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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

Cast Bullet Database - A Work In Progress

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rsterne:
I have updated the Database in the first post to Version 14.... I have added data on 6mm /.243 slugs, and the heavier/longer slugs in .257 cal in a 10" Twist barrel....

Bob

rsterne:
Version 15 is now in the first post for download.... I have added .25 cal NOE cast pellets, and a few other things....

Bob

Scotchmo:
Looking at the airgun bullet database, my initial tests of projectiles from a NOE 154gr BT mold have the G1 Act. BC as a higher value than any other listed projectile. G1 BC = 0.350 at 1050fps in a 1:10 twist. Nothing else even close.

ballisticboy:
It will be partly because G1 is totally the wrong reference drag law for that type of projectile at those speeds, giving an artificially high BC value. Use RA4 or even G7.

Scotchmo:

--- Quote from: ballisticboy on June 03, 2024, 08:26:27 AM ---It will be partly because G1 is totally the wrong reference drag law for that type of projectile at those speeds, giving an artificially high BC value. Use RA4 or even G7.

--- End quote ---

That’s a great point to emphasize. I actually use RA4 for these 2+ caliber long BT slugs. For the 3+ caliber long slugs, G7 might be even better. The three models (G1, G7, RA4) have three different scale factors, so we can’t compare the values directly. Bob gave a link to a drag model conversion calculator. Knowing that G1 was inappropriate for this slug, I still used the converter to get a G1 number for comparison, since G1 is what Bob’s chart uses. RA4 is definitely a better match in this instance, especially when shot at velocities over 1000fps. The RA4 value for this slug came out to 0.270.

When I started my magnum slug journey, I was using G1 and needed to use the multi BC function in Strelok in order to get a good trajectory match for my .257 as I got close to 1000fps. The multi BC function is a work around for a poor drag model match.

I think the G1 model is only appropriate for “bragging rights” when shooting these long slugs at near sonic velocities. For actual trajectory calculation, we should use a more appropriate drag model.

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