Many of us have a set of "magic" numbers embedded in our memory, numbers that allow us to do what we do...sometimes better than others. When teaching or shooting for fun with other shooters I often get bombarded with requests for come-ups... How much for 387 yards?...How much for 925 yards? (Mind you, we're shooting Iron Maidens so they're BIG targets (23 x 48 " generally))
Most long time shooters have a set of "magic" numbers that they can readily pull out of their grommet...mine happen to be trajectory. I'll share them and the method I use to alter them for non-standard (non 308 Winchester) trajectories.
I keep these numbers according to 3 general classes or trajectories, 308 Win (base set), 300 Winchester class, and the super flat shooters like 7MM-STW/257 Weatherby (with lighter bullets) and the 22-250.
These come-ups are cumulative MOA, 2 + 3.5 =5.5 for 300 yards, 2 + 3.5 + 3.5 =8 for 400 yards with the 308.
I know the 308 standard come-ups and use those in the following manner, for the 300 Win mag class (190 MatchKing load) I use a value equal to 75% the 308 value, for the real flat shooters I use a value between 66% and 50%... These numbers will get nearly all rifle on steel out to about 1000 yards.
With these numbers a shooter can pick up any rifle that has been zeroed at some known distance and make the necessary adjustment to shoot well to other reasonable distances.
This is the basic premiss of the "standard" reticles used in autoranging scopes (Cabela's, Shephard, etc)
Check your come-ups and let me know. You should be pretty close.
Ian has a standard set of wind values he shared with me a while back that work very well too. I believe that by using the 75% and 50% factor(s) with them they would be quite useful too. Perhaps he'll post them here and we can try them.
Anyone else have other numbers they've learned to use?
I have one drop-chart in my mind - 19minutes at 700 yards, the rest is pretty much fuzz. Maybe we shoot at 700 too much, more likely that I am too dumb to remember the rest. Problem with this is I make a few shots at 100 yards that hit 19 inches high every so often...
Your comeups are good, here are some for the 175 BHA match ammo, as per the Ballisticard that BHA has had made up.
100 0.0 600 15.7
150 0.8 650 17.9
200 2.0 700 20.2
250 3.3 750 22.7
300 4.8 800 25.3
350 6.4 850 28.1
400 8.0 900 31.0
450 9.8 950 34.1
500 11.7 1000 37.4
(hope that this does not turn into a dog's-breakfast when it hits the internet)
The wind card for these 175's for a 10mph full value wind is one moa at 1 & 200, then one less number than the first digit of the distance out to 1000. Even I can remember that one, 9 minutes at 1000. For the 168 it works out to 800, then the same number as the distance ie 10 at 1000. Surprising how well this works, at least it is a good starting point. Your offsets sound very reasonable. I have the .300Win card, also one for a Weatherby that jibe.
These are only numbers, I usually use 18.75-19.5 moa at 700 rather than 20.2, but they are close. Obviously barometric pressure, barrel length etc. are involved when fine-tuning.
What the hell is a grommet? Do I really need one to shoot long [img]images/icons/grin.gif[/img] You always have all the good toys...
Would you think that using the basic premiss that a rifle with 50% the ballistic arc of a 308 Win would also have only 50% the wind drift? Would a 7mm STW and a sleek bullet at top speed have 5 MOA drift at 600 yards in a 10mph wind (STP)?
You all are so much more advanced in this game that I do not get to post here often, so I am not going to miss this chance.
Wind drift with my .300 WSM 190 SMK @ 2981 av fps mv, 15 mph full value wind, hold off .25 mil per hundred yds to 600 yds, add an extra .25 mil at 700 and 800 yds, add 2 extra .25 mil at 900 and 1000 yds.
With comeups at 775 yds I also have the hold under in mils down to 100 yds where the 5 mil tic mark in my IOR scope is precise.
[ 07-04-2003: Message edited by: RuffHewn ]
Rapid fire is the crutch of an incompetent marksman. ONE SHOT, ONE KILL