Airsoft PTRD
First Draft: January 18, 2025
First Revision, Start of CAD: February 5, 2025
Something awesome about Gun Gamers Productions is that they allow some damn cool stuff on their fields. They have dedicated rules for Heavy Machine Guns, something that I've never seen from other promoters. They've shown an openness to custom projects beyond what most would probably consider. People bring out tekkies, hundreds of taginns, and everything from replicas of WW1 rifles to the hottest, newest stuff. LARP units are everything from "park rangers with hunting rifles and handguns" to the usual special forces getups. The sheer amount of freedom to push the fun, LARP-y side of airsoft in their games has led to my usual playgroup asking some funny quesitons like:
"Hey CDP, does GGP have rules for anti-material rifles? Hypothetically, would I be able to commission an airsoft Anzio 20mm?"
"Do you think staff would approve something modeled around dummy 14.5x114?"
"If we had a tekkie, I wonder if we could drag a Pak 41 that shoots Taginns?"
Years ago, I started on a PTRS-41 project. It didn't get too far off the ground but I told myself some day I'd revisit it in a simpler form, a single-shot like the PTRD-41, and then start developing back up from there. With lots of good inspiration and other big guns out there these days, why not get to it?
Specs and Requirements
The GGP rules state the following rules for a marksman rifle: The maximum muzzle velocity is 2.8 Joules, 250 0.4g BBs will be issued at startex for ammo, and it must replicate a real-world military marksman rifle or have a manual action with rifle stock and 16+ inch barrel/a semi-auto action with stock, magnified optic, bipod, and 18+ inch barrel.
A PTRD-41 has a manual action, a (mildly uncomfortable) beefy stock, a 1350mm long barrel, and irons or a PU scope. I have an idea of a power source that should get around ~2-2.5J of output at the muzzle. So far, so good.
Step 1 - Shells
Disclaimer: I entirely understand that making an oversized VSR is the smarter idea. I will probably eventually create a VSR-based version, something that's decently accurate out to range, but for now I want to run shells. I don't think an oversized VSR sounds very fun, I've used shell-ejecting guns for some time now, and I've been considering entering the APS shotgun market for some time now. Plus, this gives me some freedom to run something like say .50 FSRs, 8mm BBs, "shotshells", or whatever other rounds I come up with through the gun via barrel swap.
Everything needs a power source and I'm a sucker for inefficient methods. I've been an APS CAM870 user for some time now. Their shells have proven quite sweet, they don't explode like their pistol magazines and they're always available at a cheaper price than their fairly untested-in-the-grand-scheme-of-things M50 system. Wouldn't it be neat to just embed CAM870 shell bases into large hulls shaped like 14.5x114 casings that held a single BB (or a single .50 First Strike as a form of "anti-tank" munitions)?
14.5x114mm brass is quite big. There's a 26.95mm x 2.5mm head, it cuts down to a 23mm x 4mm extractor groove, the brass tapers at a 45-degree angle over 2mm back up to a 26.95mm diameter, it slowly tapers down to 25.5mm across 79.87mm of wall, there's an 11mm neck bringing the radius down to 16.5mm, and that neck goes on for 14.63mm for an overall length of 114mm. APS shells are a fair bit smaller, a 21mm x 1.5mm rim which goes right down to a 19mm diameter for the whole length of the hull and base. With that said, I think it's more than feasable to squeeze one of those bases into the back end of a dummy 14.5x114 "casing" having the "primer" (gas release trigger) line up with the firing pin of a PTRD-41. Said shell base wouldn't even take up the whole 88.37mm from the head to the start of the shoulder, a big hollow "expansion chamber" could be left for the gas to dump into before necking down into a small channel...
With the gas reservoir "figured out", the other thing that needs done is said small channel to hold at least one BB. I think this is going to be simple enough as tons of others have made 3D printable shells for airsoft revolvers or I could go the gas grenade method of having a tube with some o-rings that hold BBs in place. Wouldn't that be funny, a PTRD shotshell? CQB AT Rifle. I'll have to keep that one for the future.
Progress (Latest Update: February 12th, 2025)
A four-pack of APS SMART shells are arriving by February 15th for me to experiment on. I'm starting CAD today, modelling a solid 14.5mm "casing" which I'll take cuts from to create the chamber for the SMART base to sit in and tube for the BB.
February 6: V0.1 of the shell, the "solid casing", came out without a hitch. I copied a drawing of the shell into CAD, revolved it, and this was the result:
February 7: V0.2 of the shell, the "solid casing" with a few additions (a 21mm x 1.5mm cut in the head, a 6.5mm through-cut, and a 1.5mm x 5mm ring at the top of the neck for a new idea) has been printed.
The "new idea" mentioned goes as-follows: In issued ammo games, with BBs needing to be loaded directly into the cartridge, this means that a person could only reasonably carry something like fifty shots. We're issued 250 BBs at the beginning of the game, if the user goes down with 200 loose BBs then that gives the enemy a really good opportunity to screw the gunner over until resupply. Why not do what APS shotgun users do, making cheap/small removable bits that you can pre-load ammo into instead of it sitting in speedloaders? A simple projectile was modeled with a 6.1mm through-hole and a 1.4mm x 4mm ring on the bottom, it looks something like this:
At the moment there are some "issues" with the tip design, notably the fact that they don't sit in very securely (I'm thinking a little more upsizing and using 95A TPU might help that) and that the BB could flop out the back end into the shell body. That said, I like it! We'll see how well it works.
"V0.3" will be completed when the APS bases come in - I'm going to make enough of a cut that you can friction-fit them in place. If it works, great! It'll be onto threading after that.
February 9 - Jumping Ahead: As I'm still waiting on those APS bases to finish the shells, I figured why not start working on a bolt design? I found some pictures of a real PTRD bolt and decided to (poorly) mimic some of the features I saw in it, here's the resulting "bolt head" I came up with:
I'm honestly surprised that the extractor is working as well as it's proven for being a janky plastic piece with some magnet wire as a cross-pin. If I clip the casing onto it and then shove it into a tube, the round consistently pulls out and falls downwards as it should. I can see some possible issues coming up in relation to the round not actually indexing onto the extractor, I'll need to figure out how to make that happen more consistently (headspacing so that there's always room for that 4mm rim to get clicked over, I imagine) but that's for later.
February 12: I fit an APS base inside the shell! My first guess was a little too tight, my second works great. Because of that, say hello to the silliest thing I could make with a functional shell:
It functions great, the APS base takes ~1.78g of liquid propane which propels the whole plastic tip assembly at about 105ft/s (It's a 2.82g piece of plastic which gives us 1.44J of kinetic energy, not too shabby.) - this is amazing because it means things will work out, this is scary because 1.44J on a 2.82g projectile means a 0.40g projectile may be over joule limits...
As previously mentioned, this whizzbanger existing and working now means the shell portion of the build is complete! I guess that means I'm on to Step 2, the action (Bolt, Breech, Chamber) of the rifle.
