Range Report Question cause I'm illiterate at maff....

[Phylodog]

Quick question. If two shooters were laying side by side, one with a .308 shooting Fed GMM 168gr (@ 2650 FPS) and the other with a 300WM shooting Fed GMM 190gr (@ 2900 FPS), and both fired at the same instant and at the same POA at a target 100 yards away, how much distance would there be between the 190gr and the 168gr projectile when the 190gr hit the target?

 

[ewoaf]

Re: Question cause I'm illiterate at maff....

2 and a half feet......or so?

 

[MitchAlsup]

Re: Question cause I'm illiterate at maff....

100 yards at 3000 fps is 100 milliseconds (300 feet/3000 fps)

100 yards from a 168 SMK at 2650 is 117 ms
100 yards from a 190 SMK at 2900 is 107 ms

10 ms difference at (2728-2458) = 270 fps = 2.7 feet.

So, ewoaf gets the gold star today.

 

[Lindy]

Re: Question cause I'm illiterate at maff....

I'd take a little different approach to that calculation.

Assume a standard atmosphere, BP 29.92", 59 degrees F., RH 78 percent.

For the 190 grain Matchking on such a day, my ballistics program calculates that the terminal velocity at 100 yards is 2720 fps.

For the 168 grain Matchking, the terminal velocity is 2452 fps.

Therefore, the average velocity for the 190SMK is 2810 fps, and the average velocity for the 168SMK is 2551 fps.

Therefore, the travel time for the 190SMK is 106.8 ms. The travel time for the 168SMK is 117.6 ms.

So, the 190SMK arrives 10.8 ms sooner. You'd really need integral calculus to calculate precisely how far that 168SMK travels in its last 10.8 ms, but just using the terminal velocity times 10.8 ms will give you around 26 feet 6 inches or so. So, that's <span style="font-style: italic">about</span> how far away the 168SMK is when the 190SMK arrives at the target.

 

[Phylodog]

Re: Question cause I'm illiterate at maff....

Thank you gentlemen. As expected I am completely unable to understand much of anything that you said except for the final answer. It was both the answer I was hoping for and the answer I suspected and will prove useful for my purposes.

 

[fx77]

Re: Question cause I'm illiterate at maff....

How will this answer make a difference 4 U?

 

[MitchAlsup]

Re: Question cause I'm illiterate at maff....

I ran JBM with appropriate data with 1 yd increments on distance

When the 2900 fps 190 SMK reaches 100 yards, the 2650 fps 168 SMK is at 91.5 yards

When the 2650 fps 175 SMK reaches 100 yards, the 2900 fps 190 SMK is at 109.5 yards.

Don't know if JBM is accurate down at these step sizes, though.

 

[Lindy]

Re: Question cause I'm illiterate at maff....

Well, 8.5 yards - which is the distance between 100 and 91.5 - is 25 feet 6 inches, while I estimated 26 feet 6 inches, so I'd say that we're both in the same ballpark.

 

[MitchAlsup]

Re: Question cause I'm illiterate at maff....

I must have screwed up with a decimal digit on my first calculation getting 2.7 instead of the (now visibly) more reasonable 27.

Sorry everybody.

 

[ewoaf]

Re: Question cause I'm illiterate at maff....

hmmm...good point

 

[Phylodog]

Re: Question cause I'm illiterate at maff....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fx77</div><div class="ubbcode-body">How will this answer make a difference 4 U? </div></div>

I've been looking at the necessity of shooting through glass lately. It got me thinking about our procedure for this which involves more than one shooter. We have a dozen rifles in .308 and one WM. I was curious about having the WM and a .308 fire onto the same target at the same instant and whether the WM might get to the glass far enough ahead of the .308 to have accomplished it's task of compromising the structural integrity of the barrier before the .308 gets there.

Going to give it a shot next time we have an opportunity to shoot glass.

 

[ewoaf]

Re: Question cause I'm illiterate at maff....

ha! good point

 

[Lindy]

Re: Question cause I'm illiterate at maff....

Well, the arrival time difference is only about 11 milliseconds, i.e., 0.011 seconds.

I seriously doubt two shooters can synchonize two simultaneous shots to an accuracy sufficient to ensure that the .300 WinMag shot will arrive first.

Also, you want some time for the glass to scatter sufficiently to ensure that the falling glass doesn't impede the second shot.

So, perhaps you might wish to consider that one second between shots would be a better operational technique. If you're using a countdown from 5, the .300 WM shooter could fire on "two", and the .308 shooter could fire on "one".

With some kinds of glass, like highly-tempered window glass typical of office buildings, you might want two seconds between shots.

 

[Phylodog]

Re: Question cause I'm illiterate at maff....

Thanks Lindy. We train for simultaneous shots every month and the team as a whole has gotten very proficient at it. Your point is well taken however and I'll be evaluating as best I can when we have the opportunity again.

The biggest challenge is in obtaining the commercial glass to shoot through. We've shot through residential several times this year and have been experiencing surprisingly little deviation using both Fed GMM 168gr and our soft point 165gr bonded rounds. I expect dramatically different results when we get the glass for testing.

 

[Lindy]

Re: Question cause I'm illiterate at maff....

Well, I'm sure you know about the collateral damage from the glass fragments. However, the tough part about this business is that sometimes there are only two options - bad and worse.

 

[Queequeg]

Re: Question cause I'm illiterate at maff....

Perhaps a stupid suggestion, but have you spoken to any glazing companies about commercial glass they may be holding that may no longer be needed. A lot of projects have been put on indefinite hold or cancelled out right. Additionally, sometimes when glass panels are broken, the replacements are refused due to an insufficient color match to the existing glass on the building or a mistake in sizing.

Additionally, sometimes building management keeps an inventory of glass that may have been left over from the initial construction of the building.

Sometimes the only thing preventing happiness is the lack of a question?

 

[Phylodog]

Re: Question cause I'm illiterate at maff....

You are correct Lindy, shooting through glass is a worst case scenario that I hope we never have to experience here.

QQ I haven't asked around for any but I plan to. We need to get our hands on some for some realistic testing.

 

[RBrady308]

Re: Question cause I'm illiterate at maff....

If there both on scope then BANG!! KILL SHOT!!!!lol

 

[Queequeg]

Re: Question cause I'm illiterate at maff....

Maybe, if you come down here to watch the Colts destroy the Bucs this year, I can get you some in exchange for some stippling on my Glock, M&P and XD and, cough, cough, Taurus .45!

Seriously, it should be doable given the slowdown and the general pack rat tendencies of building owners/Managers as well as commercial glazers.

Good luck

 

[9H_Cracka]

Re: Question cause I'm illiterate at maff....

I just did a simple percentage calc times the distance from the initial velocity - 2650/2900 * 100 (and *3 for feet from yards) and get within a foot of the complicated number. But I too was edumicated in Indiana Cory.

More precision could be added by averaging the initial and 100 yard calculated velocities and using those in my simple calculation.

Regarding glass break capability, you might want to read up on NAVSEA's work with the MK 319 MOD 0 standard. While I know for your work Cory you probably can't modify your ammo, but an industry supporter and maker of various tools says that you can achieve what the MK 319 MOD 0 does with aggressive meplat trimming...

This is a pretty good document.

www.dtic.mil/ndia/2009infantrysmallarms/tuesdaysessioniii8524.pdf