The Mongoose gets an upgrade.

The Mongoose gets an upgrade.

This is a discussion on The Mongoose gets an upgrade. within the General Firearm Discussion forums, part of the Related Topics category; Well, the AR lower receiver did anyhow. I installed a LaRue MBT-2S trigger. It's supposed to be a "two-stage" trigger, but I don't see any ...

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Thread: The Mongoose gets an upgrade.

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    VIP Member Array OldVet's Avatar
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    Red face The Mongoose gets an upgrade.

    Well, the AR lower receiver did anyhow. I installed a LaRue MBT-2S trigger. It's supposed to be a "two-stage" trigger, but I don't see any difference. But for sure, it is lighter and a cleaner break than the OEM mil-spec trigger. It's supposed to break at 4.5 pounds, but I can judge that with only my finger.

    I'm no gunsmith, but it took all of thirty minutes to swap it out, and much of that was my cleaning the receiver nooks and crannies, lubing the sear points and pins, etc. While I haven't made it back to the range yet, the functional tests showed it to be a big improvement.

    If anyone is interested in an inexpensive AR upgrade and can't drop $200-300 for a match trigger, LaRue has them on sale for about $95 shipped. It comes complete with new pins and a heavier hammer spring (6 lb?) for those who prefer a bit heavier trigger.

    Hopefully I can make it to the range Monday.
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    Sounds good @OldVet . It will be interesting to see what you think of the trigger after a range trip. I bet you're gonna like it!
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    VIP Member Array Chuck R.'s Avatar
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    It's a 2-stage...

    Buuuut, if you're used to shooting a trigger with some pre-travel, you're probably not noticing it that much. I've got a couple MBT-2S and 4 Geissel SSA-Es, and I've installed a bunch of MBT-2S for the guys at work. I equate the MBT-2S as sort of a poor mans SSA-E, good enough to the point it's tough to justify the extra $140 for the Geissele depending on the application.
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    Quote Originally Posted by Chuck R. View Post
    It's a 2-stage...

    Buuuut, if you're used to shooting a trigger with some pre-travel, you're probably not noticing it that much. I've got a couple MBT-2S and 4 Geissel SSA-Es, and I've installed a bunch of MBT-2S for the guys at work. I equate the MBT-2S as sort of a poor mans SSA-E, good enough to the point it's tough to justify the extra $140 for the Geissele depending on the application.
    Tried it out today. Yeah, just seems like light pre-travel and then a light break. I'm pretty pleased with the trigger, the Mongoose upper not so much. Still having erratic feeding issues. The lower works fine with its .223 upper but balks with the Mongoose upper, and I can't pinpoint why. Different BCG didn't seem to help. Back to the drawing board.
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    VIP Member Array Chuck R.'s Avatar
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    Quote Originally Posted by OldVet View Post
    Tried it out today. Yeah, just seems like light pre-travel and then a light break. I'm pretty pleased with the trigger, the Mongoose upper not so much. Still having erratic feeding issues. The lower works fine with its .223 upper but balks with the Mongoose upper, and I can't pinpoint why. Different BCG didn't seem to help. Back to the drawing board.
    What's it doing????
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    Erratic feeding. I adjusted the resizing die to allow more headspace as the bolt was tight to unlock on an unfired round. That helped with that issue.

    First try, 5 rounds in a magpul mag. Cycled fine and locked back on last. Yahoo. Short lived. Next round of 5, didn't pick up the third round, did not lock back on last. Tried three ASC mags of 5 & 10 round size, sometimes wouldn't strip the first round from the mag (5-rd in particular, very tight fit) and iffy lock back. Doesn't feed consistently. The Magpul works better, but not 100%.

    Tried a different BCG with no real improvement.

    It seems like a lot of pressure on the BCG from the mag and rounds. I'm going to recheck the case headspacing again but the die is about bottomed out on the shell holder already. At least it's gone from never cycling to now erratic cycling.

    Put my 5.56 upper back on and 30 rounds of reloads worked fine except for one failed to lock back on last rd.
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    what caliber is it you're having trouble with? Is this a new issue, or could it be ammo related?
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    Quote Originally Posted by Havok View Post
    what caliber is it you're having trouble with? Is this a new issue, or could it be ammo related?
    It's a true wildcat, a 6mm Mongoose. Made from the .223 case, slightly shortened, case taper lessened, shoulder angle changed, necked up to 6mm. Pretty potent. I found after shooting the .223/5.56 for many years to be ho-hum. I've made wildcat rounds before but not for a semiauto. I think the case headspace may have been part of the problem as it's working "better." I believe the bolt was binding on unlocking and slowing the bolt cycle. I have other options I can try--replacing the carbine buffer set up with a rifle buffer, etc.--but I don't want to make several changes and then not know what resolved it. So it's one change at a time for now. It's just a PITA to drive 45 minutes to the range to have marginal performance.

    The rounds shoots well, considering the old scope I slapped on and the old eyes looking through it. The new trigger was a nice upgrade. Now just to get it functioning as it should.
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    I don't want to make several changes and then not know what resolved it.


    Very wise.
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    Quote Originally Posted by QKShooter View Post
    I don't want to make several changes and then not know what resolved it.


    Very wise.
    Of course!
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    It sounds like it could well be a combination of being under-gassed and a magazine issue.

    I would isolate the mag issue, by sticking with the Magpul(s). Then I'd just shoot several single rounds to verify that it's consistently locking back. Excessive pressure usually is indicated by primer issues and marks on the brass to include bent rims, etc. So I'd check the brass on single rounds you've fired looking for those symptoms.

    IF it is under-gassed, then it could be the usual suspects; misaligned gas block, too small of a gas port, loose gay key etc. or maybe even weak ammo. You could also try a lighter buffer, but I always like sorting out the gas system 1st.

    It does suck commuting to sort stuff out...So I'd probably bring a back-up gun just in case teh "fix" doesn't work out.
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    Quote Originally Posted by Chuck R. View Post
    Excessive pressure usually is indicated by primer issues and marks on the brass to include bent rims, etc. So I'd check the brass on single rounds you've fired looking for those symptoms.
    You mean like leaky or popped primers? BTDT. Found the "over-the-top" limit on that load and another.

    Gas block alignment and key are good. Gas port was opened, which got it from never cycling to sometimes cycling. Adjusting the case head space improved cycling more. There are no bent rims but some cases faces have a bright smear, possibly from the ejector rubbing when the bolt locks. I'm rechecking the cases tomorrow when I resize them. They may still be a bit tight in the chamber.

    The ASC mags were recommended as they allow a longer COL than Magpuls. But they function worse--so far. Actually, the first 15 rounds in the Magpul cycled fine with a fail to lock back on the last round, the highest load. The rest were a different load--lighter bullet, 65 versus 70 grains--but not by much and the Magpuls didn't work so well with them either.

    It will get ironed out eventually.
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    Quote Originally Posted by OldVet View Post
    You mean like leaky or popped primers? BTDT. Found the "over-the-top" limit on that load and another.

    Gas block alignment and key are good. Gas port was opened, which got it from never cycling to sometimes cycling. Adjusting the case head space improved cycling more. There are no bent rims but some cases faces have a bright smear, possibly from the ejector rubbing when the bolt locks. I'm rechecking the cases tomorrow when I resize them. They may still be a bit tight in the chamber.

    The ASC mags were recommended as they allow a longer COL than Magpuls. But they function worse--so far. Actually, the first 15 rounds in the Magpul cycled fine with a fail to lock back on the last round, the highest load. The rest were a different load--lighter bullet, 65 versus 70 grains--but not by much and the Magpuls didn't work so well with them either.

    It will get ironed out eventually.
    Isn't this what "Wildcatting" is all about? Sounds like a fun problem. Good luck.
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    Quote Originally Posted by oldbadger View Post
    Isn't this what "Wildcatting" is all about? Sounds like a fun problem. Good luck.
    Well, the functioning part isn't so much fun. Developing loads does remind me of Elmer Keith seeing how much powder he can use before the top strap blows off!
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    Took my Mongoose back to the range today. Shoot 100 rounds using my Armalite lower and one of my son's lowers. The Armalite still has persistent feeding issues (not feeding from mags, misfeeds, etc.) but the upper ran fine with the son's lower. There is some sort of tolerance mismatch between the Armalite lower and Aero Precision upper. My lower runs fine with its Armalite upper.

    So, I've ordered a lower parts kit and rifle buffer assembly. I have a (preferred) A2 stock and will hit the LGS this weekend. They had an Aero Precision stripped lower for about $80 last time I was in there.

    FYI--Sonny loaned me a Colt 20-roundmag, and in one more "fail-to-check" move, I didn't discover until I got to the range that the Colt mag is a wee bit shorter than the HK or ASC mags, so the rounds I loaded for them did not fit in the Colt mag. One more D'oh! for my growing list of D'oh!s.
    Last edited by OldVet; May 31st, 2019 at 07:18 PM.
    Retired USAF E-8. Curmudgeon on the loose.
    Lighten up and enjoy life because:
    Paranoia strikes deep, into your life it will creep. It starts when you're always afraid... Buffalo Springfield - For What It's Worth

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