1-in-12" or 1-in-14" twists. Either one is proper for the .223 Remington.
I once had an older Sako Model L-46 in .222 Remington. This particular Sako had a 1-in-16" twist and wouldn't stabolize any bullet weight over 50 grains. The 55 grain Bolttail bullets just "Key-holed" their way into a target.Back in the 1960's, was a run of Savage 340's in .222 that somehow ended up with a 1:16 twist barrel. Probably a slip up from old blanks in stock used for the .22 hornets. Those .222's have trouble stablizing 55gr. bullets. ALL that i've heard about were stamped with "house brands", with most being Montgomery Ward branded. your 340E isn't one of them, and while it may not like 55's, it doesn't send them tumbling.