.25 King Heavy Mk I vs Mk II Ballistic Coefficient

[ctilley79]

I'm looking through the cartridge database in Strelok pro and I can't help but notice the difference between the two pellets' ballistic coefficient. I understand that an accurate ballistic coefficient comes down to velocity, and even spin rates etc, but the numbers below should still be a decent indicator that there is a measurable difference between the two pellets.

Exact King Heavy .25 MKI: 0.053
Exact King Heavy .25 MKII 0.043

I understand the reason for releasing the MKII is that the smaller skirt would fit more magazines. My question is if the MKI will fit your magazine, would it make better sense to use that version of the pellet?

 

[Mark_Walt]

I found for me in my Wildcat that the MkI provided much more accuracy than the MkII. I don't feel as though ballistic coefficients have as much of an effect as how well does the gun shoot the pellet. If both of the pellets provide the same accuracy then I might look at BC's.

 

[Guest]

"ctilley79"I'm looking through the cartridge database in Strelok pro and I can't help but notice the difference between the two pellets' ballistic coefficient. I understand that an accurate ballistic coefficient comes down to velocity, and even spin rates etc, but the numbers below should still be a decent indicator that there is a measurable difference between the two pellets.

Exact King Heavy .25 MKI: 0.053
Exact King Heavy .25 MKII 0.043

I understand the reason for releasing the MKII is that the smaller skirt would fit more magazines. My question is if the MKI will fit your magazine, would it make better sense to use that version of the pellet?

It is probably best to measure your BC from you gun. The Mk1 weighs 25.39gr and the MkII weighs 33.95gr. That is about 25% heavier. That means the SD is going to be higher and very likely the BC will be higher as well. Measuring BC accurately after the third decimal place is pretty much a crap shoot. Mix in different shooting platforms etc... etc... and you wind up with a situation like the above, where the output doesn't make sense. I'm not saying it is wrong. It just doesn't make sense.

Chairgun Pro lists the Mk1 at 0.390 BC. It doesn't list the Mk2. That doesn't mean it is right either. By the way, BC is what matters in this scenario not weight so lets suppose that we shoot three pellets one with a BC 0.03, one with a BC 0.04, and one with a BC 0.05. Usually pellets with a higher BC weigh a bit more so lets let each pellet weigh 1 grain more. The 0.03 pellet shall weigh 10gr. The 0.04 pellet shall weigh 11gr. The 0.05 pellet shall weigh 12gr. We will shoot each pellet at 20 fpe. We get the following data from CGP:

Pellet Velocity Actual Drop from LOD at 100 yds
1 949 27 in
2 905 27 in
3 866 28 in

Interesting result, eh? Now lets do it with pellets that weigh the same and are shot at 900 fps the only thing changing is the BC. Same BCs as before

Pellet Actual Drop from LOD at 100 yds
1 30 in
2 28 in
3 26 in

So the take away here is that a little error in BC is just that, a little error. You should measure the BC of your pellet in your rifle because it makes a difference. Pellets are so much lighter and less dense than bullets that each rifle acts like a sizing device and small variations in pellet diameter and muzzle velocity make large differences (percentage wise) in BC. The percentage difference between 0.039 and 0.053 is slightly more than 25%. The reason isn't measurement errors. It is because at pellet dimensions and weights (in smaller calibers) a very small difference in diameter makes a large difference in BC, a very small difference in weight can as well.

 

[zhoy19]

Actually I think he is referring to the king heavy mk1 and mk2 which are both 34 grain with changes in the design of the skirt. The mk1 has a larger diameter which doesn't cycle is some mags. I have measured the bc of the two from my Vulcan, Mrod, and my Wildcat. The Vulcan had the best bc with the mk2 at 870fps of 0.0596. The wildcat had a better bc with the mk1 at 808 fps measuring 0.0391( mk2 was 0.0356 ). The Mrod at 763fps was very close between the two with 0.041 mk1 and 0.043 mk2. So bc is extremely variable depending on so many factors. The numbers in calculators and software are good places to start and correct for the barrel, speed, and ambient conditions they tested at. The only way to truly get your bc is by carefully measuring it yourself. I used three chronographs at the time. However they could be calibrated differently which would also add another variable. I say fill your at, pick the most acurate diet she likes, and have fun. The more you practice the better you will be at estimating your holds.

 

[Guest]

"zhoy19"Actually I think he is referring to the king heavy mk1 and mk2 which are both 34 grain with changes in the design of the skirt. The mk1 has a larger diameter which doesn't cycle is some mags. I have measured the bc of the two from my Vulcan, Mrod, and my Wildcat. The Vulcan had the best bc with the mk2 at 870fps of 0.0596. The wildcat had a better bc with the mk1 at 808 fps measuring 0.0391( mk2 was 0.0356 ). The Mrod at 763fps was very close between the two with 0.041 mk1 and 0.043 mk2. So bc is extremely variable depending on so many factors. The numbers in calculators and software are good places to start and correct for the barrel, speed, and ambient conditions they tested at. The only way to truly get your bc is by carefully measuring it yourself. I used three chronographs at the time. However they could be calibrated differently which would also add another variable. I say fill your at, pick the most acurate diet she likes, and have fun. The more you practice the better you will be at estimating your holds.

oops... =)

 

[AirSupply]

If the mk1's work better for you and you want to use them but they are not running smoothly through your
magazine try running them through a sizing die first. I haven't been able to get hold of any mk2 pellets
but found the mk1's worked perfectly in my fx magazine once I'd sized them. More work of course. 
Could I suppose effect the bc but fixed indexing issues for me. 

 

[ctilley79]

That's interesting results. I'm also shooting with a Marauder.I'm thinking about installing a regulator for mine while I save up for an Impact. That way I can tune the heavies around 800-830fps.

When I upgrade to an FX rifle, I'll also invest in a CF filling tank, Omega compressor etc. That's going to be quite the bill lol. I figure spending $100 in the meantime is a good way to further increase the consistency/tunability of my Marauder which is an excellent gun for the money. My only issue is you have to be careful about filling your tank to the proper level. If you go up to the max 3k psi, the first 4 shots are inconsistent. After that I can put pellets in a nickel sized group at 50 yards. I'd like to get consistent shots regardless of fill pressure.