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For Those Still Upgrading their 930

Joker18

.410
I don't know how many of you are still adding upgrades to your 930. I feel like I have added so much that I almost have a 940 (with the exception of the redesigned 940 buttstock).
Many of my add-ons have been internal parts from SBE Precision and OR3Gun. The purpose of this post is to share something I learned from installing the OR3Gun ASR and CSP (Adjustable Spring Retainer and Competition Spring Plunger respectively).
Disassembly is pretty straight forward, remove two Phillip's head screws securing the recoil pad, remove 3/4" nut and underlying spacer, remove oval washer that was under the spacer, and slide buttstock off of receiver.

At the end of the spring plunger tube is a cross pin (do not lose) that holds in the spring retainer. Apply enough pressure to the end of the spring retainer to push out the cross pin that holds it in being careful to remember the plunger spring is compressed and under tension. Gradually release pressure on the spring retainer and allow spring to decompress and put retainer aside and remove spring from plunger tube. Invert receiver and spring plunger should drop out of plunger tube.
Now is a good time to take a cleaning rod and clean factory oil and gunk from the plunger tube and re-lubricate with your preferred lubricant. Also check the plunger spring ends for any sharp edges and file or smooth.
Re-assembly - this is where I ran into an issue and the purpose of this post.
OR3Gun includes a good set of instruction regarding orientation of the spring plunger and the spring retainer, and the instructions state that the concave end of the spring plunger must fit to a point on the rear of the bolt assembly. Before installing the spring plunger with the spring attached, PULL THE BOLT TO THE REAR UNTIL IT LOCKS OPEN! Then slide the spring with the spring plunger attached to the end of it into the plunger tube. You may feel when the plunger engages with the bolt. To check proper attachment to the bolt, you can compress the spring enough to put pressure on the bolt. While holding slight spring pressure on the bolt, hit the bolt release and the bolt should close on its own. While maintaining slight pressure on the spring, check and insure the bolt will open again, and reclose it.
Last step is to insert the spring retainer into the end of the plunger spring and push it into the plunger tube.
Align the holes in the spring retainer with the holes in the plunger tube and replace the pin you removed during disassembly. You may have to apply pressure to the spring to set the pin all the way through the plunger tube.
Once that is complete, check to insure bolt opens and closes freely. Slide buttstock over plunger tube and fit it to the rear of the receiver. Slide oval washer on to plunger tube and set it into its recess in the buttstock. Slide the spacer over the plunger tube and secure with the 3/4" nut. The threads on the nut are very fine so take care not to cross thread it. Tighten the nut with a socket and replace the recoil pad with the two Phillips head screws and you're done.
The reason for my post is when I was initially installing the spring plunger and spring, I had the bolt closed. For some reason the spring plunger can not engage the bolt properly and locks the bolt shut and will not open. It happened twice with the bolt closed and both times the plunger would not drop out of the plunger tube freely. I had to invert the receiver and gently tap on the plunger tube with a plastic gunsmith hammer until it dropped out. I decided to try and install the spring and plunger with the bolt locked open and discovered the plunger would properly mate with the bolt.
It is a scary thing when you think you did it right and afterward discover you bolt is locked shut.
Hopefully this post will prevent someone else from having the same situation.
BTW the OR3Gun competition plunger kit works really well and is well made as is the rest of their products.
I kind of felt weird for investing so much into my 930 until I saw the MSRP of the 940 JM Pro (if you can find one). I have about the same amount invested in my 930 mostly due to my custom Mossberg barrel. It is a standard 18 1/2" security barrel which I sent to Carlson's Choke Tubes and had the muzzle threaded for extended RemChoke choke tubes. This gave me a short barrel that will hold patterns farther than a plain cylinder bore barrel.
 
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I just got my JM 930 last week used so I'm putting the or3gun spacer with Factory weight so it stays close to stock and I'm going to mount my Red Dot that I already have on to it looking to get the short 18 and 1/2 inch barrel and reduce the magazine capacity to match the barrel so basically I'll have a home defense shotgun and I also have a hunting shotgun but other than that I do not plan on doing anything else to it for my needs it should be perfect and I only plan on cycling heavy loads through it

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