zero difference between 55 and 77 grain bullets

[DacoRoman]

Hey there guys. Great site!

If one was to zero a rifle with 77 grainers where would the 55 grainers fly in relation (and vice versa)? Say with a 50m/200m zero.

How about 62 grainers?

Many Thanks!

[Parabellum9x19mm]

55 grain groups a couple inches higher than 75 grain at 100 yards. 62 grain should split the difference.

http://m4carbine.net/showthread.php?t=18007

[DacoRoman]

thanks for that link

I also found this ballistics calculator, but I am not sure what to put in for the "ball coefficient", anybody know?

http://www.handloads.com/calc/

Also, can someone remind me what the standard AR sight height is above the bore line? 2"?

[Parabellum9x19mm]

I am not sure what to put in for the "ball coefficient", anybody know?




if you are a bench-rest shooter or a scout sniper you might need to worry about ballistics software or plotting every shot you take, but for most of us, i wouldn't really let it be a concern.

[Iraqgunz]

I commented on this a while back in another thread. I had an M16A4 that was equipped with an ACOG. I zeroed the weapon with LC M855 ammo. I was later given about 400 rounds of Black Hills 77gr. Match ammo. When I went to check my zero the rounds were not about 18 inches higher than previous.

I have no idea if it was normal, or maybe my scope got "whacked" but it was not on target. When I did the same with my iron sights I got similar results.

[Parabellum9x19mm]

wow. 18 inches is very significant! a drop of 18" is like going from 200 yards to 350 yards with 75 grain ammo.

what range were you shooting at?

[Iraqgunz]

Para,

This was on our 25M death range as that was all that we had available. IIRC, I then switched back to the 62gr. as I was sure that I was on target with those. There may have been other factors at work, but I isn't smart enough to figure them out.


wow. 18 inches is very significant! a drop of 18" is like going from 200 yards to 350 yards with 75 grain ammo.

what range were you shooting at?

[Parabellum9x19mm]

I isn't smart enough to figure them out.

neither is me :confused: ;)

[smithjd]

I've always heard from suppliers that want to sell us expensive 75 gr practice ammo that there is a difference, but I haven't found it to be so...in my limited experience:

SIG 551 and 552's with 55 gr American Eagle or Fiocchi and 75 gr Hornaday TAP (red box...zero'd at 50), it is POA / POI out to at least 200. I've loaded magazines with 5 of each and shot 10 shot groups at 50 yards. There were two separate 5 shot groups in the center of the bull, about 1/2 to 3/4 inch apart. American Eagle does seem to be more accurate than Fiocchi...

Out of my Noveske Afghan, zero'd for 75 gr Hornaday TAP, not a significant enough difffernce to notice in training until you get out a ways. Last time I shot at 300, my 5 shot group of TAP was about 2 inches left on the head (POA) due to a full value 3 O'clock wind for which I didn't compensate enough.

A 10 shot group of 55 gr PMC ball was about 10" high, and blown farther to the left, so it did make a difference at 300.

I've found that for most normal training scenarios, zero with 75 gr TAP at my desired yardage and shoot 55 for normal training. Usually fire an "Initial Radial Dispertion" (see Jeff Cooper) cold bore shot to check zero before going on in training, and I've never had a mysterious zero shift.

Edited to Add Conclusionary Statement:

So you just need to check your rifle as they may vary...

[DacoRoman]

if you are a bench-rest shooter or a scout sniper you might need to worry about ballistics software or plotting every shot you take, but for most of us, i wouldn't really let it be a concern.

I don't disagree, but I was looking for a generic figure to put in there to see if the calculator can answer the basic question of the trajectory differences between the rounds

It looks like I'll just have to go for some good old fashioned empirical testing :D

[NWPilgrim]

Ballistic coefficients for a few example .224" bullets:

Speer 55 gr. FMJ-BT = 0.269
Speer 62 gr. FMJ-BT = 0.307
Sierra 69 gr HPBTMK = 0.317
Sierra 77 gr. HPBTMK = 0.362

Link to Sierra Bullets (rifle) chart:
http://www.sierrabullets.com/bullets/BallisticCoefficient-rifle.pdf

[JSantoro]

I commented on this a while back in another thread. I had an M16A4 that was equipped with an ACOG. I zeroed the weapon with LC M855 ammo. I was later given about 400 rounds of Black Hills 77gr. Match ammo. When I went to check my zero the rounds were not about 18 inches higher than previous.

I have no idea if it was normal, or maybe my scope got "whacked" but it was not on target. When I did the same with my iron sights I got similar results.

It's normal; your RCO was probably fine, and it's still happening. On my last tour, everybody with an M4 got the 77gr rounds once we got in-country. Fortunately, we did a BZO confirmation once we got to Haditha; our rounds were sailing over our targets while doing the 36yd initial. Long story short, we figured it out, stopped the show, found the right LBS offset and started from scratch.

We were more fortunate, because we had the distance to do a 100m confirmation, and got everything dialed in right. Still had to have the first 5 rnds be 62gr tracer for EOF purposes, and the last 2 the same for a visual indicator that a mag change was coming up. per RCT SOP. It was pretty stupid.

When we run an RCO package for deploying battalions at my job, we try to clue them in to this, because the shooting done CONUS is almost universally with M855, and for some reason The Word hasn't gotten around to the ballistics rocks that some Bn Ops Chiefs can be. Rehashing the "Same barrel, totally different round, THAT'S why!" conversation with them is tiresome after the 3rd time.

[Iraqgunz]

Riverine,

Thanks for that info. I was starting to think that the crack in my pipe was bad or something.


It's normal; your RCO was probably fine, and it's still happening. On my last tour, everybody with an M4 got the 77gr rounds once we got in-country. Fortunately, we did a BZO confirmation once we got to Haditha; our rounds were sailing over our targets while doing the 36yd initial. Long story short, we figured it out, stopped the show, found the right LBS offset and started from scratch.

We were more fortunate, because we had the distance to do a 100m confirmation, and got everything dialed in right. Still had to have the first 5 rnds be 62gr tracer for EOF purposes, and the last 2 the same for a visual indicator that a mag change was coming up. per RCT SOP. It was pretty stupid.

When we run an RCO package for deploying battalions at my job, we try to clue them in to this, because the shooting done CONUS is almost universally with M855, and for some reason The Word hasn't gotten around to the ballistics rocks that some Bn Ops Chiefs can be. Rehashing the "Same barrel, totally different round, THAT'S why!" conversation with them is tiresome after the 3rd time.

[DacoRoman]

Ballistic coefficients for a few example .224" bullets:

Speer 55 gr. FMJ-BT = 0.269
Speer 62 gr. FMJ-BT = 0.307
Sierra 69 gr HPBTMK = 0.317
Sierra 77 gr. HPBTMK = 0.362

Link to Sierra Bullets (rifle) chart:
http://www.sierrabullets.com/bullets/BallisticCoefficient-rifle.pdf

Thanks, really appreciate the info.

Also thanks for the replies guys.

[JSantoro]

Riverine,

Thanks for that info. I was starting to think that the crack in my pipe was bad or something.

It's important that one ensures the quality of their crack from time to time.

[Iraqgunz]

Especially with all the fake stuff on the market. Hell I am surprised that the Chinese haven't started marketing knock off crack yet!


It's important that one ensures the quality of their crack from time to time.