SHotgun Tuning?

[t1nm4n]

I tried searching for the thread I read this in last week, So no apologies if duped.

I am relatively naïve about shotgun barrels and there design, so it struck me as odd when I read some was trying to have the barrel tuned to reduce felt recoil, something about the forcing cone. I have since looked more closely at the side profile picture of the barrel and notice there is a noticeable reduction in the circumference of the barrel as the shot gets forced through the barrel.

I see where the resizing of the barrel is, but how much material is there to remove so that you are lengthening the that forcing cone and able to increase the distance at which the shot is forced into a smaller path to exit the barrel? Is this actually a viable option in reducing recoil or just a gimmick? I can run rough calculations through my head and understand that there might be benefits, but reducing material on the barrel also has some drawbacks, anyone done this and noticed any fatigue in there barrels? They were also talking about polishing the chamber, and I completely agree with this as long as you don't take material away, or am I wrong in thinking that you still want a good seal around the shell as to not lose pressure, or is this a moot point with the shells being plastic and they will expand more when fired to keep the seal?

Also, I think I understand what everyone means when talking about "Welding" the lifter, I sort of feel dumb even asking, but the only dumb question is a question not asked.

Welding the lifter is adding material to the lifter so it doesn't have that forked tongue look to it, I like this, just doing some practice drills loading I jammed my thumb in there, good thing it wasn't under a clock, I might of hurt myself, lol. Also, opening the loading port if machine the material off the frame so as to give you a larger opening to throw rounds in the tube, I am guessing this is right.

This ?? is primarily for the JM Pro owners out there, I have read that the breech lock pin is hollow and has a spring in there, making drilling and tapping a bit difficult, but would it not be easier to open the pass-through hole on the frame up a bit and tap the outside of the button to add a larger surface to the button, this kinda makes sense, if I had a machine to make a larger button I would attempt it.

Appreciate any help you might be able to offer and look forward to any razzing I get for asking too many questions in one topic.

[BobS761]

Here is what load port modifications look like on my JM Pro, along with welded lifter. Can't offer any advice on forcing cone, because I don't have a clue.

[t1nm4n]

Looks pretty darn good there BobS, Looks well uniformed, almost as if it were the stock lifter. I do think this is something I want to get done.

[frankge]

Help me understand the welded lifter mod on the JM. I just bought 24" today (actually found one) to replace my 1100 Tac4 which has always run like s#$& to the point I cant stand it anymore.

[BobS761]

Help me understand the welded lifter mod on the JM. I just bought 24" today (actually found one) to replace my 1100 Tac4 which has always run like s#$& to the point I cant stand it anymore.

Fo me, unless you have flawless technique, the forked lifter will grab your thumb in the heat of reloading. But it doesn't really hurt until you yank your thumb out, leaving flesh and bits of thumbnail in the loading port. Some don't need it done, but I'll wager they practice, A LOT. My setup allows for weakhand, load 2, and load 4. None of which I am expert at, but I have options. Honestly, my JM Pro was a lemon, and I thought I wasted my money. But, after having a very competent gunsmith go through it, it's the bees knees now.

[larry weeks]

On lengthening the forcing cone - I work for Brownells and we sell the reamers and gauges to help you do this. BUT, if you have a chrome lined barrel, as on a Benelli, you'll just dull the reamer. It has been a standby in the trap game for a lot of years (I've been here 34 and we carried them when I got here). More and more factory guns are coming with lengthened, gentle forcing cones so you might check for more info on your specific gun. The process gives a longer, gentler transition from the chamber to the bore. The theory is that the shot and cup enter the bore more easily causing less deformation of the shot and reducing recoil. I've never tried to measure it, I've done it to a couple of guns on which I was doing other work, just because we had the reamers in our R&D shop. I don't know that I could feel any reduction in recoil and never patterned the guns before to see if I could tell a difference, after.

[314shane]

I have a Remington 3200 a friend of mine has one with legenthend forceing cones I can't tell a difference when shooting them back to back. The same thing goes for porting barrels. As far as fatigue the barrels on a 3200 are very thin to start with and he shoots the crap out of that gun and I can't see anything wrong with it.

[kurtm]

I know of one "pro shooter" that had this done to his Benelli...yes it can be done to a chrome lined bore, but you have to find the right people. He said it didn't really help with recoil that he could tell, but it went from shooting slugs really well to scttering them far and wide. Now each barrel is different, but I certainly wouldn't worry about it if hadn't come that way.

[t1nm4n]

OK so in theory it works great but in its actual application there haven't been any real improvements, that's what I was looking for. I appreciate the answers, not sure how long the forcing cone is supposed to be or how short it needs to be to see a an improvement, and the 24" JM I Purchased doesn't need to be modified in a theoretical way, well, not until it probably almost worn out and I got nothing left to throw at it to keep performance up, and I doubt that day will ever come.

[mpom]

t1,

If you have time there is a good summary of mods and items that need to be watched on the JM930, all in one post, so you don't have to spend hours reading threads.

Mark

[T Bacus]

Welding the lifter is like buying insurance. You might never have needed it, but the one time you do, and you don't have it you'll be wishing you had.

It's a cheap mod, fast and easy to have done, and beats the hell out of messing up one time and leaving half your thumb nail in the gun.

[t1nm4n]

t1,

If you have time there is a good summary of mods and items that need to be watched on the JM930, all in one post, so you don't have to spend hours reading threads.

Mark

I think I might of found that post, but it was so long I could only get to the part of cleaning the gun, lol. I'll have to read the rest of it, IF I can find it again.

[rtp]

t1,

If you have time there is a good summary of mods and items that need to be watched on the JM930, all in one post, so you don't have to spend hours reading threads.

Mark

I think I might of found that post, but it was so long I could only get to the part of cleaning the gun, lol. I'll have to read the rest of it, IF I can find it again.

Here's my version of 'the rolling 930 list'..hope it's of use..

1. De-grease the heck out of it from factory. This includes taking the rings off the piston. Green brake cleaner, gun scrubber, whatever.

2. Check for lip at mag tube/extension joint, bevel/file lightly if need be to avoid possible follower hangup.

3. Check if inner larger gas system spring wears on mag tube (do you see scratches on disassembly/barrel removal?), tweak with extension + 19-22mm socket inside the spring to center it, and/or dremel/buff sharp edges inside of spring. You do not generally want to remove the big spring from the outboard side of the barrel gas cylinder!

4. Minor buff on shell stop, polish chamber. You can polish the chamber by removing the barrel then polish w/dremel w/cratex or felt wheel + polish, or drill + steel wool wrapped around a cleaning rod/barb. Intent is to at minimum to smooth out any roughness in the chamber where the shell brass contacts, will help w/consistent ejection.

5. Check mag tube spring length and tension, especially on non JMs - seems a mixed random bag-o-springs was used for at least a while. Spring should be ~12-16" past end of extension tube for the SPX and JMs.

6. Disassemble rings from piston for cleaning, scrub/soak it + gas tube - clean every ~200 rounds for 930, possibly a bit longer for JM with the chromed/hard plated components.

7. Run the action on the wet side, while the piston/gas system should run as dry as possible while still supplying some lube. I'm currently trying some dry lube after some polishing, but the jury's still out on that one at the moment..

8. If your gas piston isn't sliding in and out of the gas cylinder fairly easily...you either need to clean it, or didn't clean it properly with rings off the piston. Can do some light polishing of the barrel's gas cylinder if desired.

9. Brownell's link for fix for feed issues, again amounting to light polishing: Brownell's 930 video

10. Polish extractor, extractor plunger, + extractor groove in barrel.

11. Light primer strikers - seems hit and miss, but if you have this issue or simply want to be pre-emptive, replace the hammer spring with a Wolff Extra Power 10/22 hammer spring, left at full length (it will be slightly longer than the MB spring) or trimmed down slightly.

12. The barrel clamp if so equipped can impact POI. On the Nordics, you can tighten down the mag tube, then loosen the mag tube from the nut slightly(1/8-1/4 turn), then tighten up the clamp, no more POA/POI changes.

13. Polish the stock follower or replace it. The main point here IMO is to debur any minor imperfections, and allow it to easily make it over the joint where the tube + extension join together. I didn't have issues with the stock follower, but many have griped about it.

14. The screws for the rail may be 'lacking' in Loc-tite, with or without a rail. Check if they're snug (I had some loosen up), and if not or if you desire, unscrew, drip a small dab of Blue Loc-tite (or green, just not red unless you want to have to heat it to remove later!), and re-assemble. Be careful as a typical small flathead screwdriver is too big - use a gunsmith small screwdriver or jewelers screwdriver if possible.

15. 'slop' in trigger assembly. With the weapon cleared, wiggle the trigger assembly. You'll note some amount of side to side wiggle, but almost no front to rear. Loaded and in functionality, should be no impact - seems like they all pretty much have this minor 'slop' side to side. If truly concerned about it (I'm not, have left it alone), look here: http://gunsumerreports.com/review_mossberg_930_tactical_p7.php

16. The hammer end of the firing pin may mushroom over time/use; may be something that stops and may or may not affect functionality. Just an item to 'be aware' of at this point.

17. Most barrel clamps w/out grooves in the mag tube can move under shooting conditions. You can put a piece of double sided carpet tape between the clamp and tube to eliminate this movement and finish wear.