Hey there Dixie Dude,
Your comment in the first sentance, "-------- some mixed case brass -----------." rang my bell!
Loading with compressed loads may or may not be a problem, depending on powder, powder lot#, brand and/or lot # of brass, type of primers and/or lot# etc.
That is why we are cautioned to back off from safe worked up loads anytime we make a change in brand, type or lot numbers of components.
Back quite a number of years ago, I was working up loads for my son's 30/06. During the process, I ran out of hulls from the batch of "known" Rem. brass, falling 5 or so cases short of the number needed for the searies.
I went to my 06 brass supply and chose enough cases to finish up the tests, choosing cases with head markings identical to those already in use.
As it turned out, these "odd" cases were used in the two sets of test rounds with the highest and next to highest powder charges.
The "odd" cases were trimmed to correct trim length before loading.
Upon firing the last two sets of test rounds, the lower of the two threw fliers - as I recall - from the odd cases, but with the top loading not only threw the shots out of the group, but showed very high pressures.
At least one of the cases, one which I have saved as an example, streached BEYOND THE NEEDS TO BE "trimed length" in just that one firing.
That was way before the days of my digital scale, but my best case is that lot of brass had very thick case walls, which in turn lead to the VERY!! high pressures.
Point is, don't mix brass or any other component if you are anywhere close to maximum pressures.
As per the compressed loads, I many times load rounds with the powder well up towards the top of the case neck. NO PROBLEM. However, these are loads which have been "worked up" to, and are showing no signs of pressure problems.
Also, as has already been noted, different rifles react differently and it is very likely loading just one load and expecting good perforence from two or more rifles of the same caliber will lead to so - so results.
Your best results will come from "working up" loads for each rifle, as well as keeping the brass separated by rifle along with separation by lot #, brand AND NUMBER OF TIMES FIRED.
Be safe and keep em coming!
CDOC