The issue isn’t with M2’s BCM, it’s the fact that the pmags have swelled or flexed enough to have an effect on performance. I doubt the lower shrank
The issue isn’t with M2’s BCM, it’s the fact that the pmags have swelled or flexed enough to have an effect on performance. I doubt the lower shrank
So since the thread title is Recommended serious use AR mags? would we be remiss in suggesting pmags, if they flex or swell?Originally Posted by theJanitor
The issue isn’t with M2’s BCM, it’s the fact that the pmags have swelled or flexed enough to have an effect on performance. I doubt the lower shrank
Have there been any problems with USGI aluminum mags in this regard?
No. Nothing is perfect and AR mags are consumables.
Aluminum USGI mags can have issues with the feed lips spreading under similar conditions which effects reliably. This is why there is a gauge available via brownells (which has an NSN number) to check feed lip spread on Aluminum GI mags.
This can happen to PMAGS too but results in visible cracks before it causes issues.
I’d rather have mags that don’t drop free than mags puking rounds and causing malfunctions.
M3 Pmags were recommended over Gen 2s for a reason.
M3 Pmags are also now standard issue for the USMC and USAF so they are now also “GI” mags.
Same.
I don’t know how or why, but I am pretty sure that those 5 mags dropped free from that BCM plenty of times since I put them to use back in Oct or November. But I am starting to doubt myself.
Because.
I just tried about 10 other Gen M3s, some loaded, some never used and NONE of them dropped free either.
The magwell is tight front to back. I can see where they’re rubbing in the magwell.
Every last one of those mags is nowhere close to a tight fit in any of my other lowers.
I have one BCM lower AR. Gen M3 PMags will insert fine and drop free but I have heard numerous accounts from others about incompatibility between the two. I wouldn’t worry about it one way or the other but I also don’t prioritize reload speed to the point where I worry about the extra half a second to second needed to manually remove the old mag from the mag well if the mag doesn’t drop free. Like @HCM I value the added functional reliability and durability of the Gen M3 PMag enough that I’d be okay sacrificing the faster reload. My Gen M3 PMags also have no issues with the Colt lower AR I’m issued and a Wilson Combat lower AR I have.
My posts only represent my personal opinion and do not necessarily reflect the opinions or official policies of any employer, past or present. Obvious spelling errors are likely the result of an iPhone keyboard.
As pointed out, +/-0.060 is A LOT. How much cost would it add to stick an end mill in there and clean it up back to zero so you're not dependent on the as-forged condition? Wonder how many other lower manufacturers do that?
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Not another dime.
I believe I mentioned magazines are consumables in an earlier post - also that I'd rather pay $9-10 bucks versus $3-5 (minimum) more.
Right now, I just don't think the juice is worth the squeeze for MY particular needs.
My mags aren't carried as part of the same basic load out for days on end, either in a patrol unit, mil vehicle, or dismounted patrol.
My mags are used in rotation, by the numbers, reloaded with -2, and put back at the end of the order. I keep four to six beater mags loose for loading as needed with less rounds for range drills.
I rarely, almost never, drop a mag on a hard surface, and almost never step on a mag (admittedly more of a problem with aluminum mags than pmags).
So the plethora of aluminum mags I have suit my needs.
I haven't had to dump one of my numbered mags for puking rounds, but have had the experience of a beater mag puke rounds upon over vigorous insertion.
I figure don't seat the mag like you are trying to beat demons from the rifle, don't routinely drop on hard surfaces, and don't step on them too much, aluminum USGI's run right in MY wheelhouse, based on a semi-informed decision, which is what I would encourage.
Even though I choose to use USGI's, pmags are becoming a ubiquitous choice. It would make sense for BCM to open their magwell tolerances a bit to accomodate them.
It could be a matter of not that many problems compared to the cost of doing that, but that certainly isn't the way BCM advertises.
A matter of semantics, but because I'm an engineer, it's one that matters to me. "Opening tolerances" means increasing the allowed variation. What is needed is "tightening tolerances" to reduce the allowed variation. Maybe something like +0.060/-0.030 or +0.060/-0.005. Even the latter is basically a mile if they actually add a step to CNC the feature rather than leaving it as-forged.
It would be appropriate to say, "opening the minimum dimension."
I'm not going to write an essay, but I do wish more people on the internet understood and were precise about the differences between dimension, tolerance, and fit or clearance.
An observation I've made about BCM's production in the past is that they do a lot of fancy-looking QC inspecting of parts they don't actually manufacture. The QC manager where I used to work had a quote he liked to use that, "You can't inspect quality into a part." The point is that quality starts looong before anything is inspected.
Does anyone know if BCM actually machines their lowers? Or do they rely on another shop that's invested the many $100ks for good CNC equipment to do that work?
Based on my experience in manufacturing and business, if I knew that a tolerance on my part varied such that a noticeable fraction of my user base would have sub-par performance when using it with what is likely the most popular version of an accessory necessary for it to operate, I would take steps to tighten that tolerance to eliminate the problem, at least to the extent that doing so did not take it outside of whatever set of specs I needed to say it complied with. Going from +/-0.060 to +0.060/-0.030 or +0.060/-0.005 doesn't make it non-compliant with the mil spec, it just eliminates the chance of sub-par performance for a big slice of the user base. I can think of only two reasons to not do that. The first would be cost, which shouldn't prevent me from doing the right thing for a product that is marketed as a premium, ultra-functional product and sold at a premium price. The second would be if I couldn't make the change using the available control I had over the production process, which would be the case if I wasn't actually machining the stuff in-house, and instead relying on a vendor to do it and they were unwilling to add the steps at a cost that was reasonable.
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Not another dime.
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