RCBS Match Master

[hounddawg]

What's the best way to claim accuracy? Smallest or largest few shot groups fired?

accuracy of the rifle or accuracy of the shooter? I don't really consider anything less than a 20 round group or composite to show much of anything, Five shot groups show me what can happen if the moon and stars all align and the hummingbird of happiness drops a load on the target. Ten Shot groups show me the likelihood of the load/barrel throwing a flyer. Twenty shot groups show me what can be, Sixty shot composites from a match show me the accuracy of both the gun and myself.

All three targets shot with same rifle and same load.

835 yards sixty shots real world conditions, 300 yards twenty shots, again real world conditions, 300 yards five shots on a perfect windless cloudy morning doing load testing. The 60 round target shows me how much I was off on my wind/mirage. The second shows me the same. The five shot group shows me what the rifle is capable of if that hummingbird comes along. My normal 5 shot group at 300 is around 1.25 - 1.5 inches. That .17 MOA group was hummingbird poop and pure luck which is why I dismiss 5 shot groups for anything except rough load testing

Notice how real world mirage and wind can totally mess it all up and the farther out the more those little errors add up

edit Savage 12 action, Criterion 6BR 8 twist, Boyds stock, glass and pillar bedded, Berger 105 Hybrids, Varget powder, Peterson brass, CCI 400 primers. Loaded on a Lee turret press

 

[Unclenick]

National Match ammunition used to be evaluated by firing 200 rounds and finding the size of the smallest circle that could still include the centers of half the shots. Radial SD is a better measure, though, as you can use it to predict what portion of future shots will average any given distance from their mean. However, another factor is the Standard Error (SE). It is the radial standard deviation of the location of the mean itself from one sample group to the next. It is calculated by taking the radial SD of a group and dividing it by the square root of the sample size (number of shots). So the smaller the sample, the more uncertain it is that the mean point of impact of your group is representative of the mean you will get in the future from that same load in that same gun, and the less certain any sight correction you make is to be correct for future shots.

Generally speaking, the more shots you fire, the bigger the group gets because you are giving the lower probability outliers and other widely dispersed shots more chances to occur.

 

[RC20]

That brings up the other workaround, which is to use a slightly compressed load so the grains are locked into place by the seated bullet and don't shift with normal handling. That is what you find when you pull bullets from Federal GM308M.

So, as with many load-related matters, it depends.

I was wondering if slighly compresed might be a help.

And the Depends, its like English class, I before E except after Y (or whatever that was).

So much for just doing it right and getting what you have every rightr to expect, sigh.

 

[hounddawg]

in regards to case fill the loads in the above targets were 29.2 gns of Varget, the case will hold 31.2 filled to the bottom of the neck with no drop tube or packing/settling etc methods. That would be about a 93% fill rate. The 6BR is a remarkably forgiving cartridge as far as powder fill. Just about all of my go to loads in .223, 6 CM, .260 Rem, and .308 have at least .2 gns leeway on either side of target weight for accuracy if I am doing my part. The environment is a much bigger factor in my groups than the ammo. Finding a good node and seating depth is the easy part, making the right wind calls for a 20 round session is a pure T b***h