Neck busing size for 260 AI ?

[rsbhunter]

I am building a 260 rem AI and have some questions before i order a bushing for neck sizing.By the way this is a multi purpose rifle, not dedicated bench. I have read that the bushing should be .003 smaller than the Dia. (neck) of a loaded round. With unformed brass loaded for fireforming, the neck Dia. is .291....after fireforming, the dia. is .297...is that about right for expansion? If i get a .288 bushing (.291-.003) that will be working the brass .009 everytime i neck size....is that ok? Seems like alot to me, but this isn't a custom chamber (reamer wise) ...Thanks for any help...rsbhunter

 

[rsbhunter]

Any Idea's????? rsbhunter

 

[jonbearman]

Sounds about right,I use a .290 for my tighter chamber.

 

[dennisinaz]

.291 sounds awfully small to me! What kind of brass are you using? I use a .291 bushing and I have a .294 neck that is so tight that I have to neck turn any brass i use but the crappy Remington stuff. Even necking .243 Lapua up I have to neck turn or it is too tight.

You will need two or more bushing most likely to get this just right. Nosler brass is the only other stuff that thin- at least the one lot I bought was. In fact, it is so thin that I cannot adequately resize it with a full-length die small enough that I can't press the bullet home with my thumb! Had to order a special die to use the stuff... Can't wait till the 260 brass is available from Lapua!!

 

[alf]

rsbhunter,

Here's what I'd do,

Sounds like you have a standard, Sammi chamber, (read huge) neck diameter.

First, you have to know the chamber neck dimension you're dealing with. If you don't have access to the print or if the reamer isn't marked, I'd get some cerosafe, do a chamber cast and find actual neck dimension.

Next, I'd neck down 308 brass, (Lapua) seat a bullet, and measure loaded round diameter.

Determine neck clearance, (.003 min.) neck turn to suit, if needed, and order appropriate bushing(s) for desired neck tension.