This is info that may help some of you get most of your "JM Pro" items in one place. This is my first shotgun ever and your personal results or professional opinions may vary. These are "my" opinions and findings. They will help many people for sure. I did shoot USPSA for 9 years limited and open ranked A class. I 've usually found that many parts could be better and learned to "optimize" things to function better or to my taste and this new shotgun is not different. I always seem to the the one built on a Fri or Monday hangover. Mine is the 930 JM Pro, 22 inch 8+1 (9+1 w/XL Nordic) and has about 250 bird loads and 50 slugs:
-Length of pull reduced 1.5 inches: Mine is 13 inches from cocked trigger to mid recoil pad. I did not reduce the recoil spring length or tube length of the spring housing section.
--How: 2 items will remove 1.5 inches of the length of pull, one is a low profile limbsaver Model 10544 grind to fit recoil pad (5/8 inch thick, 5 1/2 X 1 31/32 grindable to 3 7/8 x 1 11/32 & rest is stock/tube/spacer mods. 1st remove the orig recoil pad. Determine how much lower the alum spacer can be trimmed/grinded down so as to still allow threads of the recoild spring tube to be just below alum spacer. Also measure how much tube threads to remove so that appx 1/3 thickness of the nut will tighten over threads. Once remove nut, alum spacer and w/grinder remove two thirds of nut height (appx). Grind down the alum spacer removing appx 1/4 to 1/3 height. The nut is not easy to find at local hw, so be careful and make sure you debur the sharp edges on nut & alum spacer. Once nut, alum spacer complete, and recoil tube threads cut off, install everything except the recoild pad and using stiff tape of item to mark straight line on stock, mark line on stock so top of recoil tube is 1/8 to 1/4 above the line you will cut the stock off (to get 13 inch LOP, you cannot cut to much of the tube off or nut, spacer and tube would have to be cut to far). I used a band saw and a leveling device of your choice and went slow w/little pressure so blade didn't bend much. When you are done, without the low profile limbsaver pad, the tube & nut should be just sticking out above the stock. Install the limbsaver pad (orig form), you will need to redrill one new hole in the recoil pad to install to stock and using scribe, mark around the now cut down stock. Remove recoil pad and grind to match stock.
-Sights: If you gun shoots slugs to high or left and you just want adj sights, you can try one option that works and another that I have read about but not tested. Use a tall front sight and add rear adj sight or you can try to see if barrel clamp removal fixes the high shooting issue.
--My fix-Use pliers and untwist front sight. Order TRUGLO Tru Bead Turkey Extreme w/ghost, universal PN TG950XD front & rear sight pkg. This pkg has multiple screws and will fit the Mossberg 930. When installing the front sight, I suggest using some good JB Weld under the base since there is only one screw holding the front sight on & use a good Loctite ( I like to mix red/blue and I don't plan on removing the sights) but don't trust blue enough. Install the rear sight as far back on the rib while still having even pressure on the rear mount plate. Use good locktite on the 4 rear base screws. The rear is adjustable up/down via one screw that with tension screws in or out to raise/lower rear sight. The front sight is 2 colors green outside and red middle. Front sight is large but if you aim/hold properly using the top of the front sight in middle of object to hit, no problem. The front sight is twice as high or more than the orig. My RIO low recoil slugs group inside a std mouse pad at 100 yds and my bird loads at 20 yds pattern spot on with these sights. Fiber optic pieces are known to break off the end tips and then the whole fiber will slide out of the sights ( I know). Use a good "clear" epoxy for light gathering and apply epoxy around the fiber optic tubes enough to meet the metal around the fiber, this may allow the fiber tubes to stay in the front/rear sight holder better in case you bump a prop during recoil or during dumping.
Ext Tube: Many complaints of the tube connect joint is uneven. This may/may not be a one item fix. Mine didn't appear to jam during live fire, but it's like having a bump in your piston wall (can't be good, can only hurt). With barrel clamp, tube ext all tight, remove the end cap (buy a Nordic XL for +1) and w/flashlight look down tube and rotate looking for high spot typically on on side only. Determine if it's the chromed tube of the Mossberg sticking up or the Nordic ext tube and you can dremel/polish this side down and try to loosely slide spring/follower down. Some have said to loosen the Nordic tube nut and rotate the ext tube and this may even up everything, I don't like leaving it loose, but also ensure the barrel clamp is not causing the issue by pulling/pushing the tube up or down causing the alignment issue. In short a combo of sanding the angle of the front foregrip/stock where the nut tightens, polishing down the rear chrome tube and minor polishing of the underside of the Nordic barrel clamp is what mine took. What a pain in the rear. I also have a GG&G follower, but others should suffice.
Tube Spring: The tube that comes with is thin and seems ok, but I replaced with a noticeably stouter Nordic spring and have it at 12 inches past end of ext tube. I suggest you curl the tips on both ends of the spring (follower & end tube) and round/polish the ends so the spring doesn't twist or bind when removing the tube cap (could cause some problems w/spring wrap).
Load Port Opened: Dremel or file and sand the openings on the side and the front. Take care on the side that holds the small pin visible from the bottom and don't grind down to far of you'll hit the section of pin that holds the shell stop/bolt open item in place. Polish the alum with fine eraser type dremel polishers or 2,000 grit sandpaper to taste. You need to also remove & angle the forward load port since this is the primary area that will prevent double/quad reload speed. Grind out wide & forward enough but do not go into the follower stop areas or your going to pay for new receiver. Also grinded down the front grip area forward of load port to help with reloading. I've only been loading a shotgun for a couple of hours and I feel like a monkey doing a football versus loading a semi pistol.
Firing Pin Spring & Trigger: There are far to many complaints of fails to fire on this weapon so before I even shot it, I replaced the firing pin spring w/the Ruger 10/22 (extra power I think) and cut about 3 coils off. No ignition probs in 350 rds.
Stipple grip & forward grip-My first time, but just using a stock little soldering iron and pointed tip made the grips much nicer to hold and for flipping the gun for reloading. Took about 3 hours for me and was quite annoying to do this long (next time will cut the sharp tip off and use a larger rounded profile tip). Don't use big gougy pits or it's gonna stay stuck with all kinds of sweat, dirt, oil, food. You will like the look and feel.
Shell Stop Assembly & Lifter-What a pain these items can be. C-Rums did a good job on the lifter. Before I got this gun I'd read about the scattered issues and knew I'd get the one with at least half of the reported issues. I had some double feeds, rounds would not come out of the tube, gun would lock open when the tube still had shells. All during live fire. I think the combo of rounding off the forward shell stop, rounding off the rear (by back of lifter gate/port bottom side of shell stop (part that locks lifter) and tweeking the lifter a little more to the opposite side. This is not always a one polish piece fix as I've determined. Several areas of the shell stop ie...front side to the tube, back side shell stop that could be hitting the lifter, or lifter is cocked to one side a hair to much can cause the issues listed.
JAMS/MALFUNCTIONS: Many have stated you must fire 50-100 high power/full load/magnums or some crap. Look, it's just a semi-auto. Do directions ever state a brand new pistol needs magnum ammo for first 100 rds, no just std ammo? Problem w/shotgun ammo is your ammo can be 1150 fps or 1350 fps which is a big diff in power for same weight projectiles. After about 100-150 rds you gun, metal parts are pretty much broken in. If you have to shoot 500 rds on any gun to "break it in" the gun specs/tolerances are the problem. One thing I've notice is some loads may eject the spent casing but will not load a new round because it never released from the tube. I think the bolt comes back far enough to eject the casing but doesn't come back quite far or hard enough to release the shell stop. This could be the gun cycles and goes click and when you rack the bolt it loads fine. It amazes me that no aftermarket companies make hardly any recoil springs (except a few browning & benneli) in less or more weights when there are options for AR's & semi pistols. The rear recoil spring has about 96 or so coils, so I'm going to try the puss loads (1150 fps) with appx 10% of the coils cut off now that my gun is broke in. I cut off 9 coils and will see how this works. Don't want to do to much since this spring is crucial to feeding shells in to the chamber as well as recoil control and when using magnum or hot loads keeps from beat the gun apart.
Chamber & internals: I rounded & polished the chamber opening, extractor hook ends, barrel extractor groove cut down deeper and more forward & polished. Polished any hard or rough, peened areas felt after first 75 rds.
-The forward chrome part of tube threads had gouges on one side just like some online reports. I believe the fix is to dremel down a steel O-ring joint about 1/3 up into the barrel part of gas chamber (run your finger up there and look for the o-ring where it would almost come together). If this doesn't fix it it's in the chrome piston area, but it puts a nasty line down the threads and the chrome upper tube.
Side Saddles: Put a GG&G side saddle on and immediately had function problems. Surprisingly, not much online as to why, hence why I was also surprised people use lots of Velcro versions (now I know one reason why). I have the answer. If your side saddle requires removing the trigger housing pins and replaces with screws or pins that will screw from one side to the other side into a nut or into a thread on the other side, Tightening the screw/nut can cause the bottom of the receiver to pinch/bend inward causing cycling problems, slight receiver bending, pressure to trigger/lift gate area etc... I used longer screws but only slightly firm and the other side nuts built into the side saddle and additional pressure nuts on top of that to prevent backing out. I also made my own version of a device similar to what a matchsaver shell holder to hold the one OH s---? round. Bought 5-6 ft length of PEX tube 3/4 inch is all I can find and some counter sunk screws and nuts and velcro I made 2 single shell holders, one for each side for $15 for both and still have tubing to make 15 more with a band saw and dremel and could make about 20 of these and cost is about $3 bucks on a stretch, likely half that in materials.
-Briley Light Mod ext choke
-AP Custom 4x4 (don't like grabbing the rear 4, but good for space)
-Carbon Arms FLS 8's (ok but I need a few more months to see). Quad loads & petting is tough to do fast, so could be need more practice time or these sryle, not for me. Hope this helps some of you.
