Need help translating 50 yd group size to 100 yd size

[Riss]

My geometry is poor but if I remember correctly the group size at 50 yards cannot simply be doubled to equal what it would be at 100 yards. Just rebarreled my Savage 10FP Tactical 300 WSM and got to the range to sight it in. I am posting 2 shot center to center groups of 1/4" and 5 shot groups of 5/8" at 50 yards. How does this translate to a group size at 100 yards ?

 

[burrhead]

Double it. It's not perfect but close enough.

 

[Jim K]

As far as geometry goes, you just double it, but we are not dealing with pure geometry. The greater distance allows more things to affect the bullet, such as wind, air resistance, drift, etc. So getting a 1/4 inch group at 50 yards does not guarantee a 1/2 inch group at 100 yards.

A worst case example is the wadcutter pistol bullets used by target shooters. These will give good groups at 25 and 50 yards, but generally go all over the place at 100. Those bullets have low velocity to begin with and beyond 50 yards air resistance and drop just play hob with groups.

Nevertheless, that rifle sounds like a fine shooter and one a lot of folks would envy.

Jim

 

[Mannlicher]

there are too many factors involved, to just say 'double it' for your possible group size. Only way to tell, is to set your target up at 100 yards.

 

[JohnKSa]

With the setup you describe, simply doubling the number should give you a pretty good estimate of your 100 yard groups.

BTW, minimum number of shots before you can really call it a "group" is probably 3.

 

[P95Carry]

I reckon actually ..... it is worth applying the ''inverse square law'' ........ rather as with optics. Seems to work better for me.

If you shine a beam of light from distance #1 ...... and that illuminates a square foot .... then twice the distance will have you covering four square feet ... three times distance 9 square feet .... four times, 16 square feet ... etc. This of course is beam divergance, and light intensity falls off as the inverse ... not the same as a bullet but ..... from past experience the simple scaling by doubling does not always seem to hold good .... wind factors ....... shooter tremor etc

The longer time of bullet flight permits more time for early aberent behavior to manifest itself in poorer results.

We could say therefore that applying a more ''logarithmic'' accuracy decay would probably represent greater truth. Thus .... I might expect a 1" error at 50 yds to translate into a 4" error at 100 yds ... certainly with longer range handgun shooting this fits in for me .... benchrest rifle may another matter .... tho I'd still expect a non-linear extrapolation.

 

[Clemson]

Doubling the size of the 50 yard group will give you an estimate. I have one rifle that does not obey the laws of physics. It is a 7x57 mm with a Shilen stainless steel barrel. It will virtually always shoot 1 1/2 to 1 3/4 inch groups at 200 yards, but it will usually do no better than 1 1/4 inch groups at 100 yards. I shoot it at both ranges whenever I check the zero, and it is consistent in delivering slightly worse than MOA at one hundred and slightly better at 200. Go figure......

Clemson

 

[benEzra]

If you shine a beam of light from distance #1 ...... and that illuminates a square foot .... then twice the distance will have you covering four square feet ... three times distance 9 square feet ....

True, but if you measure the linear distance across the light beam (the way we measure rifle groups), it will be 1 unit across at 50 yards, 2 units across at 100, 3 units at 150, 4 units at 200, and so on. The area increases exponentially because it is the square of the linear dimensions. (In the same way, the area covered by a 2" shot group is 4 times the area covered by a 1" group.)

I think the doubling rule is an OK rule of thumb, but you can look at it as more of a minimum size. Like others have said, other factors come into play at greater distances that are nonlinear. Out of a machine rest on a perfectly calm day, however, you would expect the relationship to be pretty linear.

 

[VG]

It's true that you double the Minutes Of Arc (MOA) going from 50 to 100.

But that's not to say that is what happens in the real world - or everyone would test at 50 yards.

 

[Redlg155]

Just double it and hope you can shoot that well!

Good Shooting
Red