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Conference vmsnet::hunting$note:hunting

Title:	The Hunting Notesfile
Notice:	Registry #7, For Sale #15, Success #270
Moderator:	SALEM::PAPPALARDO

Created:	Wed Sep 02 1987
Last Modified:	Tue Jun 03 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	1561
Total number of notes:	17784

1132.0. "Ballistics at high altitude" by DECALP::HOHWY (Just another Programmer) Wed Jan 29 1992 13:54


	I have this problem, which our Colorado residents (or anybody
	else with an opinion :-) might be able to help me solve. Any
	comment is wellcome.

	It is a well known fact, that external ballistics are influenced 
	by air resistance, causing the bullet to drop more than what 
	would be expected if you only considered gravity. Thus, at higher
	altitude,  where air-resistance is less prominent, bullets tend
	impact higher than what our sea-level ballistical tables would 
	like us to believe. I have two problem with this:

	- we are told that if we sight in at sea-level and then go to
	high altitude, our point of impact will be higher than expected.
	OK, but how much higher? I have a table up till 2500m (approx 
	7500 ft) but what about at, say, 12000 ft??

	- assuming that you always have the the opportunity to sight in
	when you arrive in camp - in the general area/altitude where you
	would like to hunt - once you have sighted in at high altitude,
	how is the trajectory influenced by the "lack" of air resistance?
	Or do you still figure, you have about the same trajectory as on
	sea-level? (maybe a reasonable approximation, but hardly exact).

	I have heard, and from my climbing days it sounds reasonable, that
	air-resistance/drag decreases about 10% per 1000m (3000 ft). That is
	roughly how barometric pressure falls off, so... But I have yet
	to see a general explanation of what that will do to trajectories,
	except from ensuring higher POI... This is true in particular
	when we are talking altitudes of 10-12000 ft (other than short breath,
	what will be the effect :-)

	Practical advice accepted as much as theoretical...

	Thanks in advance


							 _ Mike

T.R	Title	User	Personal Name	Date	Lines
1132.1		DROMO::BULLARD		`Wed Jan 29 1992 14:37`	27
	I hunt at varying altitudes here in Colorado and have never thought about that factor. Since I hunt with a "flat shooting" rifle sighted in dead zero at 250 yds, and probably would'nt shoot past that range I don't think I need to worry about that. I have my trajectory table memorized in case I do (only with a VERY steady position). I think a greater concern would be uphill/downhill (not perpendicular to gravity) would be a greater concern. Since high elevations usually have mountains that would be more the thing to worry about. In practical terms, always check your rifle for accuracy before hunting, especially if it got handled by them baggage gorillas at the airports :^) My 7mm Mag bullet compared to the Line of Sight would exit the barrel about 1 1/2" below the LOS and climb (depending on scope center to center of barrel dimension). At 25 yds it would cross the LOS and continue to climb. Somewhere a little past 110 yds it would reach its peak of 1.8" above LOS and begin dropping. At 250 yds it would again pass through the line of sight as it continues to drop. After that would I have a concern. The vitals on a deer are 9" zone, out to 250 yds I dont worry about much...just aim and shoot (for the above reasons). When sighting in a rifle the first time I always get it to hit dead zero at 25 yds (conserve bullets and hassle). Then fine tune to hit usually 1 1/2 high at 100 yds (usually it will be right on if ya done the 25yds correctly). Then I know that anywhere between 0 to 250 yds is plus or minus 2 inches (or less)...more than enough for a vital organ shot. I don't think air resistance high vs low altitude would make any noticable difference. chuck
1132.2	Info in G&A mid '91 issue	JUPITR::FERRARO	I'm the NRA	`Wed Jan 29 1992 22:41`	17
	Mike, I'm not much on balistics but do remember reading an article on just this subject. It was in a Guns & Ammo magazine, probably Aug. '91 issue. I'm still in the unpacking stages of moving, but if I find it in reasonable time I'll bring it in and enter the finer points as a reply. I do remember there was some sort of calculations that could help figure out where a bullet would hit at 10k ft if zero'ed at sea level. Also, it was mentioned the best way was to get to your spot early enough to re-zero. (no kidding).. Greg
1132.3		ODIXIE::RHARRIS	Ultralight forever	`Thu Jan 30 1992 17:22`	6
	I know that there is a definite difference in trajectory, as when the PGA tour hits Colorado, instead of a 7 iron from the green at 170 yds, it's a pitching wedge. bob
1132.4	Golf club = GA deer hunting instrument?...	DECALP::HOHWY	Just another Programmer	`Fri Jan 31 1992 04:11`	10
	>> I know that there is a definite difference in trajectory, as when the >> PGA tour hits Colorado, instead of a 7 iron from the green at 170 yds, >> it's a pitching wedge. bob, the real question is, of course, do they sight in when they arrive? :-) - Mike
1132.5	Thinner air = much flatter shooting	SALEM::MACGREGOR		`Fri Feb 07 1992 14:50`	11
	A few years back I went out west to Jackson Hole, Wy. and noticed a big difference in point of impact between out there and here in N.H. Bullet drop was much less at the higher altitude. I had my 30/06 zeroed for about 225 yards here in N.H. and when I went out there it seemed like my zero suddenly changed to about 275 yards. At first I thought it was me. But when I tried my 300 Win Mag which I had zeroed at home for 250 yards, all of a sudden my zero seemed to be greater than 300 yards. The city firing range in Jackson was over 6200 ft. in elevation. I believe I posted a similar note in the firearms notesfile back around October of 1988. Bret