I'm getting ready to purchase parts for my R700 LA build (currently a old 30.06 sporter ADL) and was set on chambering 6.5X55. However, I've been told I could stay with 30.06 or even go 30.06 AI. The advange for me is that I already load the .06 and have dies, components, surplus HXP, etc. The gun will be use for long range shooting and hunting deer, to a lesser degree. Any thoughts?
To make sure we are trying to solve the right problem, I highlighted the OP's preferences in his first post.
Rather than getting immediately hung up on certain cartridges, lets look at the ballistic realities first. For each caliber there is a range of bullet weights that yield high ballistic coefficients (BC). A high BC matters for long range shooting as it is vitally important to retain velocity downrange to stay out of the trans-sonic region and to reduce the total flight time and with this the wind drift.
The ideal weight for "long range" bullets in each caliber is somewhat arguable but in .30 caliber we are looking at around 210 grains and for 6.5mm at around 140 grains. Now, we need to accelerate these bullets to a sufficient muzzle velocity and that takes a certain amount of powder volume and will generate a certain amount of recoil. Obviously, the heavier bullets will need more powder volume and generate more recoil if we try to achieve similar muzzle velocities.
This is as far as physics go. Now, my personal opinion is that in .30 caliber we should use a case along the volume of a 300 WinMag and in 6.5 caliber a case with the volume of a 6.5x55 to achieve sufficient muzzle velocities with sane pressures. We can use short magnums that are a little more efficient burning the powder consistently but in the end it is a certain powder volume that we need. If a case is too small for a given bullet diameter, we have to resort to lighter and subsequently shorter bullets with a lower BC and that is not what we want for long range shooting.
(BTW: the .308 Win case is one of the worst choices for a long range gun in .30 caliber and we are only using and abusing this round because our military could not choose anything better due to standardization. The powder volume of a .308 Win case is great for 6mm bullets though as proven by the success of the 6mm CM and similar rounds)
Keeping this and the OP's needs in mind, my vote goes to the 6.5x55 due to the significantly better downrange performance and the lesser recoil. Even a .30-06AI does not have enough powder volume to beat a 6.5x55 for long range paper-punching or steel ringing. Also, you do not need a .30-06 to reliably and ethically kill deer. If you line up all the Moose and Elk-like critters killed in Europe with a 6.5 by something, they probably reach to the moon and back. I personally penetrated both shoulders of a big European boar with a 140grain Nosler partiton out of a 6.5x55 Swede.
That was after first pushing my .30-06 in a 98 Mauser action towards .300 WinMag levels, then getting a real .300 WinMag, and finally realizing that the heavier recoil even out of a heavier gun is simply not beneficial either on the range or when stalking meat.
