Hi SeekHer - a buddy of mine has the same barrel(bore/make/twist), only chambered for the 6.5x68. It loves 120gr. XLC's and 140 Partitions.
: I shoot 3 of Bevin's barrels - all excellent - and incredibly innexpensive as good barrels go.
: While I've not had a 6.5/06, I did build up a longated .260 Rem (.143" longer) for my Daughter that came out with 60gr. Capacity(about the same as the .284 case necked to 6.5mm. It matched my friend's 6.5x68 for velocity with 120gr. XLC's at 3,300fps. The '06's case's slightly extra capacity (63gr. or so) will likely give no more or no better ballistics than this, and may do 150fps less, due to stiff bolt from the tapered case. In other words, the .284 case, also about 60 gr. capapcity will give everything the '06 case will give.
: My daughter's Lawrence barrel is a very fast one, as at the same time, my own .264 MAG(smae barrel length of 24", topped out at 3,250fps with same bullet and every powder tried - up to 85gr. of it, compared to 53gr. for the long .260.
: 60gr. capicity seems to be the top-end for the 6.5 bore size for best efficiency.
: The 6.5/06 is very close and should do about the same, but no better. It and the 6.5X284 are about equal in ballistics.
: My 22" 6.5X55 Swede (brand new original barrel) with 129gr. Hornady's gets 2,966fps at max loads with Re#19.