.223 55gr load trajectory? School me. [Archive] - Glock Talk

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GlockSupremacy
10-20-2011, 21:30
Went to an outdoor range today and at the end I was planning on seeing how far my plinking load could shoot accurately with a red dot.

I am a little confused by the results... The load is 24.7 gr TAC behind a hornady 55gr bullet.

This load should be at 2900fps, if I recall sierras loading manual correctly. (posting from my phone) Anyway it shot perfectly at 50 yards, the standard indoor range length. 5-6 inches high at 100yards and at 200 yards even higher! ( another 4-5inches). I felt the red dot was adequate at 200 yards but assumed with a 50 yard zero it would be an inch or two low at 200.

Hand loads.com shows 2.5 in low @100 and 10.56 in low @200 with the .243 ballistic coefficient of hornady 55gr projectile.

Let me know where I went wrong!?

ColoCG
10-20-2011, 21:56
Went to an outdoor range today and at the end I was planning on seeing how far my plinking load could shoot accurately with a red dot.

I am a little confused by the results... The load is 24.7 gr TAC behind a hornady 55gr bullet.

This load should be at 2900fps, if I recall sierras loading manual correctly. (posting from my phone) Anyway it shot perfectly at 50 yards, the standard indoor range length. 5-6 inches high at 100yards and at 200 yards even higher! ( another 4-5inches). I felt the red dot was adequate at 200 yards but assumed with a 50 yard zero it would be an inch or two low at 200.

Hand loads.com shows 2.5 in low @100 and 10.56 in low @200 with the .243 ballistic coefficient of hornady 55gr projectile.

Let me know where I went wrong!?


I'm not sure what went wrong. The hornady 55gr fmjbt with a BC of .243 with a muzzle vel. of 2900fps sighted in dead on at 50yd. should be .33"low at 100yd. and 3.27" low at 200yds. not sure where handloads got their info.

One thing you have to remember is what moa is your red dot sight. Most red dots are 2 or 3 moa, this means that at 200yds. your dot will cover 4" to 6" of target.

Not conducive to great accuracy if you throw in any aiming errors. Hope this helps.

If your hitting 5" to 6" high at 100yds. your gun should be sighted in closer to 300yds. or more with that bullet and velocity.

Boxerglocker
10-20-2011, 22:08
One thing you have to remember is what moa is your red dot sight. Most red dots are 2 or 3 moa, this means that at 200yds. your dot will cover 4" to 6" of target.




:agree: that's the ticket

PCJim
10-20-2011, 22:25
With the normal sight-in and a scope mounted at 1.5" above the bore, a bullet will first cross the sight plane at around 25 yards in its upward arc before beginning the downward tail, thus the general hunting rule of thumb that you sight in at 25 yards and you're good at 100 yards. If you have adjusted your sight such that the first crossing of the sight plane is at 50 yards, the bullet is stretching much further out for the first crossing, thus raising the impact in relation to the sight plane at longer distances. Add to this that if you are using a scope mounted higher than the typical 1.5", as on an AR, the effect is exaggerated. Then, add the inaccuracy of the typical red dot at distance as Colo stated above, and you've fairly well explained the possible reasons for your results.

If you had some good glass on the rifle and a very steady rest, I think you would have found that you were slightly high at 100yds and just slightly low at 200yds. Hornady has a quick ballistics calculator available online that you could experiment with.

GlockSupremacy
10-20-2011, 22:25
I'm not sure what went wrong. The hornady 55gr fmjbt with a BC of .243 with a muzzle vel. of 2900fps sighted in dead on at 50yd. should be .33"low at 100yd. and 3.27" low at 200yds. not sure where handloads got their info.

One thing you have to remember is what moa is your red dot sight. Most red dots are 2 or 3 moa, this means that at 200yds. your dot will cover 4" to 6" of target.

Not conducive to great accuracy if you throw in any aiming errors. Hope this helps.

If your hitting 5" to 6" high at 100yds. your gun should be sighted in closer to 300yds. or more with that bullet and velocity.

It makes sense, it is a 2 moa dot. I turned down the brightness to get the "smallest" dot possible too. I figured I'd be able to do better with how much faster and easier the dot is....but I think I am better with irons at this point.

I know i do love magnification, even with a 22lr at 50 yards I crank it to 24x and shoot the tightest groups at highest magnification. Heck I pretty much leave that scope on 24x and use the parallax adjustment.

I know most people prefer not to see breathing movement etc but it doesn't bother me.

Bob2223
10-20-2011, 22:29
Scope hight makes a difference sighting in at that short of a distance, you shooting a bolt gun, an AR-15 flat top or an AR with a carry handle mounted sight ?

Don't know if it would make that much difference though, just a thought?

Bob

GlockSupremacy
10-20-2011, 22:35
With the normal sight-in and a scope mounted at 1.5" above the bore, a bullet will first cross the sight plane at around 25 yards in its upward arc before beginning the downward tail, thus the general hunting rule of thumb that you sight in at 25 yards and you're good at 100 yards. If you have adjusted your sight such that the first crossing of the sight plane is at 50 yards, the bullet is stretching much further out for the first crossing, thus raising the impact in relation to the sight plane at longer distances. Add to this that if you are using a scope mounted higher than the typical 1.5", as on an AR, the effect is exaggerated. Then, add the inaccuracy of the typical red dot at distance as Colo stated above, and you've fairly well explained the possible reasons for your results.

If you had some good glass on the rifle and a very steady rest, I think you would have found that you were slightly high at 100yds and just slightly low at 200yds. Hornady has a quick ballistics calculator available online that you could experiment with.

Thanks for the post Jim!

It is on a AR15 flat top with a riser for 1/3 cowitness. If nothing is wrong with my load....What kind of accuracy can a person expect with a 2 moa red dot at 200, 300 yards?

Boxerglocker
10-20-2011, 22:59
Thanks for the post Jim!

It is on a AR15 flat top with a riser for 1/3 cowitness. If nothing is wrong with my load....What kind of accuracy can a person expect with a 2 moa red dot at 200, 300 yards?

That depends on the shooter, It's all about consistency and technique, not the size of the dot. A good well trained marksman can easily do a 1" group at 100 yards with either a 4 MOA Aimpoint or even standard iron sights. At 200-300 I would imagine 4-8 inches.

I will tell you for sure though your load of 24.7g TAC will never get 2 MOA accuracy even at 100 yards. I have tried along with several others. I've bumped it above 25.6g for the best result.

Zombie Steve
10-20-2011, 23:10
Went to an outdoor range today and at the end I was planning on seeing how far my plinking load could shoot accurately with a red dot.

I am a little confused by the results... The load is 24.7 gr TAC behind a hornady 55gr bullet.

This load should be at 2900fps, if I recall sierras loading manual correctly. (posting from my phone) Anyway it shot perfectly at 50 yards, the standard indoor range length. 5-6 inches high at 100yards and at 200 yards even higher! ( another 4-5inches). I felt the red dot was adequate at 200 yards but assumed with a 50 yard zero it would be an inch or two low at 200.

Hand loads.com shows 2.5 in low @100 and 10.56 in low @200 with the .243 ballistic coefficient of hornady 55gr projectile.

Let me know where I went wrong!?

Is it?

93GT
10-21-2011, 10:53
It is time to buy a chronograph or borrow one.

fredj338
10-21-2011, 14:14
Well, first you are guessing @ the vel. Most book loads are taken in 22"-24" bbls, most AR are quite a bit shorter. If you are on @ 50 & 5-6" high @ 100, then it's how you are seeing the dot. On @ 50 is usually on or close to on @ 100 for any caliber, any vel. Well within shooter error. So on @ 100, you should be a couple inches low @ 200. Dots are diff than irons or scopes as to how the shooter sees the sight. I would parctice @ 100, off the bench, adjust to hit dead on, then move to 200 & see where it hits for you.

GlockSupremacy
10-23-2011, 22:39
That depends on the shooter, It's all about consistency and technique, not the size of the dot. A good well trained marksman can easily do a 1" group at 100 yards with either a 4 MOA Aimpoint or even standard iron sights. At 200-300 I would imagine 4-8 inches.

I will tell you for sure though your load of 24.7g TAC will never get 2 MOA accuracy even at 100 yards. I have tried along with several others. I've bumped it above 25.6g for the best result.

I would be very happy with 8in at 300 yards...after this last outing :)

I will bump the load up and see if the accuracy increases...probably scope it for those tests.

I figured the load would be at 2moa from how it shoots @50 yards indoors (max range I normally visit) always thought it was the cheap 55gr bullets out of a CL barrel.... powder will be an easy fix.

Well, first you are guessing @ the vel. Most book loads are taken in 22"-24" bbls, most AR are quite a bit shorter. If you are on @ 50 & 5-6" high @ 100, then it's how you are seeing the dot. On @ 50 is usually on or close to on @ 100 for any caliber, any vel. Well within shooter error. So on @ 100, you should be a couple inches low @ 200. Dots are diff than irons or scopes as to how the shooter sees the sight. I would parctice @ 100, off the bench, adjust to hit dead on, then move to 200 & see where it hits for you.

Thanks for the info guys!

Hopefully the next outdoor range trip will go better... now to go search threads for a decent chronograph.

leeward419
10-24-2011, 04:49
Could it be the height of the Red DOt above the centerline of the bore? this can vary greatly depending on mounting.

F106 Fan
10-24-2011, 08:02
As others have said, you really need to chronograph the loads. I have NEVER gotten a load to match the published velocity. There are just too many variables: firearm type, barrel length, case, primer, etc. Sometimes the data is given for actual firearms, sometimes it comes from a test barrel that you can never match.

But, assuming you actually got 2900 fps from an AR-15 type barrel and that the sight was 2.5" above the barrel (just to pick a number), if you were dead on at 50 yards, you should be 1.3" high at 100 yards, 0.33 inches low at 200 yards and 9.35 inches low at 300 yards. So sayeth my Sierra Infinity V6 software for a 55 gr FMJBT bullet. I spend a lot of time with this software...

I also have an app called Shooter on my Droid cell phone and on my Samsung Galaxy tablet. It's useless on my Droid, I can't read the tiny fonts but it looks like it might be workable on my Galaxy. I'm going to look around and see if I can find an iPad version. I don't have an iPad but I would buy one if the ballistic software was useful.

I am using the CED M2 chronograph and I like it a lot. I particularly like having the electronics back on the bench rather than in the line of fire. I also have a couple of older Ohler chronos but they are too complicated to set up with 10' spacing between sensors. They were great back in the day but the CED is a lot easier to transport and use.

Richard

StaTiK
10-24-2011, 10:22
With the normal sight-in and a scope mounted at 1.5" above the bore, a bullet will first cross the sight plane at around 25 yards in its upward arc before beginning the downward tail
...
Add to this that if you are using a scope mounted higher than the typical 1.5", as on an AR, the effect is exaggerated.

Jim nailed it. When you "zero" a rifle you are intersecting the line of sight with the trajectory arc at a given distance (sight isn't affected by gravity but the path of the bullet is). If you zero a weapon at a close distance you are intersecting the two lines while the bullet is still rising.** This is exaggerated if the optic is further from the bore axis (as with an optic mounted on the A2 carrying handle vs an A4 flat top).

With an M16 using issued ammo, a zero at 36 meters will intersect again at 300 meters. In between these two distances an impact would be HIGHER than point of aim. Your situation may or may not be similar because you're making custom ammo.

http://t3.gstatic.com/images?q=tbn:ANd9GcQCyLD3CFKwFWYz731VhJL7bqlXusTcZP3r103bsZdmRtHj-KyzVA

-StaTiK-

** the bullet is still rising due to the angle of the bore axis, not due to the bullet still gaining speed as some mistakenly believe. The bullet obviously begins losing speed the moment it exits the barrel.

njl
10-24-2011, 17:32
IIRC, AR15 M193 zero is 25/300 or 50/250 depending on whether you use the military method or IBSZ. With a 50/250 zero, you will be a few inches high at 100yds. By 200yds, it should be on its way back down and be hitting less high than at 100yds.

Your rifle wouldn't happen to have a free floated barrel would it? When you shot at 100 and 200yds, what were you using for a rest, and which part of your rifle was resting on it?