Ruger Ar-556 Trajectory Problem

[Matthew15]

Howdy,

I have a Ruger Ar-556 that has me perplexed. It is all stock except a 3 lb CNC aftermarket trigger and free float handgaurd. I have a Vortex Crossfire 3-9x40 mounted on it. The rings are fairly tall (3 inches from center of bore to center of scope) for me to get a good sight picture/cheek weld. Everything is tight and the gun cycles just fine.

The other day I worked up some handloads with 77 gr tmk bullets. From what I have seen online/loading data, I estimate they are traveling about 2500-2600 fps using 24.4 gr of VV N540 and CCI 450 primers. Of a bipod, I am shooting sub 1 inch groups with the best being 0.70" at 100 yards. Ballistic calculator says 0" at 50 yards, 1.8" high at 100 yards and again 0" at 200 yards.

I sighted it in dead on at 50 yards this morning. At 100 yards, the bullets strike 2 inches high which is about what I expected. Now at 200 yards, I was expecting them to be dead on or no more than 2" lower than the point of aim. However, at 200 yards, the bullets stuck the target 4 inches below the point of aim. That is a 6" drop from 100 yards to 200 yards. I have also experienced this with other loads (Frontier factory ammo with a 68 gr hollow point and 77 gr tmk handloads with H322) which acts in the same way. This happens both off a shooting bench and prone.

Another thing I should also mention is that something has changed but I do not know what it would be. When I was shooting it back in the spring with the 77 gr tmk handloads with H322, I had it sighted in dead on at 200 and 2.5" high at 100 yards. Since then, I did nothing to the gun and now it drops low at 200 yards.

What do you guys think could be wrong?

 

[snox801]

Try zero at 100 then see what it does at 50 and 200. 50 yards zero is never the way to do it. You can adjust your 100 to get what you want at 50 but I think your problem lays in that. Other than that you have me real idea without a chrono. Gotta start somewhere. And without proper measurements to start you are chasing your tail.

 

[Matthew15]

Thank you, I will try to find a chono and zero at 100 yards.

 

[cohunt]

Are you using a ballistic app to figure out your drop? Or what means are you using?

The scope height will affect your zero and drop and you'll need a more accurate form of figuring out your speeds than just guessing.

 

[Deleted member 115360]

3" to get good cheek weld?

Are you a horse?

 

[milo-2]

Before anything else, do you have any idea of the pressures you are generating with the N540 load? Your bullet is traveling way faster than you have estimated, which skews your downrange projections.
2nd, use a free ballistic app, or buy one for your phone, through your ramblings, there is one huge difference between 2" high and 2.5" at 100 yards.
Not trying to be a jerk, but you need to sit back and revisit all you are doing. Please, find some help close by.

 

[Kansaswoodguy]

3" to get good cheek weld?

Are you a horse?

3" is pretty normal for AR rifles

 

[Kansaswoodguy]

50 yard zero is just to get you on paper. What I would do is sight in at 200yds then measure how high your hitting at 100yds and adjust you muzzle velocity on your app to match that measurement. Then shoot at 300yds and see if your numbers are working out any better.

 

[SDPlinker]

+1 on chronograph!

 

[Deleted member 115360]

3" is pretty normal for AR rifles

I own a dozen of them or more. I just checked my highest one with a ridiculously tall Burris preper mount, and it looks like it's about 2.25". I can't imagine it being any higher than that, but, I have a really normal face.

 

[Kansaswoodguy]

I have maybe 1/2 dozen AR's using that Burris PEPR mount but I add 1/2" riser rails to all of my AR's in addition to the high rings. For guys that shoot a few shots and call it good being all crushed up behind an AR scope is fine. I will shoot for hours and am there to enjoy myself i have no interest in being uncomfortable behind the rifle. In addition I shoot out to 1000yds with many of my AR's so the rails I add are 20MOA. This puts your scope pretty close to 3" above the barrel. Try it you will like it.

Here are the 20MOA rails I use

Buy Flattop Riser Rails and More | Weaver Optics

Shopping for the Flattop Riser Rails - Learn more about the latest One Piece and other hunting or shooting gear at Weaver Optics.

www.weaveroptics.com

 

[hoffbill]

Before anything else, do you have any idea of the pressures you are generating with the N540 load? Your bullet is traveling way faster than you have estimated, which skews your downrange projections.
2nd, use a free ballistic app, or buy one for your phone, through your ramblings, there is one huge difference between 2" high and 2.5" at 100 yards.
Not trying to be a jerk, but you need to sit back and revisit all you are doing. Please, find some help close by.

I agree and would add that if you use 223 load data many of those loads are based on test barrels. When you go to a gas gun aka AR15 velocity will often be significantly less than load data estimates. Velocity can also be significantly affected by the gas block used. The only way I have found to determine MV accurately on AR15's is use a chrony. I found MV varied from load data and also from gun to gun because of differences in gas systems.

 

[Reelamin]

Nothing matters until you can get your actual velocity if your having problems as you described. Just worked with my uncle yesterday......after weeks of "the book/internet/book/internet/box/internet/book/internet/ said" we finally put his rifle and loads over the chronograph. The very first words were "but the box said..." and I stopped him and replied. If I fudgin hear one more time what the book/internet said it should be when the hard facts show something else and you argue it should be what the book/internet says I'm out and you can use the book and internet to help you figure it out. Well it must have registered....have not heard it since when facts show different.

 

[hoffbill]

Nothing matters until you can get your actual velocity if your having problems as you described. Just worked with my uncle yesterday......after weeks of "the book/internet/book/internet/box/internet/book/internet/ said" we finally put his rifle and loads over the chronograph. The very first words were "but the box said..." and I stopped him and replied. If I fudgin hear one more time what the book/internet said it should be when the hard facts show something else and you argue it should be what the book/internet says I'm out and you can use the book and internet to help you figure it out. Well it must have registered....have not heard it since when facts show different.

100% dead on. Until exact actual muzzle velocity is known, not guessed, all the other data is just random numbers that could mean a lot of things or nothing.