Sorry for the necro post, however, reading this brought to mind a question. I have a 553 sb that I ordered a suppressor gas plug for. It has a 0.9 mm port. It is very soft shooting and pleasant suppressed. I also have a 553 lb. It came with a 1.1/1.2 mm port. It was overgrazed and unpleasantly snappy. I used the chart above and ordered a 1.05/1.1 mm plug which helped some but is no where as soft as my 553 sb suppressed.

My question is why wouldn’t the lb require at least as small of a port as the 553 sb suppressed? Also does anybody know if you can custom order gas ports not listed on that chart?

To the question of why a 553 lb vs 551 it is a very well balanced natural pointing firearm, for me anyway.