Wednesday, July 8, 2015

Chronography note.

Had a brief chance (everything's brief, with a seven-week-old in the house) to set up the new chrono and run a string over it with the TalonP set to absolute minimum power on the power wheel.

Some notes, mostly for myself, in no particular order:
  • Used the chrono without skyscreens at all, based on a Tom Gaylord comment I saw recently.  This seemed to work well in the direct sunshine.
  • I tried a very close distance-to-chrono this time;  about one foot.  Mostly this was in order to do it fast, rather than perfectly;  I will want to back off to about three feet as there is noticeable muzzle blast from the TalonP, and one foot seems kinda rude.
  • The .25 pellets may be less susceptible than the .177s to get "missed" by one or both screens unless they are "close enough" down to the top of the chrono unit, but it can still happen.
  • Power wheel was set to absolute minimum;  I wanted to see what the gun did here.  AirForce owners would refer to the setting as "1.1" on the wheel, and I understand that this is highly individualized to each gun;  that is, a setting of "8.11" on one gun is not going to translate to a second gun sitting right next to it.  It's a relative measure for that gun of how wide open the valve is.  The shooter uses it to make his own notes.
  • Top hat was also set to the most polite setting, and over 20 shots later it is still tight.  We'll see how long that continues!
  • Performance was interesting.  It was much more erratic than I was expecting, and it may be that this is my first taste of what Tom Gaylord calls "finding the right power curve" for a given gun and pellet.   Here's the string data--note some wide variations between successive shots:
#    FPS / FT-LBS

20    657 / 30
19    673 / 31
18    690 / 33
17    898 / 56
16    727 / 36
15    739 / 38
14    848 / 50
13    774 / 41
12    ERROR 3
11    ERROR 3
10    806 / 45
9    811 / 45
8    829 / 47
7    ERROR 3
6    847 / 49
5    850 / 50
4    791 / 43
3    846 / 49
2    791 / 43
1    793 / 43
Average: 786.5 FPS
SD: 68.6 FPS
Min: 657 FPS
Max: 898 FPS
Spread: 241 FPS

Starting fill was about 2900psi (two un-chronoed shots down from a 3000psi fill), and based on what the Hill pump told me when refilling afterwards, the end pressure was about 1200psi.  I was deliberately shooting until I could clearly see the gun dropping off, and after shot #17 threw me for a loop (how did that happen?), the next three pretty clearly showed the trend I was looking for.  These guns are known for maintaining a pretty tight spread over their ideal "shots per fill", and owners of TalonP and Escape models (which use the same 210cc air tank) seem to confirm a very reliable 10 full power shots per fill--sometimes more, but almost never less--once you've found the right setting(s).  (Interestingly, the ideal string of tight-spread, full-power shots doesn't necessarily begin with shot #1, but sometimes after a few "wake-up-the-valve" shots.  

It's quite possible that this "absolute minimum" setting is just not right for the gun, and next time I am going to try going up to "2.1".  (Of interest:  the test-fire data from Pyramyd Air, when I bought the gun, with a different pellet and power wheel setting at "4.6", showed a much tighter ES (118fps) and SD (42fps) for their 10 shots, with a clearly linear pattern of slightly-descending-velocity for each shot.)  

I'm interested to see what this gun's "miser mode" (whatever that turns out to be) can give me in terms of shots-per-fill;  also what "max power mode" (whatever that may be, and it may not be "full open", either) will yield, and finally I suspect I'm going to settle on whatever setting gives me the tightest spread for the 10-15 shots I think I can expect from the piece.  (For anyone reading this who is new to PCP guns:  there are many PCPs out there which can get many more shots-per-fill than this one;  AirForce's own "Talon" rifle, with a different valve and tank than the "TalonP", is one of them.)  The attraction of the TalonP, for me at least, was 1) short carbine length, 2) adjustable LOP, 3) more power for its size and ergonomics than anything I have yet found, and 4) "quickly" and easily topped off (refilled for a new string) with a hand pump.  The idea of having 10 shots at hand for hunting or pests, and then hand-pumping a refill in a matter of minutes, is just fine for what I wanted.  (Once I can afford a SCUBA tank and/or a 3000psi compressor, it could get just plain addicting.)

And jeez, look at the power at this minimum setting.  An It's actually so high that I again wonder if this is out of the valve's optimum range, and I might see some more sedate performance with the power wheel set a little higher.  At any rate, I was figuring that even at minimum wheel settings this gun (known for its gonzo valve) would have power to spare for whatever I'd want to do, and--yeah, you could say that.  That last shot, at 30 foot-pounds, is still pretty whopping for a smallbore airgun;  if my charts are correct, it will still retain about 12 foot-pounds at fifty yards.  

Thus all the testing.  Ultimately,  I don't know how serious I'm going to get or be about maintaining a statistically tight spread over those 10-15 shots, but I do want to see the data myself and maybe start to develop a spidey sense with it.  At heart I'm a functional guy:  I'll obsess over data just long enough to find the pattern I want.  And here, what I want is:  1) enough field accuracy to hit that 1" squirrel brain at 50 (yes, that's gonna be through glass), 2) enough power to anchor a snowshoe hare at the same distance, and 3) enough consistency from shot to shot that I can learn one trajectory and lean on it.  I suspect that the TalonP is going to provide multiple pellet options that can do a half-inch at 50 off the bench, leaving me a little wiggle room to guarantee the inch from a field position when it counts. 


I also ran a string through the Bronco with the half-pint-milk-box wadcutters from Crosman (mostly to test the chrono before firing the .25s over it) and learned only afterward that the otherwise nice iOS app for the "Ballistic Precision" chrono does not allow you to capture and save a string in arrears--you have to declare that you're going to save the string before you shoot it!  Okay, so this is a minor matter and I'm glad I figured it out now rather than later, but you should have seen this string!  Other than a few errors when I got the tiny pellet too far above the screens (this is becoming a consistent pattern), there were probably 20 shots in the string and the extreme spread was less than 5fps (first standard deviation was under 2!)  I was impressed, and will have to try that again to see if it was a fluke.

I'd like to construct/fashion, if I can, a "plug-and-play" bench for doing chrono testing with the airguns, since I plan to do a lot of that:  something that I can quickly lay the chrono and the gun on and have their alignment be very close to ready-to-go.  The initial thought was a simple board that would "mount" the chrono, on a small tripod, at a height in the middle of the tripod's adjustment range, and at the other end perhaps mount my "Site-N-Clean" cleaning vise/rest to match it.  In theory, small elevation adjustments for different guns could be handled by the tripod's vertical crank, and I would just point the aligned shebang at a suitable target, permitting me to do both accuracy testing and chronography at the same time.  (Not so much an issue for the Bronco, where pellets and powerplant are both cheap, but right now at least--still looking for work--.25 pellets do cost noticeably more, and as marvelous a device as that Hill pump is, I'm not going to be able to do hundreds of rounds at a time with a hand pump only.  :-)

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