of a good shooter. Would think he would only use a reliable, well built sg, not prone to break down in the middle of match. No doubt he is getting paid to be a Mossberg spokesman and his name is on the product, but unless the internals have been replaced with super duper alloy parts, it seems to be going the distance. Mark

Fair enough. My 930 has about 500 rounds through it, so barely broken in. Will take a while to get past 2000. Hope it holds up. Mark