Hodgdons manual #26 shows 28.5 grains h414 as the top load with no starting load and a speed of 3100 fps with 40800 cup. No fireball out of a 21 inch barrel. I did not realize that cousin Clem worked for hodgdon a while back that s great for him so successful!H-414 is a different type of powder than Varget. Varget is an extruded powder and when the case is filled there is some space around the granules. Compressing will reduce this some but not enough as a rule to cause severe pressure spikes. H-414 is a ball powder and can often lead to some sudden pressure increases as the load is compressed. Unless Hodgdon has tested H-414 with Compressed loads which are usually indicated in their load data I would avoid compressing it. Just because "Cousin Clem" wrote in a Forum that "I've dun it and ain't had no problems" doesn't mean that you won't.
FWIW, Hodgdon's online manual doesn't list H-414 as a recommended powder for the .223 with a 55 gr bullet. Way too slow and doesn't show up on their data until you get to the 82 and 90 gr bullets. The heavier bullets can utilize the slower burn rates. What you may find with a "case full" of 414 is a slow bullet and a nice large fireball in front of the muzzle.