Muzzle Velocity question..

[dogdoc]

Ok guys, I am not a rifle guru and I don't have a way of measuring muzzle velocity with my AR. My AR has a 16" barrel with a 1:9 twist. I am shooting the Hornady 55gr SP bullet. Shoots great out of my gun. It advertises a muzzle velocity of 3240. It is my understanding that the speed is measured from a 20" barrel? Does a shorter barrel change the muzzle velocity. So what I am trying to figure out is bullet drop at distances past 200 yards.

thanks
todd

 

[Native Hunter]

Todd, yes your velocity will be somewhat lower, but you will still be shooting nice and flat.

Just going by memory this will be close:

Sight the gun to be dead on at 200 yards. You will be around 1.0 to 1.5 inches high at 100 yards. At 300 yards you will be hitting about from 7 to 8 inches low. At 400 yards you will be around 19 to 21 inches low.

This all depends on a lot of factors such as ballistic coefficient, scope height, elevation, etc., etc. but this will get you in the ballpark.

 

[Elkaddict]

NH has given you pretty good info. There is more to it though. Having chronographed lots of factory loads over the decades, I've found very few that are close to advertised velocities (Weatherby ammo is a notable exception). The other oddity is there are fast and slow barrels. I've chronograghed equal length barrels and seen 100fps differences, even out of the same model guns. I'd check your zero using NH's data and see how close you are. If you know your precise range, trajectory and bullet BC, you can also come pretty close to backing into your velocity. If I were to guess, I'd say your probably closer to 3,000 fps.

 

[Native Hunter]

Just to check my memory I went to handloads.com and used their ballistic calculator with some assumptions:

I assumed a premium boat tail bullet with a BC = .267 (a Nosler Ballistic Tip 55 grain)
I assumed an elevation of 2,000 feet above sea level
I assumed a sight height of 2.0 inches
I assumed a velocity of 3,050 fps
I assumed a temp of 85 deg F

100 yards = 1.36 inches high (I said between 1.0 and 1.5)
200 yards = zero
300 yards = 7.32 inches low (I said between 7 and 8 inches low)
400 yards = 22.24 inches low (I said between 19 and 21, so I was off 1.24+ inches)

So, I was close if my assumptions were correct. But as Elkaddict said - you won't know for sure until you actually check it.

Good luck.

 

[dogdoc]

Now that's a pretty darn impressive memory for an old man

Thanks guys.

 

[dogghr]

Now that's a pretty darn impressive memory for an old man

Thanks guys.

I'd never argue with the Daniel Boone of KY. I agree Elk said, they do vary . I think longer barrels are not as necessary these days as todays ammo seem to get a more complete burn in a shorter time, thus not the necessity of the longer barrel for a complete burn as one variable in the equation. But thats just an amateur opinion.
Do you shoot to 400 Yds, Doc? And what scope are you using if you do?

 

[dogdoc]

I'd never argue with the Daniel Boone of KY. I agree Elk said, they do vary . I think longer barrels are not as necessary these days as todays ammo seem to get a more complete burn in a shorter time, thus not the necessity of the longer barrel for a complete burn as one variable in the equation. But thats just an amateur opinion.
Do you shoot to 400 Yds, Doc? And what scope are you using if you do?

No I don't but I would like to feel comfortable shooting out to 300 yards with my AR. I have a Nikon P223 scope. The scope is designed for an AR and the exact bullet/velocity that I shoot. The reticle is designed to be sighted in at 100 yards then has marks at 50 yard increments out to 600 yards. It also has a calibrated elevation turret you can manually change if you want to hold on center. I know I'll just have to get out and shoot it to see if Nikon's "Spot on ballistic match technology" actually works with my gun.

 

[swat1018]

You're taking all the fun out of it! Go shoot it! Chrono's aren't that expensive, buy or borrow one. With that data you can get a turret engraved with the elevation marked in yardage (in case your memory isn't as good as N.H.)

 

[DocHolladay]

Hornady tests using a 24" barrel. A rough guess is 50fps per inch(that is the avg i see with a chrono). I would guess that your bullet is traveling in the 2800-2900fps range. Miles may vary based on conditions of where you live and the barrel. If you can chrono the load, you may have to play with the BC a little to get it to match up as the BC changes with velocity. These guys have a really good Ballistics calculator that works. I also attached some video of how they use it.
online software- http://www.gunwerks.com/ballistics
Playlist- G7 Free Online Ballistics Calculator
Good video-

 

[Native Hunter]

His post said that he was shooting a Hornady bullet, but he didn't say he was using Hornday factory ammo.

If it is Hornday factory ammo, I agree with Doc Hol. that Hornady uses a 24 inch barrel (rather than a 20 inch barrel as was stated) to derive most of their published velocities, and I would also agree that with a 16 inch barrel, you will be down in the range of 2,800 to 2,900 fps. That would give you more drop than the velocity I assumed.

The fun part will be going to the field and finding out. Good luck!

 

[DocHolladay]

His post said that he was shooting a Hornady bullet, but he didn't say he was using Hornday factory ammo.

I assumed it was factory ammo, since he stated that the advertised muzzle velocity was 3240.

 

[Native Hunter]

I assumed it was factory ammo, since he stated that the advertised muzzle velocity was 3240.

And I would say that is a good assumption.

 

[Native Hunter]

Todd, if we assume 2,900 fps using the same data as above, you should be close to this

100 yards = +1.62
200 Yards = zero
300 Yards = - 8.28
400 Yards = - 25.08

If you take the published data of 3,240 fps it would look like this:

100 yards = + 1.09
200 yards = zero
300 yards = - 6.33
400 yards = - 19.25

So, basically what this tells you is that out to 300 yards the drop in velocity doesn't affect the bullet trajectory a great deal (around 2 inches) if zeroed at 200 yards. At 400 yards it will be around 6 inches difference, which might be enough to make you miss a coyote.

So this gives you a ballpark estimate on the difference that a drop in velocity of that magnitude would actually make. But as everyone has stated, you won't know precisely until you actually shoot it.

 

[dogdoc]

yes, it is a factory load.

http://www.hornady.com/store/223-REM-55-GR-SP/

 

[dogdoc]

I'm going to get the new scope mounted. I have a laser bore sight so I will put the laser on with the scope already on the rifle and mark it on a target at the house and then put the new scope and get it lined up at the laser point on the old scope. That should get me on paper and then try to go shoot later next week at the farm. My biggest problem with sighting in is getting the ability to shoot on a day that is not windy. Lots of wind this time of year. Start getting out past 200 yards and that a decent cross wind really affects that 223 bullet.

I'll post up pics after I get her sighted in. Most of my shots on yotes will be within 100 yards but I do hunt a few big fields where I could take a 300 yard shot so just want to try to get dialed in where I have a decent chance of connecting on a shot out that far.

thanks again for all the help guys.
todd

 

[Native Hunter]

I'm going to get the new scope mounted. I have a laser bore sight so I will put the laser on with the scope already on the rifle and mark it on a target at the house and then put the new scope and get it lined up at the laser point on the old scope. That should get me on paper and then try to go shoot later next week at the farm. My biggest problem with sighting in is getting the ability to shoot on a day that is not windy. Lots of wind this time of year. Start getting out past 200 yards and that a decent cross wind really affects that 223 bullet.

I'll post up pics after I get her sighted in. Most of my shots on yotes will be within 100 yards but I do hunt a few big fields where I could take a 300 yard shot so just want to try to get dialed in where I have a decent chance of connecting on a shot out that far.

thanks again for all the help guys.
todd

Good luck Todd.

There's no way to know exactly until you start shooting, but if you sight in dead on at 200 yds with your 200 yard crosshair, my guess is that at 300 yds you will be 3 or 4 inches low with your 300 yard crosshair. That's about how much difference I would expect. It will be in the ballpark......

 

[DocHolladay]

I entered info into the app on my phone and got 9.2" drop with a 200yd zero, at 300yds. 400yds gives a 28.4" drop. I used Oklahoma City for base info(temp next week, elevation{approx 1200ft}, humidity). Its been spot on for me, as long as I enter correct info. I have to change things like the BC, because of factory errors, barrel lengths, enviromental effects. I use the iSnipe App.