Checking zero.

[thx997303]

While I was up elk hunting with JTknives, we decided we would check the zero on our rifles by firing at a tree at a little over 100 yards. Reason being that the loads had been worked up and zeroed at half the elevation and in roughly 30* warmer temperatures.

The aiming point was a dark band on a quaking aspen. The band was roughly 6" tall (guessing) The tree was of decent diameter. Guessing doesn't do me much good here because my only scale is the band and the boolit holes. Being unknowns, I will just say it was a decent sized quakey.

JTknives fired first. His rifle being a .500 S&W Handi Rifle recently purchased from another member here. It has aperature sights. He was shooting a 440 gr Flat nose boolit at 1800 fps I believe.

Though I am unsure of his exact point of aim, his boolit struck roughly an inch below the band.

I fired next. My rifle is an 1895 Marlin guide gun in 45-70 that I purchased earlier this year. My boolit is the 350 gr Ranch Dog moving at 1300 fps.

My point of aim was a six o-clock hold on the center of the band. My boolit impacted at POA.

The 500 S&W boolit tore bark from the tree around the entry hole. It also exhibited cracks radiating from the hole.

The 45-70 boolit also tore bark from the tree, but less than the 500. Cracks radiating from the entry hole were also apparent.

Neither boolit exited the tree.

http://i312.photobucket.com/albums/ll331/thx997303/10-10-10_1343.jpg

At another point, I took a shot at small animal. I was aiming for it's head to keep from damaging the small amount of meat. I had intended to roast it over the fire that night.

Unfortunately, the animal moved and it was difficult to see. I made the shot, but missed the animal. (Yes, I did verify the target was indeed what I believed it to be, and was shooting into an acceptable back stop.)

The boolit impacted POA, range being somewhere around 30 yards. The boolit passed through a small piece of deadfall roughly 6-8" in diameter, and was recovered buried roughly 1' into the hill side. The ground was wet and compact. The boolit was cast of 50/50 wheel weight alloy and pure.

Once home, I measured both the recovered boolit and an unfired, never loaded boolit.

Unfired Recovered
.876" Long .874" Long
.461" Diameter .458" Diameter
.330" Nose dia. .361" Nose dia.

http://i312.photobucket.com/albums/ll331/thx997303/100_3018.jpg

Here are the things I believe this shows me, maybe I am wrong, and maybe this is old news, but I'm bored and decided to post this thread anyway.

1. It appears that at 9100 feet, my load in my 45-70 impacts slightly lower than when it was sighted in at 4500 feet. Though the difference is largely negligible, and quite possibly caused by shooting error on my part.

2. Unique (which is the powder in my load) does not appear to be very temperature sensitive. Any significant change in velocity from temperature sensitivity would have shown up on the target. I assume that a difference in velocity would result in a different point of impact.

3. The cracks radiating from the entry hole suggests a large amount of trauma to the tree upon impact and penetration. It appears that in this limited test, a large flat nose does indeed impart quite the shock to the target. It appears that in soft tissue, it is likely that a larger than diameter wound channel would be left as a result of the shock delivered to the target.

4. From this limited test, and impacting a less than perfect test media, My 350 gr Ranch dog boolits out of 50/50 alloy expand .031" at the nose. The .458" body diameter matches the groove diameter of my rifle. Is it possible that I would get the same results in a living animal?

Any thoughts on my thoughts?

[Will]

One would think the thinner air would give less resistance resulting in a slightly higher impact. Although at 100yds this would be very slight.

[Larry Gibson]

That small a tep drop and the increase in altitude many times do even things out at short range. You don't say what your rifle was zeroed for but with a POA/POI at 100 yards was this a different zero?

Also subtle things like shooting from a solid bench to zero and then using another type of rest can change zero a bit. Quite frankly a one shot group is not really enough to make an educated guess on. However, were that tree and deer/elk it wouldn't have really mattered;-)

Larry Gibson

[white eagle]

looks like minute o elk to me

[thx997303]

Oh, yeah the rifle was zeroed from a prone position, and it was sighted for a 6 o-clock hold at 100 yards.

The boolit impacted exactly where the sights were held instead of directly above.

So apparently at that elevation, it is sighted for a dead on hold at 100 yards.

The shots were entirely focused on whether that first cold bore shot would be on target. With the areas I hunt being heavily wooded, a follow up shot is quite rare.

[runfiverun]

i have seen many rifles impact lower due to higher velocity.
the lighting and shadows could have played as much a part also.
at 10 yds my ackley impacts to the crosshairs as i found out holding a bit low on a grouse for camp dinner recently.
dawn had to shoot her own grouse, and her x57 shoots a bit low at 15 yds good thing she shot from the side.