<repost from original locked thread>

I was lucky enough to have been selected by Kevin to receive one of the M261 T&E mags this week. When I opened the padded envelope he mailed to me (thank you again Kevin), I have to admit, I exclaimed "Holy sh*t, this thing is sweet." The magazine's quality, fit, finish and overall feel is more impressive than I even imagined from the pictures of the Ciener full size version. The mag is top notch. It feels good in the hand, and solid as a rock. The internal webbing adds to the solid union of the two mag body halves, resulting in no rattling, body flex, gaps or hollow feeling. The feed lips appear a little thicker than previous mags BDM produced, but that's just a guess. It's 200% better than any Butler Creek 10/22 mag. This thing looks like it's designed to be abused. And best of all, it looks like it was born to be on an AR. It locks up solidly in the mag well with my M261 bolt closed. It's a snug fit in my RRA mag well, with no play to speak of. The angle of the rounds when the mag is seated looks perfect for good feeding. I loaded up about 20 rounds, let it sit a while, and loaded up the last 5 with a little extra effort. I can't wait to shoot this mag.<BR><BR>It's been raining heavily here in Dallas for the past 48 hours, but plan to get to the range down the street by Sat and put 3~400 rounds of Federal, Mini Mags and Stingers through it. I'll post a range report when I'm done. For now, all I have are a few pics...

More to follow. Stay tuned.

Just got my beta-test example this very morning and it is exactly as BWhalen describes it. In fact, he just saved me a bunch of typing and photography! It is a VERY impressive looking product.

Unfortunately I won't get a chance to shoot the thing until this Sunday--possibly Saturday depending on how things shake out.

Many thanks to BDM for making this MUCH-NEEDED product. If it works as good as it looks, it's going to be a hit!

Nice!

Range Report on my 261 T&E mag:

Ammo used:
100 rounds CCI Mini Mags
175 rounds of Federal 550 bulk pack (hollow point)

FTFire: 23
FTE: 14
OOB: 2

I loaded the mag up last night and let it sit over night to help break the spring in and make loading easier. Not sure if this had any effect on the feeding of the mag or not. Each full magazine shot started out fine for the first 6~10 rounds. Then somewhere in this middle of the load, it would load the next round, but fail to fire. Examination of the ejected round showed no primer hit, and a deformation on the bullet that looks like it was impacting the bottom of the chamber mouth at a steep angle and slightly deforming the bullet base. In some cases, slingshot on the charging handle to load the first round showed what appeared to be a round about 95% in battery, but not with the bolt fully closed. I'd eject this round, see the same deformation and try again. My theory was confirmed as the testing proceeded with more FTF and later, two OOB detonations within 5 minutes of each other occured. At this point, I stopped my testing, and took inventory of the results. The cases of the OOB rounds looked like they were exposed about 10% outside the chamber when the hammer struck. Very slightly out of battery, and hard to tell when shooting until it occurred. Butt it confirmed the mag was not pushing the nose of the round up enough to feed reliably, and and while most deformed rounds were chambering enough to fire, two didn't.

Overall, I shot about 275 rounds, and will confirm the recommended changes BDM is making to the feed ramp height should alleviate the FTF issue I encountered. I will say, the mag took TWO OOB detonations and didn't look any worse for wear. I can't say this for the DPMS or V22 mags I hear fall apart with just one of these. Pics attached of some failed rounds, and the feed lips after the abuse. I also included a photo comparing the follower height of the stock M261 insert and the BDM T&E mag.

I think a slight change in the shape of the follower from being flat and level at the front edge to a constant upward angle from front to back (similar to the stock follower) might also help feed rounds at a slightly higher angle into the chamber without the miss feeds experienced today.

All in all, this product is destined for greatness. I'm ready to buy three as soon as Kevin makes any final changes he's mentioned, and releases the final product. That's how good I think this magazine is overall.

Best,
Brian

Typical damage after a FTF


The ejected FTF rounds


After two OOB, the mag looks like new


Follower height comparison, stock m261 insert (black) and BDM mag (red)

My testfire report:

RIFLE: Semi-dedicated (still has gas system for 5.56 use) .22 with M261. EA cast lower of late '80s manufacture, stock USAF 1:12 uppere (no forward assist). Has been extremely reliable with Fed Bulks and Remington Golden Bullets as long as the M261 unit is well lubed and the chamber is not crudded up.

MAG FIT: Mag fit perfectly front to back and side to side--no play whatsoever. Had to make conscious effort to seat the mag in the well as there is NO vertical play at all and a little tap or smack on the floorplate didn't hurt. This could be a function of my bargain-basement lower and not typical. The mag DID fit, it just took a little effort to make certain it was seated.

MAG LOADING: The first 20 rounds load quite easily, with no more effort than loading the GI M261 mag insert of 10 rounds. After 20, each round gets progressively more difficult to load, and round #25 can be a real challenge. At 25 rounds, the spring appears to be at full compression.

NOTE: I am currently right in the middle of a 1000-round dirt/leading/reliability test with this rifle and conversion. It has been exactly 500 rounds (@ 400 Remington Golden Bullets, 100 Fed Bulks) since its last chamber cleaning or lubrication of any kind. I thought testing the rifle in this condition would pose an extra challenge for the BDM magazine.

MAG 1: Loaded 25 rounds Fed Bulk (started with these because they have proven reliable in many other guns) and fired them as fast as I could pull the trigger, no malfunctions of any kind.

MAG 2: Loaded 25 rounds Fed Bulk. Rounds #8 and #9 misfed in some way. After clearing those out, the rest of the magazine fired with no problems of any kind.

MAG 3: Loaded 25 rounds Remington Golden Bullets. About halfway through the mag, a round failed to fully chamber (stopped in the chamber at an angle). I cleared this and the next one did the same thing. I interpreted this as a sign that the chamber was dirty and/or the unit (now with 550 rounds through it since any maintenance) needed lube. Ran a bore brush through the chamber,  pulled the M261 and lubed it with CLP. This made no difference. The next round misfed in the same way. I pushed the bolt home with my thumb on the bolt, fired it, and the next round also misfed. I kept this up for five or six rounds before giving up on the Rem GBs. Thought this particular box might have oversized bullets (had not fired any from THIS box in this rifle before) so I loaded the stock GI insert mag with 10 of the GBs and tried them. All ten fed and fired perfectly, as normal. The Rem GBs themselves were not the problem, but they do not seem to be compatible with this particular BDM magazine.

MAG 4: Loaded another 25 rounds Fed Bulk. Exactly as MAG 1, these fed and fired perfectly as fast as I could pull the trigger.

I concur with Kevin's conclusion that the fed ramp needs to be raised a bit. Examination of one of the Rem rounds that misfed showed a big scrape "divot" where it had apparently hit the bottom edge of the chamber going in.

The unit ran nearly perfectly with the Fed Walmart Bulks, the cheapest ammo available at the moment. Remington GBs are very reliable in MOST of my guns, but I have a few that won't feed them at all, so there must be something about the shape of the bullet.

It'll be great if Kevin's proposed feed ramp change enables the M261 to run on Rem GBs, as they are the most accurate of the cheap ammo that I've found for this rifle.

Just as BWhalen, I think this product is going to be a big hit. I'm also planning to purchase three of the final units.

Thanks, Kevin, for letting me be a tester. I enjoyed it and hope this information helps!

M261 Beta Test: I also was a selected beta test user. My results were exactly same as BWhalen. I shot about 200 rounds of Remington Gold. About 1/3 to 1/2 through the mag capacity it would jam. The mag did not like loading from a empty chamber with the bolt release. Nearly every time I had to drop one into the pipe, shoot and let the mag then feed. I had one round explode about 7/8th the way into the chamber. It did not seat correctly and the brass case blew out and looked like it was cut through by a hacksaw. I felt that one across my right hand. I believe the mods proposed by Kevin will solve the issues.

Waiting patiently for the new sample to play with.....

Originally Posted By jnorthway: Waiting patiently for the new sample to play with.....

Me too, although I plan to put another 100 rounds of the Fed Bulk ammo through my first-gen this weekend, since it seemed to work well with that.

Does that mean that some of us get the old mags that the testers were using ?

Ran three more full (first-gen) mags of the Federal Walmart Bulks through my 261 today. It didn't go as smoothly as last week.

I had a couple of misfeeds, usually in the first round or two of the magazine. My biggest problem of the day, however, was with duds. I had about 3 in each of the three mags. Duds in a 261 always get my attention because they are the first sign your chamber is dirty and the bolt isn't closing fully. However, I'm not at all sure that was the case here. I have been having a lot of problems with duds in this particular lot of Fed Walmart Bulks in several different guns that have been reliable with them for many years. Today I had one dud of them in a Smith K22 (very unusual) and last week I had 7 in 70 rounds in a Ciener Browning P.35--10 percent! So this is probably the ammo's major fault, although last week the M261 fired 100 of them out of the BDM mags with no duds at all. (From the very same box, too.) Odd.

I also fired 3 GI mags (30 rounds total) of Remington Golden Bullets. Except for one first-round misfeed (not uncommon if the insert gets tilted down a little sometimes), all of these fed and fired just fine with no duds.

Am really looking forward to the 2nd-Gen mag to test, because it is WAY handier being able to shoot 25 rounds at one loading than 10. I've always been happy with the 10-round mags but I didn't know what I was missing!

Originally Posted By blackdogmachine: Update for  the m261, mods to the tooling are done, mold is at the molders and I am going over tonight and getting more test parts. I am taking my gun and snail with me and if it looks like we got it will run several hundred parts. We added .05 to the length of the feed lips and raised the feed ramp .035.

How much longer of a wait till the full product is out?

Just got my 2nd Gen test sample, but probably won't be able to try it until Sunday--my club has a match Saturday and the range will be closed. Thanks Kevin!

Got my second sample mag yesterday as well. Thank you again Kevin. I hand-cycled about 40 rounds through several full magazines with hollow point Federal Bulk Pack, and CCI Mini mag. The Federal cycled perfectly, with only the slightest of scrapes on the bullet base from the mag to the barrel insert chamber ramp. The taller feed ramp seems to really do the trick compared to the first T&E mag design. I plan to shoot several hundred rounds through the second gen mag at the range Thursday or Friday night after work, time permitting.

This is not a tag.

Just got my new beta mag the other day.  Have not taken it to the range yet (will do so tomorrow), but hand cycled some rounds with it today.  This one looks like a keeper!  The first version wouldn't load any ammo - the round was presented too low and would fail to feed.  This version has corrected this problem - the feeding was flawless.  I'll give a range report later tomorrow after hitting the range.  

Range Report for Gen 2 Mag:

Kevin noted that this new mag design fed really well for him, but was ammo sensitive. I only had a hour after work, so I tried as many brands of ammo as I had. Here's the results:

Walmart Federal Bulk 550: 175 rounds fired. All fed flawlessly!
CCI Mini Mag: fired 50 rounds, 8 failures to go into battery fully
Remington Thunberbolts: Fired 50 rounds, 11 failures to go into battery

It looks like the wax coating on the Federal made a big difference in feeding. I also noticed copper jacket rounds fed better than lead nose. Kevin noted the bolt tang may leave an indentation in the top of the feed ramp, and in my case, that was true. He also noted his sample mag ran great despite this, and in my range session that also seems to be the case. A slight bevel on the leading edge of the shell tang would prevent this, but I decided to shoot it stock first to see the results.

When I was shooting the Federal is was truly awesome!! I even handed the setup to a few fellow shooters with confidence, and it fed perfectly for them as well. They all loved it, and had many questions about where to get 261 kits and the BDM mags.

Brian

(edited to add photo and some more details)

I just got back from the range as well.  Ran Federal value pack and Remington Golden bullet value packs.  The federal definitely ran better, but I was getting numerous fails to feed with both.  About 10% with Federal and 30% with Remington.  It appears that the cartridge is being presented at the correct height, but at too steep of an angle.  The failures I experienced all got the bullet into the chamber, but the case would get stuck a couple of mm from the chamber and obviously wouldn't go into battery.  I think that if the rear feed lips were raised slightly and the angle of the follower was a little flatter, it would work flawlessly.  To ensure it was the mag and not the conversion kit, I ran with the m261 inserts afterwards, and they ran flawlessly without a single fail to feed.  When you compare the 2 mags side by side and loaded, you can see that the bullet end of each are at the same height, but the case end of the m261 was slightly higher (very slightly).  Thus the m261 insert presents the cartridge at a flatter angle.  I think this is the difference that is causing the fail to feeds.  I hope this helps!

Woohoo, that's the same FTF that I got on the Remington and CCI Mini Mag. It would chamber the nose, but the case would get stuck on the lip of the chamber and stop. When i would eject the round, the bullet was clearly bent to the side inside the case at a slight angle. I also ran the stock inserts with 10 rounds of each and they fed flawlessly. I never noticed the feed lips on the BDM mag were slightly lower than the inserts. This might explain the angle the rounds were getting stuck in.

I think it's the back part of the cartridge entering the chamber too low - i.e. the cartridge is at too much of an angle with respect to the chamber, and although the nose chambers, the case gets stuck and bends.   Maybe if the nose of the bullet remained at the same height and the back end of the case is raised slightly so that the cartridge loads more flat all of our problems would go away.  BDM is so close that it hurts to say anything bad at all!  My Gen1 mag wouldn't feed anything consistently, but the Gen2 mag feeds most of the time.  I'm sure Kevin at BDM will make 1 final adjustment and it'll be perfect.  

One other thing - this mag is really high quality, as we've come to expect from BDM.  I applaud BDM for taking the lead on High Cap mags for the M261 kit, and although there have been some minor teething problems, they'll get it right. I have no doubts whatsoever about that!

Originally Posted By Woohoo: My Gen1 mag wouldn't feed anything consistently, but the Gen2 mag feeds most of the time.  I'm sure Kevin at BDM will make 1 final adjustment and it'll be perfect.   One other thing - this mag is really high quality, as we've come to expect from BDM.  I applaud BDM for taking the lead on High Cap mags for the M261 kit, and although there have been some minor teething problems, they'll get it right. I have no doubts whatsoever about that!

I'll echo those sentiments as well. Kevin's got a top-notch product here, and I'm very priviledged to be one of his testers. I love my 261 kit, but the 10 round inserts are just too damn annoying to load every 10 rounds. This mag will bring hi-cap goodness to all 261 owners, and that is truly a great thing.

Originally Posted By Woohoo: BDM is so close that it hurts to say anything bad at all!

I know how you feel, which is why I did not post the results of my Gen 2 shooting this morning, though I emailed them to Kevin and to both of you. My Gen 1 actually worked better.

I asked Kevin if he thought it would help if I raised the mag catch notch about .010", since I have to seat the mags in my gun with a firm tap to the bottom. I thought this might also help out with the too-high feeding, but I like Woohoo's idea that raising the back of the case/feed lips might reduce the angle and help. I don't think it would be too much trouble to do a little shaving of that area tonight with an XActo knife, and I can retest tomorrow morning. What do you think--should I give that a try first?

Snake - what would you shave off to raise the end of the case and make the cartridge a little more level? I would love to try that too if you can think of a way!

Looks like there's plenty of meat to shave a few thou from the insides of the rear of the lips, which should let the round sit a little more level in the back and feed straighter.

Let me do mine and see how it works (I can test tomorrow morning) before you mess with yours. If your 2nd Gen worked at all, it's doing better than mine. I've got pretty much nothing to lose by messing with it, as right now it won't feed more than the last 10 rounds of anything reliably, meaning it has no advantage over a stock unit. My 1st Gen will reliably feed 20 rounds of Fed Bulks, even though it won't work with Rem GBs (which is what I really want to use because they are more accurate in this rifle).

PS: Did you get my email?

Yep - pretty detailed!  Thanks!

Okay, I did mine. Unfortunately, as is so often the case in my life, I went too far. I took about .020 or so off the inside of each lip. Sadly, this doesn't leave enough meat to hold the round in place. The first round will stay, just barely, but put two rounds in and the spring pressure pops the second one right out. I should have thinned it only .010 or even less.

I've put some aluminum tape in there to build it back up, and now the rounds will hold, but this sure won't last, and I'm not even sure the rounds will feed at all now due to the increased friction. If it makes it though the first five rounds of a 15-round mag of Rem GBs, though, I guess it will prove that the general idea is on the right track.

If I do another one, it will be with a small file, not a knife, as it was too easy to go too far. Also, be advised that it helps a lot to disassemble the mag before doing this.

Hey, I noticed from you guys' pics that the front of your mags are quite dirty. Mine too! This seems to be MUCH dirtier than magazines from other guns, such as 10/22s. Is this a GOOD sign that the gas tube is still unclogged and blowing debris into the bolt area? I'm now at 700 rounds through my barrel since its last blow-out with .223 and I'm going for 1000 as a test. I'll probably do another 100 rounds tomorrow, putting me that much closer.

I'm not sure that will fix the problem - that will lower the front end of the cartridge, but as soon as the bolt starts pushing the cartridge in, the angle will return.  I think the answer is to find a way to raise the rear of the feed lips so that the height of the cartridge does not change in the mag with respect to the chamber, and the cartridge is pushed into the chamber at a more flat trajectory.  It probably still has to be at an angle, just not quite as steep. Do you have a 261 insert that you can load up and compare to one of the test mags?  That's when I saw the slight discrepency in the way the round sits.  See if you can load up each, and put the 261 mag behind the test mag and eyeball it.  It looks to me like the front height of the cartridges match, but the m261 mag's cartridge is just slightly higher in the back.  

Originally Posted By BWhalen: Woohoo, that's the same FTF that I got on the Remington and CCI Mini Mag. It would chamber the nose, but the case would get stuck on the lip of the chamber and stop. When i would eject the round, the bullet was clearly bent to the side inside the case at a slight angle. I also ran the stock inserts with 10 rounds of each and they fed flawlessly. I never noticed the feed lips on the BDM mag were slightly lower than the inserts. This might explain the angle the rounds were getting stuck in.

The same thing happened to me with CCI Mini Mags with second mag. I have more success with the Federal Bulk Pack and Remington Std. Velocity although not a 100%.

Ironically, I have less problem with the first protype compared to the second one. I am not as mechanically inclined as some of you guys, but my observations are 1) that the angle of the follower is too low in the rear section, 2) I have to tap the mag really hard to get it seated in the magwell. May have to raise the notch just a tad

Just got back from a test session, and I DEFINITELY think we are on to something with opening up the mag lips just a bit to raise the rear of the round and make it sit flatter.

I loaded my now-buggered-up mag with 15 rounds of Rem GBs three times. It worked much better than I thought it would. In fact, I didn't think it would work AT ALL because last night, it was very difficult to push the rounds forward with my fingers, the aluminum tape being much "grabbier" of the rim than the bare plastic.

The first 9-10 rounds of each of these mags had the same problem, the round would hang up about halfway into the chamber and the bolt had to be seated home by hand. BUT the rounds seemed to be making it further into the chamber this time before hanging up, and at a bit of a flatter angle. I THINK if I hadn't taken so much out, and then had to replace some of it with the aluminum tape, that it might have worked. The last five or six rounds in each mag fed, chambered, and fired normally. I was surprised that the aluminum tape held up to 45 feed cycles without peeling or tearing off. It went better than I expected.

I think I shall try heating the lips and bending them in, and then opening them up to the proper dimension, as Kevin suggested.

That done, I loaded my 1st Gen with 20 rounds of Fed Walmart Bulks, and the GI mag with ten rounds of Rem GBs, three times each. There were several duds in the 60 rounds of Fed Bulks, which is not surprising because this ammo has been giving me a lot of duds in ALL my guns lately (I think this was the last box I have of this particular shitty lot). I think there was only one slight feed hangup in these 60 rounds.

Likewise, I had one dud and one feed hangup in the 30 rounds of Rem GBs in the GI mag. Duds aren't unknown with this ammo, either; I get right around 1 dud per 100 rounds of this stuff in my Ciener 1911 but have had hardly any of them with the GI mags in my 261. I think I might at this point have a dirty gun or lube problem, as it now has been 800 rounds since its last good cleaning, though only about 250 since a quick chamber brush-out and quick lubing.

I'll take a dial caliper to several different types of .22 magazine later today and see if I can come up with a dimension we should be going for on this magazine.

Okay, I think I might have something.

The opening at the rear of my 261 GI mag mikes .182" The BDM mag mikes pretty close to this.

As we move forward, however, the 261 feed lips spread/siden a bit, and at the forward edge they're about .205. The BDM lips widen only a little, if any, to maybe .192.

This means that as the round moves forward in the GI mag, the rim is also moving UPWARD, whereas with the BDM mag, it's not, or not anywhere near as much. This means that the round is staying flatter in the GI mag, which is what we want, and it's going forward at more of an up angle in the BDM, which is what seems to be causing many of our problems.

Try tapering the feed lips to widen just a bit at the front. I wish I'd done this examination last night before I started cutting. I could have cut or filed mine this way and I'll bet it would work today.

Oh, BTW, I have seen NO indication that the little notch/groove that the unmodified 261 bolt cuts into the forward feed ramp is interfering with anything in any way. Looks to me like as long as you get the little "shaving" that this can make out of there, this isn't going to be an issue.

Excellent suggestions, Snake.   I think slightly widening the feed lips in the front and raising the rear of the cartridge slightly will fix the problem.  I'm going to try to widen the front feed lips slightly to see if that fixes it.  I won't be able to get to the range until this weekend at the earliest tho.   It's definitely the angle IMHO.  The bullet is entering the chamber at the correct height, but the cartridge is entering too steep and is getting stuck (at least that's what it looks like to me)

Observation: M261 Metal Mag Insert versus Beta 2 Mag.

The metal mag insert has the round sitting on top and following forward
the metal follower plate the round sits on top of. The follower plate
actually provides the lift the round needs to properly chamber.

The Beta 2 mag has the round sitting on top of the red plastic follower
and the lift is provided by hitting the clear raised portion of the mag
in front of the red follower.

Conclusion: it appears the metal mag insert metal follower plate the round
sits on top of actually keeps the round high and allowing the round to
chamber. On the Beta 2 the round gets no lift by sitting on top off the
red follower and does not begin to rise until it hits the clear raised portion
of the Beta 2 mag.

I agree the metal mag insert begins to widen out from the back to front of the mag.
The Beta 2 does not.

When the metal mag insert is properly installed into an AR mag, it has an
upward tilt at the bullet end of the cartridge. This seems to keep the nose
of the cartridge higher in the front as compared to the Beta 2.

Snake,

I took your suggestion and tapered the feed lips on my Gen2 T&E mag from the back end of .182 (my measured insert specs) to .211 (ditto). I used a small jewlers file to widen them. It looks like this makes the round hand-cycle at a slightly shallower angle into the chamber. I won't have a chance to test shoot this mod until this coming weekend, but this change seems to result in a better feed angle of the round.

BWhalen--Glad to hear it. I THOUGHT that might work. Wish I had another 2G to play with. I might try this on my 1G and see if it will then function Rem GBs--but frankly the 1G now works so well with Fed Bulks that I hate to mess with it.

About the follower--don't worry about that. The follower only has anything to do with the very last round in the mag. For all the other rounds, the "follower" is the round underneath. Look at the fully loaded mag and you'll see that the follower only touches the rounds at the front end--the follower back is hanging down and doesn't touch anything.

Ok - tried something a little different but it seems to work.  I widened the front of the feed lips and I shaved a few mils off the feed ramp.  This allows the cartridge to enter the chamber a little bit more flat.  I wasn't able to try it at the range, but I was able to hand cycle a mag without any getting jammed....  I won't be able to get to the range until next sunday, but maybe someone else with a Gen2 mag can try it on theirs.  Leave the back of the feed lips alone - just widen the front 1/3rd or so of the feed lips as was mentioned in the above post.  Then just grind down the feed ramp slightly....
I noticed that before I did this the case would either get jammed and dented just after the cartridge entered the chamber, and on some of the cartridges the bullet was getting damaged (on the top) - you could see some of the cladding getting shaved off by the top of hte chamber.  This leads me to believe that the cartridge is entering the chamber slightly too high at the beginning (that's why I shaved down the feed ramp) and then it is entering the chamber at too steep of an angle (that's why you widen the feed lips a little at the front)

Yesterday I blew my M261 apart for a thorough cleaning, after 900 rounds. Pretty nasty, but I guess y'all know that.

This morining I put four more 20-round 1G mags of Fed Bulk through it without incident, save two duds (the same bad ammo lot) and a couple minor hangups in the last mag. On the way home from the range I figgered out how to possibly salvage the 2G mag I buggered up and prolly get it working. If I'd have had the idea yesterday, I could have done it and tested it today--ain't it always the way!

I finished my 261 session today with a .223 blowout/cleanout, but that's the subject of a different thread.

I got my Olympic M261 back from the factory. The chamber insert was cracked and the blowback was not enough to cock my hammer on a Colt LE 6920. I was getting double tap slam fires. The unit was less than two months old. Olympic checked my bolt return spring for proper tension. The spring was OK and the only issue was lost blowback from a crack in the chamber insert. It was replaced at no charge. Olympic is also a Beta tester and they are carefully inspecting the testing the Beta mags.

I tried the Gen 2 mag again yesterday and it clearly does not load rounds correctly. They either jam half way in or will not fully chamber and the bolt does not close completely.

I went back to the M261 adaptor today and fired 400 rounds and the mag adaptor
insert works perfectly. I checked the M261 again and each round will fully drop into
the chamber completely and do not have to be pushed in.

It is odd when I go back to the Gen 2 adaptor, the round will not correctly chamber
or they chamber but do not go fully in. With respect to my weapon, it is not an issue of dirt or a bad M261 adaptor. I am watching for dirt in the field and clean in the field as needed. The M261 was just factory serviced and they tested it on two other rifles and one new one they had made up to test my M261 unit.

Originally Posted By Snake45: Look at the fully loaded mag and you'll see that the follower only touches the rounds at the front end--the follower back is hanging down and doesn't touch anything.

And herein, at least it's my pet theory, is the man reason the BDM mag doesn't feed reliably with all ammo brands. One of the unique and interesting features (or lack of) of the M261 for the AR15/M16 is the lack of an integrated barrel feed ramp. Look at ANY other rifle, pistol rim fire or center fire, and they all have a feed ramp machined as part of the breech face/barrel. So, with that unique design characteristic in mind, I don't think we should think of the 261 mag in typical terms of operation. It has to do more than a standard magazine that relies on a barrel feed ramp to chamber rounds. When you examine the M261 mag insert and hand-cycle rounds into the barrel adapter you see that, despite the lack of a feed ramp, it does a wonderful and reliable job of getting each round out of the feed lips, nose pointed up, into the chamber and up the bolt face into the extractor claw.

So, I've spent the better part of 3~4 hours over the past week inspecting and documenting the features and design specs of the stock mag insert. I've measured and recorded the width of the feed lips, the distance from the front edge of the feed lips, the shallow "feed ramp" depression width and distance from a seated round and the location, width and spring pressure distribution. With all this documented and analyzed as best I could, I came up with my theory that the front-bias location of the mag spring in the body and under the follower is not ideal for a M261.

To test my pet theory, I'm in the process of fitting a second additional spring to the mag body and follower behind the first with the goal of creating even pressure and lift on the follower from front to back. During my testing and eval of hand-cycling both T&E mags it was clear there was little or no lift of the round's nose until it directly hit the BDM mag's feed ramp. By then, the round was nearly 75% out of the feed lips and the resulting angle (in testing at the range) to be too sharp to chamber the round without gouging it on the chamber mouth. I believe the forward-only pressure on the ammo stack when the mag is loaded puts plenty of pressure on the bullet end of the stack, but in doing so, binds the stack against the front edge of the feed lips as the stack is pushed up. Most magazines are designed with a full-width spring that spreads the lift pressure over the whole width of the stack, from rim to nose. If you hand-cycle a stock M261 insert, you'll notice with nothing more than a very shallow cut out at the front edge of the insert, the round is levered up as it leaves the feed lips, and is "popped" up into the bolt face and extractor when it leaves the feed lips completely. My theory is this is due to the full-width spring pushing up on the round's rim edge as much as the bullet. I've noticed once the top round starts to move forward, it deflects off the shallow depression in the insert's mouth and angles up about 5~10 degrees. Once it moves out about 50% the length of the feed lips the #2 round in the stack starts to rise in the rear slightly. When this happens there is a lever effect on the top round, and it's nose rises dramatically. As this happens it's aimed right at the chamber mouth, with no interaction of a tall feed ramp. The final "popping up" effect on the top round occurs when it has cleared the feed lips and the round below it pushes directly up. The rim jumps up the bolt face and into the extractor claw, giving us that elusive shallow feed angle we all agree is necessary for proper feeding.

The other mod I'm performing is building up the front edge of the mag to duplicate the shallow feed depression as seen on the stock insert. I'm building up this area about .045" with some hardening epoxy and rounding it over slightly. From my measurements of a stock insert, there seems to be more space from the nose of a loaded round to the BDM 261 mag body's "feed ramp" than what's ideal. I believe the closer distance the depression is to the loaded round's nose like the stock insert, the more it should act like a fulcrum on the entire round as it is pushed forward by the bolt, and less like a ramp for the nose only. This I hope will reduce the amount of binding and the sharp angle of attack that my Gen 2 seemed to give.

At least that's what I've theorized from my limited research and testing. I should put a disclaimer in now that states:

"The ideas expressed above are those of a non-engineer with NO mag design or firearms gun smithing experience outside of fitting a 1911 mag well with a file and assembling two AR15s from parts. They may, and probably are complete bunk, and your mileage may vary."

When I get the spring mod and built up ramp complete, I'll test it at my local range and report back to Kevin with the results. I've been in contact with him about my idea, and he's been supportive in exploring any ideas that improve the design and add to it's reliability. If the results turn out to be positive and Kevin gives me the thumbs up, I'll post them here.

Brian

Originally Posted By BWhalen: One of the unique and interesting features (or lack of) of the M261 for the AR15/M16 is the lack of an integrated barrel feed ramp. Look at ANY other rifle, pistol rim fire or center fire, and they all have a feed ramp machined as part of the breech face/barrel. So, with that unique design characteristic in mind, I don't think we should think of the 261 mag in typical terms of operation. It has to do more than a standard magazine that relies on a barrel feed ramp to chamber rounds. Brian

I'm not sure I agree with that. I believe I have a number of .22s that don't have a feed ramp per se, they just have the bullet pointing in the general direction of the chamber and they rely on some (just about any) portion of the .22's round nose getting inside the chamber opening and then sort of camming/guiding the rest of the round in from there. One I can think of that doesn't have a feed ramp is the Stoeger Luger. I believe I also have at least three bolt action .22s with no feed ramp, just the bullet hanging out there in space more or less pointed in the general direction of the chamber.

My 1G mag is still feeding the Fed Bulks up almost flawlessly. I might try opening up the front of the lips just a bit to see if it will then feed the Rems I want to use, but it works so well with the Feds that I hate to mess with it. I did figure out a way to mod my ruined 2G so that it might work again--now I just have to come down with a "fit of industry" and DO it.

I agree with BWhalen assessment. The stock mag adaptor presents the rounds
to the chamber much better than the Beta 1 or 2. When looking at the stock
mag adaptor, you can see the difference in how the round is held slightly higher
upward. The rounds seem to chamber much better. With the stock adaptor, it does not matter what brand is used.

Might the follower problems of this mag possibly be releated in roughly the same way the 30 round 556x45 mags have the green follower*, which replaced the black follower (from the original 20 round mag)

* which Magpul created a orange follower to replace the green one.

saw a couple of things today that I never noticed before.  First of all, I think that widening the feed lips up towards the front works for both Gen1 and Gen2 mags (try to mimic the measurements of the M261 insert).  By doing this, I was able to load either mag with 5 rounds and it would work for all 5 rounds.  Any more than that and it would jam (the bullet would get chambered, but the case would get stuck on the edge of the chamber- just like we've been seeing  all along.)   HOWEVER, I did notice that the bullet immediately following a jammed cartridge would be shaved on top by the bolt.  You can see where the copper wash was completely shaved off by the bolt riding over it.  I think the cause of this is that the cartridge at the top of the magazine stack is held is very loose - Load an M261 insert and try to wiggle the bullet end of the top cartridge.  You'll note that there's only a little bit of play.  In the Gen1/Gen2 mags, there is a LOT of side to side play at the bullet end (2-3 times more play).  In addition, you can actually lift the bullet end straight up (perpendicular to the cases still in the mag below it) and remove it.  You can only remove a case from an M261 mag by sliding it towards the front, as is done by the bolt when chambering.  I think that the problem is that when the spent case is being ejected and the bolt is recoiling, it is lifting the bullet end of the next case and tilting it up.  Then it tries to feed it and jams,  which is giving us the impression that the case is entering at too steep of an angle when in actuality, the case just too loose in the feed lips.   I think if we can solve the side to side slop at the bullet end of the feed lips and also make it so that the bullet can only be removed by sliding it to the front, our problem will be solved.  Load an M261 insert and look at how little slop there is up at the bullet end, and note how you can not lift the front end up at all.  Solve this problem with the Gen1 or Gen2 mag, and I think it'll work!

Here is sample pic of a the FTF from gen2 that bwhalen had.

pic 1
pic 2

Olympic Arms, the manufacturer of the new M261 RFA (Rim Fire Adaptor), is also testing the Beta 1 and 2 mags. Alex, is their Beta tester. I would feel more comfortable if Olympic can test and ensure the Beta mags work. They have the engineering and gunsmithing staff and if the Beta has any chance of working, I
believe Olympic stands the best chance of making it happen.

Once they approve it, we can be assured of a product that works, since they intend
to offer it and provide warranty.

Cool