Can anybody shed some light on the following:

Hunting Rifle (.270 Weatherby) is sighted in 100 yds - 600 yds in Arizona during 90 - 110 Degree temps at the 1000 yd range. Elevation is approx 200 ft.

The hunt for elk will take place in Colorado as approx 4k elevation, with temps ranging from 0 - 10 Degrees.

Does anybody have any idea as to the approx difference in point of impact based on the different climate (hunt)? Any and all help is always appreciated!

*** NEVER TAKE LIFE TO SERIOUSLY - IT'S ONLY A TEMPORARY SITUATION ANYWAY ***

Joseph
600 yards is a long shot in uncontroled conditions!
A rough rule of thumb is 2 feet per second per every degree of temperature change, but this will vary with the powder you are using.
The change in altitude will make you shoot about 3 inches flatter at 600 yards.
I ran the numbers on a ballistic calculator and the numbers pretty much cancel each other out.

The thing that I think is really going to bite you is how your gun and load will shoot at the lower temperatures. Unless you tested with your loads packed in a cooler, I think you are in for a nasty surprise. Try it and see how it changes your point of impact, group size, and your velocity.
Even if the tested loads group well you should have lots of ammo to sight in with. You may also want to bring a couple of boxes of factory or another load just in case.

Good luck!

Jamie

I think that X-man is giving your the right advise. Even with the "extreme" temperature stable ammo, harmonics of the rifle are going to change at 10 degrees.

I suppose if you had the dedication, you could pack your rifle in a freezer chest, and invest in some dry ice, and fire a group with frozen ammo and a frozen rifle (shoot, re-freeze the rifle with the dry ice, etc). I've never been that dedicated, but I've never even thought of shooting at game at that distance, either.

The altitude thing is pretty much a matter of calculation (go to huntingnut.com and download "pointblank", it does a quite passable job estimating such things).

It is not just a matter of muzzle velocity, because the rifle harmonics could well play a major role at changing poi at that distance. HTH, Dutch.

Joseph34, here's what I and my buds used to do, when we lived in Los Angeles. Zeroing at the southern Calif. ranges was very similar to your conditions.

But, when we booked an elk hunt in Colo., or Wyoming, or whatever, we'd always check our rifles' zero, when we got to the area, when it was plenty cold. We'd either check them at the outfitter's home, if he had a range setup, or, if not, there'd usually be a range near a town we could use.

Or, on a couple occasions, we'd check in camp, depending on the setup.

You shouldn't have too much trouble finding a place near where you hunt in Colo., to check zero.

Here's a suggestion. If you think you'll be hunting in really cold weather, -- 15 degrees and less -- before you leave home, strip the bolt and completely degrease it with a good solvent. (I just use white gas.) Those cold temperatures can cause an oiled firing pin to freeze, or to be so sluggish it won't pop the primer. I've seen it both in Colorado and Wyoming in elk camps.

A few days without oil in that bolt won't hurt it a bit.

FWIW. L.W.

The behavior change for a particular rifle cannot be predicted imperically with any degree of certainty based upon knowledge of temperature and altitude changes. Higher altitude does make a rifle shoot flatter, but lower temperatures not only cause lower muzzle velocities because of changes in powder burning rates; lower temperatures also decrease density altitude due to the greater air density, thus reducing somewhat the benefit of higher altitude. Combine these factors, and it is probable that your trajectory will not be much flatter.

I once zeroed two rifles in summer Central Texas temperatures for an elk hunt in Montana in December. One was a 7mm firing a 175-grain Nosler Partition @ 3070 FPS MV, and the other a .30 caliber firing a 200 grain Nosler Partition @ 2700 FPS MV in Texas. Both rifles were zeroed to put their group centers + 3" @ 100 yards. Upon arrival in Montana, at an elevation about 4000 feet higher than that where the rifles were originally zeroed, AND at temperatures at least 80 degrees colder, the guns were fired to check zeroes. BOTH put their bullets 3" ABOVE the original zero POI, or about + 6" @ 100 yards!! Both had to be readjusted to get back to + 3".

I suggest you check for POI changes after you get to CO, which is a good idea under any circumstances, as I'm sure you know!

[ 08-27-2003, 19:44: Message edited by: eldeguello ]

There is no way to tell to a certainty what YOUR rifle will do with the change in alt and temp.
you should always re-check the zero of your rifle on reaching the hunting area. In addition to weather changes, no telling what the gremlins have done to your scope.

Thank you everyone for your input - it was valuable, as always!

Good Shooting to Everyone!