7 replies to this topic

[Z4]

Hello everyone. After fabricating a +bow and enjoying the process greatly, I decided to try my hand at designing and building a homemade. NOTE:****This is not my entirely my own design. I am using a SNAP style plunger/catch/trigger and plan to use an Ompa Clip. The cocking and round advancement are my own ideas.****

My main project aim was to create a pump action rifle that could achieve 80+' and would both prime and chamber a round in the same action.

The rifle is almost fully built. I have to add a clothespin trigger, a pump grip, and the breach/clip.

The plunger:


The charge rod is 1/2" CPVC. The plunger head and pressure chamber are as detailed in Carbon's SNAP-1 mk2. The stock is 3/4" PVC. The pump grip will be 2" PVC. There will be a long slot in the stock, through which a length of #8-32 threaded rod will slide, connected to two pieces of aluminum. The aluminum will be attached to the pump grip, and will prime the blaster with a backwards motion. The pump grip will be split into two pieces, when the back (priming) grip is pushed forward, the hand will then move onto the front grip, which is pushed forward, chambering a round. This grip is then pulled back to its original position. The gun is now ready to fire. The clip will be ten rounds. The gun should have a fairly high ROF, probably 1 round per second or so. I have all the materials to complete the design, I just wanted to go ahead and post this so I can get some help if I hit any snags.

I haven't read much in the homemades section but looked through the entire picture thread and viewed as many of the directory entries as I could, but if this has been done before, please tell me.

Any questions or comments?

*Much credit to Carbon for his excellent SNAP design.*

Edited by .Z4., 11 August 2008 - 06:08 PM.

[rork]

Are you planning to add a rubber washer assembly to that plunger? E-tape is great and all, but a seal it's not. Check out my compact plunger head in the SNAPbow thread; it's super-simple, and will streamline things quite a bit. I'm not sure about your breech system; a diagram would be helpful. Although, the whole 2-stage priming system sounds interesting, and I wish you the best of luck. ~Rork

PS: out of curiosity, what spring are you using? It looks an awful lot like a plusbow spring, in which case your assembly is likely to get really long, really fast...

[Z4]

I was originally using a plunger head identical to the SNAP ones, but the rubber washer was too big and interfered with the plunger travel. The E-tape is actually good, it's only one layer. The endcap fits in the chamber almost perfectly without it. I'll take a look at you design though, if it's smaller than this I might change it for the increase in power. I'll try to upload some MS Paint drawings of the priming/breach system later. Thanks!

And yes, that is a +bow spring. The full plunger travel is 7", and I've allowed 5" for the breach. It'll be pretty big (it's going to cover the whole length of the chamber), but it'll work.

EDIT: I really like your plunger design. With your permission, I will include it to the design.

Edited by .Z4., 11 August 2008 - 06:06 PM.

[rork]

If your goal is 80 feet, you can probably shave off some length by going to a somewhat shorter barrel; if you use my plunger head design, the plunger/tube system will be identical to that of my SNAPbow, which gets a solid, consistent 110-120 with a 12'' barrel. It would really depend on your darts. I'm not terribly familiar with Ompa's breech system (I've never tried building one), but from what I know, the seal is quite good, so you shouldn't lose too much range there. Also, the 2-stage priming sounds like a good way to simplify the design, but I highly doubt that you'll be able to prime a plusbow spring, switch hand positions, work a breech, and fire in a second. The ROF should be very good, but not quite that good. Good luck with your build. ~Rork

[Z4]

Here's the promised diagram.

The priming method I designed should not require a change in hand position. Due to the strength of the spring, I may need to add some PVC ridges to the main pump for a bit more stability.

Sorry about the bad quality/size of the image. Imageshack wouldn't upload the JPEG version so I had to convert it to a GIF. I'll reload it to make it bigger in a sec.

EDIT: In order to view all the text on the image, click it so it's a much bigger picture. I didn't want to post an image of that size for fear of angering someone.

Edited by .Z4., 11 August 2008 - 07:12 PM.

[Llama Boy]

This seems really cool. So if its the breech Im thinking of its brass that slides over more brass. Right? Right now Im working on a .50 CAL replica with a deodorant clip.

[rork]

By my measurements, using my plunger head, the trigger pin needs to be a minimum of 4'' from the point where the spring contacts the back of the blaster. Thus, you'll need to mount a handle on the back coupler (or add some linkage). This could simplify your stock design considerably. Also, according to your diagram, the slots are cut into the 3/4" T fitting; I doubt that the fittings will retain the stock if they are cut up. I daresay the slots need to be moved to the rear so that the slots are cut in the stock only.

[Z4]

Llama Boy: Yes, it's going to be a 17/32" inside 9/16".

Rork: I was planning on using an extended one. I'll enclose the workings in some 1/2 or 3/4" PVC, and fabricate the 2"PVC pump grip with a slot in it and a piece of 1" or something cemented to it to retain stability. About the tee fitting, that's a good point. I hadn't really thought of that, but I'll use some cement and if it doesn't hold, another tee is about 20 cents and I can change the design. I'll try the way I have it first and if it doesn't work I'll fiddle with it some more. By the way, thanks for all the input, I really appreciate it.

EDIT: Unfortunately, RealLife is throwing a bunch of things my way, so I'm going to have to postpone changes and updates until I get back on track. I expect to start working on this again in a month or two.

Edited by .Z4., 26 August 2008 - 06:36 PM.