Shorter barrel/power loss

energy = force x distance.

force is determined by the pressure and bore area which will stay unchanged

distance is the barrel length so you can expect the fpe to be reduced by a factor of 12/19 after replacement. It works out to be about 15 fpe

A whole lot of it depends on how it is tuned right now. To say that you will go from 24fpe to 15fpe is assuming that it is tuned for max FPE at the 19" barrel length. If however you are only at 2/3's of your max you could very well change the barrels and have the FPE stay exactly the same.

To explain, a PCP tuned at "max" will have the valve closing just prior to the pellet exiting the barrel. If your gun is tuned so that the valve is closing when the pellet reaches the 12" point in the 19" barrel you will not see any change by putting on a 12" barrel, in fact it could very well see an increase due to the less friction of the added 7" after you have turned off the gas. You could also make other changes to the valve/air path to get some of the lost power back.

Without knowing how you are tuned or what your valve/pathways look like any assumption is a guess at best. There are however some formulas out there to calculate theoretical max power.

To find out, you have to shoot over a chrony, and turn out the hammerspring adjuster, and see if the velocity drops from the first adjustment. If it doeas not, you are already at max speed, and is wasting air. You then have to lower the velocity some until accuracy increase on target. 

700~ FPS @ 15.4~ FPE would be my guesstimate with a 12" barrel and the gun of course would be even louder than it is now...



-Matt

We used to use a 50 fps per inch loss/gain figure when changing barrel lengths.

You will have to substitute more air per shot to bring the velocity back up. Lower shot count due to more air per shot.

Have you considered a 14" or 16" barrel? Much less impact on performance.....and it is a noticeable difference in length.

if you look on PA and then look at the Diana 34 it has a barrel of 19 inches and 15.75 and they show no drop in FPS in .177, do I believe that, probably not but the drop would slight

now the Air Arms Pro Sport has a 9.5 inch barrel and states 700 FPS in .22

so if I had to guess on your cut I would say 780 fps

so if I did the cut it would be 1 inch at a time and chrono it, a little crown prep between cuts but you will know when to stop

I don't think there is a definitive answer but I've seen 10fps per inch of barrel used as a baseline before.