Help with high and low impacts

[Three57]

I am getting the occasional and all too often, high and low impacts.
I would like some opinions on how to fix this and improve my group sizes.
I think a good possibility is that the new brass that I am using doesn't have consistent headspace sizes, which could cause inconsistent pressures and speeds. They all measure under my chamber size. The headspace measurement varies from 1.621 to 1.624. My chamber's headspace is 1.628, so I am not resizing the brass. I could also be way off on what is causing the problem.
Here are my 200 and 300 yard test targets.
Let me know your thoughts

 

[AZ.noob]

I'd be interested to see some chrono numbers; specifically ES & SD.

Based on your measurements, you've got upwards of .007 headspace tolerance... that is quite a lot.
You might consider resizing your new brass, or at the very least running an expander ball through them. With a bag of new brass, there's no telling just how consistent the neck tension will be from one to the next, or if they've got dings in them from packaging, etc. Resizing will help 'standardize', or at the very least make them all as close to identical as possible (which is what we're after).

Weight sorting, flash hole sizing, primer pocket uniforming, neck turning... all done to make each piece as identical as possible. Bullet meplat uniforming & bearing surface matching too, but this is extreme long range stuff and not likely to make a big difference at only 300 yards.

All this is assuming you're working within an accuracy node. If you haven't done it, dry Dan Newberry's OCW process. Good stuff


Edit: I just saw your post over in Semi-Autos. If shooting an autoloader, you may not see the same gains from all this obsessive-compulsive stuff... that bolt gun sickos do for 'fun' I'll let the precision semi-auto guys take it from here.

 

[wvlapua]

Follow through and try spotting your hits. This is more important in a semi auto as lock time is much slower than in a bolt gun.

 

[Three57]

Follow through and try spotting your hits. This is more important in a semi auto as lock time is much slower than in a bolt gun.

I really think this could be the problem, but as AZ pointed out, I wonder if the headspace variance could cause the speed issues. If so I would resize my brass all down to a consistent size. If it would help. It is semi auto, it has been suggested the headspace won't make that much difference.