Hey guys,

Been a while since I've posted in the rimfire section, but I need a little help troubleshooting some BDM mags.


Setup: F4 Colt M16A1 with CMMG 4.5" upper, running with BB adjustable ABW with tungsten weights, BB EFP, & CMMG solid charging handle.  BDM Gen 2 mags (3 steel + 3 nylon lips.)  Mags are about a decade old and probably have about ~1000 rounds through each nylon lip mag and ~500 each steel lip.  Mags are stored empty until day of shooting.

Situation: When loaded to 25 rounds, the stick mags will choke on the first few rounds (semi and full auto.)  No issues with a drum, it'll run all 50 without skipping a beat.  When downloaded to 20 rounds, the stick mags will run >99% FA - both bursts and mag dumps.  The upper only chokes when empty cases get jammed in action.

Troubleshooting: where should I look next?  I suspect it's a tension issue, but I'm unsure which way to check.  Is it too much tension on the bolt at the beginning of the mag?  If it was weak mag spring tension, wouldn't it choke at the end of the mag instead of the beginning?  I pulled all the mag springs and very lightly lubed them, but it didn't seem to make any difference.  

I have some new BDM mags and 11" springs on the way to see how they do, but I'd really like to get these (formerly) reliable mags running again.  While 20 rounds is FAR superior 0 rounds, I'd like to figure out this last hiccup so I can spend more time shooting and less time loading mags.


TIA,
cosmos556



PS - how are you transporting your BDM mags to the range?  I can fit about 7 in an old ALICE SAW ammo pouch, but they're too long for USGI bandoliers.

+1....that is all that I've been using since they came out.  Don't even bother with stick mags anymore.  Combine that with the McFadden loader and don't see any need to use stick mags.  I put (4) drums in a 50 cal ammo can w/ a 500 round brick of ammo.

Sounds like your timing is off using the BDM 25 round mags.   The upward pressure from the full mag is increasing drag on the bottom of the bolt causing stoppage.   If you added weight I’d decrease bolt weight to increase bolt speed.    

It is possible the 25 round BDM mag spring is weak but I have never seen that issue.   My bet is the bolt isn’t cycling the same distance or speed when using the BDM drum compared to the 25 round single stack mag.   The stiff spring upward pressure on the bottom of the bolt can add significant drag.  As the mag empties there is less upward pressure and the actions runs reliably.

Try replacing the tungsten internal weights with some steel and see if that helps.  

What type of malfunction are you experiencing on the first few rounds?

@Renaissancemann
It's not stripping a round from the magazine.  I charge and it's fine after the first few rounds, so I downloaded to keep shooting.  I'll swap the weights to steel and see if it helps.  I assumed I needed the weight of tungsten because the non-adjustable weight would only run a few rounds from the drum (and none from a stick mag.)  
Also, are you the guy behind Bore Buddy?  If so, I'd like to extend my heartfelt thanks for your work innovating this niche.  I was running out of variables to try with my M16, and this has changed my experience 180* from frustration to fun.  Even with downloaded mags, this is an absolute hoot!


ETA:
@amphibian, I see your point on the drum mags.  It's very tempting, given how well they run.  I'm a sucker for the stick mags; I don't know why, but I've always liked the look and balance.  The Lightning Grip is a great loader.  I remember when the $150 contraption (sold by M60Joe?) was the only game in town, but this is a great addition - and more portable.
@VASCAR2 it seems like weight is a culprit.  I'll have to tinker and see where the sweet spot is with this configuration.  Being able to run downloaded mags is quite a step in the right direction, so hopefully I'm close enough to get it running like a clock.

Bore buddy has answered questions people have been asking for years.

I'm not a full auto fellow, so if my observation is stupid, discount it.

If you rounds aren't being stripped from your stick magazines, the remedy may be a more powerful recoil spring.  High bolt velocities aren't your friend, so you could keep the extra weight, but the extra spring weight would shove the weight with enough velocity to push the 25th round into the chamber.

Full disclosure, I hate BDM/CMMG magazines like God hates sin.  I don't understand why a magazine would be made so the first round in takes a couple of ounces to push in,  but the 25th puts a callous on your thumb.  Switch to S&W magazines.

I ran into similar feeding problems with my CMMG conversion using the Black Dog X magazines with the stainless investment cast lips and sonic welded construction... with CCI Blazer ... the follower was jamming the top cartridge into the feed lip with a force that made it extremely difficult to be stripped off the feed lips of the magazine....I was able to strip the top round by hand only if I vertically depressed the cartridge and used a punch to "scrape" it off... the follower ran smoothly in its track in the magazine, and I could not determine any way that it was being cammed into a locked position

I replaced the metal lip magazines with some original BDM  magazines with vinyl  lips, and they strip rounds easily as do the new  vinyl lipped mags that have a somewhat different feed lip geometry

This has helped me...

I had Beta drum mags that use graphite. It is part of the package.
I have tried it on mags and drums that were sluggish, as an experiment.

They sell graphite in tubes, at the hardware store or locksmith shop.

1.   Put five .22 rounds in a ziploc bag, with some graphite powder. Shake it around, and when the rounds are coated load them first.
If that didn't work, go to step 2.



I have been a spring maker for over 35 years. This trick has even helped antique guns...

2.   Take the mag spring out and degrease it. Measure the over all length.
If the spring is X, carefully stretch it to X times 1.5.
Maintain squareness.

Drums may not have a compression spring, they usually have a torsion spring.
And it may be beyond help

If a magnet will stick on it, it is carbon steel.
Most mag springs are.
Put it on a cookie sheet, and put it in a 450 degree oven for one half hour.

If a magnet wont stick well on it, it is stainless.
Those get as close to 600 degrees as your oven can get. Heat for one half hour.

3.   Reassemble mag...

Buff any rough spots on follower. A lady's emery board works well.
CLEAN IT WELL, after treatment.

Clean inside of mag body.

Put spring and follower in ziploc bag, and graphite treat them.
Reassemble magazine.

Fully load mag, and let it set over night.

Pray...
Try it if it works, name your firstborn Otto.

"And this is our olderst daughter, Otto..."

I also second the heavier recoil spring -- check out the lakewood spring kit.  I am the owner of BoreBuddy, but I'm not permitted to be vocal about our products on this board.  I do chime in and answer questions as an AR22 user like everyone else from time to time, however.

No full auto, just a Binary trigger..But all my BDM stick mags and my drums run great..

I feel your frustration!  I have a M16A1 with a POF full auto cartridge trigger installed,  which I think is more .22 friendly than the standard FA FCG.  I use a 9 inch CMMG upper, CMMG sear trip and anti bounce weight and BDM magazines, CCI standard velocity ammo (which runs very clean) and a Dead Air Mask HD silencer.   I only load 24 rounds in the BDM magazines.  The 25th round generally will not go, and if it does it will cause feeding issues.  BDM drum runs fine.

When my upper acts up, the first thing I look at is the recoil spring, which are standard strength CMMG springs.   After about 5,000 rounds they are toast and will cause cycling and feeding issues that seem to arise out of nowhere.  I have not had any issues with the BDM mag springs, however I do disassemble and clean the magazines periodically.  Other than the recoil spring, the only thing I can say, is:  keep it clean and use plenty of Mobile 1 synthetic.  If you try different spring weights or different weight weights, try to change one thing at a time, so you know what is working and what is not.  

Good luck.

Recently I've been lubing everything 22lr related with hexagonal boron nitride suspended in denatured alcohol.  Mine is mixed so it looks about the "thickness" of whole milk when shaken.  It seems to do a good job and is pretty easy to make and apply.  The alcohol wicks into cracks and then dries leaving the film behind.