I get the best results by necking down .270 brass.
I start with a .270 F/L die and remove the expander button & decap unit. I then size the brass but but with minus head-space (not enough head space). This reduces neck diameter and leaves some allowance for a nice crush fit after subsequent operations..
I then size the brass in a 6.5-06 die with an expander button. This forms the inside of the neck to the correct diameter for holding the bullet. Head space in adjusted so bolt just closes. Stripped bolt will have a tiny bit of resistance on closing
Then trim to 2.484.
Excess neck wall thickness if forming .30-06 brass, fix is to neck turn. I turn my 6.5-06 necks to .288 to fit my tight neck chambers.
From .25-06, possibility of run out, part of .25-06 shoulder becomes 6.5-06 neck, axis of neck not in line with chamber if necking up .25-06 brass but after fire forming this will be fixed. Not much difference in bore size .257 vs .264, like .007. Not much of a concern. Take a cotton swab dip it into 3 in 1 graphite lock lube, lube inside of neck and run .25-06 brass into 6.5-06 F/L die with an expander button. Probably the easiest way to make 6.5-06. Keep on reading and this will probably mean .25-06 brass will be used.
Fired brass has work hardened necks and spring back making for neck tension variations, fix is to anneal brass.
After firing brass should allow a nice slip fit with .264 bullet placed in neck of fired cartridge.
You will need:
6.5-06 F/L die, or F/L bushing die with a the right size bushing. Fired cases should allow for a slip fit .264 bullet into neck. This means measuring fired cases. Chambers vary.
Caliper to measure case length.
Then getting deeper;
Neck turner with 6.5 pilot
Way to anneal brass - I use a simple loop tip with a propane torch. Brass necks are held just outside of flame and toasted for 30 seconds then tipped over into 1/2 inch of water in a shallow pan. http://www.woodchuckden.com/catalog/catalog2016.pdf, page 6, right side, $53.95.
It would be a good idea to measure your rifle's twist rate. Many older 6.5-06 rifles have 1-10 twists that will not stabilize 140 or some 130 grain bullets. Tight patch on rod then shoved into bore, tape on rod with mark, then pull rod out watching for 1 complete rev of rod then measure from some fixed reference point.
Your rifle might be a M98 Mauser type. If so stripping the bolt involves pulling back cocking piece then placing dime between coking piece & bolt shroud, depressing bolt lock & turning out pin assembly from bolt body. Good idea to check this out. The M98 is one of the better battle rifles & designed for field maintenance with very simple tools.
Looks like some project! Feel free to send PM for specific help.
I have made cases from .280 Rem, .270 Win and .25-06. I agree that the .25-06 cases are the best even though they cost nearly double what .270 Win cases cost. .270 case necks end up thicker and you may need to turn the necks. One of the lower cost alternatives, the Serbian Partizan cases in .25-06 have worked well for me. Anneal your case necks.
What is the twist of your barrel? What bullets interest you? I will send you some data.