.224 build advice needed (in progress)

[rsterne]

Sort of.... That would give you the maximum possible FPE without "wasting" any air (but you are using that air very inefficiently).... HOWEVER, if you close the valve when the pellet is only halfway to the muzzle, you have used only half that much air.... but the velocity will only be about 2-3% less.... Obviously getting 95% of the energy on half the air is MUCH more efficient....

1.  If you keep the valve open until the reservoir is empty (long after Elvis departed), your efficiency approaches zero....
2.  If you close that valve the instant Elvis goes out the door, it will be around 0.3-0.5 FPE/CI.... but the same power as #1....
3.  If you close the valve when he is only halfway to the exit, the efficiency will be about 0.8-1.0 FPE/CI.... with about 98% of the velocity still there....
4.  If you close the valve when Elvis has only managed to get 1/4 of the way to the door, the efficiency will be about 1.2-1.3 FPE/CI.... but he will still be going 95% of the velocity of #1 when he gets to the exit (because the expanding air is still pushing him for the remaining 3/4 of the barrel length)….

This is the reason we don't tune our guns "flat out" and operate them on the plateau (although a few big bores are incorrectly tuned that way)…. Just closing the valve at about the halfway point can double your shot count with hardly any velocity loss.... That is a very good way to tune a gun that you are going to tether, but you still want a couple of shots off tether.... If you want a bell curve with a reasonable shot count, you will be closing the valve MUCH earlier.... and sacrificing maximum power for shot count and efficiency.... This occurs at about 95% of the plateau velocity (roughly 90% of peak FPE)…. Therefore, if you figure your gun is good for 100 FPE maximum, you will end up tuning it for about 90 FPE.... Otherwise you will get a shot string where the velocity falls with every shot, and the gun will be an air hog....

Bob

[darkcharisma]

Thanks for your input. I haven't thought that far ahead other than fpe focused. Efficiency at 95% of maximum fpe sounds excellent. I thinK I will plateau it out and then tune it back for efficiency. I have a 2900psi parts gun on The way.

[rsterne]

I think I will plateau it out and then tune it back for efficiency.

EXACTLY the way to proceed.... Unregulated you will have to tune it back far enough to get a shallow bell curve anyways.... If you want to shoot at over 100 yards, you will want a narrow ES, which means you won't have to tune it back very far.... Good Luck....

Bob

[darkcharisma]

I think I will plateau it out and then tune it back for efficiency.

EXACTLY the way to proceed.... Unregulated you will have to tune it back far enough to get a shallow bell curve anyways.... If you want to shoot at over 100 yards, you will want a narrow ES, which means you won't have to tune it back very far.... Good Luck....

Bob

Thank you. I actually have a 2900psi tube coming in and will want to regulate to get the narrow ES. I think I am fine regulating it  2800-2900psi with a burst of 3k. I think I may have a limit of extending the plenum to 50cc max. I need to see the actual tube from a parts gun to figure that out. Still limited in plenum but much better than 25cc for sure.

[rsterne]

What are you going to feed the tube from, with an output pressure of 2900 psi?.... The bottle on the Gauntlet is only 3000 psi.... Are you getting a 4500 psi bottle?.... If not, you will only get a couple of shots before dropping below the setpoint....

Bob

[darkcharisma]

I have a 4500 psi bottle I can tether from And is ordering a smaller 4500psi bottle. Will need to make a custom dropblock unless someone can point me to dropblock rated for 3000/4500psi?

[rsterne]

Ask Travis at JSAR, they may have something.... I know of no other source.... The fastening to the tube is the issue, if you are running a 4500 psi bottle, they need to have a full 3:1 or more safety margin at 3000 psi, as do the valve screws, because a regulator failure will instantly reduce that to 2:1....

Bob

[darkcharisma]

What do you think about four 10-32 low head alloys that fits flush with the head bearing the pressure at 1/4's end of the tube? Should I go 1/2? The same type of alloy screws that is supplied with conthran valve kit. The valve will also be secured with 3 of the 10-32 low heads.

[rsterne]

That should be fine, providing they are not too close to the end of the tube.... You want the distance from the C/L of the hole to be at least 1.5 hole diameters from the end of the tube.... ie the remaining web between the hole and the end must be at least as large as the hole.... The holes and screws must, of course, be accurately located, so that the load is shared equally....

Bob

[darkcharisma]

just got me 2 molds for .225 39grains and .172 26 grains during the 10 year anniversay sale from NOE.
.172 barrel coming from LW Germany (might as well). and my 2900psi tube got here not too long ago from a Storm Rider. just waiting on carbon bottle and a drop block

the only hick up is that the Cothran valve is puffing air every shot by the securing 10-32 screws and back at the valve pin. looks like i need to seal it with an oring groove and thread tape. hmmm...

[darkcharisma]

 so i have been playing with the how and why i should go with the gaunlet and working out the kinks with the cothran valve.

with the slightly longer than the stock tube shooting 33.95gr and my own custom 46 grains in .25 cal. these are the results

1300psi=855fps/34gr-55fpe
1300psi=756fps/46gr-58fpe

1700psi=880fps/34gr-58fpe
1700psi=788fps/46gr-63fpe

2000psi=924fps/34gr-64fpe
2000psi=835fps/46gr-71fpe
---------
modded gauntlet valve.

1300psi=800fps/34gr-48fpe
2000psi=909fps/34gr-62fpe
-------
.22 pellets

2800psi=1140fps/14.3gr
2800psi=980fps  /28.6gr=61fpe
2800psi=835fps  /42.9gr=67fpe

based on this i am going to go with the 2900psi tube cut to the QBs tube length.

the Cothran valve's long retaining screws has been shortened. the valve pin has a micro groove for oring later on, it has been wasting air and loosing pressure before hitting the pellet. also machined the valve retaining block on the gaunlet to fit the cothran valve and added a small push rod pin.

[Hobbyman2007]

Nice work . Out of curiosity do you know the mag length ? Looks like you’re well On your way .

[darkcharisma]

Nice work . Out of curiosity do you know the mag length ? Looks like you’re well On your way .

the max pellet the Gauntlet .25cal mag will take is .455. the 225 mold i ordered has slug length .410 and my custom pellet is .421.

the width of the .25 mag is .685

i updated the higher psi regulator testings...i am stoked. im going to swap the stock valve and compare. but that valve has bouncing problems, while the Cothran is minimal. i recorded the action with slow motion. i am not too worried about that right now.

[cosmic]

Wow , great work Duy !!!

[darkcharisma]

Wow , great work Duy !!!

thanks bother, looks like some parts are coming in. still lots of work to do to the breech and barrel before final assembly but things are moving along. really need to convert that 2900 psi tube before the carbon bottle arrives.

[mackeral5]

Wow , great work Duy !!!

thanks bother, looks like some parts are coming in. still lots of work to do to the breech and barrel before final assembly but things are moving along. really need to convert that 2900 psi tube before the carbon bottle arrives.

Nice build, nice work. 

Once you start getting into the higher FPE range the Gauntlet/QB repeaters have a weak link....  The breech flexes at the mag slot.  Something to think about.  I've thought of many ways to reinforce the breech, the easiest would be some type of solid scope mount that traverses the mag slot.  it would have to be notched  on the right side for the magazine to clear, if using mags. 

I look forward to seeing this one progress.

[rsterne]

If the receiver is flexing, somebody should manufacture a figure-eight barrel band to fit over the shroud and main tube, immediately in front of the receiver.... to clamp the front of it down....

Bob

[darkcharisma]

I assume it flexes during the shot cycle via the transfer port?

 if so, making a clamp and attaches the front of the breech to the main tube should work, so will Bobs suggestion. well, the barrel is kind of pointing up towards 12 oclock via the barrel band, i need to address it by clamping the receiver down...more work

[darkcharisma]

Bob, i am ready to sit and absorp some lessons about 1cc per fpe. is there a reason to why this is better against low cc vs high fpe?

[mackeral5]

Bob's suggestion would definitely help with the flex.  it occurs at the breech mounting screw, if you consider what is expected of that area, there isn't much metal to do the job....