If one shot a group makes, I have to wonder what you consider "group sex"....

That's classic, Steve.


Are five shot groups really the right ticket? That's the impression I'm under. What do you shoot to evaluate, every group I've seen of yours it's hard to tell how many shots caused the irregular singular hold.

theBOSS...



You only partially understand.



The Central Limit Theorem requires that any process that is governed by many small sources of variation will be normally distributed.



Shooter flinch, barrel rubs, barrel whip, hot barrels, etc. constitute "special cause", i.e, a "few large sources". Once special cause is eliminated, all that remains is "many small sources of variation", which will be normally distributed.



Given all that, you can safely model the firearm's performance by vectorially adding two normal random distributions, to get a two-dimensional pattern. When you do that, you get the result I have described.



My statement is correct, as is Audette's.



If you remove all the special causes, and if your rifle has a long term mean five-shot group size of 1", the 95% Prediction Interval for five-shot group size falls very close to 1/2" and to 1 1/2". This result is scalable, so if you have a 2" gun, you just multiply the limits by 2.



Any one group size within that range is easily explained by normal, random variation, and it is futile to try to assign any particular reason to a difference between any two groups.



Do the math, and put away the intuitive arguments.

Quote:

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another which averages the same 1 inch but has a SD of 1/16 inch

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is not physically possible. If you have an SD of 1/16", your mean group size will be roughly 3/8", and the normal random variation of your group size will be from about 3/16" to 9/16".

My final determinations are 5-shot groups at 200-yards.

What Riciardelli said.

I keep saying this, and it's true: If your rifle's long term average for many five-shot groups is 1", your five-shot groups will vary from .5" to 1.5", just due to normal, random variation. Five-shot groups in that range do not give ANY evidence of ANY change in the rifle, the cartridge, or the shooter's technique. Three-shot groups are even weaker evidence.

By this rule, if you shoot a 5/8" group with one type of ammo, and then shoot a second, 1 3/8" group with another type of ammo, you have absolutely no convincing evidence that the first type is better.

I seem to be getting some strange groupings while working up a load. This is for a pre-64 custom .270, Win. super grade action, 26 in. Douglas barrell. I am using IMR 4350 with 140 gr. Nosler AccuBonds. I am working up my loads normally, but now seem to have gotten to a place where my three shot groups (at 100 yds.) have 2 shots touching and the 3rd shot 1.5 to 2 in. away. This is happpening with some regularity. Any thoughts? I am kind of stumped on this one.

Barrel is getting warm, or you are flinching.

And 3 shots is not a good number to base any decision on...

For Jim In Texas: You may have reached a point where your barrel harmonics are lousy. A common symptom is two holes close and one distant for a three shot group. You must change something to improve them. You could increase/decrease powder wt., change powders, change bullet seating depth, etc. For example, I have a 7-08 that shoots 1/4" groups with 140 BT's and Varget. I substituted 140 SAF's with no other changes and got groups of two touching and one an inch away. Switched to IMR 4064 and got consistent 3/8" groups. Velocities for these loads run in the high 2800's to 2900.

For Denton: You may wish to look into the mathematical relationships called statistics. You may find the concepts of variability and standard deviation very enlightening.

For Others: I get one hole groups with every shot I make.

Had a BAR that'd do that - shot two separate groups. The first two touching, and the next three in about 1.5", and 2" or more above the first two. Had to be due to barrel warping.

A .270Win. isn't exactly a varmint caliber. I imagine many rifles in that caliber would become quite hot after 2 shots, especially on a warm day. I usually test this by reaching around and grabbing the barrel about an inch or so beyond the action. If I can comfortably keep my fingers there I shoot. If not I go for a whiz, smoke a cigarette, drink a cola, anything to let that barrel cool down before continuing. A hot barrel will throw that last shot somewhat. Just one mans opinion. Best wishes.

Cal - Montreal