Details and background:
First 28 shots of JSB 25.39g over chrony and got average 840fps.
Then shot 28 of the JSB Heavy Mk2 33.95g and averaged 740fps.
After watching Earnest’s FX videos on tuning (twice), a couple of other videos, and reading some forum threads, I made some tweaks:
I then shot a full string shot over chrony with JSB Heavies 33.95g , and here of the details:
I decided to go and shoot some targets (at 30 yards) to check accuracy at these speeds with the following:
(See attached pics)
I then checked the bottle gauge to see how much these 25 shots consumed and realized/remembered that I’d not refilled after the last string shot (135 shots) over the chrony. The gauge read 110 bar. While these targets are absolutely nothing to brag about, it seems that they’re pretty good considering they were shots 136-160 on one fill.
Something odd that I noticed was the bottle gauge does not move smoothly while filling — It jumps like a watch’s second hand, I’m using the same fill system/adapter/tanks for years with my other FX Wildcats and never saw the jumping, so I think we can rule that element out of the equation.
I guess here are the questions:
Reg & Valve
Shots 136-160
One note. Immediately after realizing that I’d not refilled the bottle, I then refilled it to 25bar, shot 25 (5 shots at each target) Heavies, checked the bottle gauge, and it read 200bar. The 50 bar used for 25 shots is more in line with what I was expecting from this rifle. The targets (while nothing to brag about, again) were pretty good for my level of ability.
- .25cal 600mm slug liner installed instead of the pellet liner
- DonnyFL Sumo moderator
- New, purchased from one of the primary dealers. From the markings on the box, it appears as though it was a 700mm from the factory and the barrels were swapped. Not a concern, as I’m sure this is done as most dealers since Impact supplies are always back-ordered. The shop I ordered it from was great. The sales guy was great to work with.
- Reg was set @ 110 bar upon receipt
- Valve control knob was at stock #2 position
- Power wheel was set at max
First 28 shots of JSB 25.39g over chrony and got average 840fps.
Then shot 28 of the JSB Heavy Mk2 33.95g and averaged 740fps.
After watching Earnest’s FX videos on tuning (twice), a couple of other videos, and reading some forum threads, I made some tweaks:
- Increased the reg to ~135bar
- Backed the Valve knob out to the 4th line
- Tried to use 2.5mm Allen wrench to tighten the Power Wheel’s slop — however, I never saw the screw threads turn, used both metric and standard Allen wrenches larger and smaller than the 2.5mm, and never felt like the screw moved. In fact, there is visible thread-locker (blue) on the screw, and it never budged, BUT I don’t think any of the wrenches ever seated into the screw head either. The Power Wheel still moves freely as it came out of the box.
- After that, I shot 28 Heavies over chrony and couldn’t break 800fps, so I then bumped the reg up to 145bar. After shooting another 28 Heavies over chrony, the average was still in the 780-790 fps range. After re-watching Earnest’s tuning video again (3rd time), I removed the air bottle, decocked the gun to release the rest of the air, then dialed the reg back, reattached the bottle, and adjusted the reg back to 135bar. Shot another 28 over chrony and the fps was largely unaffected.
I then shot a full string shot over chrony with JSB Heavies 33.95g , and here of the details:
- Filled bottle to 250bar
- Reg set at 135bar
- Power Wheel at Max
- Valve Knobe at 4
- Got somewhere between 125-130 shots before it fell off the regulator (see attached graph), however, shots 125-135 were still 748+fps.
- I monitored the bottle gauge while shooting, noticed it reached ~135bar after shot 112 and expected to see rapid drop-off with the following shots. To my surprise, the next 10-13 were still in the 800s
I decided to go and shoot some targets (at 30 yards) to check accuracy at these speeds with the following:
- 5 shots of Nielsen 26.8g slugs
- 5 shots of Nielsen 33.5g slugs
- 5 shots (each at 3 targets) of the JSB King 25.39
(See attached pics)
I then checked the bottle gauge to see how much these 25 shots consumed and realized/remembered that I’d not refilled after the last string shot (135 shots) over the chrony. The gauge read 110 bar. While these targets are absolutely nothing to brag about, it seems that they’re pretty good considering they were shots 136-160 on one fill.
Something odd that I noticed was the bottle gauge does not move smoothly while filling — It jumps like a watch’s second hand, I’m using the same fill system/adapter/tanks for years with my other FX Wildcats and never saw the jumping, so I think we can rule that element out of the equation.
I guess here are the questions:
- with only ~300 pellets fired thus far through a new Impact, should I shoot it a bit longer before expecting any meaningful stats/numbers to consider?
- What’s up with the Power Knob’s screw? Why can’t I get an Allen wrench to seat and turn?
- To get 160 usable shots out of a .25 cal, is it possible the bottle gauge is not reading correctly and there is more than 250 bar in it after filling?
- How much (if any) does the slug liner affect the FPS on pellets? I’ve seen a number of posts where people (far more knowledgeable on the subject than I’ll ever obtain) are using slug liners (in place of the smooth twist) and finding great success with shooting pellets through them.
Reg & Valve
Shots 136-160
One note. Immediately after realizing that I’d not refilled the bottle, I then refilled it to 25bar, shot 25 (5 shots at each target) Heavies, checked the bottle gauge, and it read 200bar. The 50 bar used for 25 shots is more in line with what I was expecting from this rifle. The targets (while nothing to brag about, again) were pretty good for my level of ability.
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