I just ordered my first custom barrel, and I'm looking for some guidance on how much distance to allow for chasing the lands. Obviously whatever smith I eventually go with will have a lot to say about it, but I want to get some other opinions as well and basically just get a feel for what to expect.

The chambering will be 260rem, loaded around book max I expect. Running a Wyatt's box at 2.995" for a little breathing room.

Thoughts?

After having gotten "stuck" with virgin chambers too long for my happiness, I've decided I'd rather start short and chase it like you.
For example, I had a wonderful 223 barrel that started at 2.315 and ran out of neck grab at 2.415 -- the last group before "vacation" was a .463. It would have been nice to start at 2.26 and have the extra 75 thou...or maybe go a little shorter in the beginning for .175 total wear allowance.
That barrel is in the "stash" now, I am going to turn it down and thread it for an AR-15 with the shortest throat I dare so I can finally touch lands and fit rounds in the magazine.
You should at least try for .125 at a minimum.
I have a couple of projects in the works where I'm going to ream with a "no-throat" reamer and then use a separate throating reamer on the same set-up.
Hopefully your barrel is going to be the same, cut with a no-throater and throated separately.
You have some options, as the regular 260 Rem isn't as much of a rocket as the 260AI -- which is not THAT "wild."
Your judgement call is probably going to be where your max box is. See what you have for neck grab at full length 2,995 with the bullets you want to run -- that's your full "burnout" and you come short from there.
2.995 minus .175 gets you 2.820 -- maybe give yourself a little more recoil room in the box for your maximum length.
On the other hand, if with the bullets you want to use, 2.995 is way too long: Then, your start point will be the length where neck contact is "just enough" and you'll want your "chase" to be shorter than the grab (not box) maximum.
Sniff around for "burn rate" and round count, somebody has to have tracked erosion and total accurate life.
Have some fun searching and with your calculator. Good luck.

Thanks Dave for the detailed info... exactly the kind of number crunching I'm looking for. I'm not familiar with the term 'neck grab', is that the same as a kiss? Or jam?

If you have a particular bullet in mind that you intend to use then make a dummy round with the start of the boattail seated even with the neck/shoulder junction of the case. Tell the gunsmith to cut the throat so that dummy round kisses the lands.

A thinking man's thread, this 'un.

I'm unfamiliar with the term "neck grab, as well" and all ears.

GTC

I'd rather have the rear of the ogive at the mouth of the neck. Don't really care how much of the bullet is below the base of the neck.

Thanks JB. I posted this up in your neighborhood hoping you'd weigh in, so you gotta give me more than that. What kind of rough numbers can you give me regarding shot count and resulting erosion? How fast/how far kind of thing. Any chambering is fine, I'll extrapolate.

Hard to say about shot count, since it depends on so many things: the particular powder, rate of fire, barrel steel, etc. All that can really be established is a minimum throat length to provide as much room as possible to allow seating the bullet further out.

Which is why I suggested seating a bullet so the rear of the ogive is right at the mouth of the case. Have the chamber cut for that, and you'll have as much throat life as possible before running out of magazine space.

One thing I have found that helps with a worn throat is shooting a few fire-lapping bullets after the throat starts to lengthen. They'll smooth and even out the rough throat and (usually) improve accuracy.

Personally, I'd chamber the 6.5 Creedmoor rather than the .260. The Creedmoor not only has a longer neck but a steeper shoulder, both of which extend barrel life, and the shorter case is designed to allow seating even very long, high-BC bullets out to the lands in a standard 2.8" short magazine. In fact, that's the basic reason for the 6.5 Creedmoor case. The case capacity is so close to the .260's there's no practical difference in velocity.

I agree with what John says about the back of the ogive, or conversely, the front of the bullet shank, the straight, parallel part. You MIGHT give up maximum velocity at some point of the game, but 100-200 FPS doesn't matter that much to the target unless the supersonic yardage point is a factor for you. For me, it usually isn't.

Neck Grab:

That's the amount of bullet shank that is in contact with case neck. It can be ALL of the neck with really long bullets.

You can get a measure of your grab by taking calipers/dial thingie and measuring overall length of a bullet plus a case with the bullet sitting in the case mouth.

Then you seat and fit your bullet to the rifle. The difference is your "grab." The voodoo witch docktors recommend "one caliber" of minimum grab, for a .243 it's .243.
The reason is so bullets don't fall out of the case or set back from recoil or whatever. But the real minimum neck grab is "whatever works" -- where normal handling will not knock the loaded round crooked, or where bullets stay put while in the magazine. That can be pretty small -- I have gotten away with .085 for .223, but that was it.
I had the same problem with a 204, which taught me something else... You can cheat on "grab" by going from a boattail to a flat-base of similar weight. The 39 Blitz King in 204, for example, has a much smaller boattail than Hornady and Remington's 40 grainers -- which made a HUGE difference in accuracy. I was also able to use 32 grain BKs because they had a flat base, the 35 Bergers had a BT and were all over the paper again.

One other thing -- when "grab" is marginal, sometimes you can salvage the situation with a bushing die, going smaller in order to get more tension on the grab you have -- but that raises concentricity and brass-working problems as you move the case brass more. It's just less aggravating to have a properly-throated chamber in the first place.

There's a bunch of 300 Win mags out there the witch doctors don't know about.

Everybody "knows" a .300 WM isn't any good for precision long range shooting because of that "less than caliber" neck.

Just like everybody "knows" a bumblebee can't fly...

Ed

I just, yesterday, clocked my 2530th round down one of my 6.5x47 barrels yesterday. For the purposes of of this thread, I just now went down and measured throat burn out, using 1/2 dozen different kinds of bullets I used to measure the throat when it was new vs what I just now measured. I'd say i've burned out .086" of throat. The Berger 140 Hybrid, when seated .025" off the lands has the junction of the bearing surface and boat tail, 1/2 way down the neck. I'm nearly out of of mag room of my AI 5-rd mag which has an internal max length of 2.905". The advantage of the 6.5CM and the 6.5x47 is, as John alluded to, the ability to chase the lands without running out of mag length. To beat the chest of the 6.5x47, I just shot several .36 moa groups at 1010 yds yesterday, even with as many rounds as this barrel has.

Alan

Thanks all for the info, especially Alan for going through the trouble of taking those measurements.

Alan - have you actually been taking periodic measurements and adjusting your seating depth? Or just check it if accuracy drops off... or?