Sig Cross head space question

[Hailstate]

Gun: Sig Cross
Caliber: .308 Winchester 16” barrel
Brass: Lake City
Powder: Varget
Charge weight: 39.8 - 44.1g (load test)

I have had this gun for quite a while and it’s one of my favorite guns. This will be a long story to get to my question so please bear with me but it’s important back story information.

(1.) I hand load but am still relatively new to the craft. I have always used an RCBS Rock Chucker SS press but was presented an opportunity to trade it for a Dillon 550 (straight up). I couldn’t refuse so I made the swap. Of note, my issues in this story started when I changed presses.

(2.). Some friends and I decided to get into the world of distance shooting. I’ve used this rifle for hunting and plinking and it’s an absolute joy to shoot, I decided to buy an additional barrel (6 Creedmoor) and rebarrel the rifle instead of buying a whole new rig. I bought the new barrel and started to change the barrel out and realized my armorer’s tool wasn’t the correct tool and stopped. However, I checked the head space with a go and no go gauge to ensure nothing had changed and the rifle was safe. The bolt closed smoothly on the go gauge and will not close on the no go gauge.

(3.). Fast forward a couple of days, I went to the range with my brother and was testing some loads with different bullets and Varget and I ruptured a case head as I was working my way up the charge weights (still under max charge by .7 grains). While I saw no other excessive pressure signs, I immediately stopped running that bullet and swapped to another worked up load with a different bullet (I associated the failure to the charge weight and the bullet). I had no other issues with case heads splitting.

(4.) A couple of weeks go by and I’m shooting with a friend (30 years of reloading experience and I didn’t mention the prior case head failure to him) and have another case head rupture (scares the bee jees out of me). Again NO pressure signs.

(5.). Searching for the cause of now (2) case head ruptures I inspect the fired brass and find “faint rings” around the case head. I take a factory round (Federal 150g soft point) and fire it and get a “small crack” in the case head.

(6.). Suspecting head spacing issues, I check the chamber again with a go/no gauge and again the bolt closes on the go and doesn’t close on the no.

(7.) I inspect the loaded rounds and use a comparator kit and find the shoulders have been bump back .0005-.0009 on the remaining rounds in my load test. I am assuming the excessive and inconsistent shoulder bump is due to the new press and my inexperience with it.

(8.) To rule out any other mitigating factors with the factory ammunition I shot, I checked the shoulder and found .0003 shoulder bump. I feel like I was able to rule out the factory ammunition allowing for excessive head space and causing the case head to rupture on the factory round.

Now to my question(s).

Is it possible that I still have head spacing issues (in the rifle) even after checking the rifle with go and no gauges? I ask because I can’t figure out why the factory round failed with adequate shoulder bump.

Is it more likely that the excessive shoulder bump is the root cause of the case head rupture? Again, the only part of this puzzle that doesn’t make sense to me is the factory round failing. Had that not happened, I would have completely concluded it was excessive sizing that created excessive head space and would have taken the rounds I had made up apart and discarded the brass and moved on. Of note, my issues with the failed cases started when I changed from the RCBS SS press to the Dillon progressive press.

Also, the brass I was using for my load test on the 2nd rupture was from the same lot of “firing” when I had the first rupture. I annealed, cleaned, sized, and reloaded. I suspect the prior rounds were over sized as well as I didn’t verify the shoulder bump on them either (I am embarrassed!).

Thanks in advance!