optimizing the P-rod

[darryl]

Power is great, but diddley-poop with only a few good POI shots. So far I can put three shots in the same hole at 30 yards. How many shots can you place with your P-rod before the POI starts drifting? I'm new to the PCP world, so I don't know a lot, except to ask.
darryl

[Ribbonstone]

This might help:

All standard P-Rod parts:

IF YOU ARE GOING TO PLAY WITH THE ADJUSTMENTS, then  start off at “zero”. Can back the striker spring adjustment counter clockwise (lessening the tension) until it stops. Call that zero.  Can counter clockwise the striker stroke adjustment (increasing striker travel) stops and call that zero.  Now if you keep track, should be able to get back to whatever setting you find.

Easiest for me is to keep track of the big allen key first (spring tension) and the small allen key second (stroke length).  Will write down something like 6/4, which would be 6 turns in for the spring tension (increasing power) and 4 turns in for the stroke (decreasing power).

The thing to remember is that the adjustments are OPPOSITE..  the farther IN your turn the stringer spring tension, the stronger the hit to the valve....the farther IN your turn the striker strokle, the weaker the hit to the valve.

Used basic CPHPs for the velocity/shot count tests.  They do not group worth a &^^&, but the velocity readings have been consistent (and I suspect its the pellet Crosman refers to in their published velocities).  I ended u with this at a 7/3 setting (7 turns in on the striker spring and 3 turns in on the stroke).

That gave  the following:
 709  688 fps  12 shots  2950psi  (call the average 695fps/ +15.3 foot pounds)

YE-HAAA...made it to advertised speeds without doing any mods (just adjusting supplied screws).

I might have been able to strangle out a little more, but basically think that if you want more power, are going to need to change the transfer port to a larger one.

Besides the previously reported shot counts, tried several setting decreasing from the above. Keeping in the 20fps velocity variation range,  using all stock parts and just the adjustments to change things, the basic out look is this:

15 foot pounds  12-13 shots - ..top of sweet spot: 3000psi
14 foot pounds  18-20 shots-  top of sweet spot: 2850psi
13 foot pounds  21-23 shots- top of sweet spot: 2700psi
12 foot pounds  24-26 shots- top of sweet spot: 2600psi
10 foot pounds  27  30shots- top of sweet spot: 2400psi

For the record: With all standard parts, set this one at 12.6 foot pounds, which give me 25 good shots (3% rule) and runs right at 2600psi.
PELLET TESTS:
5/shot @ 20 yards
Set to 12.5 foot pounds, prettywell limit myself to 20-25 shots.

[darryl]

Hi Ribb,
I see from your image that you've reached a point I'm looking for, maintaining the POI for as many shots as possible. I've improved my numbers in that area since my original post. Using your description reference, I'm at 7/2 right now. I'm judging my results at 30 yards, and I don't have a chronograph at my disposal. Yeah, it would be handy to have one, but I figure if I can place the shot where I want, and through X shots then I'm as good to go as I need to be. But I will say that I took a few shots at my inside plywood backstop to judge penetration, and feel confident from the results that a squirrel's skull would not fare well inside 30 yards. I'm going to enjoy tweaking this pistol. But as you point out, the CPHPs I'm using aren't the best. I need some better pellets.
I'm finding that the fill pressure should be around 2.7k/psi, and a refill at 2k/psi is where I'm at now, so I know I have more work to do; the POI changes enough with the lower pressure after about 11 shots (the hole is growing larger at this point) that a miss is likely. That's not bad if you're stalking a nutter, and thinking one shot-one kill. But for the challenge of it, I'll see what I can do to improve it. I'm trying to understand more about this PCP world I've fallen into.
thanks for replying,
darryl

[Ribbonstone]

Different gun in this example, but can do some figuring without a chronograph.

Shoot groups on identical targets (would be best at 25 yards or more).
Cut out targets.
Line them up
Find the center of each target.
Join them with a line.

Can squish them with a photo program if you like'

Can pretty well figure where the best of this gun's velocity curve lies even without a chronograph...of course, you wont know how fast it is going, but that's secondary to knowing where the best shots lie.

This from a second rifle:

[darryl]

Hi Ribb,
An interesting idea, and it sure speaks to the point of shot placement. Seeing the flight of the pellet displayed this way can only be a good thing. I may take that idea, and give it a whirl, but with fewer targets in line (space limited for setup). I'd have to fill in the blanks.
darryl

[bstaley]

They don't need to all be lined up when you shoot them, just line them up in order after you've shot the entire string to do the analysis.

[darryl]

thanks Boyd. I'll try to set something up. here's to discovery.

[Ribbonstone]

He's right... wasn't clear... can have the targets all over the paper so long as they are the same size and you do not touch the scope adjustments.  Just shoot them, keeop them in order, cut them out, and arrange them in an even horizontal line.  Would be good to note down the gun's pressure after every 5 shots.

Can pretty well see where the gun is doing its best, and with the pressure numbers, can just fill it to the best pressure found and refill it at the dorp off point (avoiding the climb-up and drop-down shots at the start and end of a run).  Figure there is no good reason to shoot unless the gun is able to give you its best.