Ballistic Coefficients for some Magma Mold boolits?

[emmett22405]

0 replies to this query on another site. I have zero luck calculating or, more importantly finding bc's for the magma molds boolits in: 30-30 165 gr 0.308 diam., 40-65 260 grain .408 diam., 300 grain 45-70 0.458 diam., and 350 grain 45-70 0.458 diam. Even called Magma and they do not have them and made some reference to an old out of print (unremembered title by Magma) publication which I have been unable to find and reference to. Any info much appreciated. Thanks

[dondiego]

You might have to contact Magma to get the info you need.

[megasupermagnum]

I don't know what the Magma bullets look like, but I'm assuming they are similar to the following. Estimated BC is in the bottom right.

https://i.ibb.co/svRjPx2/R-C-B-S-Mold-40-300-CSA-300-gr-Sketch.jpg (https://ibb.co/svRjPx2) https://i.ibb.co/GVpfNPc/N-O-E-Mold-311-165-GC-RF-168-gr-Sketch.jpg (https://ibb.co/GVpfNPc) https://i.ibb.co/tpnmdj5/Lyman-Mold-457121-385-385-gr-Sketch.jpg (https://ibb.co/tpnmdj5)

[outdoorfan]

I have measured the NOE 30 xcb BC in my 30-06 at roughly .25.

For pistol bullets with the typical .7-.8 meplat, BC really suffers. Maybe .16-.2 depending on sectional density, at least for light to medium for weight for caliber bullets.

[W.R.Buchanan]

I have one Magma Mould. It is for a .44 cal 190 gr SWC. It has a BC of about -25. It is shorter than it's dia ! It was also useless.

The mould itself worked great.

Randy

[TurnipEaterDown]

It happens that published ballistic coefficients are sometimes incorrect, and it may be due to modeling or other factors.
Not that I want to "bad mouth" any company, but it USED TO BE that the Barnes published BCs were way off. Maybe they corrected this, maybe there is some reason behind it I don't know, but I do know that when we used their BC, and measured Muzzle Velocity out of firearms we had years ago, the drop at known distance was Much more than they predicted.
One particular factor that comes in to account in field shooing is bullet stability. A bullet doesn't have to be grossly unstable (keyhole) or just shoot "bad" groups for there to be a pronounced effect. Another is atmospheric density (barometric pressure). Thinner air makes the bullet calculate as more "sleek", IF you assume std atmospheric conditions.
Models assume certain things, and testing (by bullet companies) is either done at standard conditions or corrected to the same.
There are means to determine a BC of a bullet yourself. Known yardage (distance change over bullet course of flight) and drop, or better yet, known distance change and velocity change.
I do not know for a fact, as I do not have one, but I think if the bullet is large enough of diameter, the velocities given by a Lab Radar chronograph should let you compute the BC (if it does not give it straight out to you).
Anyone have a Lab Radar Chronograph and able to comment?

[outdoorfan]

I have actually chronographed bullets at 100,200, and even 300 yards, so I am not guessing.

I agree that manufacturers tend to embilish the numbers. NOE is isn't too bad, but usually a bit optimistic.

And I've also measured the 165 gr Barnes TSX in my 30-06, and I also found that to be optimistic (according to Barnes published BC) as well.

[megasupermagnum]

It's possible that the software estimates BC at a low velocity, which from what I can tell often higher than when the same bullet is fired at higher velocity.