GunCat

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=2ahUKEwjNmsrI7aLoAhVvUN8KHc_YBtcQFjABegQIAhAB&url=http%3A%2F%2Fns.hodgdon.com%2FPDF%2FMEC_BUSHING_CHART.pdf&usg=AOvVaw2N734AOC7yzsY7X1Brqbtb Link opens the MEC bushing chart as a PDF file

How much of the vent rib do you see in your sight picture? If you see any of the rib (between the front sight back to the rib's “ramp” a couple of inches in front of the receiver) the slug POI is probably going to be high at 50 yards....gotta say though that 3' high at 100 is quite extreme. ABarrow's question about a barrel clamp comes into play too, pressure from some clamps can put upward pressure on the barrel causing the POI to rise

I checked Amazon and Brownells...no luck. Same with BassPro... You probably need to check with the guy that invented them. Last I heard he was somewhere North of EDEN...Wyoming

Does a shell exit the mag tube and remaining laying on the lifter when the bolt locks open? Does this happen when firing the gun - or only when you hand cycle the shells out of the mag tube? When you manually activate the cartridge drop lever (sliver tab) will shells exit the magtube - or will the shell move side to side and sometimes fail to get past the shell latch?

Has the loading port been opened significantly? Has the shell latch been "tuned" in some way?

Good to know, thanks for the follow up.

The bolt release/cartridge catch part is a different part # on the 1301 TACTICAL vs the 1301 COMP. That A400 / 1301 Tactical part may not work in the longer COMP receiver.

Almost...See the difference explained by Tom Hart (Openclassterror) in this thread

This... I added just a single screw through my lower into the (Rock River / Colt mag) mag block after I pulled the block out with an empty mag once. Colt used to pin the block in place as seen below (They may still do so AFAIK)

The plate is easily removed/replaced when the spring and strut is removed - that is normal. Did your plate break while the trigger group was in the receiver? I have seen that issue 1 or 2 times (out of the many guns we've seen).

Other than the Roth I have never seen any “new” receivers available from the factory. I have seen a few (of assorted brands) for sale from someone's parted out a gun. Try GunBroker....and remember that the receiver is the “gun” so all ATF rules apply when purchasing. Your port does not look to be damaged. A little more could be done to make it as good a the 930 port allows, but the overall size and shape will still be limited by what Mossberg gave you to work with.

The first shell coming out of the mag tube has to have enough spring pressure to exit to the mag tube and move fully back into the receiver to disengage the the shell latch that is holding the bolt locked open. Notice who much pressure you have to apply to the bolt release to close the bolt on your conventional M2 action. With the auto lifter the shell popping out of the mag tube has to exert that pressure when the shell rim contacts the shell latch on the inside of the receiver. A weak mag spring may not propel the round far enough back into the receiver to make this happen.

The height is not critical. Enough to keep the lifter from overriding the shell latch will fix the lock back problem. A lot less height that you see in the earlier pictures will fix the lock back issue.

In addition to keeping the lifter lowered for easier loading, that modification also stops a rare but potential issue of the bolt locking open with rounds in the tube (I've seen 3 guns out of hundreds that would do this - lowering the lifter just a bit stopped the problem)

The guys in the U.K. have been doing that mod for some time. Good to see that Beretta is listening to customer input.

Search for " 2019 Rockcastle 3 Man 3 Gun ". (The match is full and registration is closed)

Gene, Your 590 barrel can be threaded for the standard Mossberg Accu-Choke tubes. More details sent via P. Message

Yes, the after market bolt handles for the M2 will work in the SBE2. (the bolt carrier is the same part in both guns). Same with large bolt release buttons and tabs (some will require drilling and tapping the factory release - the RNT part does not require any alteration to the factory release)

True. Good looks are important, but in this instance capacity is more importantner. Too much magazine capacity is rarely an issue in this game.

Brownells is showing 1 +8B in stock tonight

https://www.brownells.com/shooting-accessories/slings-sling-swivels/shotgun-sling-mounts/remington-sling-mount-prod12519.aspx

Contact Roth Performance (link in my first post) to ask if they can export the parts.

The follower is starting to jam in the aluminum area where the magazine tube meets the receiver. Likely a bit too much metal was removed from the receiver when the port was opened, and with use more metal has worn away. If not corrected eventually the follower and spring will push into the receiver. Roth Performance sell a connector and captured follower that solves this problem. Other fixes include installing a set screw through the receiver and magtube to stop the follower before is exits into the receiver.

Carlson choke tubes are good. Here is another source of Tru-choke tubes: https://trulockchokes.com/. (By looking at that name you can probably figure out where this style of tube got its start)