Factory ballistic twins in different categories?

[philthygeezer]

Fr'instance, is a factory 1300fps .45-70 trapdoor load the twin of a 1280 fps HVHP .22LR for all intents and purposes? Are the .223 and .308 ballistic twins at certain bullet weights, or do you have to match the .223 55-grainer with say, a 7mm magnum at ~3###x fps?

How would this work? If one could ballistically 'pair up' a cheaper load with one's medium bore, one could save scads of coin practicing at all ranges and then be right on the mark with the more expensive rounds.

 

[Ruffed Grouse]

Trajectory-wise, could sometimes come close, at least at modest range. Otherwise, no.

RG

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[stevesummit]

if you match the B.C and velocity it wont matter if one is 50 cal and the other 17 cal they will fly the same trajectory out to the end of the flight

 

[curtmg]

if you match the B.C and velocity it wont matter if one is 50 cal and the other 17 cal they will fly the same trajectory out to the end of the flight

This is correct. But a quick peak in my Speer manual, shows the bigger caliber bullets tend to have much higher BC's, so it might not be as easy in practice as in theory.

 

[ENIGMATIC1]

How would this work? If one could ballistically 'pair up' a cheaper load with one's medium bore, one could save scads of coin practicing at all ranges and then be right on the mark with the more expensive rounds.

if you match the B.C and velocity it wont matter if one is 50 cal and the other 17 cal they will fly the same trajectory out to the end of the flight

Wouldn't wind still affect them differently...

 

[Eagleye]

Wouldn't wind still affect them differently...

Not noticeably. Eagleye.

 

[ENIGMATIC1]

Not noticeably. Eagleye.

Hmmm, doesn't make sense in my mind, but I fiddled with the ballistics calculator and it backs up what you say.

Interesting, thanks!

 

[curtmg]

Hmmm, doesn't make sense in my mind, but I fiddled with the ballistics calculator and it backs up what you say.

Interesting, thanks!

Again, the problem will be your 22 caliber bullets typically have BC's in the .2-.3 range, and 30 caliber bullets are usually .4+. So if you have a very efficient 22 cal bullet and run it against a very inefficient 30 cal, with identical BC's they'll run the same. This is why bigger calibres with higher BC's are usually chosen over smaller ones. Not to say of course that you can't do very well with smaller rounds, you just need more correction for drop and wind.

 

[220Swifty]

Recoil and the handling characteristics of the rifle come into play as well.

I would sooner load a cheap cup and core bullet and hammer away all summer with my favorite deer rifle, than to try and find something that flies similar and practice with a rifle i wont be hunting with.

That being said, i find any time spent behind any rifle is good for keeping in form.

 

[mmattockx]

Wouldn't wind still affect them differently...

Wind drift is solely dependent on BC and muzzle velocity.

Mark

 

[ENIGMATIC1]

Wind drift is solely dependent on BC and muzzle velocity.

Mark

I was thinking that the weight, as well as side profile would have some effect on it, but according to the ballistics calculator it does not.

Still doesn't make sense in my brain however.

 

[Juster]

I was thinking that the weight, as well as side profile would have some effect on it, but according to the ballistics calculator it does not.

Still doesn't make sense in my brain however.

Drop a bullet by hand 12" in a 10MPH wind. How far sideways does does the the bullet go? Not noticeably.
A bullet traveling a few hundred yards with the same drop will move sideways several inches in the same wind.
Not because the wind is pushing it sideways, but because the bullet yaws, and changes direction.

 

[mmattockx]

I was thinking that the weight, as well as side profile would have some effect on it, but according to the ballistics calculator it does not.

Still doesn't make sense in my brain however.

That's because the wind does not push on the side of the bullet.

Not because the wind is pushing it sideways, but because the bullet yaws, and changes direction.

Juster has it right.

Due to the spin stabilization of the bullet, it will yaw and point into the wind (like an arrow shot with a side wind, it weathervanes into the wind). The nature of the stabilization makes the bullet always want to point into the wind. The reason that the bullet drifts with the wind is that the aerodynamic drag force acting on the bullet is always in line with the bullet axis. When the bullet yaws into the wind, the drag force is now acting slightly offline from the trajectory and the misalignment generates a sideforce that pulls the bullet to the side.

Mark

 

[ENIGMATIC1]

Not sure if my brain is feeling any better or not.. but that is really interesting guys. Never thought of it like the arrow analogy.

Thanks again.

Wait why am I thanking you.. my brain hurts now...

 

[Rman]

If you have some software, you can load up different combos, on different loads and calibres to find how close they match. For example, a .243AI shooting a 105 Amax at 3200, is very close to a .338 LM shooting a 300 grain MK at 2800. These loads can be easily adjusted via fps to match each other.

R.

 

[mmattockx]

If you have some software, you can load up different combos, on different loads and calibres to find how close they match. For example, a .243AI shooting a 105 Amax at 3200, is very close to a .338 LM shooting a 300 grain MK at 2800. These loads can be easily adjusted via fps to match each other.

R.

As noted on the first page, all you need to do is match BC and muzzle velocity and the two loads/calibers will match perfectly, for trajectory and wind drift.

Mark

 

[tjhaile]

I was thinking that the weight, as well as side profile would have some effect on it, but according to the ballistics calculator it does not.

Still doesn't make sense in my brain however.

Ballistic coefficient is a function of both weight and shape. A projectile made of depleted uranium, for example, would have a higher ballistic coefficient than one made of lead with the same size and shape.

 

[rem338win]

I was thinking that the weight, as well as side profile would have some effect on it, but according to the ballistics calculator it does not.

Still doesn't make sense in my brain however.

That's because our brains don't thinl at 2800fps nor can it comprehend travelling 7 football fields in less than a second. Frankly, its over our
heads

 

[Rman]

As noted on the first page, all you need to do is match BC and muzzle velocity and the two loads/calibers will match perfectly, for trajectory and wind drift.

Mark

I was trying to suggest that niether the BC and muzzle velocity have to match. You can correct with more/less velocity, or more/less BC, to make up differences between the two.

R.

 

[Grizzlypeg]

That's because the wind does not push on the side of the bullet.



Juster has it right.

Due to the spin stabilization of the bullet, it will yaw and point into the wind (like an arrow shot with a side wind, it weathervanes into the wind).
Mark

So if it points into the wind, but carries down wind, doesn't that mean the bullet is going sideways to some degree wrt to the target? That must really compound the drag.