Range Report 75 grain .223 out of an SPR-ish rifle, odd issue

[*Nine]

A couple of buddies and I went out to the range yesterday to gather some real-world data. I've got a tactical match coming up in a few weeks where I'll have to wield my SPR-ish AR at up to 500 yards. I didn't have any real world dope data for this rifle, so I figured yesterday would be a great opportunity to get some. I had ballistics calculator data all ready to go to get me close at various ranges, then I figured I'd make the fine adjustments and see what my observed results were. The only issue was that I'm using Prvi 75 grain bullets to load, and there isn't a published BC number for them. I was able to find a number of sources online though that pegged a G1 number of ~.350, which seems reasonable for a bullet like that. I chronographed a number of my loads, and found the average MV to be 2551. I also knew the environmental conditions.

The rifle is zeroed at 50 yards.

My calculated numbers are as follows for the ranges I was able to shoot at.

200 -.2 mils
300 -1.2 mils
500 -3.7 mils

My observed numbers are as follows:

200 -.5 mils
300 -1.6 mils
500 -4.5 mils

Now, I know that calcualtor data is just a ballpark, but I'm amazed that it was off by nearly a mil at 500 yards. I was using the same calculator to give me numbers for my 6.5 Creedmoor rifle, and it was within .1 mil all the way out to 600 yards.

Is this much variation in observed vs. calculated numbers reasonable, or is there something else going on? For my elevation adjustments I was using holdovers with my Accupoint mil-dot scope. The only thing I can think of is that the mil reticle on the Accupoint isn't perfectly accurate. This was all shot with the scope set at 9x, which is the prescribed magnification for using the mil reticle.

To add in one additional point, my buddy I was shooting with has a rifle that is almost identical to mine, with the same optic and all, and his observed numbers were the same as mine.

Any thoughts?

 

[ORD]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

I can't remember where I tracked down some more information on the PRVI bullets, but for some reason I have a ballistic coeff of 0.324 plugged into my ballistics program for the PRVI 75gr bullet.

You might try loading that data and see what kind of difference it makes in your calculations. That kind of a BC difference may explain a 0.8mil differential between observed and estimated data. Also, were the atmospheric numbers for your program correct for the conditions you were shooting in yesterday?

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

The atmospheric numbers are correct. Also, changing the BC by that much doesn't come close to making the numbers match my observed result. If I input the BC as .275 (which is obviously very low) I get the 500 yard data to match up with what I observed, but the 200 and 300 yard data is still off (the calculation is showing LESS drop than I saw.) Basically, I'd need a BC even lower than .275 to replicate my 200 and 300 yard numbers, and then a BC of .275 to replicate my 500 yard numbers. That's why this doesn't make sense, and the only thing I can really think of is that the Accupoint's mil dot reticle (both mine and my buddy's) isn't really correct.

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

How long is your barrel?

Yesterday I shot a 16" N4 at 633 yrds / 28.15" Hg Station Pressure / 3800 DA / 60 degrees and I needed 21 MOA or 6.1 MILs.

In looking at the calculated data for my 18" Noveske (24.2 RE15 / 77 grn SMK .362 G1 Drag / 2,592 fps / 48.5 degrees / 69.5% RH / 28.51" Hg / 1050 DA)

200 = .5
300 = 1.1
500 = 3.0
625 = 4.3 (Yesterday a 175 SMK needed 4.5 MILs at 633 as a reference - I find my 175s and 77s fly very much the same inside of 650)

I find this to be pretty close but it needs some fine tuning depending on atmospherics. Regardless, it's certainly on paper.


Good luck

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

Mine's a 18" barrel. Both mine and my buddy's are the same barrel, we got the same chrono numbers, and we saw the same results shooting from the various ranges. If it were just my rifle, I'd say something was up, but the fact that we had 2 almost identical setups shooting the same way, and we have chronograph numbers, makes me wonder what really was going on.

 

[WRM]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

I'm going to take a stab in the dark and say that the scope height above bore on the program is set at the default of around 1.5", and you need to set it at ~3" above bore. Multipy that 1.5" time 10 (500/50) and you found your "missing mil"....

Bill

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WRM</div><div class="ubbcode-body">I'm going to take a stab in the dark and say that the scope height above bore on the program is set at the default of around 1.5", and you need to set it at ~3" above bore. Multipy that 1.5" time 10 (500/50) and you found your "missing mil"....

Bill</div></div>

Nope. I was using 2.6" Actually, setting it to 1.5" gets me closer to my observed values.

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

This is what I input:

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

I am still confused as to why you need / did it really take - 4.5 MILs to reach 500?

Good luck

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

It really did take 4.5 to reach 500. At least... I held what the scope showed at 4.5 mils high to hit at 500. Believe me, I'm somewhat confused too.

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

Have you checked your scope?


Good luck

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

No, that's the one thing I have left to check.

 

[ker2222]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

you gotta trust your actual dope......

 

[sobrbiker883]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ker2222</div><div class="ubbcode-body">you gotta trust your actual dope...... </div></div>

ding ding ding, we have a winner!!

Now the key is to tweak JBM by adjusting speed and BC until you get a matching trajectory for your known values at the environmental condiotions you shot in. Once that's done, Lindy has a paper on making DA cards using JBM, and you can use your tweaked ballisitcs program to project changes under different conditions.....

Still, 5 mils is A LOT at 500 for 75gr'ers......

 

[sobrbiker883]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

Are you sure on the 500yds being 500yds???

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ker2222</div><div class="ubbcode-body">you gotta trust your actual dope...... </div></div>

ding ding ding, we have a winner!!

Now the key is to tweak JBM by adjusting speed and BC until you get a matching trajectory for your known values at the environmental condiotions you shot in. Once that's done, Lindy has a paper on making DA cards using JBM, and you can use your tweaked ballisitcs program to project changes under different conditions.....

Still, 5 mils is A LOT at 500 for 75gr'ers......</div></div>

Of course I'll trust my actual dope, I'm just trying to figure out how the calculated values were so far off from my observed values.

As for the 500 yards, it's really 500 yards. The range is a NRA High Power range, so I trust their 500 yards, and I also measured it with Google Earth.

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

I checked out my scope this afternoon by milling objects at various distances, and comparing it to another, known-good scope. The Accupoint seems to be right on at its intended milling magnification of 9x. I'm really at a loss here as to what would cause me to see these numbers be so far off the calculated values.

 

[Victor Co Heather]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ker2222</div><div class="ubbcode-body">you gotta trust your actual dope...... </div></div>

Yepper. +1

That's why we shoot for dope. If everything followed the BC programs it wouldn't be fun.

 

[Victor Co Heather]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Market Garden</div><div class="ubbcode-body">I checked out my scope this afternoon by milling objects at various distances, and comparing it to another, known-good scope. The Accupoint seems to be right on at its intended milling magnification of 9x. I'm really at a loss here as to what would cause me to see these numbers be so far off the calculated values. </div></div>

I'm no expert at drag models but I think the G1 is your problem. Try a G7 drag model.

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: M.45</div><div class="ubbcode-body">
I'm no expert at drag models but I think the G1 is your problem. Try a G7 drag model.
</div></div>

It was tough enough finding a G1 number for these bullets. I doubt there's anything at all out there as G7 goes.

 

[Victor Co Heather]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

It should be the same BC number then select G7 in the menu.

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: M.45</div><div class="ubbcode-body">It should be the same BC number then select G7 in the menu.</div></div>

G1 and G7 BCs aren't the same number.

For a quick overview of how ballistic profiles work, check out http://www.longrangehunting.com/articles/berger-g7-ballistic-coefficient-1.php

 

[gunman_7]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

How many grns of powder? 2551 seems awful slow. I'm pushing a 75 grn projectile close to 3200fps with varget...What powder you using?

 

[*Nine]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

23.2 of Tac. My buddy is seeing similar numbers with his Tac loads in his rifle, which has the same barrel as mine.

You're really getting 3200fps with a 75 grain bullet in a standard .223 case?

 

[Victor Co Heather]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Market Garden</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: M.45</div><div class="ubbcode-body">It should be the same BC number then select G7 in the menu.</div></div>

G1 and G7 BCs aren't the same number.

For a quick overview of how ballistic profiles work, check out http://www.longrangehunting.com/articles/berger-g7-ballistic-coefficient-1.php </div></div>

Maybe that's why I can't hit anything.

(with my ballistic calculator)

 

[gunman_7]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Market Garden</div><div class="ubbcode-body">23.2 of Tac. My buddy is seeing similar numbers with his Tac loads in his rifle, which has the same barrel as mine.

You're really getting 3200fps with a 75 grain bullet in a standard .223 case? </div></div>Yea it's somewhere between 3100-3200fps, been awhile since I cronod it. I flatten primers and get a little crater but nothing bad, have had very good brass life to boot, and man is it a tack driver. Sorry but I have zero experience with Tac powder...

 

[Trigger Monkey]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

Way back when I ran some Prvi Partisan 75 gr match through an Oehler 43 and got a BC of .295 with a velocity of 2486 fps out of a 16" barrel.

Using a .295 BC on the G1 setting with all of your posted data JBM spit this out:

yd) (mil) (MOA) (mil) (MOA) (ft/s) (none) (ft•lbs) (s) (mil) (MOA)
0 *** *** *** *** 2551.0 2.294 1083.6 0.000 *** ***
100 -0.0 -0.0 0.4 1.2 2265.1 2.037 854.3 0.125 6.1 21.0
200 -0.6 -2.1 0.7 2.6 1997.9 1.796 664.6 0.266 6.5 22.3
300 -1.6 -5.5 1.2 4.1 1750.7 1.574 510.3 0.426 6.9 23.9
400 -2.9 -10.0 1.7 5.9 1527.2 1.373 388.4 0.610 7.5 25.6
500 -4.5 -15.5 2.3 7.8 1333.4 1.199 296.0 0.820 8.0 27.6
600 -6.5 -22.4 2.9 9.9 1177.2 1.058 230.7 1.060 8.6 29.7
700 -8.9 -30.7 3.5 12.1 1064.7 0.957 188.8 1.329 9.3 31.9
800 -11.8 -40.5 4.2 14.3 986.6 0.887 162.1 1.623 9.9 34.1

200 is pretty close, while 300 and 500 are dead on from what you observed. So there you have it, use a .295 BC for that bullet from now on and you should be good to go.

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gunman_7</div><div class="ubbcode-body">How many grns of powder? 2551 seems awful slow. I'm pushing a 75 grn projectile close to 3200fps with varget...What powder you using? </div></div>

What are you shooting and how long is the barrel?


Good luck

 

[Austan]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mo_Zam_Beek</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gunman_7</div><div class="ubbcode-body">How many grns of powder? 2551 seems awful slow. I'm pushing a 75 grn projectile close to 3200fps with varget...What powder you using? </div></div>

What are you shooting and how long is the barrel?


Good luck</div></div>

IIRC, he's running a savage 10 tactical in a B&C stock. 24" barrel. MOA or better at 700 a couple of weeks ago, ridiculously fast, yep.

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd iss

Apples and oranges then.


Good luck

 

[steve123]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

IMO...Those PVRI 75's have a large hollow point,resulting in lower BC and drop compared to say Hornady 75 HPBT match.That's a really low velocity.I'm getting 2770fps out of my reloads with a 15" barrel/75's.

 

[Mo_Zam_Beek]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: steve123</div><div class="ubbcode-body">I'm getting 2770fps out of my reloads with a 15" barrel/75's. </div></div>

You're getting this out of an AR?


Good luck

 

[steve123]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

Yep...23.8gr H4895

 

[BCP]

Re: 75 grain .223 out of an SPR-ish rifle, odd issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mo_Zam_Beek</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: steve123</div><div class="ubbcode-body">I'm getting 2770fps out of my reloads with a 15" barrel/75's. </div></div>

You're getting this out of an AR?


Good luck


</div></div>

He's also at 7k feet elevation.