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Discussion Starter · #1 · (Edited)
Not affiliated just been looking for a long time. Preordered 2 myself at just under $100 shipped. They are not expected to ship until December.

They look very well done considering the limitations in place.

I’d order more but don’t want to go in too deep sans testing or without personal history with the company.

Here is the link:


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63 Posts
Discussion Starter · #4 ·
I like the MP7-like look. However, I worry about reliability . . . after all even factory mags aren't the greatest. Hopefully the OP will let us know how well they work out.

For sure! Just requested to change my order to the smooth mags... I think the option was just added / I totally missed it last time.

Also it looks like they are rolling their own springs to accommodate as well. I sent an email asking for some more deets and I'll share whatever comes back.

Honestly even if it just gives me 40 rounds vs the 25 I normally run I'll be happy. I do imagine the alignment / fit is critical and I'll probably have to finish the part some / use TPFE / keep them pretty clean....

The spring is welcome news for me since I'm down to 8 mags after a tragic misstep to go find a sprung spring. I'll now have 7 30's and 2 50's with an extra 30 spring if all works out.

I'm a tad optimistic about all the extra length added for 20 rounds and the new spring. It could allow for gentler pushing on the quad stack and allow for all 50 without denting rounds.

Here is a pic of the smooth mag and the spring:

Rectangle Font Material property Slope Handwriting

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Discussion Starter · #5 · (Edited)
Got a reply back from Will at S&T:

The extensions are printed out of Nylon 12 on a Fuse 1 SLS printer, which allows for high-quality prints with good durability. We re-designed the springs so they're not only longer, but they also load easier than the original Keltec 30 rounders. The bottom piece is held in place by an aluminum insert and locked in with a set screw and in theory you could attach as many as you want together to make a mega mag, but good luck getting the springs to work, hahaha! Hope that gave you a little more info, and if you want to know anything else, feel free to let me know.
Sounds promising, apparently they will also start to ship some of the preorders starting next week and hopefully I should have a review shortly after.

I was pretty sure the part was SLS printed, that and the material should keep parts tolerance nice 👍

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Discussion Starter · #6 · (Edited)
Air gun Trigger Machine gun Gun barrel Gun accessory

Behold the CMR-50!

Still have not shot, but already mixed feelings.

First one I put together I loaded 5 for the mags 'week' state and cycled 5 through the gun no issues and it locked open. Then I loaded to 50 and and cycled 5 with no issues. This was just done by charging by and and 'popping' the release of the charging handle, 1st round was loaded off bolt hold open each time. All 10 function test worked. The mag was easy to load... this is the best part, the mag loads like a charm, much easier than a stock mag. The 50th round had the smallest of dents from the Maglula loader, I actually rubbed it as I wasn't 100% sure it was a dent at first. The heft of the loaded mag feels considerable compared to stock mag, it is easy to insert and remove the mag with extension installed... it is rather satisfying actually. Even with the reduced profile MCARBO release.

There is a little play between extension and the mag under stress. As far as I can tell only 10 or so rounds actually go into the extension / perhaps not quite an inch. The rest is there to accommodate the new spring, which looks to make this work very well so far. Trying to get the follower to bind up going from the extension to the mag was not possible for me... just just worked.

If I could stop here I would be 100% stoked about these and ready for a live fire test, and to be clear I expect it to function... it feels great loading and feeding I’m even more optimistic about these working well... but now the bad.

While all is well for the first one I put together, I can't say the same for the first one I TRIED to put together. Unfortunately I dropped the extension from chest height on some hardwood while attempting to remove the retention shim. It dropped ~5ft and landed in the worst spot / corner you could hit and broke:

White Computer keyboard Light Black Input device

It would seem that perhaps a stronger, or even a more pliable material may help here? As chunky as the extension is it looks like addition support may be warranted here on the lip.

While I'm concerned about this some, I'm not sure how much I should be. The one that I didn't drop does appear to have considerable strength though I have not been pushing it either by not testing it to the degree I would like. Given my accidental drop test and only having one now haha I have just done what I consider a nominal test. I picked up the gun as photoed above while fully loaded by the extension and turn it around gently. So clearly the extension also has some considered strength and connects well with the mags.

I think it would be hard to cause the same damage with the extension on the mag as the angle of hit would be impossible... this is my only concern and it is unfortunate that it appears to be a significant one at the moment.

Right now my impression is that it is functional range toy material... just treat with a touch of care. Durability is a long term concern for me... but I'll let data play out there. If it wasn't for the drop breaking the lip, my impression is that I would be raving at the build quality.

This may have just been a bunch of crazy bad luck that no one reproduces, but I expect materials is a factor here.

I'll report back after some rage time later this week.

I’ve let the manufacturer know about my butterfinger experience and hopefully improvements may be made where a recommendation can be made caveat free for these… anyhow still more testing to do.

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Discussion Starter · #7 ·
First mag was flawless. All 50 rounds just as I expected. It was a very satisfying long shoot.

Then I started to load some old Armscore I had into the mag. After about 25-30ish rounds I thought I should probably do a better test as I have issues with this stock of Armscore due to it's wild OAL fluctuations... anyhow just wanting to clear them out real quick I dumped them as fast as I could per range rules 3 round 'burst' max before a pause, and my pauses are not long… Everything just fired. The amount of smoke rolling from the gun from the combo of dirty Armscore and about 30 rounds in short order while indoors was impressive. There is still a tear in my eye from the blowback ahaha. I've never seen the smoke like that from my CMR it was silly. I don’t think I’ll be shooting the Armscore suppressed much going forward 🤣

Anyhow long story short after this I started to get crazy failures and the rounds stopped feeding and where loose in the mag… I was so saddened having just been amazed by the performance, but when I got home to inspect it appeared to have been a freak incident. After dissembling the mags there was powder crammed into the track between the follower and the mag… it was crunchy and made the flower hard to move… not crazy hard but more than enough to know it was the root cause.

So I can't really blame the extension here.

While I expect that there is more sensitivity to a dirty mag with the extension I think this is not a super demonstration of what that normally looks like... I'll clean the mag out and try again this weekend... I'll keep the Armscore at home lol as this and some bad luck shooting suppressed was certainly my culprit.

Function wise these extensions may just mean you need to clean the mags more of often and I'm fine with that / expected that anyhow in the best case.

Any how more testing inbound.

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Discussion Starter · #8 · (Edited)
So the testing shall continue.

I have shot enough for some conclusions IMO though.

TLDR: These extensions can work with caveats. You can absolutely shoot 50 problem free rounds with these. That being said it hasn't been my experience that this is what you should expect reliably, downloading to 40 appears to help.

The main negatives from my analysis is too loose tolerances on the print believe to be rounds hanging up on the transition at the extension during feeding. This is allowing too much play, at first this didn't appear to be an issue, however I had a few instances of what I believe is the rim of round catching causing the rounds to stop feeding.

Tapping the mag would get it to feed, eventually the mag would start feeding correctly.

I'll do more testing though it looks like downloading the mag to 40 rounds may help... the idea here is that the rounds I believe all stay inside of the mag and prevents this issue. At least once I got down to about 40 rounds left on a mag two separate times the mag started to feed and the rest of the mag feed without issue. The last mag I loaded to 40 and shot w/o issue and then had to call it a day.

The second thing going against it is the weaker lowest pushing force of the spring... there has to be a technical term for this.. anyhow while this makes the mag work IMO... this also makes the mag more sensitive to dirt and debris. That being said I can't attribute failures I've had to the 'weaker' spring. I only expect to have to clean the mag earlier than an OEM mag; still regular maintenance with the CMR by my account.

As an aside on my reported first mag jam I thought I'd show what a mess ~120 rounds with the last ~30 rounds being that Armscore dump I had mentioned looks like. If you look at the image of the bolt below you will see two balls of carbon, powder, and oil that where scraped off the rails... if I had to guess I got unlucky and one of these balls got into the mag. I've shot this a lot, done plenty of mag dumps / heavy shooting having a giggle... this is by far the most carbon choked I've seen it lol even shooting 400+ suppressed rounds of CCI. I’m sure my suppressor is a hot mess.

Anyhow here are the pics for perspective:

Water Material property Font Bicycle part Engineering
Automotive tire Bumper Automotive exterior Automotive wheel system Engineering
Sleeve Embellishment Necklace Black hair Jewellery
Automotive tire Motor vehicle Tire Vehicle Automotive design

I will continue to play around and work on these, I'm determined to get a reliable box of ammo fed through this gun per mag now lol. I've a few things I want to try out still as I believe it is possible with a little TLC.

I will also note on the mag that broke, it appears to have been printed along a different axis allowing a short z-axis across the extension's lip... This could have been a factor in what otherwise appears to be a well constructed part as vertical layers typically don’t bond as well and represent the week axis on printed parts. I'm not even 100% sure I'm interpreting what I'm looking at correctly having not much experience with SLS printing to say the least lol. But believe this may have been a factor. Another difference is the post processing or mayhaps different printing parameters... I can only guess. I speculate that one of my mags was a prototype / early production example... this is based off the z-axis delta (this could be a print space fill / cost engineering factor though), look, texture, and the retention tab included... on the broken one, the retention tab was painted, shown some wear, and was too short, to the point you could 'loose' the tab in it's slot, and it was very difficult to remove as the paint appeared to bind with some loose Nylon powder and had to be 'broken' out... anyhow after I pushed too far I had to back out the retention nut and 'scrape' it out... it isn't even long enough that when placed to hold the mag the nut lands on the edge of the tab. While I’m not sure how much of this (other than the tab) is just print and process variations.

Regardless of what the actual reasons behind the differences between them, these deltas give me the impression of possible revisions and improvements between the two extensions.

I sent Will at S&T an inquiry just before the holidays and haven't heard back, I'll include some of these new details. I'll post back anything relevant.

I've included some photos below so you can see the differences in the mags.

Retention tab difference:

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extension difference - enlarge to see z-axis lines (ignoring drop damage):

Automotive tire Synthetic rubber Grey Tread Carbon
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Lastly the included springs appear to rust a bit easier than OEM. Mostly I mention this to recommend a light coat of oil before installation just as I do on the OEM springs, they are both going rust unprotected.

Below is new OEM, new S&T, after ~80 rounds inspected 4 days later:

Hood Azure Eyewear Font Art

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63 Posts
Discussion Starter · #10 ·
Thanks for the testing! I hope that they will be available for sale soon, I'd love to try a couple!
Last I checked they are for sale.

Update: I’ve been rather busy but got a bit of a breather. I sent Will at S&T a couple emails and thought I was being ghosted post purchase… long story short there is something wrong with my email assumedly as I received a brand new extension in new retail packaging… I still can’t share any further details from questions I asked as I’ve not seen any emails but post sales support is good as far as I can tell 😂

Experimenting more with the mags I have sourced the feeding issues to the follower and the extension transition / the extension space.

Here you will see what this failure can look like:

Finger Bullet Nail Thumb Gun accessory

This can also manifest itself in reduced pushing force that can cause failures. Meaning rounds feed but so slowly it causes a malfunction.

I believe this is caused by print variation. The parts do not mate tightly and there is play.

This may cause a misalignment adding friction or stopping feeding all together by catching on the follower. I wonder if an aftermarket follower could improve this or if OEM parts could be modified but those are thoughts for another day.

I’ve shimmed both of my mags now, both needed different areas that needed shimmed before I felt like the transition was as smooth as possible. I just tore some foil off a package and dropped it in… in the example pictured below the lockup is much tighter, if there wasn’t a little side to side play you would assume it was one part from feel.

Bumper Auto part Wood Audio equipment Electric blue

The other mag needed shimmed from the back of the mag.

After being able to reproduce the failure fairly regularly I wasn’t after shimming. Both mags I took the top 10 rounds of and reloaded 2x.

So far my rule of thumb is if the top round is loose after seating the mag with the bolt closed then the follower is in a state that will lead to a failure.

As an aside I cleaned the mags and rubbed everything down with graphite as an experiment over my typical TPFE treatment.

I’m reasonably optimistic that these mags will feed right, but time will tell and also will they continue to function without constant tweaking is another concern.

My only real findings currently is allowing for higher confidence when the mag will fail for sure and that the failures are follower related.
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