My Speer #13 Reloading Manual provides many good 223 loads. Their Test Firearm is a 22" Ruger barrel with a 1-12 twist.

I want to load for a 26" Remington with a 1-12 twist. Do I need to start with middle of the road loads and work up? Does the extra four inches significantly increase pressure?
Thanks in advance for your advice.

Extra barrel length will not increase chamber pressure.

Brewster, you should follow the "Start low and work up" rule in ALL instances.

A longer barrel may or may not result in slightly more velocity, but will not increase pressure. It may also produce a bit less muzzle blast, but those are about the only performance differences.

Brewster, you should follow the "Start low and work up" rule in ALL instances.

A longer barrel may or may not result in slightly more velocity, but will not increase pressure. It may also produce a bit less muzzle blast, but those are about the only performance differences.
Rocky hit the nail on the head. I am currently loading for a 26" barrel Remington SPS Varmint in .223 and was hoping for an increase in velocity compared to my old 24" barrel Savage. No such luck, as my loads are chronographing at very similar velocities despite the 2" longer tube. It does seem to be a little less noisy and the recoil is almost non-existent with the 26" bull barrel.