my 100 FPE Co2 rifle prototype ( shotgun )

[Rob M]

Dump valves up to 50% of bore volume are not unusual, although smaller ones are much more efficient.... Once you need more power than you can get with a dump valve of reasonable volume, you are better off to use a strike-open valve (and a much larger plenum) that closes before the bullet gets to the muzzle.... After all, any gas exiting the valve/chamber after that is completely wasted....

Bob

one way to circumvent that on the dump valve model is to oversize, and then create exact displacement inserts.. In other words, I could make it 80cc , shoot .. then pull the drop block and add a 20cc spacer near the block that wont affect the valve.. Shoot again.. chart the losses.. add another 10 cc spacer , chart the losses.. and now find the happy medium where the cliff is , the cliff where there is no gain , just a lot of wasted gas.

[Rob M]

circumvent is the wrong word, I mean offset 

[rsterne]

You will always get "some" gain with a larger dump chamber, because the decrease in pressure during the shot is slower, so you have more pressure accelerating the bullet as it travels down the bore.... However, you have to weigh those gains against the volume of gas used.... Here is a typical chart of what happens as you enlarge the chamber, relative to barrel length....



I didn't chart out CO2 when I did that, but you get the idea....

Bob

[Rob M]

makes perfect sense, thanks for the graph.. My efficiency will suffer as I chase more power, I might even be in a good range right now.. I think ill go to 60cc and get back on the chrony tomorrow.. this all depends on academy filling my 24 ounce tank later tonight which is hit or miss ...  That being said , I never anticipated any efficiency to begin with 


id also considered a convetional valve for the task .. But , it would require a lot of work.. I don't think I could start with any readily available valve, and the porting would need to be very large.. id have lower poppet resistance, seeing as how im working with co2 , but the duration might have been an issue I didn't want to come across.

[Rob M]

volume has been increased to 57 ish ccs.. NOW , I did anticiptate volume changes and the drop block is threaded on the tube side.. so I simply make another insert after opening the bore of the tube , thread that insert on with a compressed oring at the back and generally im good for the next power level.. The issue here is the block retention.,. As you increase that face size ( of the inserted block ) you also increase the force pushing the block out of the tube.. my previous number was 350 lbs outward, now im well over 500 ( 540 to be exact ).;. Ive now added 3 screws , 8-32 radially as retention , but with the thinner tube wall , im a bit nervous to fill the gun this time.gotta get quality 8-32 screws

20180525_154822 by murphyrobert9, on Flickr

so we will see , if the block sheers the 3 screws through the tube wall and lands 100 feet away , ill report it.. the good news is , im aware of the situation at hand.

[rsterne]

I don't understand the problem.... Are you increasing the ID of the reservoir?.... If you are only making it longer (more volume) the force stays the same....

or did you have to make a new block, with a larger diameter stub, because the tube ID is bigger?....

Bob

[Rob M]

Increased the bore. The latter. I was clarifying for people so they know its not a simple matter.the block was designed that the inserted portion of the drop block was threaded 1/2-28.. this way , I could simple swap oringed adapters as needed when I increased the bore volume of the tube.. the tube was oringinally .250 wall , so I knew there would come a time where id need or want more volume and the easiest way was to bore it from the front.now were at .875 by 1.00 od.. SO im at the limit unless I go deeper torward the piston cavity for another 10 ccs max. I guess I would have skipped mentioning it if we didn't have a recent tank block failure on the forum.. anyway ,it held fine , but im getting some grade 8 8-32 over the weekend just to be safe.

[Gippeto]

Started drafting something up and realized I already had something that shows the idea of stepped areas.



Al

[Rob M]

the small step exhausts the chamber this retracting the larger cylinder, very nice.in this diagram , id still need to reset the front piston manually I assume.. Im thinking of how to translate that to a machined part. I made a drawing of gen 2.0 \


IMG_52491 by murphyrobert9, on Flickr

still appears to be a cannon, but the 2 inch main tube could house a lot more volume , and any kind of valve.

[Gippeto]

Spool is reset by filling from the rear (port opposite the poppet vent is the fill). Poppet spring (not shown) may provide some assist as well.

Get the fill/vent orifice sizes right and you can supply it from a constant pressure source...will reset itself, and all that needs being done is cocking the striker for the poppet valve. Reducing dwell on poppet will have an effect on how far down the reservoir pressure gets too...can be self regulating to a degree.

still appears to be a cannon

....This is a problem how?

Al

[Rob M]

I see now , the tiny fill area, makes perfect sense.. there is a pressure bias at the rear, keeping things sealed till the small poppet dumps the equalizing pressure. the valve would need to be made as 2 pieces , sealed in a common housing I suspect. The rear portion would be somewhat similar to a conventional production valve with 2 bleed areas. /.

still appears to be a cannon

....This is a problem how?


LOL , good point , who cares !

[WyoMan]

Wow!... that's some pretty creative and innovative work, Rob. I don't understand everything you did, but it was a very good and informative read about what can be done with co2. It looks like you have really developed your machining skills!

Wyo

[Rob M]

Wow!... that's some pretty creative and innovative work, Rob. I don't understand everything you did, but it was a very good and informative read about what can be done with co2. It looks like you have really developed your machining skills!

Wyo

thanks WYO.. The concept is pretty simple , just a piston being pushed out of the way by co2 pressure in a large chamber.. So very very little " lock time" as they say.. the next version will be more user friendly , better looking , and likely use a different valve system.. I now know the potential is there, im just gathering materials to get started.I actually want the next one to be a 600 fps version , or 142 fpe.. I think I can get there, its gonna be a lot of time making chips (-'

I know you are also at the forefront of co2 power, and it pains me to see people regard co2 as only " a plinking gas " since it has a lot more potential when applied correctly.. Sadly , no valves really cater to co2 power, with the cothran and art/sikes valves being the rare exceptions.

[WyoMan]

That sounds awesome!... looking forward to it. And I do agree with your premise about co2. There are a lot of "toy" guns that are powered by co2... maybe that's the reason. And there really isn't anything out there (drop-in) to get you into the 100+ fpe range (that I'm aware of). You've shown it can be done. Co2 does has a nagging velocity limit... hard to get north of 700 fps. But you can make the energy with more projectile mass... with the porting / gas consumption.

Cool stuff 

Wyo

[Rob M]

funny you say that;.. aside from this project , was considering making a max velocity co2 rifle in 177..
had one tuned to shoot 801 fps , not sure how much would be possible with 2 merged 18 inch crosman barrels. Start at 36 inch barrel , max the valve and see where I end up.. Might do that in the future , for now , I have 100 bux in aluminum and steel on order for co2 cannon V2.0