Help calculate muzzle velocity and drop

[sasquatch]

So, I don’t know if this is even possible, I’d assume it is. But here goes

I do not have a Chronograph to run calculations, however I have shot a few different yardages and have the measured drops to reference.

I am hoping to figure out from these bullet drops what the muzzle velocity should be to achieve these known drops. I figured if anyone can it’s one of you guys.

I am shooting a 280 AI. The ammo is loaded by cooper creek. The bullet is Hornady 162 gr ELD-X

Now, the ammo box says 2970 for the muzzle velocity, but comparing to the bullet drop on the ammo box what I am achieving cant be right.

With a 100yd sighted zero, I am 3-1/4" low at 200yards, and then 13.5" low at 300yds.

i am wondering what kind of true velocity i may be getting and also from this what should my 400 and 500yd drop be??

This picture is of the manufactures calculations. The drops I got are like 50% more than they say it should be

Sent from my iPhone using Tapatalk Pro

 

[hereinaz]

Look up Gravity Ballistics. It’s specifically for calculating actual drop off of data you provide.

 

[hereinaz]

I still question the moon landing, your existence and whether aliens crashed at Roswell.

 

[Bluumoon]

Either of these two will do it. You’ll get better data the further out you can plug in before going transonic.

 

[MuleyFever]

Download a ballistics calculator and input your bullet data and weather then play with the velocity until it matches your drops. Make sure the sight over bore measurement is correct.

 

[sasquatch]

Thanks fellas, looks like I’m only coming up with like 2720 FPS

Seems really slow for the caliber.


Sent from my iPhone using Tapatalk Pro

 

[Koda_]

I came up with the same 2720mv as you. If your actually getting -3.25" drop at 200yds then your mv is not 2970fps. That said, Ive never had factory ammo live up to its advertised velocity. If your going to hunt past 300yds then you need to buy a chrono because you also don't want to hunt past the bullets terminal velocity, especially with that low of a muzzle velocity.

Here's a link to your data out to 500yds but it wont be precise without your altitude and actual mv average.

ShootersCalculator.com | Ballistic Trajectory Calculator

Calculates the ballistic trajectory of a bullet fired from a rifle, handgun or other firearm. Produces a ballistic trajectory chart and table that shows the drop, velocity, kinetic energy, windage, and trajectory of a bullet.

shooterscalculator.com

 

[hereinaz]

Thanks fellas, looks like I’m only coming up with like 2720 FPS

Seems really slow for the caliber.


Sent from my iPhone using Tapatalk Pro

Bullets don’t lie.

If it’s not the bullet, then it’s something else. Some things to consider as I think out loud for exclusion. Hard to see one of these as being the sole cause, but I would scratch my head too…

Is your barrel slow?
Was it extremely cold when you shot? Is the powder temp sensitive?
What is your barrel length vs. the box barrel?
How are you shooting and measuring drop?
If dialing, does your scope dial accurately?
Is it actually 200 and 300 yards?
Is your 100 yard zero perfect?
How many rounds did you shoot to verify your drop numbers? How large were the groups?
Did you change positions drastically to shoot the different yardages?
Have you asked Copper Creek?

 

[EdP]

Your calculated MV does seem low. My .280AI Cooper w/24" barrel gives 2900fps shooting 160gr Accubonds.

Hereinaz listed a bunch of factors that can become variables in calculating MV. You can get a decent chronograph for about $150 and get an accurate reading and not have to worry about those factors.

 

[Macintosh]

The truing function on a ballistics app is designed specifically for this. You can start with a chrono velocity or a box velocity, but regardless, once you true it the app will spit out accurate solutions INSIDE the range you trued. If you velocity true at 300 yards, dont expect it to give you a perfect solution at 600 or 900 yards.

However 3+” at 200 yards seems like too much to me (edit—did not plug in that bullet but based on my 6.5 at under 2700fps, even at 2720fps MV it seems like a lot of drop). My suspicion is you have a couple small issues stacked on top of each other that are giving you an incorrect result. For example, if you zeroed off 3-round groups causing your zero to be off by 1/4”, then you checked drop at 200 off a 3-round group causing your group center to be off by 1/2 or 3/4 inch in the opposite direction—then you’d have an extra inch or more of calculated drop from your actual drop. An inch doesnt matter at 100 or 200 yards, but it will compound as distance increases, and as you stack that error on top of your mechanical precision error, your wobble, etc, it can quickly cause inexplicable problems. You need to base your adjustments and truing off more than just a 3-round group, since those 3 rounds often dont represent the average group-center that the gun will shoot-to for any random 3 shots.

 

[sasquatch]

Bullets don’t lie.

If it’s not the bullet, then it’s something else. Some things to consider as I think out loud for exclusion. Hard to see one of these as being the sole cause, but I would scratch my head too…

Is your barrel slow?
Was it extremely cold when you shot? Is the powder temp sensitive?
What is your barrel length vs. the box barrel?
How are you shooting and measuring drop?
If dialing, does your scope dial accurately?
Is it actually 200 and 300 yards?
Is your 100 yard zero perfect?
How many rounds did you shoot to verify your drop numbers? How large were the groups?
Did you change positions drastically to shoot the different yardages?
Have you asked Copper Creek?

Barrel slow? No idea, need to test some more ammo when I have time

Not sure if the question on how I’m shooting and measuring drop. But I shot it off a shooting bench, no dialing. Just shot a tall target to find out how low the bullet drops at 200/300 yards.

The yardages were ranged with a quality rangefinder

I did not shoot a lot of bullets. I zeroed it last year, and yesterday verified my zero is at 100. I prob have 10 total shots verifying the zero. The groups are pretty tight, under MOA.

For the shots to check bullet drop. I did not shoot a lot of times, just 2x each. Those two shots were still under MOA.

It was pretty calm, and temp was about 60 degrees

The barrel is 24”, the rifle is a Kimber MA

Sent from my iPhone using Tapatalk Pro

 

[SDHNTR]

My bet is your true zero is a bit low. Or your drops aren’t as true as you think. 2x shots is not enough. And you need more yardage. I want at least 500 when I true drops.

You may have a slowish barrel too.

 

[sasquatch]

My bet is your true zero is a bit low. Or your drops aren’t as true as you think. 2x shots is not enough. And you need more yardage. I want at least 500 when I true drops.

You may have a slowish barrel too.

There will be more testing to come as time allows and I get more ammo. But I’d say my true zero, if anything, is high not low.


Sent from my iPhone using Tapatalk Pro

 

[2five7]

You should always test drops at least out to the maximum range you're wanting to shoot, or farther. Shooting at 300 and extrapolating to 500 is not the best way to go.

 

[Koda_]

What makes a barrel, "slow"?

 

[Harvey_NW]

What makes a barrel, "slow"?

Bullets not coming out as fast as expected.

Kidding aside, some barrels are just slow. Tikka barrels are notorious for it. Some theorize that lapped cut rifled barrels are often faster because they're nearly perfect and polished with the least resistance. I've never found any credible information on the subject, it seems like it's just one of those unknowns.

 

[Koda_]

Barrel slow? No idea, need to test some more ammo when I have time

Not sure if the question on how I’m shooting and measuring drop. But I shot it off a shooting bench, no dialing. Just shot a tall target to find out how low the bullet drops at 200/300 yards.

The yardages were ranged with a quality rangefinder

I did not shoot a lot of bullets. I zeroed it last year, and yesterday verified my zero is at 100. I prob have 10 total shots verifying the zero. The groups are pretty tight, under MOA.

For the shots to check bullet drop. I did not shoot a lot of times, just 2x each. Those two shots were still under MOA.

It was pretty calm, and temp was about 60 degrees

The barrel is 24”, the rifle is a Kimber MA

Sent from my iPhone using Tapatalk Pro

Based on what you describe i suspect the ammo is bad. I wouldnt wast time and money testing more of the ammo. That said, the last thing you need to do to prove its the ammo is actually measure its muzzle velocity. Older chronos are affordable and, IMO, a must have for anyone wanting to shoot past their MPBR zero with factory ammo.

All the factory ammo Ive chronod has ran slow, one brand ran really slow like your estimating so I wouldnt be surprised if thats what your experiencing. But at this point the only way to validate your estimate is to chrono the ammo. At least 3 rounds to get a rough avaerage.

 

[TaperPin]

It is a bit of a mental adjustment to let go of what’s printed on the box and use info from actual groups, and even a chronograph can’t change it. I can remember the disappointment of a slow rifle more than once.

Make sure your scope height over the bore is correct - the difference isn’t huge if it’s off slightly, but it is a thing.

New barrels are slow until the bore roughens up some, ammo is usually slower than what’s on the box, perhaps this is an extra slow lot, and some barrels simply don’t produce the top velocity even after a few hundred rounds.

 

[Koda_]

Bullets not coming out as fast as expected.

Kidding aside, some barrels are just slow. Tikka barrels are notorious for it. Some theorize that lapped cut rifled barrels are often faster because they're nearly perfect and polished with the least resistance. I've never found any credible information on the subject, it seems like it's just one of those unknowns.

The only way Im aware of is if a barrel is brand new and its chamber isnt firecracked enough yet to increase pressure and speed up the MV.

So the question is, is the OPs gun brand new?

 

[Megalodon]

put 150 rounds of cheap ammo through it as practice, then test again with the copper creek stuff. It's very common for mass produced factory barrels to speed up over the first 100-200 rounds. I doubt you pick up 200 fps, but 100 isn't out of the question.