JSB King Heavy Mk2 .25 33.95gr BC check

[MushroomPsyche]

I chrono'ed the JSB King Heavy Mk2 .25 at 25 meters to find the BC. I just want to double check my results because the numbers I'm getting is quite a bit higher than expected. I'm shooting them at 835 FPS at the muzzle and with the chronograph at 25 meters away, I'm getting a BC of 0.073. This is with air pressure and elevation corrected. This is very high for what I'm expecting out of this projectile. In contrast, all the test I've done using the same calculations with my .22 caliber has always yielded much lower results than what most people report. For example, with the JSB Hades .22 15.89gr, I'm only getting 0.017 BC. Even all the .22 slugs I've tested. Some of those slugs are rated at 0.07+ BC but the highest I've ever seen with .22 slugs is only 0.056 BC. Yes, I know I'm using G1 drag function but in my experience the calculations are spot on at the distances I shoot at with the .22 caliber up to 70 meters away.

 

[Airgun-hobbyist]

Other's opinions will differ, but it it works for you and is accurate then run with it. As an experiment, maybe try a different app like Chairgun and see if the pellet profile GA works just as accurately with the same inputted rifle and pellet data.

 

[JungleShooter]

Francis,

there are a few things that could have brought the BC a bit off track:

➊ Make sure the atmospheric conditions are entered, especially the current air pressure at your location (not the one adjusted for sea level).

➋ How many measurements do you make before averaging out?
To have a reasonable confidence in your data that they are not chance results you'd need at least 10 measurements (with two chronies). With only one chronie, where you average out MV⁰ and MV²⁵ you'd need a lot more.


➌ How are you measuring the velocities at the muzzle and 25y?
▪ With one chrony only? Then you're only measuring averages, and fluctuations in your MV will make your BC numbers less sure.
▪ With two chronies? Then test if both chronies measure the same velocity — or take 10 shots in one arrangement, then switch the around and measure 10 more. Compare if the BCs of the first 10 are rather different than the second, indicating that one or both chronies read high/low.


➍ There's more, but I'm going to catch some zzzzz.

Good luck!

Matthias

 

[RavenRider]

What Chrony are you using?

 

[Blejda]

I am using .22 Jsb Monster redesigned in my Impact.
Most info obout bc for that pellet i found is 0.04.I input 0.055 in chairgun and i am hitting high at every distance.My guess is the bc is much higher then 0.055 at least what you are getting with your .25.

I didn't do the calculation though.

Regards Marko

 

[MushroomPsyche]

I'm using the Caldwell optical chronograph. And yes, I only have one and alternate between the muzzle and down range reading. Atmospheric conditions and elevation is accounted for in the calculation I posted above.

By the way, if I don't input atmospheric conditions and merely use standard pressure at elevation, I'm getting 0.063 BC for the King Heavy.

My experience with the JSB Hades when I was still learning that projectile; - I initially used the BC that is available online, which I believe is around 0.025 for the Hades .22 15.89gr. In actual usage, I found that all my calculated shots were always shooting a few cm low. That's when I put the chrono down range and found out that for my gun and conditions, the Hades only has 0.017 BC. I changed to that BC in the calculators and my shots have been spot on ever since up to the longest I've shot it at 70 meters.

 

[Arzrover]

I just put your measurements in EASYBC in GA2 and it came up with a 0.0593 bc which is only a little above what I've been getting using my LabRadar and RW with poly LW barrel(0.054) running 890. I would suspect wind being a factor as with-the-wind decreases drag and into-the-wind increases drag. I'm at 3000 ft elev for what it's worth and the 0.054 is an average across a LOT of testing...
Bob

 

[bigHUN]

I am shooting both the MK1 and MK2 's mostly at 100 M rings.
I can confirm that the MK1 has a wider=harder skirt, and not sure if that would a reason that the MK1's hitting higher about 1.5" and to the right 1.5" from a same gun and have not changed any tune on gun only loaded two different pellets in a mag.
Your BC number is off for some unknown reason.
Strelok Pro is pretty much spot on with BC for pellets.
I can check with my Labradar next time at the gun club, but that will be only somewhere a snow melts in March/April maybe

 

[airman_o]

I chrono'ed the JSB King Heavy Mk2 .25 at 25 meters to find the BC. I just want to double check my results because the numbers I'm getting is quite a bit higher than expected. I'm shooting them at 835 FPS at the muzzle and with the chronograph at 25 meters away, I'm getting a BC of 0.073. This is with air pressure and elevation corrected. This is very high for what I'm expecting out of this projectile. In contrast, all the test I've done using the same calculations with my .22 caliber has always yielded much lower results than what most people report. For example, with the JSB Hades .22 15.89gr, I'm only getting 0.017 BC. Even all the .22 slugs I've tested. Some of those slugs are rated at 0.07+ BC but the highest I've ever seen with .22 slugs is only 0.056 BC. Yes, I know I'm using G1 drag function but in my experience the calculations are spot on at the distances I shoot at with the .22 caliber up to 70 meters away.

View attachment 521710

I’ve been shooting the JSB King Heavy Mk2 .25 af 40m. My fx chronograph measures the bc consistently at 0.060. I use GA profile though, but it should be very close to G1
0.073 seems on the high side indeed

 

[MushroomPsyche]

I just retested this again with the chronograph at 33 meters and also with a bit different air pressure during the day compared to the night test I did previously. This time, I got 0.053 BC which I think is much more reasonable.

 

[MushroomPsyche]

On a different note, I also retested the .22 Hades 15.89gr. while I had the chronograph setup downrange. I've been shooting these at 940 FPS and have always gotten 0.017 BC. I reduced the velocity to 880 FPS a few weeks ago and now the BC is 0.025.

 

[JungleShooter]

Those numbers look much more likeley.

 

[MushroomPsyche]

Those numbers look much more likeley.

One thing I can think of was that on the night I tested, the weather conditions and air pressure might be changing very rapidly and the weather app I'm using was not updating real time.

On the night test as well, I had a small LED flashlight pointed at the chronograph so I could see readings after each shot. The LED might have a flicker of its own which might be interfering with the optical sensors of the chronograph.

In the end, I don't really know the cause of the big discrepancy in readings and just throwing out ideas.