from what i have read i belive that the 6.5 grendel is a better cartrige however they both have there benifits. the 6.5 is better for long rang target shooting and has a higher BC. and the 6.8 seems to be better combat round for under 300M
also i found it very interestiiong that the 6.5 is still supersonic all they way out to 1100 yards now i dont have how long the 6.8 will
now to accutally answer your question i dont think either of these will go the way of the 45 gap because these accutally solve a problem unlike the 45 gap.
these bullets will remain usefull untill something else comes along that will do it better. i would guess that their popularety will increase as years go by
also i found it very interestiiong that the 6.5 is still supersonic all they way out to 1100 yards now i dont have how long the 6.8 will
now to accutally answer your question i dont think either of these will go the way of the 45 gap because these accutally solve a problem unlike the 45 gap.
these bullets will remain usefull untill something else comes along that will do it better. i would guess that their popularety will increase as years go by