Question for the Mad Scientists here

[Privateer]

Thanks for the info and knowledge you Guys are sharing.
 

Again. I KNOW this thing will not be a big power Gun.
I only have it because I got a good buy and I really did want something not everyone has.
Just like the SMG .22? Lots of air is wasted and I consider that the price of having some different fun.
 

I have some .257 bullets ordered as I'd think those will be better given the design and shooting to 100 yards or so max.

There is very little, if any, info from anyone about possible tweeks or adjustments to this platform.
So there is that factor also. To learn and share what is learned.

[dyotat100]

I have 67, 69, 74 gr 257 bullets. I only shoot 85 and 92 gr now.

Let me know if you want some.

[Privateer]

Knifemaker is going to make some of his .257's for me.
 

One of the parts in the cart is made out of delrin.
I may change that out and do it with PEEK 1000 after reading another thread here at GTA.
Here you can see the part I'm talking about. That white part is the seal that is released to dump the air.


The whole tube assembly moves forwards with the firing pin strike lifting the white part from the seat.


And I do apologize for not being able to be super clear on explaining things.
I am new to PCP's in general.

And the danged Cookies I was promised never showed up!

[dyotat100]

Not sure I see how it works?  Does the air travel thu the stem?

If so I see why it doesn't work. Like a stock condor where the stem ID is to small to move enough air fast enough

[Privateer]

Yes. That stem has 4 holes to the left of the delrin part.
Once the firing pin strikes it lifts the delrin off it's seat and holds it open.
The air travels through the tube to behind the pellet/bullet in a total dump.
Here's a better pic.


The spring only holds the transfer shaft to the rear and the forward seal with enuff pressure to hold air until you get the pressure building. After that the pressure in the cart does the holding.
You do need the Teflon tape! It will leak if it's not applied when you put the delrin part on.
Ask me how I know.

[dyotat100]

What is the OD of the stem and the ID of it?

Peek won't change anything for the seal that I know of. I use peek for its strength and only using a .020" seal surface

The ports look small. Making them longer might help. To get more air into stem if it's not to small already

Shouldn't need the tape if that o ring was doing its job.

[Privateer]

Good observations. Same stuff I'm thinking in some ways.

I'll mic the stem and get better pics of it.

[Privateer]

Here's a few Pics.




That stem mics out at .245 OD .165 ID
.075 is the thickness of the cart itself.
Maybe 2.0 for total length inside the cart.
.785 OD on the cart itself.

You should also see the slag I found in this cart in the one pic.
Time to take them all down to check that issue.

(Figured you all are tired of the Mr. Bubbles jammies so I wore some Camo)

[dyotat100]

There is the problem. Just not enough flow. A condor stem is .217". The valve I sell is .260" and my 257 stem is .285"

Depending on what it's made of there is room open it up. At least to a letter F drill that is .257".  Then elongate the ports at least 1 1/2 what they are.

No wonder these things never made any power.

[Privateer]

I'm not really looking to make more power.
Though that would never be a bad thing.
 

I'm thinking I need to watch for a possible crushing of that tube if it's modded?
It has an outside air pressure inside the tube and whatever PSI is inside the cart.

And I can't find the post but I did read that they talked about a bigger cart in a limited edition Gun for more power.

Now say I made a larger transfer tube. That would reduce the inside volume of air.
Is that a viable trade?

[rsterne]

Certainly seems clear to me where the loss of power is....  .... It looks like the total port area is pitifully small for a Big Bore, which is what they intended it for....

You are correct, each part has to be looked at for MSWP, you can't just go drilling out things and end up with them collapsing, imploding, or rupturing.... 4500 psi is a LOT of pressure.... It seems to me like there is a lot of "stuff" inside the cartridge, robbing it of air volume.... That's not a bad thing for efficiency, in the smaller calibers.... I agree, no need to change to PEEK, once that white seal is knocked off the seat, the material will make no difference.... and the firing pin obviously has enough power to do that at 4500 psi....

I think it may be possible to make this into a decent .257 cal.... not a rip-snortin' stomper like Doug's Condors, but if we can get it to push a 70 gr. into the 900s that could be pretty useful.... I'm looking forward to getting my hands on the bits and pieces, for sure.... Take Doug up on his offer of .257 cal bullets from 67-74 gr.... they should be just what you need....

If the stem is 0.245" OD x 0.165" ID, that only leaves a 0.040" wall thickness, so I would NOT start drilling it out, because as you say, before firing there is 4500 psi around it and only atmospheric pressure inside it.... Inside volume is about 10cc, minus the guts.... should be OK for a .257.... How long is your barrel?....

Bob

[dyotat100]

Bob how would you figure the strength of the stem in the chamber? Says they are made of 303 stainless. I say 40,000 yeild but it's backwards on where the pressure comes from. Outside instead of inside

I used the wrong numbers in earlier post. I would open it up to .177" or .181" from .165". A #16 drill or #15.

Yeah I'm just thinking that you will be able to get  more air out quicker which will make for higher fps. You can also just run lower fill pressure to equal what you have.

[Privateer]

I did some cheap calculations and I'm getting just under 10cc of usable volume.
I suspect it's actually lower then that.

I can see increasing it a small amount with work on that delrin area.
But really can't see any reason to do so at this time.
In .357 it's fine for me out to about 60 yards.
I do believe the .257 will be the more accurate out to 100 - 150 yards.

[Privateer]

OK. Say I drill one of the tubes out a bit.
Would a blanket of chain saw proof pants be OK as a safety measure?
I'd think it would just collapse the tube but I do like my eyes.
And with that?
I need to take all the carts down. I just found something I'm a bit concerned about.

[rsterne]

Using the factory numbers you gave in .257, just increasing the through hole in the stem (if possible) to 3/16" (0.187") should give about another 50 fps with the 85 gr.... To get into the 900s with a 70 gr. will need a port of about 7/32" (0.219").... and who knows if you can get that big a passage through the fill fitting?.... As you go up in caliber beyond .257 cal, the numbers look much worse.... It might make a heck of a .224 cal bullet shooter, though....

Bob

[dyotat100]

Waiting to see what Bob thinks of the safety factor.

Could be made out of 17-4 or 1144 and that wold make it about 3 times stronger and able to go thinner.

I use 17-4 on my 338 stem and it's only .019" thick. Crush factor is all I have to deal with though.

[Privateer]

See that area in the transfer tube? that is the first one I've seen.
I'll check all 6 carts for that.
I know the one going to Bob does not have that.

[dyotat100]

Nice groove. So how thick is it at the groove?

[Privateer]

1st think I thought?
There's a shear point!
.235 is what that mics to.
That's .010 undersized from the tube itself.

[Privateer]

Now it's getting exciting!!
I'll need to get some more pics to show this all.
seems I have a mix of carts!!
 


If you look close? the holes in the rear are smaller on that new cart transfer tube.
You saw it first at GTA Guys!
LOL

Now if you go back to the pic about the groove?
We know why it's there.