.25 Caliber - what base model?

[NorthStaR]

Spent another day tinkering with the valve for the 14" .25cal. I have taken this thing apart SO many times!
That's the thing with valves, everything has to come off to get to it! Tally-ho! 

I cut the valve stem for the Pro-Top. I'm still using the lighter hammer spring with guide which adds a 3mm preload.

With no mods (except hammer spring and dot ring spacer installed that came with the Pro-Top) on the Pro-top setup
it was hitting 11.5'ish FPE on a 19GRN Rhino and 15.5'ishFPE with 28.4GRN WALTHER Hunter Energy pellets.

Still way to high unfortunately! Another teardown! 

The Pro-top took a different approach which was easier as the piercing stem is out the way.
I tried pre-loading the valve spring with a few metal washers which didn't do a great deal.

I finally ended up good though. I cut a 10mm length of silicone tubing to reduce the flow port in the Pro-Top that
ports the Co2 from the 12g cart into the valve. About 3/4 narrower.




I also had the dot ring spacer installed that came with the Pro-Top. On top of that I put a metric M3 locking nut.
The round head of the nut seats the valve spring nicely. This pretty much fills up the Pro-tops internal part and
preloads the valve spring.




The combination of all 3, the lighter hammer, reduced flow port and preloaded valve sping has given me what
I deem to be about right. Maybe a bit of fine tuning still.  It has to my eye has helped regulate/stabilized the shot fluctuations
seen from my previous attempts at reducing it's power levels. 

I'd guess the valve is about half to two thirds the volume it was. 



Silicone tube insert, dot ring and M3 locking nut preload on valve spring, lighter hammer spring, poly transfer port.
19 GRN Rhinos Pellets. Brand new 12g cart.

count,velocity (FPS),power (FPE)

count,velocity,power
01, 520,11.41
02, 495,10.33
03, 486,9.97
04, 505,10.76
05, 514,11.16
06, 509,10.93
07, 520,11.43
08, 510,10.96
09, 493,10.27
10, 524,11.60






WALTHER Hunter Energy (DumDums) 28.4GRN

count,velocity (FPS),power (FPE)
count,velocity,power
01, 404,10.30
02, 431,11.71
03, 473,14.09
04, 436,12.01
05, 411,10.64
06, 418,11.00
07, 433,11.84
08, 440,12.23
09, 399,10.04
10, 392,9.70






Cool. There's only about 1/2 FPE difference ( ) from 19 GRN to 28.4GRN with this mod. I am quite surprised!   

I will replace the silicone tubing with a more long term material like a brass tube or something similar.
Otherwise I'm pretty happy with it. Again it's winter and not quite as warm so the levels will rise in summer
which I will have to account for and retest to see if the ambient temp effects the numbers much.

There seems a lot more choice in pellets for this caliber versus .20 as another of the less popular calibers.

.25cal is my new favorite caliber and it's a pack-a-punch machine. 




DISCLAIMER: AS SAID THE OVER POWERED CARBINE WAS DISMANTLED TO LOOSE SPARE PARTS
DUE TO LEVELS REACHED. ONLY UK LEGAL LEVELS ARE MY AIM - NOTHING MORE. ABSOLUTE.
CHRONY TESTS ARE REQUIRED TO REACH THE CORRECT LEVEL. THIS IS A BASE LINE TO WORK FROM. 

[mr007s]

You sure are tempting me to whack off 12 inches of my old cull .25 LW barrel and place it on one of my 22xx shooters.

[NorthStaR]

You sure are tempting me to whack off 12 inches of my old cull .25 LW barrel and place it on one of my 22xx shooters.

Nothing to lose, go for it! If I'm getting these numbers then I wonder what you'd be getting with the .25 Stone Cold hpa. 
12g 850 psi versus bulk hpa 1000 psi? Could 14" be the optimum sweet spot?

It's funny, my setup is nearly the opposite from yours. Bulk v highly reduced. 

This things like trying to house train the incredible hulk - it just wants to be powerful and let loose. 

It seems to me that the bigger the caliber the more powerful the 22xx setup gets. More power? .25 it up.

[NorthStaR]

Have you got a 10 shot string with the long LW barrel on Co2 to compare?

[mr007s]

Have you got a 10 shot string with the long LW barrel on Co2 to compare?

I never got the Breech and LW set up to perform. I was using 2000 psi with 23.9 inch barrel

However, the 18 inch TOW barrel liner with 2000 psi shoots 19.6 grain H@N FTT's at 840 fps and 26 grain PolyMags at 735.

[NorthStaR]

Any idea what both those convert to in FPE foot lbs?

[mr007s]

Poly Mags, 30.5
FTT, 30.7

[NorthStaR]

  Nice

[quickster47 †]

NorthStar, thanks so much for taking the time to record this data and then post it for all to see.

It has great value for all of us considering a .25 cal pistola.   

Carl

[0351_Vet]

mr007s,

If you cut the LW Barrel, I will buy the remaining piece, assuming it's +10-12"      

[NorthStaR]

NorthStar, thanks so much for taking the time to record this data and then post it for all to see.

It has great value for all of us considering a .25 cal pistola.   

Carl

Anytime, it was fun and 100% necessary! Most of my guns are always on the low power side by
default but I check each one as I go. In this case it was for once a project of power reduction -
the .22 & .177 is always about upping power. In .25 it's the reverse! (for me!!!)

It also seems to be a niche of growing interest with little info available on here.

Now we have the numbers you ran through Noah's 2540 & 1325 with 12 inch barrels and mine with a 14" on a 2540.

I'd be interested to know if either yourself or Noah has opened up the innards of the 2550 to see
what has been done to the valve. As Noahs are they're both Mountanair rigs I wondered what the
builder may have done bar the .25 cal barrel? (Not meant in a snooty way!  )

mr007s,

If you cut the LW Barrel, I will buy the remaining piece, assuming it's +10-12"      

And if 0351_Vet says it in bold you know he means business!    It's Canon time! 

[mr007s]

mr007s,

If you cut the LW Barrel, I will buy the remaining piece, assuming it's +10-12"      

Will do Sir. If I cut it there will be almost 12 inches left and it will be the half with the choke. But, I hope to sell it  and not cut it