I'd put a rest under your stock and bring the stock up higher on your shoulder. Your head should be upright.

Here's why I don't shoot small groups to measure accuracy. http://www.thetruthaboutguns.com/2014/12/daniel-zimmerman/understanding-rifle-precision/

In order to shoot sub MOA, 95% of the shots (19 out of 20) have to fit within a 1.05" diameter circle at 100 yards (defined as 1 MOA). The 95% group is two standard deviations from the mean.  In order to accomplish this, the mean radius of the shots has to be within 0.27" from the group center. For extreme spread, a 3 shot group needs to be within 0.48" distance apart to be 1 MOA but statistically, a 10 shot group is more precise and reproducible than a 3 or 5 shot group. The smaller groups are useful for OCW determination to discount fouling and heat.

I'm not intending to permanently discount extreme spread. I'm just saying why I prefer larger groups over smaller groups.

I'm not familiar with 39/86/99% bivariate distribution rule so I'll have to investigate. Would a bivariate 2 SD be more or less accurate than a normal 2 SD?

yes it is true that a high-count groups (such as your 20-round group) will tell you how accurate your rifle if you've controlled for other factors

at the same time, a high-count group can be unnecessary if you're using it to compare loads out of the same rifle.  at some point there are diminishing returns with every additional round fired in a group.

so it really depends on your purpose, and also how well you control for the other factors.


regarding your question about the accuracy of two standard deviations when comparing single variate and bivariate scenarios, i don't have an answer.  i don't mean to offend, but i think that question is impossible to answer because it doesn't make sense.

i was adding to my other post, but i'll just move it to a new one since you quoted my last post.
read this article:  http://ballistipedia.com/index.php?title=Closed_Form_Precision
if you understand the concept and the mathematics behind the Rayleigh distribution model, then you're on the right track.  My only gripe with that article is the fact that the Rayleigh distribution model requires the assumption that the variance of the shot dispersion will be symmetrical on the x and y axes, hence the circular distribution.
if the article above didn't make your head spin, then read this article next:  http://ballistipedia.com/index.php?title=Circular_Error_Probable
like i said, i'm not a mathematician or a statistician, but i think the natural distribution of most shot groups will tend to look more elliptical in nature, which is expressed in the article as the Hoyt distribution.  i posit that this phenomenon is a result of accounting for human and mechanical errors.  if you don't believe me, then look through all of the pictures you posted of your groups; almost every single one of them, regardless of the gun/ammo/optic/load used, is not a symmetrical distribution.

RK,
You didn't mention whether the Blazers worked or not? You also didn't mention what the problem is? In other words are you getting light strikes on the cartridge rim or is it heavy enough to ignite the cartridge and the cartridge is not igniting? Are the strikes on the cartridge consistent on all cartridges?

The Blazers worked fine in the past but haven't tried the new box yet. It could be a problem with this particular box of Federals. The strikes are heavy and seem to work when I reposition the round. Perhaps the primer is not uniform in the rim. I'll try to pay more attention to the strikes next time. I have about 40 left.

Here are a couple of photos of CCI SV during the Obama time frame shortage. Some rounds would not even chamber in my target pistols due to the excess lube and the big nicks/dings in the heads.

Here are a couple of photos of CCI SV during the Obama time frame shortage. Some rounds would not even chamber in my target pistols due to the excess lube and the big nicks/dings in the heads.

heads

heads