I know this is a topic that has been written about very extensively! But what I have never seen discussed is the actual effect of each grain variation in case weight from the average weight of any specific rifle caliber.
My interest in this wasn't so much to understand the above question but rather to control velocity variations in large volume loading of various mfg & differing weight cases, hence improved accuracy and functioning of semi auto rifle ammo.
So without getting into details I used 5.56nato as well as .243Win for an intermediate volume cartridge and .300 Win Mag for a high volume cartridge as control/ confirming tests.
In the 5.56 round I used 55gr .224 FMJ and fired 10 rounds of each case weight from 88gr to 108gr "though I had to settle for less than 10 rounds of some of the heaviest over 100gr" over my chonograph, while varying the load by -0.1 powder as I increased the case weight by each +1.0gr over 94gr and +0.1gr. powder as I decreased the load under 94gr.Case Weight by each 1.0gr. The reason I chose 94gr as point to vary from is because I found that to be, in my experience as the average 5.56 case weight.
I concider this process, or call this process, Loading To Scale! First you must find a load that is safe and reliable for the average case weight in your caliber and then very your charge "as I stated above" from that. I would then recommend that you take a few rounds of the highest weight cases and lowest weight cases and very the charges to confirm what I have realized for myself. This process also shows why it is important to lower your charge from the highest listed charge in your loading manuals! That if you concider that in the 5.56 extreams I tested there is a 20gr variation in CW, that results in a 2.0gr variation in charge weight using my method.
Just one more thing I should mention is that my brass is as uniform as I can make commercial brass, the necks are turned, flashholes deburred, primer pockets swagged, and cases trimmed to uniform minimum length. If you do not uniform your brass as I do you will likely not be able obtain the results that I do! This process is not for everybody, but only for those who's goal is uniformity of large volumes of mixed types of same caliber cartridges.
I seek to get 3/4 MOA or better at 200 yards for all my hunting rifles. I do not turn any of my caliber necks but otherwise very precise on brass prep and load prep.
I do not cull any brass unless they are not worthy of firing. (Some cull because of weight variances) I do though separate brass according to manufacturer (no ifs about that) The different manufacturer's brass weight and capacity are almost always different and do make a difference.
I also try to use from the same lot my powder, bullets and primers.
Note in the beginnig thread it may not have been clear that as I decrease CW below 94gr in the 5.56 I increase the charge weight by 0.1gr for each 1.0gr decrease. Sorry for the confusion!
As I stated in my thread, absolute uniformity is a must, and my desire is to develope accuracy as well as reliability in autoloaders, but I found that uniformity in velocity in my 300 Win Mag as well as in the .243 win to be at worst in the teens and more often in the single digits especially in my .300WM and that is with several 10 round groups who's CW varied by 7.0 grain and required a 0.7 gr charge wieght variation.
There certainly is a lot of information I have intentionally left out. Simply because I cannot put it all in the minimal space of this forumn. I actually tried to write it out longhand first and quit when I was almost through the 3rd page because there was too much left to cover that couldn't be put into such a limmited area. As I stated too, this process is not for most people, only those who are interested in large volume loading of one caliber who want the best uniformioty possible, but I believe it is of great interest that of the 3 cartridges I have tested they all seam to vary uniformly by 0.1gr charge weight per1.0gr case weight variation. Or to state it another way, in my testing no matter which of the 3 cartridges I have used, 0.1gr powder equals 1.0gr case weight variation.
This is much more work than the average handloader is willing to do, but I don't believe it is any great leap of understanding, so I don't expect many handloaders to accept this study or process that I have begun using and will use in the future for all rifle ammo I develope. I hope this helps those who are interested!
Sorting cases to a 2% spread in weight's fine for use up through 300 to 400 yards. Beyond that, sort 'em to a 1% weight spread.
The spread in primer output and exact charge weights' powder burning causes a larger spread in pressure and velocity than a 1 or 2 percent difference in case weight. But you need the right combination of powder and primer to make that happen.
For accuracy, milder primers tend to perform better than hot ones. And medium speed powders for the case size tend to do better.
When one loads for highest velocity for a given bullet, they typically end up giving up some accuracy to win the race to the target.
[...]My interest in this wasn't so much to understand the above question but rather to control velocity variations in large volume loading of various mfg & differing weight cases, hence improved accuracy and functioning of semi auto rifle ammo.
(1) small variations in case weight don't translate directly to capacity/containment
(2) life's too short to mess with this when dealing with large batches of ammo for semi-auto
(3) if I was able to determine a noteworthy difference between a couple of brands e.g. rws, lapua, RP, then it might be worth tweaking the load by brand
Why bother, trim to length, clean the pocket, load, shoot. 1/2 moa. or less on 6 rifles at present, and 1-1/2 moa. on three with no scopes. Moa. on 2 others.
I've shot three different primers(all standard) and three different brands of brass into the same group with an '06 shooting a 150 grain pill and mid speed powder( twenty years ago so I forget the powder) and the group was sub inch at 100 yards with average extreme spread. I stopped screwing around with brass then and there and focused on getting a bullet the barrel likes and driving it sensibly.
Half of the people on lrh need to take 10% off the top of their powder charges and the rifle will miraculously start shooting great groups. Too many running their rifles ragged and expecting good things.