I full length resized (its mixed headstamp)...and then after firing one time, I just neck resize after that. Some were full length resized because they hadnt been shot yet, and some were only neck resized.

I have already started the return process...so we shall see when I get it back, but I will keep tabs on every single thing when I get back to enable myself to identify any issues and trace it back.

Why would you neck size only on a 300 blk out? That's odd. If you are shooting the neck sized cases, they should be perfectly formed to your chamber. This would omit any head space issue causing the primer not to go off. So, if you are having miss fires on these neck sized cases, it's not a head space issue.

Why is it odd only resizing the neck on 300blk bolt gun?

Neck sizing only is a bench rest reloading technique. A blk out round is more of a tactical caliber and on a factory Ruger rifle, and on the opposite side of a bench rest round. What is gained by neck sizing for this, that would not be gained by FL sizing? Neck sizing only can cause a lot of issues in a rifle, like unreliable chambering issues. The blk out round would be one of the last rounds I would think of for neck only resizing. I would want 100% reliable feeding, so a FL sizing would accomplish this. Neck sizing will prolong case life, and is generally thought to help increase accuracy. But with cut down military brass, the brass is not that great (good enough, but not match grade). It just seems odd to neck size for this round. With your primer issues, I would regroup and FL size everything, and seat your primers to the correct depth. I would then retest the rifle before I sent it off to Ruger, knowing the issue may be ammo related, and not firearm related. I certainly wouldn't tell Ruger all this info when sending it back.

Most benchrest guys aren't neck sizing anymore....they are FL sizing too now. Some of the old school 6ppc guys still only neck size but most of them even have started FL sizing. I think the more accurate theory has been debunked

I was shocked when he said it too.

But in the situation he's fighting that should help him rather than hurt him.

The reason I was doing it is because it's a bolt rifle and I wanted the casing to fit the chamber as well as get the most life out of my brass. That's the two main reasons.

Nothing wrong with neck sizing as long as the person realizes at some point they are going to get tight in the chamber and you'll have to use a body die or FL size for a cycle then go back to the neck sizing until they get tight again.

That is what I do much of the time with a few that are uncommon brass, wanting it to last as many reloads as I can. Then again with no more than I have been shooting lately it will last a very long time

On those I bump the shoulder back usually every third loading but those are not loaded hot either.

update...they shipped back a whole new gun.

Time to try it out and see if they fixed the issue.

Well when I got home, I further inspected it. It is the same gun...they replaced the barrel.