First strings on new synrod

[TytoTex]

Half way through can of .25 jsb exact diablos with new synrod. Shot chrony this morning and results are:

831.7. 806.4
832.0 802.0
827.2. 791.8
820.1. 785.3
822. 776.7
818.8. 770.4
813.3. 761.3
807.5. 754.8

Start psi 2800. Start psi 2300
End psi 2300. End psi 1750

No mods or tuning yet. Almost consistent negative progression seems different from others posted on forum. Other than repeating this exercise, has anyone seen this pattern before? New to PCP's. Did get first kill this morning with first shot off full charge. Camera wasn't working good then saw Ted's hold over has HS set to 240 FPS instead of 1000 FPS. Fast speed narrows view from Casio camera so cannot see scope hairs

[RayK]

Yes, that is pretty common for a gun from Crosman.

The recommended fill is 3000 psi, but the good shots are up around 3300 psi and down.

One of the changes Crosman made from Gen I to Gen II is a stiffer valve spring. It lowers the peak power, but gives tighter extreme spread resulting in more good shots per fill. It was not difficult to get Kings at 900 fps with stock 25 M-rods in Gen I, but most Gen II are shooting at a peak of around 850 - even after some adjusting.

Ray

[TytoTex]

Looks like my whole second column of numbers disappeared except to begin and end psi. Must have been confusing to understand.

Here are the numbers again

831.7
832.0
827.2
820.1
822.0
818.8
813.3
807.5 Start psi 2800. End psi 2300
806.4
802.0
791.8
785.3
776.7
770.4
761.3
754.8. Start psi 2300. End psi 1750

My concern is the way this gun seems to work is first couple of shots (5?) might stay together but the before clip is even empty shots are dropping away. So I either have to top off really often or have to compensate for less velocity due to air loss in addition to hold over for distance. Wouldn't it be better to have two chambers? The fill chamber at high psi and a valve letting a consistent charge fill the shot chamber. That way the pressure supplied for each shot is consistent not constantly decreasing leading at accuracy issues. Refill fill chamber when pressure is too low to open valve into shot chamber. How are people getting 40 shots per fill? Low power shots with mods? I do have the HDD mod coming this week. Thanks for your comments

[TytoTex]

My bad. The second was there, just scrunched up with first one

[LDD]

As RayK suggested you need to fill to a higher pressure with the rifle's current tune. Try filling to 3000 psi then chronograph it again. You will probably need to fill a 3200 psi to get on the starting side of the bell curve. If you're not willing to fill that high you will need to adjust the rifle settings to accommodate a lower fill pressure.