GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Oldblades on September 10, 2015, 09:55:29 PM
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I have been absolutely obsessed with trying to learn what makes pcps tick and getting my Crosman Challenger to where I want it.
Around 50 shots at about 625 fps with JSB/AA 10.33 heavies has been the goal.
The 625fps comes from that pellet being my favorite 'wind pellet' and on calmer days, the tune puts lighter pellets just short of 700.
Those speeds just seemed to work best for me.
After weeks of reading, asking for help, having it apart and put back together countless times, and roughly 2 tins of pellets I have it where I want it..........almost.
Could someone please take a look at the string from today and help me out. The overall curve is something I'm very happy with, actually pretty proud of.
But the jumps up and down of 1-1 1/2% during adjoining shots are bothering me. The jumps arent complete killers, but I can see the differences in the POI.
1900#-1200# 10.33 JSBs
1 620.00 630.00 625.00 636.00 632.00 625.00 625.00
2 623.00 625.00 633.00 632.00 639.00 623.00 621.00
3 629.00 621.00 625.00 632.00 631.00 625.00 619.00
4 624.00 622.00 629.00 632.00 625.00 625.00 616.00
5 622.00 627.00 630.00 633.00 632.00 624.00 615.00
6 617.00 628.00 628.00 632.00 628.00 620.00
7 621.00 625.00 633.00 635.00 628.00 627.00
8 624.00 631.00 633.00 632.00 627.00 620.00
9 624.00 626.00 634.00 629.00 635.00 624.00
10 624.00 633.00 629.00 631.00 628.00 622.00
Right now the gun has about minimum spring load with a opened up transfer port.
Maybe this is as good as can be expected from a opened up self regulated gun?
But after reading about hammers, springs, dwell etc., my impulse (guess) is to lighten the hammer, increase the spring in order to shorten the dwell. It seems I would have more control over the finite details as getting enough air to the pellet is not a problem.
This is just a 'gut' feeling that has better than a 50% chance of going south on me, so figured I'd ask before tearing in to this.
So would lightening the hammer be a practical approach to smoothing this out? Or should I leave it alone, which is not in my blood until told to do so by someone experienced. ;)
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You have about 49-50 shots staying at about 2% velocity variation....call it as good as you'll get.
Just write yourself and IOU and fiddle around with those other ideas down the road (probably saving them for when something leaks and you have to take the whole rifle apart to fix it...about then, the urge to try a whole new tune comes on strong as you've already got it fully apart).
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Thats good advice. Maybe I'll find out more of 'what not to do' in the future before I'm actually the one telling others.
Its the shot to shot variation thats going to stick in my craw, but....................I think I need to learn the gun a little better to be able to capitalize on that. Heres the accompanying 25 yd target that was in a mild (0-10mph) but wildly directionally varying wind.
The 5 shot groups have the speed ranges and group sizes noted.
Target 11, with a 2fps variation and being one of the worst of the bunch, suggests I should heed your advice and just enjoy it as is and learn to shoot better first. ;)
Interesting thing to note on the target is how the groups kept climbing up on successive targets, even with comparable earlier speed ranges. I purposely stayed low of the bull and didnt touch the scope. By the end it was on the bull, up about 3/8-1/2".
(https://farm6.staticflickr.com/5657/21121933370_7a164f7c74_o.jpg)
I'll need to laser the words "leave it alone' on the side of the stock though.
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I am no expert but I would imagine to get that string any flatter over that many shots would require a regulator. Plus if you look at your data on the target it clearly shows the velocity is not the culprit for the change of poi. Target #1 , 3 and 5 all have higher velocity than target # 11 but lower poi. The other thing you notice with the data is that some of the groups that had the widest spread are the best groups with no poi difference between the lowest and highest velocity in the group. Like you pointed out one of your groups with the tightest spread was one of the worst groups. I wouldnt touch a thing unless I was installing a reg but with a string that good at 25 yds any poi change will not be from the velocity spread you have. I say keep shooting and enjoy the rifle and work on shooting technique. Dont take that last sentence wrong I am not saying you have shooting issues. But I believe everyone can improve their ability if they try and it seems you are chasing perfection as most of us are so keep trying;)
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Maybe the gun is just burps occasionally.
(http://thumbs.gograph.com/gg3883662.jpg)
Sorry I can't help ,but that looks like a good shot string to me. Nice job tweaking it
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Plus if you look at your data on the target it clearly shows the velocity is not the culprit for the change of poi. Target #1 , 3 and 5 all have higher velocity than target # 11 but lower poi.
That lead to another question in my head as I agree with this.
But given the consistent rise in poi, I was wondering if the propulsion had anything to do with that, being sharp HPA at the beginning of the string, and lower pressure using air mass to accomplish the speed. Same speed but different ways of getting there.
Thats one of those common sense things that screams a resounding 'No' but when the deviation is on paper, given the consistent rise, it makes one wonder.
I'll need to do this again in more stable wind and a more comfortable setup, rather than just laying my rest and bag across the shop table, to see what happens with that.
And as far as installing a regulator goes, thats one of the good things about having just one primary gun.
Having just one gun, I can better afford to throw stupid money at it.
The bad part is the tendency to throw stupid money at it. :D