Generally the improvement is 5 to 8% in my experience. The 223 will gain 100fps with the heavies and a bit more with the lighter projectiles.
The calibre with almost no gain when acklied is the 308Win. It gains less than 10fps, with 1 to 2fps gain to be the norm.
@zimmer I like your reading material mate. For me the big gain is in shooting the heavies at a little faster speed.
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