Impact high power mods for slugs?

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13brv3

13brv3

Member
Feb 1, 2017
342
9
TN, United States
Greetings,

I'm starting to play with slugs in the Impact, and I'd really like to shoot the .22 cal 28gr boat tail slugs from NSA due to their excellent BC. The problem is that I'd like the ability to push them up to maybe 1000 fps if possible. Currently, my rifle is all stock, and can only manage 875 fps at 150 bar and with the hammer and valve maxed out. 

I have one of the "extra high pressure" Huma regulators on order, but I realize that there's more to increasing power. I've read that the hammer may need to be heavier, or possibly use a different spring with higher pressure. Also, I've read some comments about enlarging the transfer port on the barrel, but I don't know how much that helps, or the best method to enlarge it. Can anyone provide details for either of these mods?

Does it seem reasonable that I can get 1000 fps from 28gr slugs? If so, what mods would be needed. 

Thanks,

Rusty


 
If you search YOUTUBE, you can find a video where Ernest Rowe added a Power Plenum to the Impact. It was a very small "tank" added to where the reg. pressure gage attaches, and then he had the "tank" threaded so that the gage could be screwed in and not lose the function of having a reg. pressure gage. The small "tank" was maybe 30mm diameter and 50mm long. The effect is the same as adding the "Power Plenum" to the EDgun Matador series of air rifles - more air at reg. pressure when firing heavy pellets or slugs at higher than "normal" velocities. This would of course be in addition to the transfer port enlargement and regulator capable of higher pressure.
 
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If you search YOUTUBE, you can find a video where Ernest Rowe added a Power Plenum to the Impact. It was a very small "tank" added to where the reg. pressure gage attaches, and then he had the "tank" threaded so that the gage could be screwed in and not lose the function of having a reg. pressure gage. The small "tank" was maybe 30mm diameter and 50mm long. The effect is the same as adding the "Power Plenum" to the EDgun Matador series of air rifles - more air at reg. pressure when firing heavy pellets or slugs at higher than "normal" velocities. This would of course be in addition to the transfer port enlargement and regulator capable of higher pressure.
Click to expand...

Centercut,

I saw that video too. But did Ernest ever say what FPE his mod produced? Did he demonstrate that accuracy was maintained after this mod? I don't remember him ever revealing such information. Am I mistaken?
 
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@beemanr7, Ernest rarely talks about accuracy with any detail. All I know is what he said in the video, and its been a while since I've seen it. It does make sense that having more volume in the plenum would give more power when trying to push heavier loads at higher speeds. Like I said, same concept as EDgun and Cricket mods that add additional plenum space. Not sure why it would affect accuracy? That doesn't make much sense, unless due to the mods the pellet or slug is being pushed past the point of stability, but that isn't solely a function of the additional plenum...
 
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Hi I spoke with Ernest on the phone when he was testing the slug rounds. He was saying there was no destabilization no matter how fast he was pushing them(both normal pellets and slugs). His impact is a insane beast being able to send these rounds supersonic. I think he also mentioned the slug liners seem to make projectiles more accurate the faster he pushed them. Although don't quote me on this. It was a long time ago and slug liners are out. Plus he was testing so maybe he has realized some things.



I think you should look at reg pressure at 180 bar, increase pellet probe transfer port size, and heavier hammer spring. I can tell you that you reach a fps limit at around 160-175 bar. Any more past that and the hammer can't smack the valve open hard enough due to high pressures. 


 
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Excellent info. Thanks! I will likely try to contact Ernest for his suggestions. 

The hammer weight vs spring strength options are still a bit unclear. I've read more about increasing the hammer weight than increasing the spring strength, but it seems to me that both should work. I even ran across one article that advocated lightening the hammer and increasing the spring strength. Are stronger springs available anywhere? That would be the easiest option to try.

Also, are the brass transfer port ends available separately? I'd like to know there's a fallback plan if i screw up :)

My thinking is to start with all the stock parts, and add the Huma extra high pressure reg. I'd up the reg pressure and record the results, but as you say, I'm sure restrictions in the system will limit the effect of higher pressure. After testing with the stock parts, I'll try making mods and retesting. I'll probably do the speed testing with Monster pellets, since they're a lot cheaper than slugs. It will also be interesting to see how they perform from the slug barrel at higher speeds. 

Thanks,

Rusty


 
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