Modern Sporting Rifle Evolution
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OldVet

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Reply with quote  #1 
I built a Mongoose upper a few months back, and I believe it is jinxed! If not jinxed, it's a close relative of Murphy. I've reloaded for years and have reloaded a wildcat before (30 Herrett) but this semi-auto cat is a different breed.

Right off the bat I had feeding problems, from not picking up the rounds from the mags (several brands) and misfeeds, etc. I worked with Bruce (Bigdawg?), and he felt it was my ammo because my cases shoulder length was shorter than his cases fired in my upper.

So I reset my dies to match his recommendation, and things improved, although I had to reset again to match a new BCG I bought specifically for the Mongoose upper. Had to shorten the length .001" to get them to feed.

While the cycling issues seem to be resolved for the most part, I still have issues where the BCG doesn't pick up the first round, more so with Magpul mags than the H&K or the steel mags.

I packed a variety of mags today as well as an AR lower borrowed from my son and hit the range this AM. Murphy was there waiting...

Still had some issues with the BCG not feeding the first round, so I grabbed Junior's lower. Bam! Murphy struck. Front pivot was tight and the pin would not insert. Dang, there went that idea. Should have tried the fit before I left the house. Whodda thunk?

So then I shot some 70-grain Nosler Varmageddons over BLC2 and after fourth shot the next round locked the bolt up tight but not in battery. I had to mortar the stock to get the bolt loose. Looked the round over but didn't see anything, so I set it back in the box. About 8 rounds later the same thing--out of battery and jammed tight! Finally got that one out and called it a day.

Afterwards, I took various measurements of the suspect rounds, comparing them to resized and fired cases, and everything checked good--all a few thousandths under fired case measurements. Now I'm puzzled.

So I set the cases aside and cleaned the rifle. When I went to run a patch through the bore, it jammed too! What the heck? Pulled the rod out and it looked like a spring was wrapped around the jag and patch.

I carefully removed it and found it was copper from a bullet(s). I had this once before loading lead bullet in handguns--lead shaving. Somehow I think I missed chamfering a couple of cases and the case shaved the bullet and jammed the round. One piece of copper was a complete, intact circle of material.

You can bet when I resize this batch of cases they'll all get a fresh chamfering job.

I'm going to try another of Junior's lowers on my next trip (He has a lot of them!) but if anyone has an idea of why the BCG doesn't want to grab the first round from the mag, feel free to chime in. Other than trying a different lower, I'm running out of ideas. FYI, the brands I have are ASC, Magpul, H&K.
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Bigbassbaww

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Reply with quote  #2 
My thoughts is the feed lips on the mags your useing is needing a lil tweaking to position the round so the bcg has to pick it up.

The round should be perrty level, if it has a nose up attitude that could be your problem.

No experience with the mongoose but a mag is a mag and a case is is a case. And when I have mag related feeding issues with the grendel. That's is typically the problem the feed lip(s) need to be tweaked too allow the round too sit properly so the bcg doesn't run over it but pick it up.
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RIGGS68

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Reply with quote  #3 
Does this happen with both fresh and fireformed brass? Does the problem occur if you insert the mag with the bolt locked back - or only when the mag is inserted with the bolt closed?
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Bajabusdoc

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Reply with quote  #4 
Does this happen if you push back on the bottom of the mag or push forward. This is a cheat to see mag lip alignment...pushing forward directs bullet tip up. Pushing back lifts trailing edge to catch base and feed more parallel to bore...........
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OldVet

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Reply with quote  #5 
Quote:
Originally Posted by RIGGS68
Does this happen with both fresh and fireformed brass? Does the problem occur if you insert the mag with the bolt locked back - or only when the mag is inserted with the bolt closed?


Both fresh and fire-formed cases. With locked bolt. Doesn't happen every time but far too often to be the freak occurrence. 

FYI, the lower is an Armalite Eagle and has never had problem with the .reloaded .223 rounds or than an occasional fail to lock back on last round. Always picks up the first round of .223.

I'm using a Magpul 5-rd mag with both .223 and Mongoose rounds, and only the Mongoose is not picking up. With ASC 5-rd mags, the fifth round is very tight to seat in the mag. so I've dropped to loading 4 rounds. The ASC 10-rd mag seems to work fine.

Rounds eject at about 3:30, so the gas should be good. Fired one round from all the mags and only the Magpul did not lock back consistently. Not overly concerned about that as this is not a combat/competition rifle, just something I'd like to eliminate.
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OldVet

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Reply with quote  #6 
Quote:
Originally Posted by Bajabusdoc
Does this happen if you push back on the bottom of the mag or push forward. This is a cheat to see mag lip alignment...pushing forward directs bullet tip up. Pushing back lifts trailing edge to catch base and feed more parallel to bore...........


I'll give that a try on the next range trip, but I haven't had this issue with this lower and mags with my .223 upper.
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Bigbassbaww

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Reply with quote  #7 
Quote:
Originally Posted by OldVet
Both fresh and fire-formed cases. With locked bolt. Doesn't happen every time but far too often to be the freak occurrence. 

FYI, the lower is an Armalite Eagle and has never had problem with the .reloaded .223 rounds or than an occasional fail to lock back on last round. Always picks up the first round of .223.

I'm using a Magpul 5-rd mag with both .223 and Mongoose rounds, and only the Mongoose is not picking up. With ASC 5-rd mags, the fifth round is very tight to seat in the mag. so I've dropped to loading 4 rounds. The ASC 10-rd mag seems to work fine.

Rounds eject at about 3:30, so the gas should be good. Fired one round from all the mags and only the Magpul did not lock back consistently. Not overly concerned about that as this is not a combat/competition rifle, just something I'd like to eliminate.

Ok since its the magpul there really isn't any way to tweak the feed lips.

Could be just that particular pmag is the problem. Something too do with how it's locking into the lower.

Do you have a diffrent pmag too try?
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OldVet

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Reply with quote  #8 
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Originally Posted by Bigbassbaww
Ok since its the magpul there really isn't any way to tweak the feed lips.

Could be just that particular pmag is the problem. Something too do with how it's locking into the lower.

Do you have a diffrent pmag too try?

It's not just the one pmag, those are just the worst. 5- & 10-Rd ASCs do it also, especially if full. They work better when downloaded -1, but not 100%. Maybe there is some dimensional incompatibility between the Armalite lower and Aero upper. The Armalite lower works fine with its own upper. Changing BCGs didn't seem to help.

It's a bit of a head scratcher. I intend to build a lower for the Goose but don't want to spend the money if it still wont feed properly. I will try a different lower next trip to see what happens with it.
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Bigbassbaww

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Reply with quote  #9 
Quote:
Originally Posted by OldVet
It's not just the one pmag, those are just the worst. 5- & 10-Rd ASCs do it also, especially if full. They work better when downloaded -1, but not 100%. Maybe there is some dimensional incompatibility between the Armalite lower and Aero upper. The Armalite lower works fine with its own upper. Changing BCGs didn't seem to help.

It's a bit of a head scratcher. I intend to build a lower for the Goose but don't want to spend the money if it still wont feed properly. I will try a different lower next trip to see what happens with it.

Could be that the lower just doesn't play well with the upper.

You can check the asc mags lips, since they are metal you can tweak them if need be.
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RangerJoe

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Reply with quote  #10 
I've built and fired 4 different rifles/uppers based on the MDWS "Mongoose" family of 'cats: 2 6mm Mongooses, 1 .257 Ocelot, and 1 .20 Viper.  NONE have experienced any of the symptoms you're describing.  They all use different BCGs, uppers, charging handles, etc.  For the most part, I don't have dedicated lowers for each of my uppers, I tend to use 1 of 4 different lowers (2 fixed stock, 2 collapsible) depending on which one is handy or the type of shooting I'm going to do.  I know that between the 4 uppers, I've used all 4 lowers.  I use primary Lancer L5s (modified for x40 ammo), but have recently been using MagPul's 300BLK mags.  I've had problems with Gen 1, 2, and 3 5.56 PMags running anything other than 5.56x45/.223 which they are designed for... so I tend to limit my 5.56 PMags to 5.56 ammo.

The only reason (IMO) a bolt locked back and released would ride OVER a cartridge in the magazine is if the base of the cartridge was too low.  This could be because of a faulty magazine, out of spec lower, or tolerance stacking between the upper and lower.   Since you've used multiple magazines, it seems to remove that variable from the equation.  Whether the issue is with the upper or lower would appear to be the next question.  Since you said you tried another lower (your son's), and it WOULDN'T FIT YOUR UPPER... that might be a clue.  It sure seems to point to tolerance issues.

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Bajabusdoc

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Reply with quote  #11 
Two thoughts the feed ramp where the m4 meets barrel extension or shoulder hitting front wall of mag. But these would cause FTF and bolt would catch the side of cartridge. Not bolt would override and not pull round out of mag...am I understanding?
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RangerJoe

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Reply with quote  #12 
BBD - you are right.  The failures OldVet describes are the bolt riding OVER TOP the head of the top cartridge in the mag.  If the bolt isn't touching the cartridge head... SUM-TING-IS-WONG.
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RIGGS68

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Reply with quote  #13 
What Gen are your Pmags? I had some problems with my 5 rounders seating fully until I ground down the over-insertion stop-now they function fine. Like Ranger, I have a couple Mongoose-based cats and have never had a problem with feed or function (all have dedicated lowers except the Viper-borrowed from a 5.56 chambered AR). I will add that I primarily use Magpuls form fireforming then switch to ASCs so I can load longer, however, neither has presented a problem. 
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OldVet

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Reply with quote  #14 
I'll try to respond to several queries here. Yes, the BCG rides over the top round and goes to battery on an empty chamber. Insert loaded mag, release the bolt, drop the mag and all the rounds are still in it. More a problem with full mags, particularly 5-rounders, but any of them on occasion.

The 30-round pmag is a Gen 3, the five rounder unknown. The top round is not as tight in the 5-rd pmag as the 5-rd ASC, not nearly.

Part of going with an AR upper instead of a new rifle was, like the TC Contender, just swap uppers (barrel) and you have a new gun. Apparently not so.

I'm going to try several of Junior's lowers and see if any fit better than the one I tried. Or none, as the case may be. The Aero fits the Armalite well, barely any looseness, certainly no more than the Armalite upper.
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RangerJoe

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Reply with quote  #15 
Quote:
Originally Posted by OldVet
<snip>I'm going to try several of Junior's lowers and see if any fit better than the one I tried. Or none, as the case may be. The Aero fits the Armalite well, barely any looseness, certainly no more than the Armalite upper.

Good plan - but "fit" isn't the critical factor, function is.  Your Aero & Armalite might fit very snug, but have tolerance stacking that keeps the BCG too high to strip rounds from the mag.  Good luck and let us now what you find.  We'll help you squash Murphey into a wet-spot on the firing line dirt!!

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OldVet

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Reply with quote  #16 
Okay, made another trip to the range, with a lower that fits this time, and found--using loads with two different powders, BLC2 and H335 with 70- grain TNTs--that my upper built on an Aero Precision upper hates my lower made by Armalite. I used my son's lower and everything ran fine except for not locking back on last round once.

I can't remember the brand of his lower, a symptom of being 67, but I can say it has the stiffest dang trigger I've ever shot, but it functioned well with a variety of magazines. The grouping with his trigger was terrible compared to the LaRue MBT I installed in mine. The LaRue with the light hammer spring is a bit light for SD work, but I'd have to change out the son's trigger if it were mine.

My lower had fails to feed the top round from about any of my mags as well as a couple of misfeeds. I think his lower failed to load back on an empty mag once. So as soon as I returned home and got things cleaned up and put away, I ordered a rifle buffer assembly for the A2 stock--which I prefer--that my son gave me, a lower build kit from PSA, and will hit the LGS this weekend. The LGS had a stripped Aero Precision lower for $79 that "should" match up with its upper.

I had zero locked-up bolts this time, so I think my resetting of the case head space is good to go. I'm not sure if there is some dimensional problem with the Armalite lower or maybe a buffer issue, but enough is enough with trying to resolve its issues. I've already pulled the Larue trigger out to install in my new lower build.

I also had found a lot of brass chips/shaving on my bolt face after previous range sessions, so I removed the O-ring from the extractor, and have not had any further specks of brass nor extraction issues.

I don't plan on returning to the range until I have my new lower completed, and if it works as hoped, then I'll start working up some loads for accuracy. My accuracy results are limited by a old Bushnell 4X scope I'm currently using and the beginning stages of cataracts in my aiming eye. It's like peering through light smoke haze when shooting. Might have to finally look into getting that fixed.

I did find that 70-grain TNTs shoot very differently than 55-grain Dogtown bullets, and then again with BLC2 powder versus H335. This wildcat loading is so much fun!

And Murphy did make the trip with me. My son came by and gave me a Colt 20-round metal magazine to try. In my typical slow-to-learn fashion, I did not try it until I got to the range. Did you know that the COL is shorter on a Colt mag than a HK or ASC? Now you do!
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Bajabusdoc

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Reply with quote  #17 
Quote:
Originally Posted by OldVet
...the beginning stages of cataracts in my aiming eye. It's like peering through light smoke haze when shooting. Might have to finally look into getting that fixed.

Cataracts are most sensitive to blue light rays. This is why the new headlights are more obnoxious than the older yellowed ones. First try a yellow tinted shoot through lens cap or yellow shooting glasses to filter out blue-gray light if that helps then find a polarized pair that further filters horizontally oriented reflected light from ground and mirrage , this will sharpen contrast. Duplex crosshairs rather than red dot or illuminated help too
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OldVet

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Reply with quote  #18 
Other than picking up a new charging handle tomorrow, the Mongoose is all complete. A2 stock with rifle buffer, Aero Precision receiver, PSA lower parts kit, and LaRue MBT-25 trigger Assembly.

Mongoose1.jpg  Mongoose2.jpg

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Bajabusdoc

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Reply with quote  #19 
Sweet!
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OldVet

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Reply with quote  #20 
Eureka! 

The new Aero Precision lower build resolved all of the Mongoose feeding problems. I had two separate first-feed rounds that did not quite go into battery, but I was shooting 80-grain SPBT "seconds," some of which had battered/slightly bent lead tips. I suspect that may have been the issue, and they both occurred with the 5-round mags. The 10-round mag ran without a hitch.

I shot loads of H335 powder from 24.0 up to 26.0 grains. I knew I needed some scope adjustment, so I started at 50 yards and made a couple adjustments to bring the groups to center - 1 inch low. The load of 24.5 grains made one ragged group, the others not too bad, but I take credit for the more open groups.

Moving out to 100 yards, I made one click adjustment right and let it ride. Shooting off a Harris bipod, the groups opened up a bit naturally, but they were right on in elevation and the one click right may need to be backed out. I'm letting that setting ride for the present.
Recoil was mild, and the primers looked good--no cratering, no flattening--with only the 26.0 loads showing the barest bolt face imprint on the primers. I think it is safe to bump the powder up another grain or so.

So it took a new lower to straighten out the Goose kinks, something I intended to do all along. The A2 stock I installed feels much better than the carbine stock I previously used. My eye aligns with the scope better. I am finally a happy camper with the Mongoose.
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RangerJoe

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Reply with quote  #21 
Excellent - and completely consistent with many other happy Mongoose owners!  Thanks for closing out this issue on the forum... wouldn't want to leave a bad impression for the 'goose.
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OldVet

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Reply with quote  #22 
Quote:
Originally Posted by RangerJoe
Excellent - and completely consistent with many other happy Mongoose owners!  Thanks for closing out this issue on the forum... wouldn't want to leave a bad impression for the 'goose.

Biggdawg had pointed me toward a possible lower issue. I think there is a problem with the mag position in the lower that is not conducive with the Aero Precision upper I used, as in too much space between mag and BCG. The lower feeds fine with its OEM upper, but for whatever reason just did not mate correctly with the upper.

I can't see any difference between the two, but a few thousandths is all it takes to throw things off.
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OldVet

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Reply with quote  #23 
Ran fifty rounds of 80-grain SPBTs over BLC-2 through the Mongoose today. 100% function! I can happily say my function issues are behind me. Got a 4X12 scope on the way and hope that will help with the grouping with the current 4X Bushnell. A developing cataract isn't helping things either.
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MDWS

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Reply with quote  #24 
Quote:
Originally Posted by OldVet
Ran fifty rounds of 80-grain SPBTs over BLC-2 through the Mongoose today. 100% function! I can happily say my function issues are behind me. Got a 4X12 scope on the way and hope that will help with the grouping with the current 4X Bushnell. A developing cataract isn't helping things either.


Well congrats on getting the rifle running! Sorry to hear of the eye issues... getting older sucks.

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bbbrownfield

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Reply with quote  #25 
Quote:
... getting older sucks.

Hey, I resemble that remark...[smile]

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