Recently stumbled on a sportered 1917 rifle with 24-inch barrel marked 6.5-06.
Here is the Cerrosafe chamber cast I took yesterday next to a fired .25-06 cartridge. Looks to me like a basic, mutt-grade 6.5-06, at least not one of the Ackleys. It differs from the A-Square version in neck length; the A-Square is .319 per SAAMI specs, this one is closer to .350. If I had access to a smith with the Ackley reamer I might be tempted, but this one should be plenty capable once I can work up a load.

well.
now you gone and upset the apple cart.
the 284 and PRC guy's will mock and look at you down their noses.
how dare you mimic their magic ballistics in such an old rifle, with such a simple case to make.

Lamar, shorten the case a wee bit and you basically have Charles Newton's .256 Newton, which he introduced to the world in 1913. There really is very little under the sun that is new.

I think you made a good find there.
I'm to the point of only wanting either the 6.5-06 or a 257 weatherby as my next deer rifle.

I really don't have a 'need' for either one, and I haven't even seen a buck around here for a couple of years now.
soo [shrug] the want and or need of either is kind of pointless.
I know there's a few somewhere since I do see some doe's with fawns from time to time, but I see far more without them.

Do you have a 6.5-06 or a 6.5-270? The neck looks longer than a 6.5-06. Is the cast case length 2.54” vs 2.5”?

It does look like a very long neck.

Fellas, I need to fireform a couple of cases here real soon so I can figure out what I have.

Fireformed two rounds yesterday using Nosler 6.5-06 A-Square data: 46 grains IMR 4350 under a 129-grain Hornady. Cases look unremarkable with the normal 17-degree, 30-minute shoulder of the .30-06 family as far as I can tell by eyeballing. It appears that longish neck resembles the neck on the .270 -- .046 longer than the .30-06. The only 6.5 dies I have are for the Grendel, so I can't neck down a .270 case and see if it chambers. To be continued ...

Here is a photo of three different cases and theCerrosafe chamber cast. On the right is a fired Hornady .25-06 case; next is a .25-06 case necked up to 6.5-06 and fired in my rifle's chamber; next is the chamber cast; and last is a fired .270 Winchester case with its longer neck.
My chamber seems to have that longer neck, but there should be no harm in firing cases necked up from the slightly shorter .25-06 brass I have on hand.

A 264-270 is a cool cart!

Ordered a set of standard RCBS 6.5-06 A Square dies. Should be in business. Nosler has some nice data for this cartridge online.
By the way, John's younger brother Steve Nosler used to come in to the Medford, OR, Sportsman's Warehouse where I worked for fun post-retirement. Nice guy to talk to about bullets and his older brother. I met some interesting guys workign there. Mike Bellm dropped by occasionally, as did the late John Noveske.

My now deceased hunting buddy used a 6.5-06 for many a year.

17 Enfield action, Douglas barrel, 4X Weaver.

He killed a lot of Roosevelts, his bullet of choice was 140 grain Partition. Most one shot kills.

Woodhunter, did your late friend live in Oregon or Washington? Can't think of too many other places to hunt Rosies. I'll bet that 140-grain Partition is the nuts on larger game. Nosler data show it running up to 2900 fps.