Molon had a post on AR-15.com where he did a test to determine velocity loss due to the gas port compared to a barrel with no gas port. If I remember correctly the velocity difference averaged 1% loss in velocity due to the gas port. In many loads that is within the maximum spread of the ammunition and might not make a significant difference in accuracy. So in essence if you shot with the gas shut off on your AR-15 and your velocity is 2525 FPS you open the gas block your average might drop to 2500 FPS. In real life the velocity loss wont be that exact but gives an indication of the possible difference.
I tend to watch velocity on the chronograph for indications on pressures plus ejection patterns. I look at the brass, primer and other marks to establish if the load is safe. I rarely load to max pressure just because I like my reloads to be safe in more than one firearm. I have multiple 5.56/223 AR-15s and multiple 6.5 Grendel AR-15s. I want my reloads to function reliably in any firearm of that caliber/cartridge.
I couldnt find the Molon post but I did find this article.
https://www.shootingillustrated.com/arti...-velocity/
I tend to watch velocity on the chronograph for indications on pressures plus ejection patterns. I look at the brass, primer and other marks to establish if the load is safe. I rarely load to max pressure just because I like my reloads to be safe in more than one firearm. I have multiple 5.56/223 AR-15s and multiple 6.5 Grendel AR-15s. I want my reloads to function reliably in any firearm of that caliber/cartridge.
I couldnt find the Molon post but I did find this article.
https://www.shootingillustrated.com/arti...-velocity/