[Unclenick]

You just had a pressure sign. It surprised you because you weren't following good load development practice, even though you might have thought you were. Let me explain:

First. 1 grain is a big jump in the little .223 case. Normal procedure is to increase powder by not more than 2% at a time, or 1/5 the difference between the minimum and maximum listed loads, whichever is smaller. That would be not more than half a grain in .223 with your powder choice. It would be 1 grain in a .30-06, but you don't have that much room in a .223.

I also note you must have gone by memory on the Hodgdon load list, because 25 and 26 grains are not listed by them on their load data site for H4895 under the 55 grain Speer bullet. It always pays to write these things down. They actually list 23 grains to start and 26.2 grains maximum, with a Winchester case and a Winchester WSR primer. That means you should start with 23 grains. When no starting load is listed, the general rule of thumb is to back off 10% below the maximum. You start with that load and work up in 5 equal 2% steps (6 shots total, counting the first one), watching out for pressure signs at each step.

If you get a pressure sign at any place along the way, you reduce the charge weight that caused it by 5%. In your case, since you got a pressure sign at 26 grains, I would back down to 24.7 grains, and call that your gun's maximum for that powder with your cases and primers and bullets. It will perform close to the 25 grain charge and be safe and not put excessive wear on your gun, using your brass and primer combination. If you change brass or bullet brand (even if it's the same weight) or primer brand, or get a new bottle of the same powder with a different lot number, go back down at least 5% (23.5 grains) and work back up to be sure you're still safe.

I've seen changing primer brands change velocity and pressure equivalent to increasing the powder 4%, so I always reduce 5% for a different primer and work back up. Some brass can change pressure that much or more, but I've only seen that in .300 Win Mag and .308. In .223, the difference in brass isn't usually that big. Still, when you follow a recipe, you need to copy their brass and primer or back off an extra 5% from maximum to start.

To see the brass and primer detail in the Hodgdon data, you need to click on the Print button, and look at the preview (you don't actually have to print it).

Stay safe.