Neck bushing size for 260AI

[rsbhunter]

I have built my 1st Stevens 200 in 260 improved. I am going to buy a set of neck bushing dies and need to know some info. I have read that the bushing size should be either .002 or .003 snaller than a loaded round's neck dia. My loaded rounds are 0.291...these are 260 standard cases, before fireforming.....after fireforming, the dia of the necks are 0.297.....if i get a 0.288 dia bushing, i will be sizing the necks 0.009 each time i size...is this excessive? Thanks for any help, you guy's have gotten me this far with the tech help and advice....rsbhunter

[SHL540KB308]

Sounds like you have it correct. .009 is a bit, but there is nothing you can do with the chamber you have. .002 should be enough neck tension and work well. Bushings very on exact size sometimes, can be a little bigger or smaller. For starters I usually choose one bigger and one smaller along with the one that should work.

Later, Brad

[Slowpoke Slim]

Holy cow, that's a BUNCH of neck sizing! Yes, that is "excessive". Your brass life is going to be very, very short. Even if you anneal the necks often (like every other sizing).

Who made your barrel? Did you spec it, or have a 'smith ream a blank, or is it a "drop in"? Are you feeding this from a magazine, or shooting it as a single shot? Is this a bench gun, varmint gun, or hunting rifle?

Just for curiosity sake, what is your neck thickness on your brass (around .013-.014?)? Are you neck turning?

If you're feeding it as a single shot, in your case, I would start with .001 to .002 worth of neck tension (i.e. as little as possible), and see if you get acceptable accuracy with that, before you go cranking the necks down any tighter. If you're feeding it from a magazine, then you'll have to give it more tension, probably .003 to get the bullet to stay put on it's way into the chamber.

I would also try and find some thicker necked brass (don't know what you have now), that would only help your situation.

If it was mine, I would seriously consider a new barrel, cut with a tighter neck.

[rsbhunter]

This is one of the CBI barrels from Northland Shooter Supply......That is why i was shocked when i did the measuring...and it was done with a micrometer, the brass is new Remington.....what brass mfg. uses thicker neck brass?.......Guess i'll use it ( as i already have spent BIG$$$ on lengthing the leade, and fluting) Maybe i need to stick with the regular Krieger bbls???

[Slowpoke Slim]

You might play with the idea of necking down 308 brass. When you neck down, particularly from .308 to .264, the necks naturally thicken, as the brass has to go somewhere. If you play around with a few pieces of 308 brass, you may get a combination of neck diameter and bushing size that works for your chamber. You may have to try a couple different brands of 308 brass to end up with the right thickness when done.

[rsbhunter]

slowpoke, THANKS....that makes sense, and i wouldn't have thought of that...plus, i can get premium brass...although i think Lapua is now making 260 Rem brass....what steps will i need to go from 308 to 260...i have 7/08 dies.....308-7/08-6.5? Thanks again...i feel better about this already....rsbhunter

[earl39]

you might also want to check on Laupa brass. I belive they are making 260 brass now.

Gary

[Slowpoke Slim]

Yes, that should work. Take the decapping stem/sizer ball out of your FL sizing die (on all 3 dies), and just use the die body to "neck down" the brass. You will want to turn the die 1/4 turn past the point where the die touches the shell holder, to "cam over" your press, and make sure you are setting the shoulder back if it needs it (new brass may not need it-but it won't hurt, you're fire forming AI loads anyway). I would use all 3 dies, .308, .284, .264. Then, once you've run it through the 260 die once, I would put the decapping stem/sizer ball back into the 260 die and FL size again. I would do this just for my own peace of mind, so that the neck is more likely to be concentric.

Then measure the neck thickness of that piece of brass. If it looked pretty close, say .015-.016, I would then seat a bullet and measure the neck thickness again, with the seated bullet. If that came out right, say .294-.295, then I would load a fire forming load and fire one in your AI chamber (I would seat the bullet into the lands for the fire forming load). Then measure your fired brass again, just to be sure, and compare that to your loaded round measurement.

Just in case the sized down .308 brass comes out too thick, do you have the tools to neck turn the brass? If not, you may have to play with a few different brands of brass (the neck thicknesses tend to vary), or you may have to go down to 7-08 brass.

If it were me, I'd be looking for a loaded round neck diameter of .295, and a neck bushing diameter of .293. Or, at most a neck diameter of .294 and a bushing diameter of .292. I would still get a couple sizes up and down from my "target" bushing size, so that I can play with neck tension with load development. So if my "target" bushing was .293, I would get .291, .292, .293, and .294 bushings.

[rsbhunter]

slowpoke slim, thanks , yet again for the info....actually, i have some 7/08 rem brass that i am going to try first, maybe i can find a couple of 308 new brass to try, without having to buy 50 or 100 and find out they won't help....Yes, i do have a tool for outside neck turning...will keep you posted on the progress...and thanks to everyone for the help and advice....rsbhunter

[sinman]

If you really like the 260ai you could get your own reamer cut to how you want it with the throat and neck tightness that you want. a Std 260ai reamer measures .297". I would check with using Lapua brass or going down from 308.

[drybean]

the first thing i would do is make a cast of your chamber & neck
takes a lot guess work out
drybean

[frank1947]

all you need is .289 or .288 bushing you dont need to do all that your FF case neck dia is not excessive

my neck on my 6mm BR is .272 my FF case neck dia is .27165 I use a .264 bushing so that is .008 from FF dia means nothing my gun shoots .2 moa at 200 yards, you probably have a no turn neck as I do this a shilen barrel