On MagnetoSpeeds, BCs, and JBM

[DrThunder88]

So, I'm going to a 1000 yard match next month and am working out my drop chart. The one Dan made for me at Bang Steel using JBM Ballistics was consistent with my load out to 1000 yards, but it was set up for Summer in the mountains of Virginia and used a placeholder velocity to match the observed elevations at various ranges. I'm sure the flatlands of Lower Michigan in Fall will not be too far off, but it raised the question of what my actual muzzle velocity is.

To that end I affixed my MagnetoSpeed Sporter to the end of my rifle and got some data. The rounds I used were from the same batch I took to Bang Steel. They consist of a 115gr Berger VLD hunting bullet over 46.0gr of H1000 in a Hornady case with a CCI BR-2 primer (1% over max, do not attempt). The temperature was about the same (mid 80s), though the altitude was only 1000ft ASL compared to Bang Steel's 2500ft. Speeds averaged consistently around 2890fps, far lower than the placeholder 2960fps.

I was dinking around with JBM using this new muzzle velocity and found the resulting trajectories did not match my observations. If I nudged the BC of the bullets up a bit (0.279 to 0.32) I would get much closer to the mark. Now I'm cool with using approximated inputs to generate outputs that actually work, but I'm left wondering where the inaccuracy is.

The JBM ballistic calculator itself would be my first guess, though I ran the same inputs through another calculator and got the same results. The MagnetoSpeed is another possible source. I don't know how accurate the system is, though its reputation is pretty solid. Finally, is it possible Berger didn't get the BC right? I know Sierra lists BCs at different speeds, so maybe they market the bullet with a lower BC.

[LoneWolf]

I just recently switched from Strelok+ to Shooter (the applied ballistics app) it matches up with my 105 hybrids at 2970 confirmed with a magneto on the first try. With the Strelok+ I had to bump the humidity factor up to 90% for it to match up. that was after playing with a whole mess of factors trying to figure it out. I confirmed my dope in a Varmint match and it has held true since then.

[stomp442]

Its not the BC. Berger does more ballistics testing than anyone out there and they use G7 BC values which are not velocity dependent like G1 BC's are. The things I would check that most people forget about is the actual scope height and the actual click value that your scope is actually moving. You can test that by shooting a tall box test which not only tests the scope but the alignment also. The easy way and sure way to know your come up values is to actually shoot them. Hard data beats a computer guess any day of the week.

[gotcha]

+1, Add to that MV's with sky screens vs. Mag speed ( 10 to 15 ft. from muzzle vs. 2 in. ) and you have another "drop" variable sure to be seen at 1000 yds.

[yobuck]

Stomp is correct, all chronagraph and program data needs to be confirmed by actual shooting.
Which is why competetors depend on sighter shots. Some hunters do also lol.

[LoneWolf]

We don't get sighters where I play.

[upSLIDEdown]

We don't get sighters where I play.

Right?! Lol

[LoneWolf]

Last match had a 515yds cold bore on a horizontal 8" x 4" Oval. Better believe I center punched it too.

[upSLIDEdown]

Last match had a 515yds cold bore on a horizontal 8" x 4" Oval. Better believe I center punched it too.

Hah, well done, sir.

[yobuck]

Well, at that distance it should be an over the shoulder with a mirror shot for the really good guys. lol

[LoneWolf]

Well, at that distance it should be an over the shoulder with a mirror shot for the really good guys. lol
Unfortunately, it'll take me another what 30-40.....50 years!?!? to catch up with you yobuck? [emoji16]

Although I do have technology on my side.....

[yobuck]

Unfortunately, it'll take me another what 30-40.....50 years!?!? to catch up with you yobuck? [emoji16]

Although I do have technology on my side.....

Well you see thats where we disagree.
Technowlodgy is wonderfull, and no doubt great strides have been made in that area in the shooting sports as for equiptment.
But it didnt help 1000 yd benchrest shooters break a record that stood for 14 years.
What did help was one good shooter with a good gun finally got luckier than the others.
And it never helped (any) of them to ever duplicate their own performance.
A young Arthur Cook with an old 52 Winchester with a Unerle scope will still clean the clocks of most modern day
shooters using the most modern equiptment. I mean how much better than a perfect score is possible?

[LoneWolf]

Benchrest is for old bodies. I just don't get the same satisfaction. Too many guys although talented are just trigger pullers. They don't actually shoot their weapons using fundamentals. Not all, but I've seen a lot of weird stuff lately. I'm pretty minimalist. Bipod and a couple bag options

[upSLIDEdown]

Benchrest is for old bodies. I just don't get the same satisfaction. Too many guys although talented are just trigger pullers. They don't actually shoot their weapons using fundamentals. Not all, but I've seen a lot of weird stuff lately. I'm pretty minimalist. Bipod and a couple bag options

Exactly. Otherwise it's almost solely about the gun/load, and very little has to do with the shooter. Seems you and I shoot the same style of shooting and matches. We really need to try to get up when you get out to this side of the country.

[yobuck]

Exactly. Otherwise it's almost solely about the gun/load, and very little has to do with the shooter. Seems you and I shoot the same style of shooting and matches. We really need to try to get up when you get out to this side of the country.

Well do some reasearch and you will find Arther Cook was no bench rest shooter. Nor was my younger sister when she
became national junior girls champ with a 52 Winchester. lol
But bring your gun here and do what we do here and see if you leave with the same opinions.
You know what? we dont tell our teenage kids and grandkids to wait till someday when their as good as dad.
Their as good right now, and so are the old guys who maybe should be sitting on a porch somewhere.

[upSLIDEdown]

Well do some reasearch and you will find Arther Cook was no bench rest shooter. Nor was my younger sister when she
became national junior girls champ with a 52 Winchester. lol
But bring your gun here and do what we do here and see if you leave with the same opinions.
You know what? we dont tell our teenage kids and grandkids to wait till someday when their as good as dad.
Their as good right now, and so are the old guys who maybe should be sitting on a porch somewhere.

I never said Arther Cook was. I was replying to LoneWolf's comment, regarding benchrest. I have no clue who Arther Cook is. Never claimed to.

I don't know where 'here' is, but I'd love to if it's feasible.

[yobuck]

I never said Arther Cook was. I was replying to LoneWolf's comment, regarding benchrest. I have no clue who Arther Cook is. Never claimed to.

I don't know where 'here' is, but I'd love to if it's feasible.

Well check the milage to Driftwood PA 15832.
And excuse me for asking, but you dont really consider prone/bipod in the same realm as prone position do you?
I have shooters (mostly western) telling me they can shoot as well prone bipod on the ground as they can from a bench.
And i have no doubt some can. After all, whats more solid than the ground. But ace the bipod and use a sling and its now a
new ball game called prone shooting. Seems to me a guy named Tubbs is pretty good at it. And before him a guy named Wigger, and a gal named Murdock.
Maybe we could break down bench shooting into classes also. Rickety bench class and solid bench class. After all its only fair we all have a shot at winning. lol

[upSLIDEdown]

Well check the milage to Driftwood PA 15832.
And excuse me for asking, but you dont really consider prone/bipod in the same realm as prone position do you?
I have shooters (mostly western) telling me they can shoot as well prone bipod on the ground as they can from a bench.
And i have no doubt some can. After all, whats more solid than the ground. But ace the bipod and use a sling and its now a
new ball game called prone shooting. Seems to me a guy named Tubbs is pretty good at it. And before him a guy named Wigger, and a gal named Murdock.
Maybe we could break down bench shooting into classes also. Rickety bench class and solid bench class. After all its only fair we all have a shot at winning. lol

I'll check the drive time in a bit.
EDIT: Looks like about a 6 and a half-ish hour trip, so not awful.

No, definitely not the same thing. I might have been born at night, but it wasn't last night. I think you're going way overboard with what was said. I only said benchrest is very different that the types of shooting I do, which is mostly bipod/bag, and positional from barricades. Shooting a 30 lb flat bottom gun and rides a screw jack is much easier and takes almost all the human error out of it.

[LoneWolf]

Didn't mean any offense to benchrest or the art of shooting off a bench in general. I don't claim to be the best, but my sport forces you to be good all around in concern to the sport of shooting. Sometimes a stage in a match has you take a few shots off a bench then move to another position. Other times you have to hit an off hand shots in order to move to prone or whatever it may be.

The beauty is you never know the exact course of fire till you get there.

[upSLIDEdown]

Didn't mean any offense to benchrest or the art of shooting off a bench in general. I don't claim to be the best, but my sport forces you to be good all around in concern to the sport of shooting. Sometimes a stage in a match has you take a few shots off a bench then move to another position. Other times you have to hit an off hand shots in order to move to prone or whatever it may be.

The beauty is you never know the exact course of fire till you get there.

Exactly.