JSB King Heavy velocity (BC)

[Jenko]

Hello. 

Just a quick info, today I tested JSB King heavy out of my .25 Cricket and got this velocity numbers:

Yards - fps

0 - 865

49 - 782

77 - 725

107 - 670

Each speed is the average of three shots.

I got very good bc numbers at this speed.

For anyone that is interested, I have my Cricket regulator set at 130bar, valve return spring regulator set, so it just touches the spring and hammer spring adjuster three turns out from flush with reciever. In this setting my gun uses 32-35bar per magazine of 12 shots. 

I have made a test of air consumption at different regulator and valve spring settings, and I have found out that this is good air consumption for the power output.

Best, Jenko

 

[Anthony Jarvis]

What is your starting and ending fill pressure for how many shots?

 

[alpine84]

My cricket with the plenum uses 90 bar for 48 shots 1,875 bar per shot with heavys at 910fps reg pressure 132bar. Start at 230 bar and after 4 mags i have 140 bar left. So i can recommend to get the plenum for better airconsumption. 

 

[Jenko]

Hello.

Thanks for reply guys. Anthony I usually fill to same pressure that is in the bottle and shoot until 125 - 130bar then refill, no idea of shotcount but you can easely calculate number of shots from given data. 

alpine84 thamks very much for fhe info but i do not know of what plenum mod arenyou talking about, i guess some enlargement of the plenum, can you describe what you changed in your cricket, i would love my gun to perform as yours. You are talking about .25 cricket right?

thanks for the reply, looking forward to more discussion.

jenko

 

[alpine84]

Its a extension of the airtub in front of the regulator against the action. I think you can by it from georgia airguns. Then i have made a bolt for hammerspring so i can adjust it when ever i want. Yes its a. 25.in this picture you can se the extension of the regulator plenum. And have a gauge in the plenum so i can red regulator pressure. 

 

[Jenko]

Hello.

thank you for the quick answer alpine, i seen your thread on this extention just now, i will mamake it myself as i have a lathe at home. i am really shocked at improved performance, maybe i will set it for lower power than you but better shot count. if i go from 75 to 85j at muzzle chairgun tells me i only gain 3j at 100m so it is not that big big of a difference.

jenko

 

[Jenko]

Made the plenum extention today, came out good. Georgia airguns increases the length for 1.75 inch so roughly 44mm, i made mine 55mm long, just enough that my custom LDC still fits. Put two magazines trough, big decrease in loudness and air consumption. Tomorrow more testing and pics

 

[Jenko]

Today i tested some more my new plenum, accuracy is good but i do not get such good performance as you alpine 84. Did you do your own tuning of hammer and valve spring? Per magazine my gun uses 50 bar from 260 to 210bar at 270m/s and 80J.

Is the problem in valve return spring? How tight is yours, how much preload?

Best, Jenko

 

[SMH77]

What was the BC number you came up with from 0-49 yards? Was '0' right at the muzzle, or was it a few inches / feet away? Be sure your environmental conditions are entered in correctly to the app when calculating the BC numbers from the velocities-changes in the conditions have a pretty significant impact on the BC calc.

Do you happen to know what barrel is on the gun (who makes it, etc)?



Sean

 

[Jenko]

Hello Sean.

I have decided to use 0.06 as my bc for this speed as it is reasonably close to my measurements, and as you may know BC changes with velocity downrange so a general number works for me.

This is how i estimated, i took long range results more seriously since there the BC matters more i imagine and also for energy delivered estimation.

Best, Jenko