I have a Ruger tang safety M77 that had a new E.R. Shaw heavy varminter barrel put on last year chambered in 22/250. I worked up a load using a 55 grain Sierra spitzer bullet and H4895 in Win brass lit by a WLRP primer. This load was shot by my S-I-L because I was waiting to get cataract surgery and couldn't see that well. I was looking at the target with his spotting scope and watched him stack three shots through one hole at 200 yds. The rifle was not shot again until Thanksgiving weekend while visiting #2 son in Washington state. I fired the rifle one time and it wouldn't eject and had to remove the case with a cleaning rod after we were back at the house. The primer was blown and the pocket was severely oversized. I fired the rifle again after returning home and it was over pressure and wouldn't extract. I pulled all the bullets from my loads that were made up and dumped my powder from the 1# bottle I use out of and made the load up from fresh powder but used CCI 200 primers and lowered the charge weight 1.2 grains. Upon firing the first round of this test extraction was easy and the primer looked like the load was a little anemic, but upon firing the second cartridge loaded identical to the first the case would not extract and had to be removed with a cleaning rod and the primer was very flattened. I weighed each powder charge on my RCBS 10/10 scale and used identical components. I am just flabbergasted by the outcome of this. Oh, btw, I went to the store and bought a box of Fusion factory loaded ammo and fired four of them without a hiccup. Each of these extracted easily and they seemed to be on the hotter end of the spectrum but I didn't chronograph any of them. Have any of you guys seen or heard of any scenario like this before?

Initially one would be thinking your powder scales may be at fault, giving erratic readings. Failing that the other variable that can impact a lot on pressure is neck clearance in the chamber.

You state you are using identical components, does this extend to your cases? Are they of same brand and or number of firings? The chamber in the Shaw barrel may be of minimum dimension to the extent that with some cases there is not enough clearance to allow the neck to release the bullet without pressure spiking.

I use H4895 when reloading for my son's 223 and haven't had any issues with top loads. H4895 is actually Aussie made AR2206H powder which is temperature insensitive so temperatures should not be a cause of your pressure spikes.

Recently some Varget (Aussie made AR2208)powder came up for sale on our national online auction site and the seller stressed that he was selling because this batch of Varget seemed way hotter than the batch of same powder he had previously worked up loads for. He warned buyers to be aware that they could not just duplicate their normal Varget load with this new batch. He seemed to be inferring it was more than just a few grains difference. This seemed highly unusual but credit to the seller for posting the warning and not just on selling the powder without a word to the wiser.

Perhaps the Aussie manufacturer of the H series Hodgdon powders has changed something so newer batches are hotter than the old?

Off hand,I would suspect the brass itself. A change in brand name or lot number could REDUCE the case capacity thus increasing the chamber pressure substantially.
The only other reason that pops into my mind is that the ammo was heated by the vehicles heater or the left in the sun and the powder burned faster,which it can do if heated to over 80 degrees F.
This is sometimes refereed to a "Winter Load" which works fine but when the weather warms up or as stated above the powder is heated up causes pressures higher than in cooler/cold weather.
For this very reason the new powders such as Varget and the new triple based powders are more stable with swings of ambient temperatures.

Well what is your overall length?
Is it possible you are up against the lands with your loads?

The loads are all in Winchester brass but I don't know the number of firings of them. They are all trimmed shorter than the factory ammo cases. I am done with this powder in this cartridge even though it has been my go-to powder for other 22/250 rifles and a propellant I really liked.

If you can slide a bullet into the neck of the fired cartridges, you do not have a problem with neck thickness nor length. (gee Mom,, you mean I don't have to buy a bunch more thingies?)
It's hard to imagine a 10/10 jumping around enough (without it being apparent on the scale) to cause such a variance in obvious pressure When using my 10/10, I am in the habit of tapping the table a couple of times to settle the beam.

how many grains of powder?
I would check the head space it being a new barrel.

Excessive headspace does not cause excessive pressure.