You didn't state if these cartridges were loaded back at the time of original load development, or if you loaded them up at a different cartridge reloading event. Are you using the same powder scale, brand and model number primers, the same brass casings, the same Lot of gun powder? Do you have a weight to calibrate your powder scale with and have you checked it's accuracy?
Change any of these components and if you were already operating near max you could begin to experience excessive pressure signs.
"Both loads showed giant shiny spots on the top of the brass and the bolt was hard to open." What's a giant shiny spot on the top of the brass mean? Are you describing a relatively small (compared to the entire case head) shiny spot on the case head from a bolt face plunger hole or extractor slot?
Hard bolt lift is subjective also. I've had everything from noticable stiff bolt lift to having to slam the bolt handle up with the palm of my hand - or it wouldn't budge.
If you're experiencing a huge increase in pressures, I'd check the powder scale for calibration first, after confirming you haven't switched any of the other components or swapped over to a new Lot and container of powder.
Report back after you figure it out?
These are the items/possiblities I would be checking out. You didn't say if these reloads were loaded in a same batch that didn't display high pressure signs in the earlier firings. Or if they were loaded in a later batch of reloading. You mentioned that you use a digital scale. Have you checked its calibration? Was it provided with a calibration weight of known weight? I've never used a digital scale. I use a balance beam scale. I wouldn't want to be forced to believe the digital print-out number without having a means of proofing it with a balance beam scale. Otherwise, what assurance is there that the digital number is correct? If your ammo was loaded in a different batch than the normal pressure loads, and your bore wasn't fouled with dirt, grease, crud, water, oil, or corrosion; I'd be looking for some change in some component or powder charge as the likely culprit.
Weather is only a concern if you let the snow, water, mud, or wind-blown debris access your bore. When hunting in Alaska, always criss-cross your muzzle with two pieces of electrical tape as an effort to prevent water, snow, mud, twigs, or other debris from getting into your bore when carrying in the field and hunting. You can shoot straight through the electrical tape with no affect on accuracy or pressure.
I have no idea why factory loaded 22-250 ammo would exibit high pressure unless you're bore was dirty/fouled with oil/grease/corrosion, and even then, it should only affect your first shot.
If you confirm the accuracy of your digital scale, load another round or two, and still get excessive pressure, drop your powder charges to a safer level.
