1325XLT Valve out for delivery/ update testing

[K.O.]

I usually get my mail around 4pm or so...

I still need to notch it to let it sit back in the tube and will take the time to do it slow and get it just right.

so in the next couple days I will know what my effort brought me.

I could not help taking another look at expectations from another angle. (yep one more time)

After trimming the poppets I should end up with a valve volume of about .1-.13

so I will start with .1 @ 10 pumps, 

I get theoretical  1252 psi @ a conservative 60% efficiency

which gives an average psi with an 18.75" barrel of 688

If you look at the chart for .25 in this thread that gives about 29 fpe  with a .203 port (an oblong .187 is what I did It is .220 through the valve and transfer port)

http://www.airgunhome.com/agforum/viewtopic.php?p=78260

BUT  that is at 100%

so if you look at Wyomans chart for a .22 valve and barrel you will see that a 24" .22 barrel wants a .29 or so valve well so does a 18" .25 barrel

I did not do the math but based on a slightly flatter curve for the .25 efficiency  I think the .1 valve will give .85 as an efficiency factor(E.F.) which gives

24.6 fpe at ten pumps  H&N FTT 20.1 grain at 745 fps

I think that is actually what the pump should easily achieve  1250 psi is not that hard and I used a low efficiency for the pump...


Now here is the thing I think the pump can handle up to about 1800 psi...

with the .1 valve that is 1879 @ 15 pumps using a .65 E.F.

go thru the whole rigmarole again and I end up with  34fpe and 875 fps with the 20.1 pellets

there is probably a whole wormhole in my logic but I can not find it...

In the real world though if I get 625-650 I will feel like I did ok.

BUT

big hopes do have a bit of a reason behind them...

?

[K.O.]

well the bad news first

456-463 fps average over 15' @ ten pumps is what I got this morning when I tested.



So what is the good news,

well my project has problems.

I can hear you saying how the heck is that good news?

They are easily fixable and should provide some very substantial gains


The first problem,

I broke the beautiful .220 I.D. transfer port that Big Bore Bart made for me and my substitute only is .180 I.D.

If you go back to the  FPE vs. Caliber and Port Sizes thread you will see that alone might  cost me about 5 fpe/90-100 fps.


The second problem,

I need to pick up an oversize bolt oring I get a puff of air past the bolt not real strong but there, at the least it is costing me 20 fps and maybe

30-50 fps.


The third problem

I  used the 2100 exhaust poppet and I think it is blocking flow some I should have used a 13xx poppet it has a longer shaft and will open more fully.

this one at ten pumps could be costing me some fps but honestly it is hard to tell...

three out of ten times I got just a burp of retained air at ten pumps and at 11pumps, 3 out of 3 shots a more substantial burp.

so no testing beyond 10 pumps until I get a 13xx poppet but I am pretty sure it will dump 15 pumps when I do.



One other thing I can do that I have not is to put a pin in the intake poppet as a guide and to take up a bit of headspace passage is .25 long

that should buy me a few more fps,  because of the light valve spring(cock before pumping) pump effort  feels effortless so the smaller

passage will not be a pain...

that is the state of things right now.

I looks pretty good for hitting 600 fps at ten pumps and I just may get a lot more at 15