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930 All Purpose Field Gas Woes

Discussion in 'Mossberg 930 Autoloader' started by Arrowshooter, Oct 10, 2019.

  1. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    Since this is a long one, I am going to start with my questions: Why does this thing only have trouble cycling High Base, and how is it possible for oil from inside the receiver to migrate into the gas system?

    I have been a pump-gunner all of my life and thought the 930 would be a good introduction into semi-auto life. I actually really like the shot gun, and it has already taken its share of clays and Pheasant, but the gas system on this gun leaves much to be desired. Here is my experience so far:

    Brought the gun home and cleaned the barrel before taking it out for the first time. I did see all of the oil in the thing, but it did not seem “sticky” so I left it. My “old school” feeling is oil is good on all that moves. Right?

    The first time shooting the gun was at the end of an Elk hunting trip and we put 3 boxes of Winchester Field Loads though it without a hitch. Boy I was in 7th heaven. Cleaned the gun real good when we got home at which time I also oiled it “real good”. I still had not read the instructions.

    Second time out was with the clays, which I have never shot in all these years, and again the low base ran perfect. When we ran out of the low base, we switched to some 2 ¾” “high base” and the trouble begins. 1st shot out of the cannon the gun goes bang and then click, no round in the chamber. I hand cycled the next round in and bang click no second round again. Tried a few more times and hung it up. Got home and out comes the instruction book. Go figure that you are only supposed to lightly oil and wipe it off the gas system. OK my bad. Cleaned her all up, lightly oiled and wiped off the mag tube and the inside of the gas cylinder and put’er away.

    Third time out was a pheasant hunt and I was ready with Remington 2 ¾” High Base #6’s! 1st bird up gun went bang, bird falls and I have next round in the chamber, SWEET. 2nd bird up needed a second bang but only got a click, no round in the chamber. Next up was a double. Dropped the 1st bird but 2nd bird just got a click. Here is where the loose forearm comes into play.

    When we got back to the truck, I pulled the forearm off and everything seemed to be moving fine, but when I put the forearm back on it was now loose. This was not the case up until now as it has been tight up against the forearm retainer since new. Got out all of the different boolits that we had in the box which ran from the low base stuff to some 3” turkey loads and this thing ate them all no problem. Went home, cleaned up the right way and put away.

    Forth time out was to do some pattern testing with some duck loads which are #2 Fasteel. Since we were only shooting one round at a time I had no worries, but when we got done it was fun time. I pulled the limiter out of the mag tube and was mixing up the rounds trying to induce a failure and after about the 7th “mag dump” it finally happened with a Winchester high base leaving an empty chamber . That was the only one though so I didn’t feel too bad. But, when I got home I found that the gas system was an oily goopy mess.
  2. Rob72

    Rob72 .410

    Messages:
    67
    People will have different suggestions, but mine is:

    Use dry-lube in all areas other than the receiver/bolt rails, on the rails, use grease, unless you're somewhere really cold, then use oil.

    The loose forearm would seem to indicate that 1) it wasn't seated properly after last disassembly, and/or 2) the locking nut was not completely seated. If the forearm is loose, it can drag on the pusher, resulting in short stroking.

    Get a $5 can or two of brake cleaner from Walmart and degrease the whoooole thing. Wipe it down well, inside & out, then spray dry lube of your choice (WD-40 sells a PTFE spray, or Birchwood Casey's Barricade, while not eaxctly a "dry" lube, is an excellent protectant with moderate lubricity). Apply synthetic grease to the bolt rails, receiver rails, and the face of the hammer. Reassemble. Drop your gun lightly on the floor, butt-first, to shake & settle the barrel into the receiver, and recheck the mag cap nut and forearm fit.

    If you can't live without soaking it down, get OR3Gun's Marine Spacer Tube, and possibly SBE Precision's stainless gas piston, to help blow some of the gunk out when you're shooting.

    I have both parts, and am satisfied with their function.
  3. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    Thanks Rob, but let me clarify the "loose forearm". It's not that it slides per say back and forth on the mag tube, but you can squeeze it up to the forearm retainer. I believe that the OR3GUN CFR was designed to take up the slop left on that end of the forearm. I have no idea how the forearm was initially snugged up against the forearm retainer to begin with, nor how I was able to duplicate it the few times that I had it apart up to that point, but having it free of the forearm retainer seemed to help with the cycling. I do have my eye on the OR3GUN MST and CFR, along with the SBE Piston, but I guess my biggest concern is why my issue only happens with high base shells. I have read quite a bit on the subject including the old 71 page troubleshooting thread here, and I guess the most I have been able to pull from all of that was maybe I need a heavier mag tube spring to help counter act the recoil of the more powerful shell.

    I appreciate the lubrication advise. I have some silicon grease designed for the fork seals on motorcycles that I use on my MSR's. I may try a few dabs of that on the bolt surfaces to see how it lasts.
  4. Rob72

    Rob72 .410

    Messages:
    67
    I will say, these are entry-level guns, so there are always a few things to look at with malfunctions. A good basic gunsmith go-through consists of detail stripping the gun, then:

    1) Polish down all spring ends (action spring, magazine spring, pusher spring)
    2) Chamfer opening of magazine tube, if you have or plan to use an extension
    3) Polish (at least 300 grit, you can use a green 3M pad on a cleaning rod for this, chucked in a hand drill) the inside of the magazine tube, action spring tube and chamber. Use a light oil for cutting slurry, and degrease thoroughly afterwards.
    4) Replace the hammer spring with a Ruger 10/22 extra power spring
    5) Then the aftermarket parts...
  5. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    Roger that Rob, thanks.

    Since I have no plans for an mag tube extension on this gun, is it true that the stock "cap" on the end can simply be pried off with a screwdriver?
  6. Rob72

    Rob72 .410

    Messages:
    67
  7. Sarge

    Sarge .22LR

    Messages:
    12
    Arrowshooter:

    I had much the same problems with a new 22" JM Pro, yesterday. Burrs on the recoil spring, plunger and unfinished edges on the chamber were the culprits. The chamber was not slick and I polished that out to 1000 grit and will finish it to 2000, next time the barrel is off. Runs like a champ now. More here if you're interested.

    http://www.mossbergowners.com/forum/index.php?threads/new-jm-pro-22-initial-test-drive.19436/

    I've run my 930's 'wet' for years and they've been reliable as the sunrise. Different strokes.
  8. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    Perfect and thanks for the warning. I have mastered the perfect launch when it comes to pressurized springs. LOL

    And thanks Sarge, just so happens I read your post this morning.
    Sarge likes this.
  9. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    So I was sitting at dinner tonight and the perfect cycling of the low base and the less than perfect cycling of the high base popped up in my head. Then it hit me....Dwell Time. Even though the high base built more pressure, it was not enough to account for the extra speed of the load and the wad left the gun before the pressure could put enough oomph into the gas system, while the low base was going slow enough to give the gas system al that it needed. I learned enough about dwell time, gas systems and little fast boolits while developing loads for my MSR's so it makes total sense. I thought that Mossberg's gas system was supposed to act like an automatic adjustable gas block so to speak, but maybe all scenarios cannot be accounted for. Tomorrow will be my last test day before leaving for a duck hunt, so we'll see what happens with the couple extra boxes of Fasteel I just picked up. Should be fine since it is 3". LOL
  10. John A.

    John A. I'm "THAT" guy Staff Member Global Moderator Moderator

    Messages:
    14,459
    I don't know a lot about the 930 because I don't have one.

    However, I do have a couple other semi's and here is something you may consider looking at.

    The gas piston under the handguard, is it orientated the correct direction?

    I know on my two semi's, if the piston part is turned around backwards, it doesn't cycle right. I actually took one of those electric hand engravers and made an arrow into mine so I knew which direction to install them once I have everything apart cleaning it.

    matter of fact, that's how I acquired the first one. My buddy couldn't get it to cycle right and got tired of fooling with it and sold it to me. And that was what was ultimately causing the problem. Whoever had it before him had put it back together wrong and he didn't know to look for.

    As for the oil getting into the gas system.

    The barrel has holes drilled in it that vents the gas out of the barrel and underneath of the handguard. If oil is running down the barrel, it's a good chance that is how it is getting out of the barrel too. Not to mention, when you shoot, that barrel is pressurized and of course, that is one of the ways for the oil to get blown down in there.

    I don't think the problem has to do with dwell time, though that does make some sense.

    but the dwell time is actually the same with both shells. Though, I understand what you mean about the shot being in the barrel for less time with high brass because there is more velocity, but there is also more pressure as a result.

    Typically, if a semi doesn't like a shell, it's going to be a low brass (weaker) shell than the other way around.
  11. Arrowshooter

    Arrowshooter Copper BB

    Messages:
    8
    Hi John. The piston can only go in one way so its a no brainer.

    I am pretty sure I have my oil situation finally under control now. I cleaned out the receiver and only put a bit of oil where it should be. I have also started running a Bore Snake down the barrel before I go out to shoot just in case. At the range last weekend I ran every shell in my arsenal trying to get it to fail and it ate them all no problem plus the gas system stayed dry. I also just got back from duck hunting, and again the gun ran great and no signs of excessive oiling. I did have an email conversation with William at OR3GUN about his products, mainly the MST, and he suggested that I look at the recoil system for galling which is on my to do list for tomorrow.

    So it pretty much comes down to my using oil as if I had stock in Hoppe's. Thank you everyone for your help with this.
  12. John A.

    John A. I'm "THAT" guy Staff Member Global Moderator Moderator

    Messages:
    14,459
    I'm glad you figured out what it was. And I hope you had fun duck hunting.

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