Originally posted by u/shadowhunter55 at 2024-12-08T22:42:45Z
*DISCLAIMER: 07/02 FFL SOT *
Introducing the mostly printed P90BLK (P90 blackout) chambered in 300 blackout powered by an upside down BRN-180 firing mechanism. The barrel assembly bolt and guide rods were stripped from a gen 2 BRN-180 upper and flipped upside down to load rounds in from the top and eject out the left side. The trigger assembly is a standard AR fcg albeit rotated slightly to get the upside down bolt to work.
FN Herstal themselves sold licensing to an airsoft company to replicate the p90 in airsoft using the actual dimensions, I bought one to rip the cad from for the starting point of this project a couple months ago.
The integral suppressor system I had already developed for the original BRN-180 upper adapting it to the existing handguard. Basically there is a port hole in the side of the barrel that dumps pressure into a metal chamber behind the muzzle that then feeds that pressure into the can ahead of it. The metal chamber is made using a piece of the same fence post used for 37mm launchers and is retained inside the receiver.
The magazine was the trickiest part of this project by far getting the transition mechanism to cooperate properly and do what I wanted it to do. For those who don’t know the p90 magazine stores the rounds laterally down the body of the magazine and then rotates the bullet to point down the barrel as the round comes up to the feed lips. An absolutely genius design that I was able to replicate for the 300blk. It’s not perfect but it functions and today (thanks to A LOT of lube) it ran like a sewing machine.
I will be offering parts kits for the hardware needed once the files are dropped. It’s really not much a few bolts springs and pins but a few of the parts you have to buy 10 of when you only need one.
I will be posting the files to my odysee 1/1/25 as a late Christmas present to you all, suppressor files included.
Live fire video: https://imgur.com/a/CNvLBen
u/battlecryarms · 2024-12-09 06:14:27 UTC · score 1
Without having seen it, your issue could be the taper of the cases. 20rd AR mags are straight, but anything with greater capacity than that has to account for the curvature of the stack of cartridges. The 5.7x28 has a very straight case, allowing it to be stacked in 50rd stick mags, but it requires an exotic coating to enable reliable extraction as a result.
I find 20rd mags to be totally fine for my needs as a civilian, and would welcome a shortened design that’s mechanically simple and reliable over a larger capacity one that’s finicky. An added benefit of 20rd mags is that they feel much lighter to me than 30s when running 300 BLK. That might be even more noticeable in this format, where the added weight sits further forward.
I may be able to help come up with some ideas that could make loading easier. Shoot me a PM if you’d like me to try and contribute. Also happy to think through ideas to enable downward ejection.
u/shadowhunter55 · 2024-12-09 06:19:19 UTC · score 2
The taper of the cases is part of the problem yes. Friction seems to be the biggest limiting factor so far. That and the weight. Lots of lube is helping though it ran like a sewing machine today no mag issues at all
u/battlecryarms · 2024-12-09 07:19:09 UTC · score 1
But it ran well down-loaded to 20rd, right? I’m just saying I’d rather a reliable 20 than a tricky 20+
u/shadowhunter55 · 2024-12-09 07:19:45 UTC · score 2
Yes. Yeah same here