Testing Slugs .22 Impact 700mm Help Needed

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heavy-impact

heavy-impact

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Sep 13, 2018
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Right Coast, USA
I just installed a .22 700mm slug liner in my .30 barrel and did some testing today. This Impact is modified with a 5.8mm valve seat, a 6.5gm hammer weight and porting.

All 22.5gn testing was with the HS power adjuster set to min because I felt like the hammer weight was dumping too much air. HS power adjuster was max for 27gn. Range is 55yds and velocities are rounded because they were within 1 or 2 fps. I'm not a great shot anymore, the crosshair moves around with my pulse and I never have perfect focus on the target and crosshair due to bad vision, high cylinder prescription and bifocals. Funny thing is I hold a class A commercial license (even though I don't use it) and get a DOT physical every 2 years. My doctor says I have 20/15 vision in both eyes and my blood pressure is good.

I would really appreciate someone walking me through the tuning process in a simple way so I can get this gun shooting slugs better.

Suggestions welcomed. Thanks

1555893700_7539411145cbd0dc4cd5046.93955378_22 slug test 1 -.jpg



 
I just installed a .22 700mm slug liner in my .30 barrel and did some testing today. This Impact is modified with a 5.8mm valve seat, a 6.5gm hammer weight and porting.

All 22.5gn testing was with the HS power adjuster set to min because I felt like the hammer weight was dumping too much air. HS power adjuster was max for 27gn. Range is 55yds and velocities are rounded because they were within 1 or 2 fps. I'm not a great shot anymore, the crosshair moves around with my pulse and I never have perfect focus on the target and crosshair due to bad vision, high cylinder prescription and bifocals. Funny thing is I hold a class A commercial license (even though I don't use it) and get a DOT physical every 2 years. My doctor says I have 20/15 vision in both eyes and my blood pressure is good.

I would really appreciate someone walking me through the tuning process in a simple way so I can get this gun shooting slugs better.

Suggestions welcomed. Thanks

1555893700_7539411145cbd0dc4cd5046.93955378_22 slug test 1 -.jpg


Click to expand...

Did you say you used your .30 cal barrel with a .22 cal liner or was that a typo. Did you change out the barrel inlet to a .22 for it to work. 
 
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First of all I would suggest that you shoot at least 10 shots 

when you change your reg setting for the gun to settle in 

some of those groups are showing some good promise .



Second if your going to shoot the 22.5 grain 950 is the sweet spot

it looks like the 110-130 Bar looks to be working so I suggest to tune

to 950 fps and use as little hammer strike to achieve this . 




 
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With the 22,5 , the best group I had with the 700mm sl was at 150b wheel on 5, just below sound (on max goes sonic and you hear the crack). The pellet liner like it a lot for those 22.5 much better than the Slug liner IMO

As for the 27gn .218 same at max or 5

The 28vk also quite good as the 30 & 33lhp

I couldn't.make decent groups with other weights. 

So my finalists of that batch are 27 nsa, 28vk, 30vk, 30nsa & 33lhp, lube does help
 
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So I’ll start by saying, those groups look better than OK at 55yds... reason being is slugs group differently (the trade off is well worth it btw). Those groups may look the same at 85yds...!



my 22.5 VK’s are shooting similar patterns at 940-950fps at 55yds but they also maintain the same group size much further out - only tested to about 90yds so far on paper but have head shot squirrels to 140yds...in some wind and only holding for elevation!



groups with slugs do not necessarily grow in proportion to distance like pellets do. It’s a little wacky to what we’re used to but a pellet may shoot smaller than a given slug at 25 but much larger in comparison at 100.



Also...110bar with an ES of a few FPS is stupid nice for that power level in .22!!!
 
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I would really appreciate someone walking me through the tuning process in a simple way so I can get this gun shooting slugs better.
Click to expand...

Most people know I just got an Impact, so by no means am I speaking as an expert. But I'll describe what worked for me and I'll try my best to keep it concise. Bear in mind that I have yet to get on the range to check this tune for accuracy. It could require slight tweaks.

Also, being that we all have rifles that are set-up differently......different mods, hammer spring adjuster screws at different lengths, etc.....my reg pressure setting and power wheel position might be different than yours, but the process of tuning is the same. So, here we go!

** You need to have the hammer spring adjuster screw at a length that will allow you adequate hammer spring tension range for the pressures you'll be working with.

** You need to have a target velocity in mind before you start tuning. In my case I wanted to get the 26gr slugs going 930fps.

1. Start with the Valve Adjuster/Stop on line 4.

2. Set your reg pressure somewhere low (consider mods to the gun, barrel length and weight of slug), like 110bar.

3. Start with power wheel on 1 and shoot three shots over the chrono for a rough average velocity...you will most likely be lower than your target velocity.

4. Turn power wheel to 2 and shoot another two or three shots, velocity should increase. If lower than target velocity, turn power wheel to 3 and check velocity. Repeat at 4, 5 and Max if necessary.

5. At some point at each reg pressure, the velocity should taper off/ level out/ reach the plateau...however you want to describe it. If this is lower than your target velocity, you have found the maximum velocity for that reg pressure and you will need to start this process over at a higher reg pressure. At this point increase pressure by 5 bar.

6. Repeat the tuning process, increasing 5 bar at a time until the point when you can exceed your target velocity by 20 fps by the time you identify the plateau.

7. At this point, back off the power wheel by one step, ie; from 4 to 3 and check for a drop in velocity, say by 10 fps. Back off an additional step if necessary. You can use the Letter side of the wheel if you want a finer adjustment. The steps go like this MAX-5-A-4-B-3-C-2-D-1-E-MIN.

8. From here you will turn the valve adjuster in by one-half turn and check for a drop in velocity, say by another 10 fps.

9. At this point, you can turn the valve adjuster in smaller increments, say one hash mark at a time, and you're looking for duplicates over the chronograph.

10. From here you should be able to fine tune the velocity and Extreme Spread with the valve adjuster.



So this is how it turned out on a tune that I just put on my Impact MKII.

At 122 bar, I identified the plateau at 945 fps. Note: Velocity increased from MIN thru 2, leveled off at 3 and 4, and dropped on 5 and MAX.

I backed off the power wheel to 1 and found that my Extreme Spread wasn't good. So I closed the valve adjuster in increments until I started getting duplicates over the chronograph. When the duplicates were near my target velocity, I called it good and shot a string of 10 that you see here. The only question now is if it will be accurate. Tomorrow is supposed to rain all day and the next day I have to work. I will get out on the range as soon as possible and check for accuracy.

I hope this helps. It may not be the best way or the right way, but it's what worked for me. 

:)

1555905332_12897449985cbd3b34aa3ae4.21749285_Screenshot_20190421-221453.png





 
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Just something to add.

My most recent tune was not accurate....2" at 100yds.

So now I'll try a different tune. I'm going to target the same velocity but at a higher reg pressure.

So many things come into play.....it may not just be reg pressure. It's just what I'll try next. 

Could be a quicker burst of air at higher pressure ends up better in my gun than the lower pressure, longer burst.

I'm going to jump straight up to 145 bar.
 
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Harmonic tuning at work!! 

Just leaving the range....multiple 3-shot groups at 30yds all touching. Had one group at 50yds in a little triangle about 1/4".....this was on a clean barrel with just 60 slugs through it over the chrono. 

Out of slugs at that point (only brought one full mag with me). Besides it was raining and foggy otherwise I wouldn't have shot so many at 30yds and done a couple at 100.

In the course of shooting the 30yd groups, I opened the valve by one notch as well as closed it by one notch and both times the group doubled in size.

So try 3-shot groups at 25 - 30 yds and adjust velocity up and down by say 10fps and see if that gives an improvement.

Also it could be that the higher reg pressure with lighter hammer strike made a big difference too.

This is the tune I just put on the rifle this evening.

1555971677_9012258755cbe3e5da19343.06647936_Screenshot_20190422-164203.png



 
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With the 22,5 , the best group I had with the 700mm sl was at 150b wheel on 5, just below sound (on max goes sonic and you hear the crack). The pellet liner like it a lot for those 22.5 much better than the Slug liner IMO

As for the 27gn .218 same at max or 5

The 28vk also quite good as the 30 & 33lhp

I couldn't.make decent groups with other weights. 

So my finalists of that batch are 27 nsa, 28vk, 30vk, 30nsa & 33lhp, lube does help
Click to expand...

Edit: In reflection of my original more lengthy post, now deleted, I'll simply say that Bob spends a lot of time applying what he reads and absorbs into even more time adjusting pressures and velocities. A great chart over the chronograph doesn't necessarily translate into an accurate tuning. 
 
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