Fish head,

Could you imagine the uproar if I stated that stress relieving a barrel was a waste of time?

Everyone seems to understand that a homogenous piece of steel (the barrel) can and does move around enough to affect point of impact when heated and cooled unless the residual stresses involved in manufacture are relieved.

Now combine multiple parts and materials with vastly different rate of thermal expansion and some just can’t “see” how a zero can and does shift with changes in temp.

As for the military, if you look at the barrel of the gun on an M1 Abrams tank you will see the laser sensor that tracks the drift of the gun as the whole assembly changes temp.

If you want a first round hit in any conditions from the deserts of Iraq to Siberia you had better keep track of shifting point of impact from thermal expansion.

I too am having fun with this but now I get to have more fun am headed out the door to hunt goats with a buddy. I will be camera bitch.


Triggerguard1

A better sine bar example would have been 1 MOA instead of 3 Degrees. The 5” spacing on the normal sine bar is pretty close to the average ring spacing on a Rem 700.

Sin of 1 MOA is 0.00290888 or there about.

5” X 0.00290888 equals (drum roll please) 0.0014”. Wonder where we have seen that number before.


Teal,

Actually some of the posts above are very much questioning whether the phenomena of zero drift due to temp change is real.

The aluminum block will get to the same temp as everything else at some point in time. It is directly bolted to the action and will always be very close to the temp of the action.

In the field the key is to not allow the optic to quickly heat by leaving it exposed to strong direct sun light or any other heat source.

What the bore sighter will do is let you actually see the movement. The reticle in the scope will shift in relationship to the reticle in the bore sighter and a change in zero is very easy to discern.

I never claimed this to be the end all be all in stock selection but just an area where the aluminum bedding block had a small advantage.

So lets say I had a bedding job and it was devcon?
Devcon is aluminum putty.
That work as well as a vee block.

Im not getting the sine bar example.
It doesnt fit what were talking about.
A sine bar only works if the pivot end,is fixed.
If both points of contact on the scope are effected by growth.Then the sine bar thing kinda goes out the window.


dave

Maybe poker's not your game Ike.

http://www.youtube.com/watch?v=3qs_XHLi5aU&NR=1

You actually answered the question with your question.

You're right, a sine bar doesn't fit, because it illustrates an exact amount of movement from one end, while the other end is fixed.
This is something that DOES NOT happen with a rifle scope mounted in rings.

If you had a set of sine bar mounts on your scope, then the theory could hold water, but the expansion and contraction are obviously not going to happen like that in a normal setup. Hence the problem with the theory in the first place.

In short, the rings, scope, receiver and stock(aluminum or not), will move in conjunction with one another during normal shooting conditions to a degree that you'd be hard pressed to measure, let alone decipher through shooting, much less compensate for with any reliability.

As for the Leupold boresighter, well, don't spend the $ if you think it's gonna answer this question. Yes, I own one.

That the POI changes as the day warms up is obvious to anyone who has shot a BR match where the temperature changed a lot during the course of the day. I have shot in matches where the morning temperature was in the low 40's and the high peaked in the mid-80's. POI changed about 1/4 moa at 100 yds. Now, just how much of this change was due to movement within the rifle/scope combo (in one case the rifle was based on a Wichita mini action. The action was short and very rigid, the ring spacing was about 3 1/2 inches, the action was glued in)and how much was due to the change in air density and/or refraction, I can't say. Also, let's not forget, ballistics, internal and external, change with ambient temperature as well. At longer ranges, the question becomes even more difficult to answer because the effects of the conditions of the day are even more predominant.
For a long time, I mounted my BR scope (on those action which allowed the prectice) on a rigid rail which was screwed and glued to the receiver ring only. I did this on the theory that and unequal expansion/contraction would be isolated within the scope/mount assembly and would not affect the receiver. It worked great! In fact, it worked every bit as well as the conventional scope mounting systems other guys were using! In the end, I decided that I would leave the obsession over such phenomenae to those who felt the need to do so. I, with my near total lack of education, was unlikely to be able to really understand such things as co-efficients of expansion so it would be better if I just let it go. I found I was better served to acknowledge POI shift and simply compensate for it as required. GD

Good set of wind flags would serve better than all that monkey business.
All my BR rifles are Stolles.
All Stolle Pandas are AI.
Im thinking the expansion thing is kinda moot at that point.


dave

This I can agree with.

Usuing a vee block over a real bedding job.
I dont agree with.

dave

Your findings mimic mine......

Atmospheric conditions play the biggest role at times, but narrowing any of the multitude of factors down to a measurable degree in hopes of making a definitive claim about one of the listed components, is an exercise in futility.

Firearms are probably the biggest victim of over-analyzing. More often than not I see folks taking several unnecessary steps to make a rifle accurate, while taking just a couple necessary steps. What is missed is the fact that the rifle can arrive at the same level of accuracy without going through the unnecessary steps and do it in less time.
The whole process is only as hard as one makes it.

File 13 the Leupy and get a S&B, then no need to sweat the small sh!t then

Sounds good to me, that's why they make airplanes out of epoxy, ain't it? Oh wait, they have to use lots and lots of really expensive carbon fiber to keep that uber-strong epoxy from cracking, don't they?

Is an aluminum bedding block a perfect fit for the action? Typically not, but they do work well, the M24 proves you wrong if you say otherwise. When you skim bed on top of the bedding block, you have the best of both worlds, you have a "fail-safe" system that you sure as hell don't have with glass bedding, been there done that, and seen it fail (the glass only)