Since you shoot slugs, I have noticed you can loose some speed after a freresh barrel clean. You probably need some ammounts of shots before it is back.
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Tuning Impact MKll PP finally went off its nut
- Thread starter Vetmx
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So, when you swapped gauges you got a different reading than before, correct? New value 130b, and you left it there, and it shot as well as before? What happened next? Sounds like you did a bunch of cleaning before you swapped scopes, which suggests things weren't perfect.
40 in-lb on the shroud sounds like a lot when most scope rings are 18-20 and bases 25. SO could you have a deformity of shroud, barrel sleeve, or both? Happened to me, see thread "fliers-at the end of my wits"
40 in-lb on the shroud sounds like a lot when most scope rings are 18-20 and bases 25. SO could you have a deformity of shroud, barrel sleeve, or both? Happened to me, see thread "fliers-at the end of my wits"
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On the brass barrel inlet section of the barrel assembly there is of course a little circular mark from the grub screw. Or should be. On mine there are two, about 0.5 mm apart, because for a while I was not pushing the barrel all the way home against the stop pin during reassembly. When I finally noticed and began being careful to reinsert fully, I got a velocity jump. I think because of TP misalignment or incomplete seal from the breech O-ring. Which reminds me, how old is that O-ring?
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That makes sense as it's directly attached to the barrel which will affect any guns harmonics. But a scope affecting harmonics on a gun should never be the case.
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I’ve never had the barrel out of the gun, I only remove the liner. My probe oring is original. I never questioned it because the velocities of my shot strings are very nice. Because my slugs are lubed with silicone, my probe oring gets lubed with every shot. I will loosen the barrel when I get home and see if it has moved slightly forward because of how I tension the shroud. While I have the barrel out, I will probably add another grub screw to the opposite side of the receiver.
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I pulled the liner and scrubbed it after the scope swap because I was in the process of marking my scope turrets for distance shooting. That’s when I noticed my accuracy was horrible. I was always happy when I thought my gun was performing that well at 117b. When I put a better gauge on it I was not happy that I was actually around 130b. I played with my reg settings to to confirm what bar I needed to achieve my previously accurate speed. That’s where I may have screwed up. For right now I’m hoping I am just a couple bar off from where the gun was before a changed gauges.
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Sounds like you got it mostly sorted. It is my personal preference to have highest reg pressure(150-155 bars) when tuning for slugs. The short but high energy burst reduced muzzle turbulence which can destabilizes the slugs far more than pellets which self stabilizes by the sail. Superior liners barely have enough twist rate to stabilize the slugs so the muzzle turbulence can cause significant accuracy problem. It seems to be less of an issue with heavy or slug A liners. Part of the reason it is much easier for me to find good accuracy at lower speed than 900+ FPS, except for my .25 heavy liner with heavier slugs.
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I have debated going with the higher reg pressure thing with this gun. But what always stopped me is when you have the HS cranked up to crack the valve, your gun is more active when you squeeze the trigger. The harmonics of a 100b gun and a 150b gun are night and day. But maybe the trade offs are worth it. I will be headed home tonight so I will try a few things. I need to look at my notes again.
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I have not personally found the impact react a lot more violently at 150bars Vs 100 bars, maybe it does but it has been a while. At the end of the day it’s amount of energy produced makes a difference from my perception. At 150bars my HS isn’t anywhere near fully cranked up still and shooting 34 grain NSA at 920FPS out of 700mm barrel, very quiet even with the FX moderator, it feels very smooth and not stressed with great shot count. YMMV. It certainly is not tuned to perfect balance or sweet spot but I’m not really interested in max power and want to shoot more than 1 ammo at different speeds because…….I can I guess, I’m weird.
Over time I pretty much cranked all 3 of my FX regulators up to 140-150 bars even my crown shooting 8fpe. Only thing I hear on my crown is the hammer ping.
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Some day I might shoot you a PM and discuss the tuning at 150b method. I think Long Gun Dallas has his Crown tuned that way and I’ve seen his groups. They were impressive.
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An update. Tonight I discovered something that was throwing a wrench in my tuning. If I adjusted my reg up to let’s say 125b, when I would refill the gun to 240b, the reg would jump up 3 or 4 bar. Once I caught on to this I was able to test my gun from 120b up to 130b. I put my HS and Valve at the settings from when the gun was outstanding at 935fps. I found mind boggling accuracy at 122b. It was a single hole at 30 and 50yrds but the slug was only cruising at 910fps. I found outstanding accuracy again at 127b. One hole at 30 and all touching at 50yrds. When I hit the chronograph, it was 935fps. So, for right now it’s a fact that if I’m off by 3b on a slug tune, I’m not happy with how the gun shoots. That my friends is a sensitive gun. The next thing I’m going to do is monitor my reg pressure and make sure it stays the same as I get down to where I refill and make sure it stays put when I refill the gun. The one mistake I may have made is from the time I got the gun, I never filled to 250b. I always stopped around 225b. Recently I started to fill to 250b and I think the additional pressure on my reg seat was not something it was used to seeing. It is like I’m breaking in the reg again. Hopefully. Right now I’m tired of shooting the gun but I will test at 100yrds tomorrow night if it’s calm. Thanks for all the input. It helped get my wheels turning.
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Sensitive, or precise? I've learned to tune for the lowest ES, then go to the range, where I move the valve adjuster in barely perceptible increments til I get good groups. It's like dialing a focus knob in and out, watching the groups open up and then tighten. I find it delightful that I can dial in accuracy like that.
Now, sensitive plus unstable, that's a nightmare. But in your case it doesn't look as if the gun went crazy, rather that you changed something. That's reassuring.
Now, sensitive plus unstable, that's a nightmare. But in your case it doesn't look as if the gun went crazy, rather that you changed something. That's reassuring.
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This is a good read,
https://hardairmagazine.com/ham-columns/pellet-and-slug-stability
Heavier weight of the pellet/slug ? The wind is always less predictable than gravity.
https://hardairmagazine.com/ham-columns/pellet-and-slug-stability
Heavier weight of the pellet/slug ? The wind is always less predictable than gravity.
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Vetmx, a few days ago I ran out of the H&N .218 23 grain slugs which had been doing so well for me with reg at 95, average velocity 925. These had the oily/blotchy coating that put a lot of folks off. The newer ones have a drier, dull gray lube, and they have been shooting amazingly poorly. I had common 0.4" groups at 70 yds and now I was getting up to 3". These are all sorted by weight within 0.2 gr. Cleaning made no difference at all. So I decided to try the high reg pressure route and gradually worked my way up to about 120 bar. as I was doing this the long arm of the needle on the reg gauge broke off; I was at 115 and cranked it just a tweak so I bet it's 120 now. With the valve past line 4 I had a max speed of 960. Now instead of backing off the hammer to find the knee I began closing the valve, and at about 2 lines the groups closed up dramatically. This just happened for 2 consecutive groups so we'll see whether it's sustained. Chrono says.......928 fps, ES 7, Sd 2.7. Is this what they mean by the "short, high-pressure" tune?
Seems to put to rest the idea that slugs need to go very fast; maybe there isn't any optimal velocity per se, and it's really a matter of how you reach that velocity.
Seems to put to rest the idea that slugs need to go very fast; maybe there isn't any optimal velocity per se, and it's really a matter of how you reach that velocity.
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With the right barrel, slugs shoot well at all speeds. It’s all about air delivery. Here’s something funny. When my gun was misbehaving, I ordered a TP and probe from Huma. Figured if I couldn’t find my old tune I might as well start again with the gun flowing more air. The day after I found bliss again with my gun the stupid package arrived. I let it sit for a couple days but finally last night I said what the hell and installed it. Picked up 30fps but accuracy opened up a little. Turned the valve in .20mm and I may have found bliss again. I didn’t touch the gun today because I’m not ready to get mad and spend all night shooting. I’m shooting at 127b and I consider that far from a high reg pressure tune. You and I are in the mid pressure zone.
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Hmm. Of course, I really don't KNOW at this point what my reg pressure really is. Awaiting arrival of a new Wika gauge, and it will be very interesting to see where I am.
As I said, I sort my H&N slugs by weight; having no good way to sort by dimensions, I use weight as a proxy. When I've had good accuracy, I always attributed it in part to sorting ammo. But last night I tried three different weight groups (22.8, 23.0, 23.2) of three different lots, and they all shot well. The lighter ones had a slightly higher POI. I have several boxes of NSA in .217 and .218, 20.2 and 23 grains, which have never shot well. Now I need to revisit them, as well as Knock Outs.
Also it seems my air consumption is a little less.
It's been 15 months now of working with this gun and I'm still learning. Thank goodness. I'd be completely bored by a gun which required nothing from me to make it perform.
As I said, I sort my H&N slugs by weight; having no good way to sort by dimensions, I use weight as a proxy. When I've had good accuracy, I always attributed it in part to sorting ammo. But last night I tried three different weight groups (22.8, 23.0, 23.2) of three different lots, and they all shot well. The lighter ones had a slightly higher POI. I have several boxes of NSA in .217 and .218, 20.2 and 23 grains, which have never shot well. Now I need to revisit them, as well as Knock Outs.
Also it seems my air consumption is a little less.
It's been 15 months now of working with this gun and I'm still learning. Thank goodness. I'd be completely bored by a gun which required nothing from me to make it perform.
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Actually I trust every other gun I own more than the “Queen”. But don’t mistake that for me not liking the Queen. It’s a great gun and would be far less sensitive if I used it as a pellet gun. Maintaining a perfect tune for slugs is critical with this gun. It can be rewarding but also a pain in the butt hook.
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Finally shot at 100yrds tonight. I won’t show my groups because I will either be called a liar or I’ll get 20 PM’s requesting settings. I’m very happy. Now the million dollar question, how long will the gun stay put and keep me happy. Slug velocity is 952fps now. Here is a little info on slugs vs velocity. I have found amazing 100yrd accuracy with this gun and slug at 850, 880, 920, 935 and now 952fps. My opinion is if you have to speed up a slug chasing accuracy, something else is wrong.
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100%!!!!! Bullet stability calculator is our friend!
Before all the carbon liner sleeves shroud tensioner from Ernest my best accuracy at 100 meter/yards were found at around 820-840FPS but falls apart at higher speeds mostly due to harmonics I think. Once I got the liner sleeves and tensioner most of my settings are really quite good (1-1.5MOA) and some are really good at sub MOA and I have no issues pushing well pass 900 FPS. Although I am curious on how come you say your Impact which is setup pretty similar to mine is "sensitive". Granted I'm not the one to patiently shoot small groups over and over again so guess I wouldn't know if mine is being sensitive, I would the change the setting well before my Impact would ever get a chance to act up anyways. LOL!
However once mine is setup and my ballistic solver is setup correctly nothing I can range is safe! Haven't found a place to shoot pass 160 yards recently though. I've had 4 consecutive hits on discarded 12 gauge shotgun shells standing on the base at 145 yards, pretty pleased with the accuracy.
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