confused over chrony results

[cheewee]

ok using 14.3 benjamins in my 2240 chrony seems to be working perfect no errors. but my shot string is confusing to me.
first shot 552.7fps and then i have a steady decrease over ten shots down to 529 fps.
second string starts at 525 and decreases to 420 over ten shots. so over 20 shots i go ftom 552 down to 420.
i may be wrong but most strings i have seen fluctuate a little between shot and then drop of quickly at the end.
any ideas?

[eric]

with co2 each shot can cool the valve down if you don't let it warm up, wait about a minute or so between shots and see what happens then .

[breakfastchef]

with co2 each shot can cool the valve down if you don't let it warm up, wait about a minute or so between shots and see what happens then .

Agreed! Wait a set amount of time between shots (i.e. 10 secs., 30 secs., etc.). Also, when nearing the end of a powerlet, velocities often drop off very quickly.

[cheewee]

ok first 10 shots were just long enough to reload and write down chrony reading second group i waited 1 minute between shots.
to confuse things even more my 1740 does the exact opposite, first shot 492fps steady climbs to 550 ten shots later.
i have a new valve on its way for the 2240 want to see what a stock valve does.
powerlette was fresh when i started on both guns and second string for 2240 was shot a day later.

[1377x]

are you using a heavy hammer spring or power adjuster?

[cheewee]

are you using a heavy hammer spring or power adjuster?

nope, 1740 is stock except for a 10 inch .177 barrel
2240 has 10 inch barrel, entended probe and valve work, all springs are stock.

[1377x]

could be the mods done to the valve
when i modded my disco valve ,fill pressure changed everything
havent modded a 2240 valve yet

[cheewee]

i did get a little agressive with my valve mods and do seem to be wasting some c02 wirh the short barrel.
i have a stock valve on the way and will see what happens with that.

[1377x]

be sure to let us know your findings
if i mod my valve it will be to soften the angle on the exhaust port,maybe make it bigger.other that no other mods planned

[cheewee]

2240 stock valve
average 516.1 fps

[cheewee]

ok i am really struggling with this am trying to get a solid base line for some testing but i just cant seem to get any consistency.
removed muzzle brake on this one and waited 1 minute between shots, any ideas as to why i get a steady drop in fps, seems to go against everything i know about co2?

[1377x]

interesting!
i would like to know also.never got into co2 until now,i have no clue what so ever
hopefully someone will chime in that does have a clue
i guess i should see how my 2240 uses gas

[breakfastchef]

Change your fps axis to a minimum of 400. That will make the graph easier to digest.

[arkmaker †]

Take a look at the last post graph in this thread.
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,7333.45.html

It is what I got using a .22 10" barrel with no mods except an experimental probe and a valve reducer. See how they compare to yours. Granted, 177 vs 22, but the variance should not be much diferent.

Rich

[cheewee]

Change your fps axis to a minimum of 400. That will make the graph easier to digest.

lost me