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Impact tuning frustration

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PerkyVal

PerkyVal

Member
Nov 22, 2017
862
24
Wisconsin, United States
Hi y'all!

I have a fairly new .25 Impact which I have added a 700mm barrel that I finally got out to the range to tune.

After tuning my average fps was 838, spread 19, and sd 5.6ish.

I'm not really happy with those numbers as my Crown has a spread of 9 and a sd around 3 with the same JSB 33.9 mk2 I use for both guns.

That aside, every so often I'd get a shot with a 960ish fps. I can hear when it happens, the gun is much louder, and the LabRadar confirms what I heard.

As far as I can tell I'm not getting any reg creep, but I dont check the gage every shot, maybe I should. I do know when I do look there's no change.

On both my Impact, and Crown I took the slop out of the HS adjustment. Reg pressure on the Impact is 130ish



Any thoughts?


 
Doesn't really mean anything but I'm still within the first thousand shots and am shooting the MKI's (the MKII's shoot a little better but I want to use up what MKI's I have) . FPS is about the same, spread is a little higher as is the SD.

However, I am getting 90 shots and my 75yd target has a 88 shot hole in it that's about the size of a silver dollar. I haven't retrieved the target to measure it. There were 2 fliers high to the left. At this point, the fliers and even the group size, might be my fault, at least partially. I haven't gotten the trigger to the point where I can pull it without moving the gun but I'm getting closer. 

The whole 90 shot string/target was taken over the chrony and I have the shot string. There were some outliers but the SD over each 10 shots was petty much the same (still higher than yours around 6.3). I'm going to shoot another tin or two as is and see were the reg settles to. I turned it down from (almost 150) as delivered to about 145bar. So I want to give it some time.

Then again, I'm more focused on results on target than I am the chrony but there's no denying chrony data. I'll moving to 100y tomorrow and doing another full string over the chrony.

My next change might be adding a little more HST.


 
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@PerkyVal - I'll have to think on your situation a little more. It's strange that it's a)one shot, b)once and a while, and c)a higher fps. 

@pocholoss - Your rifle is tuned too high. If you like it how it is, leave it alone but, if you do tune it, you can do one of 2 things to start. 1) decrease spring adjustment until your fps lines up with your power settings. 2) increase your valve return. After that, if you want to tune further, you might touch the reg. But, you should be able to sort it out using those two adjustments. Be sure to record your OEM settings before you change anything. 
 
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You're getting 90 shots per fill? 

I'm getting approx 70, although I use 2 sideshot mags and top off after those. I have another sideshot mag coming but I doubt I'll be able to shoot all 3 mags on one fill. But maybe
Click to expand...


Yup, 90. Power wheel on max, hammer spring turned in a little (3 lines showing, maybe its 2, I'd have to look). I did bump the reg down to 145 per the gauge. Didn't do anything special proceedure wise, just ended up there. Maybe I got lucky but don't forget your numbers are a little better than mine. 90 is a bit of a stretch, the last 4-5 were dropping off but still usable. In regular use, I'll do the same and refill after 2 of the sideshot mags.

Odd that your reg is 15b lower than mine and you're shooting a little faster with slightly better SD. Must be the hammer spring.

Look through that tin of pellets and make sure there are no 25g mixed in. 940ish is where mine shoots those unless I back off the power wheel.


 
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I do not have an impact but I have read on other threads the gauges are not always that accurate. So if one gauge read 140 bar, the real pressure might not be that. And it could be different on another gun with same pressure. What I did on my fx crown was to cross check the gauges by comparing it to the one on my fill kit, which I know is pretty spot on (earlier compared fill kit gauge when filling another gun with a EDMU gauge). If you lower the pressure on the gun below the reg pressure (both tank, and plenum), both gauges should read the same, if they are correct. If they are not, one or both of them are off. When you then fill the gun slowly, you has to close airflow on fill kit before you reach the pressure the reg gauge usually shows (10-20 bar lower is probably fine, to make sure the reg never close), and let it equalize. Then you can write down what both gauges on the gun show compared to the fill kit gauge. So if fill kit show 110 bar, tank gauge shows 115, reg shows 120, you have to subtract 10 bar on the reg gauge to be closer to real reg pressure, when reading it on normal use. 

On my fx crown the tank gauge was pretty spot on, but the reg gauge showed about 5 bar higher.
 
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