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Mossberg 930 JM and the stock shims/spacers

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Picked up the new 9+1 930 JM, well done for the price it seems, looking forward to shooting it.

So it came with 6 or 8 stock shims to raise or lower the comb, etc etc.

Wondering how I should use these? Am I looking for a particular sight view down the rib to the bead? Or do I use them once I've shot the gun and see where POI is and adjust from there. If I use to adjust POI then which way do I go? If hitting low then do I raise the comb?

Thanks for any insight.

Jason

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Your gun will probley shoot high. Shim it to the lowest one and if it does not work, move the clamp, and if it does't work, bend the barrel.

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bigcraig   

I put 200rds thru mine, flawlessly I might add, and felt I needed to install the .250 drop shims. The gun feels better when shouldered, now.

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E53X5   

I put 200rds thru mine, flawlessly I might add, and felt I needed to install the .250 drop shims. The gun feels better when shouldered, now.

I think I need to drop my stock a little, too, and the .250 is the only drop shim available. Now, there is a set of plastic shims (that I'm assuming go between the receiver and the stock), and then there is a set of metal shims that look like they go on the tube inside the stock. Are they supposed to be used together (i.e. a plastic .250 shim along with the metal .250 shim), or do they serve different purposes and you only need to use one or the other?

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bunsen27   

I put 200rds thru mine, flawlessly I might add, and felt I needed to install the .250 drop shims. The gun feels better when shouldered, now.

I think I need to drop my stock a little, too, and the .250 is the only drop shim available. Now, there is a set of plastic shims (that I'm assuming go between the receiver and the stock), and then there is a set of metal shims that look like they go on the tube inside the stock. Are they supposed to be used together (i.e. a plastic .250 shim along with the metal .250 shim), or do they serve different purposes and you only need to use one or the other?

You need to use both the plastic and metal shims. There should be a diagram in the instruction book on how to install them.

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Nuke8401   
Now, there is a set of plastic shims (that I'm assuming go between the receiver and the stock), and then there is a set of metal shims that look like they go on the tube inside the stock. Are they supposed to be used together (i.e. a plastic .250 shim along with the metal .250 shim), or do they serve different purposes and you only need to use one or the other?

You use both a plastic shim(wedge)between the stock and reciever and a steel shim (offset hole plate) under the buttplate on the end of the buffer tube. The plastic shim/wedge just makes for a good fit between the stock and the reciever while the steel shim moves the stock up/down.

You may want to check your length of pull, mine was too short causing my head to be too close to my thumb and too high (seeing the top of the rib) even with the stock shimmed down.

But then again I don't know much about fitting a shotgun.

David E.

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E53X5   
Now, there is a set of plastic shims (that I'm assuming go between the receiver and the stock), and then there is a set of metal shims that look like they go on the tube inside the stock. Are they supposed to be used together (i.e. a plastic .250 shim along with the metal .250 shim), or do they serve different purposes and you only need to use one or the other?

You use both a plastic shim(wedge)between the stock and reciever and a steel shim (offset hole plate) under the buttplate on the end of the buffer tube. The plastic shim/wedge just makes for a good fit between the stock and the reciever while the steel shim moves the stock up/down.

You may want to check your length of pull, mine was too short causing my head to be too close to my thumb and too high (seeing the top of the rib) even with the stock shimmed down.

But then again I don't know much about fitting a shotgun.

David E.

Thanks, David. The LOP is a little too short for me, too, but I think adding the drop shim will make it pretty close. I've never fitted a shotgun before, either, but I've spent a few hours reading about it and watching YouTube videos, so at least I have a rough idea of what I need to be looking for. I've seen somewhere that you're supposed to have about 2 fingers gap between your nose and the thumb of the strong hand, so it's something you could check for to see if your head is too close to your thumb.

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Now, there is a set of plastic shims (that I'm assuming go between the receiver and the stock), and then there is a set of metal shims that look like they go on the tube inside the stock. Are they supposed to be used together (i.e. a plastic .250 shim along with the metal .250 shim), or do they serve different purposes and you only need to use one or the other?

You use both a plastic shim(wedge)between the stock and reciever and a steel shim (offset hole plate) under the buttplate on the end of the buffer tube. The plastic shim/wedge just makes for a good fit between the stock and the reciever while the steel shim moves the stock up/down.

You may want to check your length of pull, mine was too short causing my head to be too close to my thumb and too high (seeing the top of the rib) even with the stock shimmed down.

But then again I don't know much about fitting a shotgun.

David E.

Thanks, David. The LOP is a little too short for me, too, but I think adding the drop shim will make it pretty close. I've never fitted a shotgun before, either, but I've spent a few hours reading about it and watching YouTube videos, so at least I have a rough idea of what I need to be looking for. I've seen somewhere that you're supposed to have about 2 fingers gap between your nose and the thumb of the strong hand, so it's something you could check for to see if your head is too close to your thumb.

How tall are Yall? Always seems to be a link between height and LOP.

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How tall are Yall? Always seems to be a link between height and LOP.

About 6.3.

Thanks should be fairly close for me. I'm 6' even.

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swhiteh3   

So is there any source for spacers outside of the range that's included with the gun. I just installed the .250 drop, and it was a massive improvement, but I hate that there is no .125 drop or .375 drop that I can try to see where I really fall....

Scott

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JayDee   

For my jm pro, the comb was too high from the factory. I installed the shim to lower it and cheek weld was much improved so that my eye aligned naturally with the rib. This is crucial for fitting shotguns- you need to be able to mount the gun in a repeatable manner so that your sight picture is the same without moving your head to acquire the front sight/bead.

Since you asked about additional shimming, there is one more tweak I did. Even with the stock shimmed to be as low as possible, the comb was still bumping my cheek during recoil as the stock rose. The butt pad was at a bit of an angle, so I added a washer under the top bolt that attaches the recoil pad. Now the pad helps to recoil straight back, and the gun mounts properly. There is a small gap between stock and recoil pad, but it is barely noticeable.

YMMV

Edited by JayDee

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Once you get close, get some big sheets of paper 30-40" wide and head to the range. It's called patterning and many shotgun ranges will have either a frame to hold the paper or a steel patterning target that gets coated with white grease between shots. Aim at a spot and see where the pattern hits. I think traditional is 40 yards but I use 20-22 and it seems to work fine. Takes a lot of time but really pays off. The paper I use is wide "masking" paper used for auto painting. Bought a 100 foot roll years ago for a project, am still working off it.

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