Ballistics

[jmd]

Has anyone ever ran into a situation where your ballistics calculator results were way off? Maybe I've been lucky and the results have been fairly accurate with the exception being this particular rifle & load. I'm shooting a pretty mild load out of a 22-250. I haven't gotten it over a chronograph yet, but it shouldn't be going any faster than about 3450fps. I'm shooting a 55gr Berger flat base HP (.210 BC). With a 200 yard zero it should be dropping around 21-22" at 400 from what I see. However, it is actually only dropping about 12.5" at 400. My buddy checked and told me the bullet would have to be screaming out at about 4100fps to get that trajectory. I checked later & verified that he was correct. That velocity isn't possible. My question is how does this happen? I assume it has something to do with the node. Maybe it isn't a true node & the barrel is whipping up a little as the bullet exits????? If that's the case how come I don't see it at 100 & 200 yards? I know the real answer is to just figure it out by shooting at longer distances & checking velocity over a chronograph. I just haven't made it to a bigger range yet this year. Has anyone else experienced a situation similar to this? If so, what was the cause? I know strange things can happen, but I like find logical explanations for why.

 

[BigDMT]

Your guess is as good as anyone's until you chronograph the load. Do that, then come talk to us.....

PS: is your 200 yard zero guesstimated on a 100 yard target? Or did you actually shoot 200 yards to get your zero?

 

[jmd]

It's a 200 yard zero not an estimation off of a 100 yard target. Yes I need to shoot it over a chronograph as I stated, but I think we can all agree that 4100fps with a 55gr bullet out of a 22-250 is not possible. Obviously something else is going on here an it isn't that I put a horribly wrong velocity in.

 

[jmd]

As I previously stated, it was a confirmed 200 yard zero. It was not hitting 3 or 4 inches high. It was zeroed in a 5/8" equilateral triangle for a group.

 

[BigDMT]

It's a 200 yard zero not an estimation off of a 100 yard target. Yes I need to shoot it over a chronograph as I stated, but I think we can all agree that 4100fps with a 55gr bullet out of a 22-250 is not possible. Obviously something else is going on here an it isn't that I put a horribly wrong velocity in.

Yeah but we don't really know without the chronograph data.

I had a load for a Ruger MKII factory rifle in 300 Wm that pushed the 180gr bullets at 3230 fps. We tried the same exact ammo in my father's older Ruger M77 tang safety from the early 1980's and the bullets were only going 3060 fps. Both had factory 24" barrels.

I've also had many loads exceed the speeds listed in manuals. And then again, I've had loadsgo much slower than listed speeds.

The chronograph is key. Otherwise we are all just guessing here...

 

[BigDMT]

Could have also been a high magnification scope parallax issue where the focus wasn't adjusted correctly. But again, that's just a guess. Really need the chrony info.

 

[Syncrowave]

Are you sure you're inputting your scope height in the ballistics program accurately? Sounds like your scope is higher than you think.

 

[xswanted]

Shoot it at 100 and then at 300 and see what you get.

 

[dragman]

Game of thousands. A bore on the tighter side and bullets for there caliber on the thickest side raise pressure. The b.c you get is changed the second it gets fired down the barrel. I had a 300rum that was chronographed at 3225 with 215 hybrids when I zerod it and took it out to 1000 and built my chart to keep the b.c the same I had to change the fps to almost 3400fps. No its not going that fast but the b.c is increasing and its easier to adjust the fps to build your charts.

 

[Lapua40X]

.. I haven't gotten it over a chronograph yet, ...

I suspect you've answered your own question.

 

[jmd]

Well I kind answered it. I went out today and was unable to duplicate it so I have no clue what originally happened. I was actually kind of pleasantly surprised that the calculated ballistics were pretty much right on. It still doesn't explain what the hell happened at 400 yards last week. I think somebody mentioned parallax. Who knows, maybe I forgot to adjust the objective lens. Maybe there was some weird mini climate in the valley I was shooting over. I have no clue since is it didn't repeat today.

I was interested in hearing of anyone that had a situation like this because to this day my buddy swears his 30-06 shoots higher at 300 yards with a 200 yard zero. I've never seen it, but claims it some how defies the laws of physics and gains a few inches at 300.
Thanks for all the feedback.

 

[BigDMT]

...I was interested in hearing of anyone that had a situation like this because to this day my buddy swears his 30-06 shoots higher at 300 yards with a 200 yard zero. I've never seen it, but claims it some how defies the laws of physics and gains a few inches at 300.
Thanks for all the feedback.

That's not possible. He's either mistaken or doing something terribly wrong. Gravity is gravity

But glad to hear you got your mystery solved at this point. Parallax can definitely change point of impact pretty drastically on high power scopes, especially at long range. High moisture content in the air can change things a bit as well, but probably not quite that much. Take care