Double grouping is very frequently caused by two things (assuming it is not the shooter): 1. It can be a rifle bedding issue if the recoil lug isn't making contact with the stock/bedding across its entire surface. 2. It can also be a seating depth preference with your reloading in that you are just a few thousandths away from hitting that perfect depth node.
I usually start with #2, and have found that by increasing or decreasing the cartridge OAL/CBTO .005 - .010, I can much more often than not tighten things up.
Bullet seating depth has as much influence on accuracy as powder charge weights.
One way to rule out a lot of possibility on it being shooter error is to fire your group without breaking contact with/re-addressing your rifle. If you like to take a shot, then move off the rifle to record velocity etc... you are greatly increasing your chances of altering the recoil impulse and POI slightly for the next shot.
I would go with the 42gr powder charge with the low SD and then do some seating depth tests to reduce group size.
Did you come off the scope while shooting the group? I've seen that cause 2 groups.
Brass annealing or brass prep can cause this also.
Not all brass is made of the same alloy and even if it is from the same batch even Lapua you can have variances.
That is where you can see the big velocity spreads.
I have a couple rifles that will not shoot good tight groups with Lapua cases until i turn the necks.
Your groups are in a good size and if it was mine I would take it to 200 yards and see what happens.
Unless you are only shooting 100 yards with it then ultimate brass prep will need to begin.
And measuring every bullet with a comparator will help also.
Another easy thing is notice how long each loaded round is being cooked in the chamber.
If you shoot one round from cold chamber and then shoot another in 10 seconds then chamber a round and let it warm up in the chamber while you adjust the bag and blink your eyes for 45 seconds and write down velocity the group will suffer.
Be very aware of seating forces when making ammo and if you feel one seat a wee bit easier than the rest then mark that case and see if it is out of the group.
Ultimate brass prep done and you have different seating forces could be a different alloy issues.
And could also be you scratched your face before you picked up that bullet to place it on the case to be seated and the oil on your fingers lubed the bullet.
Hornady bullets have a waxy surface on some of the ones i have bought.
I wipe down every bullet with a paper towel.
That towel will do only so many bullets before all the space on it has touched a bullet.
I go as far as to dry/wipe my fingers on a paper towel before each bullet is picked up.
Think about touching a case that was prepped and has a slight amount of lube on the case then picking up a bullet.
Think your fingers are clean and dry after picking up a case.
Go into the bathroom and wipe your fingers on the mirror and see if you leave a smear.
Pick up a bullet with your fingers and do the same test to see if your bullets have a waxy film on them.
Eliminating every possible variable we can during reloading is usually why we reload rifles for accuracy.
Not all brass is made of the same alloy and even if it is from the same batch even Lapua you can have variances.
That is where you can see the big velocity spreads.
I have a couple rifles that will not shoot good tight groups with Lapua cases until i turn the necks.
Your groups are in a good size and if it was mine I would take it to 200 yards and see what happens.
Unless you are only shooting 100 yards with it then ultimate brass prep will need to begin.
And measuring every bullet with a comparator will help also.
Another easy thing is notice how long each loaded round is being cooked in the chamber.
If you shoot one round from cold chamber and then shoot another in 10 seconds then chamber a round and let it warm up in the chamber while you adjust the bag and blink your eyes for 45 seconds and write down velocity the group will suffer.
Be very aware of seating forces when making ammo and if you feel one seat a wee bit easier than the rest then mark that case and see if it is out of the group.
Ultimate brass prep done and you have different seating forces could be a different alloy issues.
And could also be you scratched your face before you picked up that bullet to place it on the case to be seated and the oil on your fingers lubed the bullet.
Hornady bullets have a waxy surface on some of the ones i have bought.
I wipe down every bullet with a paper towel.
That towel will do only so many bullets before all the space on it has touched a bullet.
I go as far as to dry/wipe my fingers on a paper towel before each bullet is picked up.
Think about touching a case that was prepped and has a slight amount of lube on the case then picking up a bullet.
Think your fingers are clean and dry after picking up a case.
Go into the bathroom and wipe your fingers on the mirror and see if you leave a smear.
Pick up a bullet with your fingers and do the same test to see if your bullets have a waxy film on them.
Eliminating every possible variable we can during reloading is usually why we reload rifles for accuracy.
Yes
Granted, I started with once fired brass, but did anneal it, trim, chamfer, debur, de crimp it. The brass was full length sized in the groups above, I wiped the brass off yesterday, neck sized them, ( I even did the swamp rat q-tip neck wipe) loaded the 42 gr loads again today. The groups opened up a bit. The only thing I changed was the way I sized the brass.
I would pay attention to my brass prep. Starting off with annealing, shoulder and neck prep. Both groups are shooting 5 o’clock with some flyers (I don’t like the 2 o’clock flyers in the 42gr group). Although these could be cold bore issues but only you would know that. Your ES of 105 for 41.5gr will look like a shotgun at distance but all of them are basically at 5 o’clock. Work up another load with this powder weight paying attention to brass prep, powder charge, and bullet seating depth. If the group stays the same but your ES/SD drop drastically in value and you’re happy with the MV, try another load this time only adjusting bullet seating depth.
The 5 o’clock position was me just getting the scope close to the bullseye, this was the second time I’ve shot the gun. I adjusted it to be on the bullseye today.
The first two shot in the 42group were the two o’clock shots, then I checked my chrono, inspected brass, then shot 3 more. The 41.5gr group had the coldbore shot in it
