FX Impact Compact .22 cal - shot count with 300 cc bottle / efficiency

[Blackpaw]

Good morning everyone: 

Before work I went out to my permission at 7:00 am to my permission and decided to see how many shots would get out of my FX Impact Compact in .22 cal.

I did two things this morning, one see how the H&N barracuda hunter extremes did in the gun and used the rest of the time for Hades. I say though “average” hammer spring setting on the impact was 3 to 4. Pressure setting for the Huma regulator is just a smidge under 120 bar so we will say 118/119 bar. I am not going to mess with it for 1 or 2 bar. Hammer spring adjustment still has plenty of “play”.

This morning I had the temps “against me” so to speak for optimum efficiency, but here is the results of this morning’s count and results with the H&N BHE. This morning’s temp was around upper 50s and in Celsius 12.5 C according to the car when I pulled up to my permission.

First my Impact does not like the H&N BHE at least as I have it tuned now, but I have focused on JSB 15.89 / Hades along with Javelin 23 grain slugs, but I find the Hades more liked by the Impact than the BHE. 

For shot count of 70 I went from 250 bar to 165 bar”ish”. This is total shot count for H&N BHE and Hades. Even at max I say I got another 8 to 10 shots left before I reach 150 bar. At warmer temps I could expect more and colder less, the laws of thermodynamics are what they are, and even Elon Musk can’t get around.

So I say I have a pretty efficient tune. Just curious if anyone else has this shot count. I am told 60 to 80 is good for the 300 CC bottle under the conditions I am using by a couple of people.

 

[bentaroh]

I get about 85 shots shooting JSB 15s at 930 FPS. Reg at 105Bar. 

 

[Blackpaw]

Thanks for the feedback, I am considering turning it down to 110 / 105 to maybe add some shots, if I give up the slugs. How would you say your hammer spring is set?

 

[bentaroh]

My hammer spring is set where it came from the factory - plenty of play either direction

 

[Blackpaw]

My impact didn’t have the front valve spring installed so we had to do that at the dealer, and there was a ton play in the hammer spring, so I tightened it and things seem to have settled down. I will though maybe back off the pressure and check results to increase the shot count. How low do you let the bottle pressure get until you call it good and refill?

 

[lenweber2]

Try the H&N Terminator for pesting out to 60 yards. And they unload in the pest better than anything tried. 3 gunners on 10000 irds and grond squirrels and a few Rock Chucks.

 

[nervoustrig]

What velocities were you getting? Need to know to evaluate efficiency.

 

[Blackpaw]

Upper 870-880 FPS, but that isn’t max setting. If I go max at current settings the Hades are pushing 960 to 980 FPS. I am doing a shoot again tomorrow before work and I will take a look.

 

[nervoustrig]

Okay thanks, that works out to an efficiency of 1.23fpe/ci. That is decent for a short barrel but can probably be improved if you are so inclined. Definitely not something that one should feel compelled to change, and even less so if it’s grouping nicely.

 

[Blackpaw]

I know I can probably lower the pressure by 5 bar at least with similar performance and that and valve setting and a tweak on the hammer spring might increase shot count by a few.

 

[nervoustrig]

As it is configured presently, you have an efficiency advantage in that you are adjusted well below the velocity plateau. Light hammer strike -> short valve dwell -> better efficiency. Sometimes that will lead to an unacceptable extreme spread (velocity fluctuations) because it is operating in a state of partial valve lock. However if the velocity is consistent, just enjoy it.