Danger Space

reubenski

First Sergeant
Jun 8, 2008
920
239
43
38
Colorado Springs, CO
#1
I'm shooting the HCP rifle match in May Its a team match requiring a bolt gunner and a carbine shooter. Without getting into the carbine I've fully assumed I'd shoot my 6SLR. Its pushing a 115 Dtac at about 3020fps. I'm running it at about 50K PSI; well below its max. For most matches all the target ranges are provided so more velocity for a given bullet really only gives a wind advantage. For this match however the targets are UKD. Shooting the same bullet faster may help when the tgt range is not correct. So I needed to perform some 3rd grade math to determine if running the SLR at 3150 was going to be an advantage over 3020. 130fps difference. Here's what a little ballistic analysis told me.

Assuming my median distance for the longer range targets is 600yds, the target size can be predicted at 2 MOA for these guys, in this part of the country. Therefore my target size is 12" or .6 mrads. This means if I aim center I have .3 mrads below and above my POA to still hit the tgt; .6 total. I ran the numbers on my AB 5700 for .3 above and below my 600yd data and determined what ranges equaled the .3mrad mistake.

If my data for 600 is 2.66 mrad then I can still hit the target, mathematically, at 2.33 and 2.93. A .6mrad difference; the tgt height in mils. So backwards engineering the yardage to those data's, I can determine how much yardage error I can have and still hit the target.

For a 115 Dtac going 3020 2.66 mrads is 559 yd data. 2.96 mrads is 642 data. So I can hit the tgt from a mistaken distance of 559 to 642 yds. Therefore my danger space is 83yds. Anywhere inside that 83yds I should mathematically still hit the tgt.

So going 3150 (assumed node) my 600 yr data is 2.38 mrads. .3 mrads on either side of that is 2.08 and 2.68 yds. My yardage data for those holds are 553 and 645 respectively. Therefore my danger space at that velocity is 92 yards.

So I gain 9 yards of error by pushing the cartridge 130fps faster. IMO not worth developing another load in the higher node for this particular match. I'll run what I got.

In the next post, I'll explain wind danger space in mph and determine the worth of 130fps. It will obviously be less so but we'll do the math anyway for diligence.
 

Attachments

reubenski

First Sergeant
Jun 8, 2008
920
239
43
38
Colorado Springs, CO
#2
Assuming the tgt is a circle, I still have .3 mrad left and right of my mathematical/ hypothetical POI. Using my Kestral 5700 AB I determine that a 5 mph wind at 600yds is a .3 Mrad. So I have a wind error of 10 mph for a .6 mrad spread. I could, mathematically, call anywhere between 0 and 10 mph and still hit a 2 moa that at 600yds. At 3020fps.

For 3150 fps a ..27 mrad wind drift happens for a 5mph ar 600yds. Round off to .3 and you get the same windage "Danger Space" as 3020fps. Again no advantage of 130fps for the DTAC.
 

Culpeper

One divided by F
Nov 25, 2006
2,041
566
113
59
Roswell NM
#5
With a .308 168SMK it is more like 2 MPH margin of error on the wind call. Keep in mind you also need to factor in rifle accuracy. If you 'think' you have a .25 moa rifle than factor in .5 moa and watch your statistical confidence level tank. And another .25 moa experienced shooter error and watch it go south real quick.
 
Last edited:

Subwrx300

Sergeant of the Hide
Jan 15, 2014
545
213
43
Cedar Springs, MI
#10
I would say that the theory is correct BUT it assumes each round hits exactly the same POA/POIbased on solution. You need to shrink the target or bracket your drop to include the size of your rifle system and precision level.

For the sake of easy math, if your rifle system and shooting position allow .2 Mil precision, you will only have -+.2mil up/down/L/R as a buffer for 100% hit probability. If a .3Mil system, you'd only have 1.5mil on either side for 100% hit.

You can use your inherent precision level to create safer brackets that will give you specific ranges based on all possible shots in your system. Kind of like WEZ analysis system from Litz but simpler version.

At least that's how I would see it. If you gain accuracy at specific node, could make sense to move up/down. YMMV. Good post! Very thought provoking!
 

reubenski

First Sergeant
Jun 8, 2008
920
239
43
38
Colorado Springs, CO
#11
No need to include independent and external influences to determine the advantage of only speed. Those other factors would apply to 3000fps AND 3150fps so like a common denominator they can be reduced to clarify the one variable that we're focusing on, the speed advantage. No need to clutter the comparison; would be like trying to do load development from the standing position. Was the 4 moa group due to MMS or the accuracy node?
 

Luke

Sergeant
May 29, 2002
926
41
28
Colorado
#12
Reubenski: Funny that I just stumbled across this post - I did the exact same math a couple weeks ago while I was debating 6.5 Creedmoor barrel lengths, and ended up used the same procedure you did. I ran the numbers out to 1000 yards on a standard E-Type silhouette and determined that with the average muzzle velocity of a 26" vs 18" barrel the difference would gain me roughly +-10 or 15 yards of danger space at 1000 yards. Wind adjustment was less than 0.1 mils between the two lengths/muzzle velocities. Both barrel lengths/muzzle velocities keep the bullet above the transonic range out to a minimum of 1100 yards. For my intended uses this definitely tipped the scale in favor of the shorter barrel.
 
Mar 29, 2012
131
25
28
41
Down Under
#13
Excuse my ignorance, but if it's an UKD target and you calculated it to be 600, and your danger space at 600 is 83yds does that mean you have an error margin of plus or minus 41.5 yards? Meaning the 2moa target could actually be from 559 to 641 and theoretically you'd still hit it with 600yd data?
 

Luke

Sergeant
May 29, 2002
926
41
28
Colorado
#14
Exactly! :)

Excuse my ignorance, but if it's an UKD target and you calculated it to be 600, and your danger space at 600 is 83yds does that mean you have an error margin of plus or minus 41.5 yards? Meaning the 2moa target could actually be from 559 to 641 and theoretically you'd still hit it with 600yd data?
 
Feb 20, 2017
315
60
28
76
SE Florida
#15
That thinking is OK for a rectangular target but flawed for a circular one. The math is OK, it is the thinking that is the problem. You must combine wind and drop figures for a circle, remember, it is only full diameter at the center.
 

Culpeper

One divided by F
Nov 25, 2006
2,041
566
113
59
Roswell NM
#16
The square is in the circle. We're gonna need a bigger circle. Also, the difference between the math and getting behind the rifle will show two completely different outcomes. There are ballistic shooters and then there are shooters. I'm not being a smartass. My simulator states I should get a 90% hit rate the reality is that is only if I call the wind correction within 2 MPH and do everything else right or just get lucky one day.
 
Last edited:
Sep 24, 2013
45
20
8
#18
Thomas Haugland has been teaching this approach for a while for UKD shooting. Here's a recent clip that's fairly relevant:
 
Apr 10, 2017
173
37
28
#20
I just came across Thomas Haugland on the weekend the only reason I knew about him was listening to franks podcast and he brought him up so I had to try sound out the name lol and found him on youtube. His videos and the scenery are second to none he should have way way more of a following I don't a lot of people know of him?
 
Top Bottom