From what I'm reading and understanding you basically have nothing but an untuned rifle with an aftermarket trigger, and new barrel not yet broken in and a heart full of hope...what EVERY one has with an new toy...no diss or flame intended and I'm NOT whizzing on your shooter, just plain truth in the real world.
From my perspective you are wasting components trying to get something that is probably not possible as your rifle sets now. But keep doing what you are doing and you WILL learn.
BEFORE you go any farther...TUNE THE RIFLE and ammo and accept the time constraints...I.E. bed it...benchrest prep your brass AND bullets...you're worried about a few thou difference in COAL and you haven't even ogive or weight sorted the bullets...Partitions can have 0.010" difference in ogive length(or more even) and several grains of weight variation. Partitions are excellent HUNTING bullets where HUNTING accuracy is expected NOT half MOA...
Sometimes, JUST SOMETIMES I get a box of Partitions that are very uniform in Ogive and weight over 85% of the box but NEVER 100% and that goes for EVERY BRAND of bullets INCLUDING factory target...custom target bullets are another story.
If you want a 1/2 MOA rifle you have to PAY for it in gunsmithing costs AND sweat equity scattered all about developing UNIFORM brass and bullets...otherwise be happy with "normal" hunting accuracy.
Shooting small groups ISN'T hard, it just takes practice working on all the basic techniques...forget about what the groups are and consentrate on learning HOW to shoot...the groups will come when you practice and when you learn.
You're basically chasing your tail by not reducing the variables as low as possible, THEN, starting your load development.
The cases can have several grains of weigh differential which basically means the internal volume is different, so futzing with powder weight is a waste of time.
You also need to measure the COAL bullet to lands length AFTER you sort the OGIVE length.
Basically you need to start over from the beginning, do all the grunt work, get things uniformed, THEN you will be in a relatively good position to start your load workup and come up with a consistent accurate load.
Check out some of the varminting and target forums to see HOW to develop accurate, benchrest prepped ammo, if you haven't already.
I guarantee if you bench prep your cases and bullets you will cut your groups in half without hardly trying...and believe me when I say you CAN'T produce consistent small groups by just grabbing brass and bullets indescriminantly...you WILL get small groups now and then, but the next time they will turn into "patterns"
One other thing you might do if you don't want to bear down and do the "hard" work...number your cases, fire them in order, set the cases that go out of the group in one place and the cases that go INTO the group in another. Load and fire both the groups again to see what happens, DON'T CHANGE THE LOAD OR THE COAL...SOMETIMES this will separate the brass into "GOOD" AND "BAD"...sometimes not, but it is one way to reduce variation. GOOD brass will continue to shoot to the same POI and the BAD stuff will keep scattering...sometimes this method is quicker than weight sorting or even MORE time consuming, water weight sorting. BAD in this case just means it shoots to a different POI, not that it's lousy brass.
One last bit of "experience"...buy yourself a digital JEWLERY scale...you can find many in the $20-40 range...a good digital caliper..same price range...and a set of Hornady headspace AND bullet seating gauges...THEN...
when you get ready to reload your next bunch...grab 5 cases at random, size and trim, weight sort and number from lightest to heaviest AND measure the shoulder length with the headspace gauge...do the same with the bullets, grab 5 bullets at random...measure the ogive length with the bullet seating gauge and sort them into lengths and number AND weigh sort them also. MARK DOWN THE MEASUREMENTS AS YOU GO...
Find the COAL bullet to lands measurement...that has bee discussed all over this forum...USING A bullet you have ogive measured as a reference. USE THIS MEASUREMENT as the "standard" seated ~0.010" off the lands with any load out of a reloading manual...one with pressure readings preferrably, picking the highest velo with the slowest powder but dropping it ~5%.
Load them up but keep in order lightest case to heaviest case with lightest bullet to heavierst bullet. Shoot them and mark the data on the target. Go reload another set, same thing grabbing components randomly, but sorting within the groups...do this for 5 sets, mark the targets from 1-5, then compare the targets.
THEN...size and trim, reweight the 25 cases and sort from lightest to heaviest and sort the cases into 5 groups with the 5 lightest cases in one group, the next heaviest cases into 5 groups...etc...get the picture?... and weigh/ogive sort 25 Partitions...reload light with light and on up the weight scale...you should be getting the total picture by now.
Fire the 5 groups on 5 different targets, mark them 1-5, lightest to heaviest and THEN compare them. You should see a big difference between the sorted and the unsorted targets...if you DON'T then you need to take a look at YOUR shooting technique and go back to basics.
I've been using this technique or a variation of it for a very long time on new, used, custom, rebarrels, rifle I've built, etc and can usually cut the group size down by 50% compared to factory ammo or randomly reloaded ammo, BEFORE mucking about with seating or powder amounts...not always...but I used to keep my component stores chocked full of goodies by doing this and maybe a bit of simple barrel channel work or bedding for people...I did the work for components NOT money.
The sad fact is doing this takes time...ACCURACY takes time...and in todays world NO ONE really wants to do the time, but they continually do the crime...wasting BOTH TIME and COMPONENTS whizzing in the wind by not sysematically developing both the rifle and the ammo.
