Hi. Sure, gladly share my settings and the journey so far. I got my rifle about two months ago, so very new to this.
Rifle: Impact Mk2 PP, 600mm Slug A liner. Fitted a pin probe and dual transfer port. That made a 50fps difference alone. No other internal mods.
Reg Pressure: +-127bar on the gauge (A gunsmith confirmed on his reg tester, that my gauge is reading high by 5 bar)
HST: 3 turns out from max (15.30mm) - this is the spot where the ES averages 7fps. (2 turns out the ES average is 23fps, 4 turns out it is 16fps). I only get to an ES of 10fps again with 12 turns out)
Valve adjuster: 8.68mm from the little lip on the housing to the bottom of the adjuster. Visually, just over three lines.
Slug diameter. Shooting Javelin and H&Ns mostly, it became clear that the .217s in the 25 to 27 grain range were more accurate, but not by much. They also have the benefit of higher speeds when compared to the .218s.
The Javelins .217 26 gr started to show promising results with a group of 4 shots ctc of 5mm (repeated twice in succession) at 36m and a 24mm group at 100m. BUT, the ES was too large for my liking, around 16fps. AND then I ran out of slugs!!
The final tune was with the H&N .217 27 grainer. The settings above are for this slug. My rifle also likes the .217 25 grainer.
Average speed is 960fps and the last string gave me an ES of 5fps and a SD of 1.8, over 10 shots. And it is very, very consistent. First shot the next morning last weekend, left the barrel at 960fps, so no reg creep!! Happiness.
I wasted a lot of slugs initially dialling the valve adjuster back from max, 4 lines, one tiny fraction at a time. I learnt to dial from just under 3 lines out as the sweet spot for my gun seems to be on three lines or just over, for a range of slugs. And I wasted a lot of slugs with the reg set at 150 bar. Macros advised me to tune it down to 125 bar or so. Thank goodness, and thank you. Gun is far happier at lower pressures and the speed is still astonishing.
I really wanted the Javelins to work as they expand far better than the H&Ns. I have subsequently received lots of .217s 26 grain Javelins but I don't yet have the courage to change the settings from where the H&Ns are shooting. I will one day but once you get the gun harmonised it just defies belief and with it, comes the angst of never getting there again. I know, not rational and I will get to tune for the Javelins soon.
I washed the gunk off the H&Ns. They were full of a greasy substance with the stuff even clogging the hollow points. I lightly lubed them with silicon spray as I did with the Javelins. The H&Ns are worth the trouble. The Javelins are very clean.
I wanted to get to a magical tune the YouTubers are talking about as quickly as possible and when it did not happen, it became very stressful. I sold some beautiful air rifles (mostly Steyrs) to afford the Impact (my first) and it is disheartening when it shoots like shotgun with slugs. I then did a reset and treated this as a journey (as Gert does on Aim Small) and it became far more enjoyable.
The method I use to harmonise the Impact is based on the advice of Bob O. (Thanks Bob) He credits Roelf from AirHunters for the method. And it works. The important part though is that the valve adjuster must be turned by a hair breadth at a time. Shoot three shot groups at closer distances and then repeat until they go through the same ragged hole. Then immediately confirm the tune at 100m, aiming for MOA or below. And don't give up and advance the valve adjuster by larger turns. I did that, it does not work!! A few times, I had great groups at 36m but when I shot the second and third group it would become inconsistent. Very frustrating. Sometimes the ES is as low as 2fps!!! but rubbish groups. And with great groups at 36m, the groups at 100m were over 50mm. This is truly a journey. If the tune does not work, up the reg pressure by 5bar. I did not have to go this far though. Got lucky otherwise I would have to turn the valve adjuster out by a fraction all over again. And don't blame the gun during the journey. Push the doubt out of your thoughts.
Its worth it though, it truly is.
I had a target set up at 36m and a gong behind it at 100m. If I got ragged holes at 36m I would shoot out to 100m to see if I could get sub MOA groups. This took three days in total, shooting three to four hours per day including on the wrong (or high) reg pressure, dialling in from 4 lines as opposed to from 3 up etc, testing different diameter and weight slugs etc.
I confirmed the tune the whole day on Sunday. I set up targets at 67m, 100m, 122m, 141m, 157m and 178m and shot more than 200 slugs, dialling from one to the next to the next. I would then have tea and repeat the exercise. Not once did the gun not perform. Up to 100m it was consistently under MOA. Up to 141m it shot MOA and below, in strongish cross winds. 157m and 178m were an issue in stronger winds but early morning groups where under 50mm ctc at 178m. At 157m I would still hit a pigeon size target 4 out of 5 times in strongish winds (15km/h wind speed, gusting).
Apologies for he length but I hope it helps.
