Chronographs change the way a shooter looks at a PCP. At short range (20yards) pretty large vel. variations make little difference, and finding the sweet-spot desn't really make for all that much better short range shooting. but if you want to play at loner ranges, then you need that chronograph.

At short range (in this case 20 yards) takes a pretty big vel. change to be noticed on the target. Just by eyeball measure, a good hold wouldnt result in a miss on a ½ target for about 45 shots.

But the chronograph does point to the best area (sweet spot), which in this case would be shots #17-47 (those 30 shots were inside of 21fps variation).
[IMG][/IMG]
(In the above picture, have pasted 11 targets (55 shots) in a row to give a better idea of the 20 yard change in trajectory a839fps to 951fps produces)

So I can see how folks without a chronograph wonder about the limited sweet-spot for PCPs; its not evident at short range when shooting targets or animate objects until a lot more shots than the chronograph sweet-spot.
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Doubling the range more than doubles the group size. Most of us know that, and 2.3 to 2.5X is more like it. Of course, can be a whole lot larger than that if the pellet has some issues along the way, but for a stable pellet, that 2.5X has been pretty close.

So if the above pellets averaged .24 at 20yards, then at 40yards they should average .55 (the 2.3X factor) to .60 (the 2.5X factor).

(Should mention, I dont get a gun rested 40yards to shoot in all that often. Wife has to be out and the neighbor out at the same time.)

Turns out, these must be stable, as these 15 shots averaged towards the low end of that .55-.60 range.
[IMG][/IMG]

Observations:

Not really noticed at the 20yard groups (although it does seem to be there at 20yards not that I look for it) is the 4-n-1 nature of the groups. Have a few ticks left to try that might cure than 4-n-1 grouping, but a switch to a more powerful scope (am using a little 2-7X) and a little more trigger work might cure it just as well.


Starting with a 20yard zero, these groups formed (average) .52 below the point of aim. Has to be some error due to the little 7X scope being used, but that much drop is about right for a pellet with a BC of .021-.024 under the following conditions:

Scope 1.37 over bore center
8.4gr. JSBs @ 955fps
Zeroed at 20yards.

So out at 50 yards, will be a little bit more than 1 low from its 20yard zero, should stay inside of ¾, and still carry about 9 foot pounds of energy. If I can get the 4-n-1 type grouping whipped, then make that about ½ groups.

Robert,

Very nicely done.  The string of 11 targets in a row is genius.  You can see the curve as plainly as if you actually did data entry and graphed it (Of course if it were a springer it would have looked like a straight line....).

I applaud your work, and thank you for the presentation.  You should join a range with indoor lanes where you can do more testing.  Its often too stressful to try to get meaningful results if you have to wait for the wife to leave.

Kris in NY

thank you.
If you play with the photo editing a bit, can "squish" the picture to make the shot graph/group center graph more noticable:
[IMG][/IMG]

especially in Visual Format.--
Seeing is believing.
You might perhaps add 'Grain Scale' also to the Equation.

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doug,P.