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Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 10:24 am
Author: hectmarr
Cool! :bounce: It is "the dream of the kid" as we say here, (the dream of all the children of the world).
Do you know how many cycles per second you have? Should they be no less than 15, so I listen, maybe a little less? :?
 

Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 10:48 am
Author: jackssmirkingrevenge
hectmarr wrote:Do you know how many cycles per second you have? Should they be no less than 15, so I listen, maybe a little less? :?


Going by the slow motion segment which is filmed at 1000 frames per second and played back at around 28 frames per second, the cyclic rate is closer to 60 per second!

I'm going to experiment with weaker springs to see how much I can reduce air usage while still having an auto cycle, then add ammunition detent and feed.

Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 11:07 am
Author: wyz2285
You're using 850 PSI right?
Since no ammo is used I'd say you don't have to worry about cocking anymore! Congratulations!
Just in case that I want to make one, the breech is pushing the hammer right? No air coming from the valve to directly recock the hammer?

Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 11:38 am
Author: jackssmirkingrevenge
wyz2285 wrote:You're using 850 PSI right?


Yup, 3000 psi bottle with 850 psi output.

Since no ammo is used I'd say you don't have to worry about cocking anymore! Congratulations!


About time indeed ;)

Just in case that I want to make one, the breech is pushing the hammer right? No air coming from the valve to directly recock the hammer?


If you look at the diagram there is no o-ring around the valve stem, meaning that air from the transfer port can leak into the hammer chamber. Indeed if I block off the top outlet, it will bounce the hammer a couple of times, but nowhere near the cycling we can see with the bolt installed.

Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 11:43 am
Author: wyz2285
The bolt however has o-ring right? Or built-in o-ring in the breech (probably better so the bolt can be smooth.)
If the hammer would bounce then the "leak" still helps, maybe help correct the tilt on the hammer at least?

Re: Caselman air machinegun

Unread postPosted: Thu Mar 14, 2019 11:51 am
Author: hectmarr
jackssmirkingrevenge wrote:
hectmarr wrote:Do you know how many cycles per second you have? Should they be no less than 15, so I listen, maybe a little less? :?


Going by the slow motion segment which is filmed at 1000 frames per second and played back at around 28 frames per second, the cyclic rate is closer to 60 per second!

I'm going to experiment with weaker springs to see how much I can reduce air usage while still having an auto cycle, then add ammunition detent and feed.

To decrease the cycles per seconds I have successfully tried to enter the "dose" of compressed air more slowly, just a little. I'm not sure if it can be applied to this automatic weapon, but a flow regulator could work. The other is to weight the hammer with weight, to give more inertia to the system, or to integrate something that increases the friction smoothly, and as you said, lower the force of the spring. You can combine two or three of these techniques, and everything should be slower, (for me, the faster I shoot the better!) But it's a matter of taste. It's just an idea. :)

Re: Caselman air machinegun

Unread postPosted: Fri Mar 15, 2019 9:25 am
Author: jackssmirkingrevenge
wyz2285 wrote:The bolt however has o-ring right? Or built-in o-ring in the breech (probably better so the bolt can be smooth.)


No, just a tight fit.

If the hammer would bounce then the "leak" still helps, maybe help correct the tilt on the hammer at least?


Marginally I suppose.

The other is to weight the hammer with weight, to give more inertia to the system, or to integrate something that increases the friction smoothly, and as you said, lower the force of the spring. You can combine two or three of these techniques, and everything should be slower, (for me, the faster I shoot the better!) But it's a matter of taste.


Heavier weight is probably the best approach with a hammer valve system, but it increases the valve dwell time, so a weaker spring is needed... quite a few variables to tweak.

In the meantime the damn poppet sealing issue has cropped up again, it's going to need another rethink as this is getting frustrating.

Re: Caselman air machinegun

Unread postPosted: Sun Mar 17, 2019 12:16 pm
Author: jackssmirkingrevenge
Some progress, finally ready for some ballistic testing:

Image

I added a copper tube as a makeshift gravity fed magazine, and a detent to stop the ammunition rolling out. On the drawing it's a pin but in practice this gave too much friction so I opted for a 1/8" steel ball instead.

Note also the weight added to the back of the hammer to bring down the cyclic rate and allow for a bit more momentum with a weaker spring.

I managed a few good bursts, here's one of them at 1000 frames per second:



Still a lot of misfeeds and jams though, unfortunately the irregular size of my chosen ammunition as well as the fact that it's made of soft lead is no help at all. I'm wondering if it's worth persisting with for #4 birdshot or if I'm better off converting it to 0.177" steel shot.

Re: Caselman air machinegun

Unread postPosted: Sun Mar 17, 2019 5:12 pm
Author: hectmarr
Cool. I have had similar problems with lead bb 5.5 mm. I had to modify the tube where the ammunition is housed to 5.7 mm and to 6 mm the hole where they enter the firing barrel. To where these cursed lead bb are going to circulate, it's a little bigger. My problem was solved in this way.
for this reason I am trying to use 3/16 "and 1/4" steel, which are almost perfect in their shape, recoverable and non-deformable.

Re: Caselman air machinegun

Unread postPosted: Thu Mar 21, 2019 9:53 am
Author: jackssmirkingrevenge
hectmarr wrote:for this reason I am trying to use 3/16 "and 1/4" steel, which are almost perfect in their shape, recoverable and non-deformable.


After a couple of days trying to make it work with the lead shot, I've decided to convert it to 0.177" for steel BBs, using a magnet as a detent. The bolt will now have a 50% greater surface area for the air to push on, hopefully this will allow me to lower the regulator pressure and increase the number of shots per fill.

Re: Caselman air machinegun

Unread postPosted: Thu Mar 21, 2019 10:38 am
Author: hectmarr
Everything will improve with these steel munitions, no doubt. I bought 800 bb of .22 of lead and now I have to introduce them in ... you know :shock:
 

Re: Caselman air machinegun

Unread postPosted: Fri Mar 22, 2019 8:09 am
Author: jackssmirkingrevenge
The switch to 0.177" with a magnet detent has worked out beautifully, and I've also been able to drop the regulator output pressure to 500 psi:



Image

There's room for a bit more tweaking but I'm going to shelve it for now and move on to something else.

Re: Caselman air machinegun

Unread postPosted: Fri Mar 22, 2019 8:24 am
Author: hectmarr
Tremendous work! The shooting speed is very good, it shoots really fast and I like that. :bounce: Congratulations for specifying it :)

Re: Caselman air machinegun

Unread postPosted: Fri Mar 22, 2019 8:46 am
Author: Anatine Duo
Superb!

I think your shelves must be interesting.

Have you chronographed a single-shot?

Re: Caselman air machinegun

Unread postPosted: Fri Mar 22, 2019 8:58 am
Author: jackssmirkingrevenge
Thanks guys. With the pressure appropriately dialed down it's shooting at around 490 feet per second with 5 grain steel BBs.