Author Topic: My Impact .22 700mm w/ slug barrel  (Read 1108 times)

Tinkerer

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My Impact .22 700mm w/ slug barrel
« on: March 02, 2020, 09:53:47 PM »
Since I started a thread on my Dream Pup .177 I might as well do the same for my Impact .22.  I bought the slug liner since I already had the .22 30 grain HPBT NOE mold.  My cast drop @ 28.4 grains consistently and I resize to .217".  They load very easily into the slug liner.
The Impact is set using Max on the hammer spring wheel, with the hex screw adjuster backed off from max.  The valve is set not quite to line four and the regulator is set @ 125 bar according to the FX gauge. 
Allan suggested that I try LLoyd's efficiency calculator and I got an efficiency of 1.33.  I was pretty surprised at the results! 
Accuracy is great out 50-60 yards with the cast slugs.  The slug will blow a hole on the entry side and leave a big dent on the opposite side of empty green propane cylinders.  We thought the cylinder would ring nicely they don't.  The 4"- 1/4" steel gongs ring and dance nicely.
The Impact is still a work in progress.  I'll wait and see how if any the tune changes after 1000 shots.


Glen

Alan

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Re: My Impact .22 700mm w/ slug barrel
« Reply #1 on: March 03, 2020, 04:32:21 AM »
I suspect you can do a bit better, but as you said, let the gun settle in.

Most all of the regulator data I have read on the Impact with the power plenum, hovers around 120 BAR, or a bit less. Big slugs might need a bit more, however. The hammer stop setting is the most critical.

In my case (Impact, PP, .25 caliber, Exacts), the regulator is just a hair below 120 BAR, the port at maximum with a tiny bit of free play, the velocity is 944 FPS ±2 FPS, now that it has settled in. An amazing statistic in my book! By the way, the efficiency is 1.44 using Sike's calculator.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

Tinkerer

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Re: My Impact .22 700mm w/ slug barrel
« Reply #2 on: March 03, 2020, 12:04:34 PM »

I can shoot various weights of pellets and slugs using the same tune.  By changing the hammer spring settings from Min to Max I get these numbers:
JSB 15.89gr, 965 fps, 33 fpe, PW: 1
JSB 18.1gr, 965 fps, 37 fpe, PW: 3   
JSB 18.1gr, 1005 fps, 40 fpe, PW4             
H&N Barracuda Hunter Extr, 18.52, 960 fps, 38 fpe, PW: 3
NSA 20.2gr, 965 fps, 42 fpe, PW4
 JSB Monster 25.4gr, 51 fpe, PW Max
Pretty versatile air gun!
« Last Edit: March 03, 2020, 12:08:05 PM by Tinkerer »
Glen

Alan

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Re: My Impact .22 700mm w/ slug barrel
« Reply #3 on: March 03, 2020, 01:14:59 PM »
Yes it is. One thing to keep in mind, however, using lower settings on the dial, doesn't mean you're using less air.
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

Tinkerer

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Re: My Impact .22 700mm w/ slug barrel
« Reply #4 on: March 03, 2020, 02:28:12 PM »
Yes, the air use changes quite a bit with the different weights.  I was very curious what kind of numbers the different settings, types, and weights would produce without tuning for each weight and type. 
I do know that the JSB Monster 25.4 use less air than the cast 28 grain I cast and get identical fpe on Max hammer spring. I get the same 3 magazines per fill. Using the slug liner too.  I forgot to to bring them along to test when I was able to shoot 50-60 yards last week.
Glen

Tinkerer

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Re: My Impact .22 700mm w/ slug barrel
« Reply #5 on: March 21, 2020, 12:57:28 PM »
I finally decided it's time to check the tune and try tuning again.  This time I got 1.43 fpe/cui average using the Sikes calculator.  Much better result. Shooting the cast 28.4 grain boattail hollow point NOE mould @ 901 avg. fps, 51fpe.  Slightly higher regulator setting of 130B and tweaked the valve adjuster and hammer spring preload.
Glen