After a week on the struggle bus, I think I’m going to throw in the towel on the Franken 9. I love the concept and there are some really clever design elements. The problem is that I just can’t see how to get standard printed Sten mags to work reliably. With a modified mag catch, I was able to get my build to accept a printed DMB Sten mag and feed dummy rounds. But it’s hard to get the mag to lock in (because it has to be held right up against the bottom of the slide) and it’s very easy to induce a failure just by bumping the mag.
The fundamental problem seems to be that printed Sten mags present the rounds about 0.8mm lower than Glock mags. That means the feed protrusion on the slide just barely catches the rim of cartridge in the magazine. It can work, but there’s no margin. Mag fit relative to the slide has to be absolutely perfect. It might work better with surplus magazines (I don’t have any to test). It also wouldn’t be too hard to remix the printed mags to be a little more compatible, but I’m just not eager to print off a set of “one build only” magazines.
Though I’d really dislike the aesthetics, I think a version of this using Glock mags would be a definite improvement in function/reliability.
My revised mag catch is up on Odysee if anyone wants to give it a try: https://odysee.com/@KopsisEngineering:a/Franken9-Revised-Magazine-Catch:e
yo, show me a pic of your front rail cavity, I think I know what’s going on
You got it …
Front rail pocket:
Front rail pocket w/ rail:
Slide on:
I should mention this is the pre-fix frame. I just printed a small part to fill the gap in the guide rod stop and glued it in place so I could finish function testing before I re-printed.
Thank you for this. I’ve got an un-tested file I’m working on - if you’re interested in trying it, I’d love your feedback. You can DM me on element about it.
Otherwise, I’m unhappy about the Franken-9 responses I’ve been hearing, and will be building one of my own today. Please don’t give up, just park it for a day or two while I address this.
Don’t worry, I’m actually pretty bad at giving up :) It tends to last about 2 days before I’ll think of something new to try.
I have a bunch of surplus sten mags I got working on my DB9. Need measurements or something?
dont think thats the main issue. the main issue as i read it, is the frame has some inherent design flaws. but im not op, so i dont want to speak for him…
but yeah to ops point… i pretty much just put the thing in its parts bin and may just recycle parts for another PDW until USK releases his own blessed version.
but for now, im printing the sporter2 xl parts… putting together a 20+ build
Thanks, but at this point I’ll wait and see if Unseen does a Glock mag version. I mentioned surplus mags just to be clear that the problems I’ve had may be entirely due to printed Sten mags and not an issue with the design itself.
I know another ’ almost sten mag mag’ option sucks but the UK sten mags have excess material on top. I was able to mod them to fit a Ruger slide which is narrower than a Glock and the round has to be presented higher in the Ruger than a Glock.
Terrible pic to show what I’m saying but you can see where the top is notched so the feed tower will fit in the slide and present the round at the right height
Of course I may be wrong on what the issue is
You’re close. It’s not an easy problem to describe. Here’s a photo that might explain it better (DMB Sten left, DMB Glock right):
This is with the DMB Sten mag, but the UK and DB9 are all very similar. I could probably mod the mag to make it work, but I think remixing with a Glock magwell would be a more robust solution.
Yeah, I just grabbed my thinned mag and it definitely won’t fit in the Glock slide enough, by quite a bit. Factory Sten mags must be quite a bit thinner than the printed version
