Newbie's quest to reduce Impact FPS deviation and spread

[qball]

Well, after plinking 200+ pellets I am happy to report my deviation is down to 6 with a sporadic spread of 12 with my current tune, very acceptable given it's a low power tune. The pellets pretty much ranging between 745-750 over 90% of the time, I could spend more time and pellets getting it lower but think I'll just stick to what's working, grouping is pretty good especially under 50 yards, a little windy to tell at longer ranges. Ballistic calculation is dead on thanks to descent consistency on speed, at lower speed 10 FPS changes the POI a lot more than at 900+ fps.



Also found this video:



https://www.youtube.com/watch?v=ZzaIXp8qgUk&t=334s





He apparently also struggled with low power tune with spread of over 20 like me, in this video he decided to use valve to limit the power while keeping the hammer/reg harmony. When I get more time I'll change my impact back to factory tune and turn down the valve to see if I can get slightly better results.

 

[scratchcoobster]

You want the smallest spread and Std. Dev. possible. 

Most people are happy with a Std. Dev. of 4 or less, and a spread under 10 . With the FX Crown I get spreads no larger than 12 and Std. Dev. of 3.2 to 3.5. Haven't done any true harmonic tuning yet, still breaking it in. After that I will be looking to tune to a tighter tolerance.

My Brocock .25 with JSB Kings has a spread of 7 to 12 with Std. Dev of 1.86 - 2.36. This is on a chrony with 40 shot strings. Very consistent due to the Huma Regulator. You should be looking for these kinds of results.

 

[qball]

You want the smallest spread and Std. Dev. possible. 

Most people are happy with a Std. Dev. of 4 or less, and a spread under 10 . With the FX Crown I get spreads no larger than 12 and Std. Dev. of 3.2 to 3.5. Haven't done any true harmonic tuning yet, still breaking it in. After that I will be looking to tune to a tighter tolerance.

My Brocock .25 with JSB Kings has a spread of 7 to 12 with Std. Dev of 1.86 - 2.36. This is on a chrony with 40 shot strings. Very consistent due to the Huma Regulator. You should be looking for these kinds of results.

oh wow! That’s a pretty tight deviation, I have a new goal for the high power tune! Thanks! 

 

[dan_house]

qball, do t know anything about Impacts (other than i want one...)



but i do know a 10 shot string is not enough data to judge spread and SD.

try a 50 shot string... better yet 100 shots..... you’ll see SD settle down to something more accurately reflecting the gun’s capabilty at that tune/power level

spread should down too. dont put a lot of emphasis on spread, every gun will toss an oddball occasionally. the bigger the data set, the more those goofball shots average out

 

[qball]

qball, do t know anything about Impacts (other than i want one...)



but i do know a 10 shot string is not enough data to judge spread and SD.

try a 50 shot string... better yet 100 shots..... you’ll see SD settle down to something more accurately reflecting the gun’s capabilty at that tune/power level

spread should down too. dont put a lot of emphasis on spread, every gun will toss an oddball occasionally. the bigger the data set, the more those goofball shots average out

Thanks, I have put in quite a few hundred rounds and my old tune is consistently inconsistent. I'm starting to get a feel of tuning it and the approach, waiting on more pellets and some free time to retune.....can't leave good enough alone but that's why we buy impact right? hahaha

 

[Drumsnguns]

I'm kind of surprised that some guys here are coming down so hard on this newbie....or maybe it's perceived. Anyway, we were all there once and I too asked a lot of questions...isn't that one of the reasons these forums exist? We are all helping each other. Yes, I would throw out a friendly tip to do a little reading before asking questions but I'm sure most would agree it's difficult sifting through threads to find answers. Sometimes I think some do not want to give out information, maybe because they compete...who knows? There are, however, starting points we can suggest keeping in mind that all guns are different. 

Qball I don't see where you mention your caliber but a JSB 25.4 would tell me that's an exact King and that would be .25 Not sure why someone told you to go get a 12ft-lb gun? What, right after you spent $2K on what you have? Also what version Impact do you have? Off the bat, I would have been the first to tell you that 70 Bar is too low for a .25 Impact shooting Kings or King Heavy. 25.4 Kings like to live in the 900-960 fps zone.

Also, my owner's manual warns "never set your regulator pressure below the "set pressure" or warranty will be voided." Set Pressure, hmmm guess that means what the gun came set at from the factory. Mine came set to 105 Bar but I see some reputable South African YouTube shooters doing fine at 90 bar with .22. So, as you see there is a lack of real info about the reg pressure. If you were shooting Kings at 920 fps out of the box then that's where FX set the tune for good results. I'm sure that the gun, out of the box, was shooting a Spread of less than 10 fps. Mine, a .25 MK2 with PP shot 9 ES at 105 bar, out of the box. It shot King Heavies at 800 fps and at 30 yards group were were one small hole.

Mine right now is re-tuned to 120 bar shooting King Heavies at 878 ave fps with an ES of 6 and an SD of 2. Works for me and I'm fine telling you that info. But find your gun's own best setting.

If you want to shoot back yard quiet then just turn the Power Wheel to MIN. and don't worry about ES and SD too much. Turn it back up when you get to the woods or where ever you can shoot.

So, looks like you're getting on track with the help of some of the guys here....keep reading and keep watching videos by Matt Dubber; Bob_O; Ted Biers and Ernest Rowe. They will teach you how to "understand" your gun and not just throw a "recipe" at you.

Tell us how you make out.

 

[dan_house]

. They will teach you how to "understand" your gun

great point. knowing the gun intimately will let you know when its gone awry in some way...... kinda like the car youce been driving for yesrs stsrs making a sound its not made before 

 

[qball]

Qball I don't see where you mention your caliber but a JSB 25.4 would tell me that's an exact King and that would be .25 Not sure why someone told you to go get a 12ft-lb gun? What, right after you spent $2K on what you have? Also what version Impact do you have? Off the bat, I would have been the first to tell you that 70 Bar is too low for a .25 Impact shooting Kings or King Heavy. 25.4 Kings like to live in the 900-960 fps zone.

Also, my owner's manual warns "never set your regulator pressure below the "set pressure" or warranty will be voided." Set Pressure, hmmm guess that means what the gun came set at from the factory. Mine came set to 105 Bar but I see some reputable South African YouTube shooters doing fine at 90 bar with .22. So, as you see there is a lack of real info about the reg pressure. If you were shooting Kings at 920 fps out of the box then that's where FX set the tune for good results. I'm sure that the gun, out of the box, was shooting a Spread of less than 10 fps. Mine, a .25 MK2 with PP shot 9 ES at 105 bar, out of the box. It shot King Heavies at 800 fps and at 30 yards group were were one small hole.

Mine right now is re-tuned to 120 bar shooting King Heavies at 878 ave fps with an ES of 6 and an SD of 2. Works for me and I'm fine telling you that info. But find your gun's own best setting.

If you want to shoot back yard quiet then just turn the Power Wheel to MIN. and don't worry about ES and SD too much. Turn it back up when you get to the woods or where ever you can shoot.

So, looks like you're getting on track with the help of some of the guys here....keep reading and keep watching videos by Matt Dubber; Bob_O; Ted Biers and Ernest Rowe. They will teach you how to "understand" your gun and not just throw a "recipe" at you.

Tell us how you make out.

thanks a bunch Drumsnguns!

Yes, my impact is 1 month old MK2 with power plenum, new gauges In .25 caliber. I kind of had a feeling that the impact might now like low power tune specifically with lower Reg pressure. My reg pressure was 90 when I got it and it was shooting JSB king at 920, it shot great but the amount of power was a bit much for back yard application hence I was mucking around trying to tune it lower. I got 3000 rounds of 26 grain hades in the mails so will try my original 90 bar reg pressure and limit the power by closing the valve. This is what the meathead marksman on YouTube ended up doing after getting same terrible deviation as me with low power tuning.


this entire exercise really helped me to get to know my impact better, one thing stuck out to me is what Ted holdover said that our ears are the best tool for tuning, when it’s not happy you can hear it and I’m starting understand her language. 1500 pellets is a lot of pellets for learning but I had a lot of fun and it’s hell a lot cheaper than even 22LRs. 

can’t disagree that for backyard there are better guns and I’m drooling all over the dreamline chassis or compact. I might spring for that when toy funds are available and a few months of time passes since the impact purchase so the boss doesn’t get upset. 

thanks again for everyone’s help. 

 

[qball]

Good thing I didn’t get a sub 12 FPE gun for back yard duty! Caught this skunk on my critter cam and it’s HUGE! I don’t want to shoot it but if it starts to eat our fruits later in the season then the wife might demand it to be “taken care” of, she loves animals .........until they eat her fruits! Obviously it will need the hollow point slug at 950+ FPS tune. 


Edit: I digress, although at 940fps the slugs shoots well but has too much of a bark even with moderator, will spend more time later to see if I can quiet it down. For now 34 grain JSB heavy at 750FPS should do the job very quietly at 42FPE. 

 

[qball]

Think I found another way to lower deviation! I was retuning for lower power again, and getting frustrated again! Then I notice something, if i shoot quickly my deviation goes up! I also hear the regulator working filling the plenum. So I paused and thought about it then count at least 10 between the shots and BAM! Spread of 9 and deviation of 3.9 and I didn’t change a damn thing! DOH!!!! This could if saved me hundreds of pellets and frustration!!!!! 


moral of the story is be patient and give it some time between the shots so the regulator can do its thing, think this is more important at lower power range. Hopefully other find this helpful and save someone some frustrations.