200g SST Ballistic Coefficient

[ronlaughlin]

This morning a trip was made to the hills to measure the ballistic coefficient of the 200g SST. When the shooting started the temperature was 68, and when completed it was 73. It was breezy. It has been my experience that one gets better results from the chronograph on cloudy days; this morning the sky was clear, the sun was brightly shining, and the angle of the sunshine was low across the sensors. Conditions couldn't have been much worse for collecting data from the chronograph.

The rifle used was the 45 caliber Omega. The load was 200g SST, 115g BH, light blue Harvester sabot, W209 primer. The first 4 shots were made from 100 yard, the top bull was the aim. Then a move was made to 46 yard, 5 shots taken; the bottom of the top bull was the aim. The set up is shown in the following photo after the shooting was complete.

The data.

A ballistic program was used to calculate the ballistic coefficient of the bullet from the average speeds of the bullet at the 2 different range.

Then the high speed numbers were left out and a new average of the speeds calculated. These speeds were 2035 fps at 100 yard, and 2178 fps at 46 yard. Using these new averages, the ballistic coefficient was calculated again.

Well.....................i must admit to being surprised by these calculation. The advertised or 'official' BC of this bullet is 0.265, and more than one person has written he thinks it is optimistic. Further shooting and measuring seem to be in order. Perhaps one day in the near future will be a cloudy morning, and more data can be collected when conditions are more better. Actually, this bullet does indeed fly as good as it's official BC say it should.

 

[LarryBud]

Interesting Ron.

Let us know if you do follow up with additional testing.

 

[sabotloader]

Ron, if you have time would go here:

http://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi

And run your ballistic information. I have tried several times and I am unable to come to the numbers that you are seeing. I do not know which program you are using but to me it seems to leave important information out. The drag factor (the G number) is an important function in computing bullet BC.

This is the explanation of the 'G' function that kinda puts some light on it.

The G1 drag function is the best standard drag model to use. We have tested several drag functions (G1 for sporting bullets; GL for lead bullets; G5 for boat tail bullets; and G6 for flat base, sharp pointed, fully jacketed bullets). For each drag function we have measured BC values referenced to that function and observed how those BC values change with bullet velocity. We have chosen G1 because the changes in BC values with bullet velocity are least, and because there is a vast database in the literature on BC values referenced to the G1 standard. Also, to our knowledge all projectile manufacturers refer their published BC values to the G1 drag function, which facilitates comparisons among bullets of different calibers, weights, shapes and manufacturers.

In your calculator I did not see a calculation for elevation which is another large factor in bullet BC.

The JBM calculator is used by most bullet manufactures to calculate most of the functions and ballistic of a given bullet not just the BC.

But anyway if you get a chance work your numbers and hopefully they will come out better than do for me...


thanks

 

[ronlaughlin]

The elevation up there is near 4700'. Using the G1 calculation gave the following result.

Makes much better sense to me. I'll not use the program in my computer for BC calculation anymore. Thank you for the suggestion, and the link to that site!

 

[LarryBud]

Interesting Fellas,

I actually had a chance to shoot at 200 today.

110 of BH 209
200 Grain SST

1.5" high at 100 yards
5" low at 200 yards

I ran the calculations using .261 and the performance matched very closely with the what the program said it would.