Size for bushing to neck size

[rsbhunter]

I am building a Rem. 260 AI, and a 6XC rifle.....i have fireformed some brass and broke in the bbl for the 260 AI before sending it off for nitriding. I have read where the resize bushing needs to be .003 smaller than the measurement (neck) of a loaded round....My measurements are...loaded new brass....0.291..Fired dia. is 0.297...is a 0.006 difference about normal? seems like alot, but maybe for a non custom reamer barrel this is right? Any way, just seemed as i would be working the neck brass an awful lot to use a 0.288 (0.291-.003) neck bushing...sizing down 0.009.....Thanks for any help....rsbhunter

 

[rscott5028]

If your loaded DIA is 0.291, then your case wall thickness is about (.291-.264)/2=.0135.

So, I'm guessing you neck turned relative to new Lapua brass which usually runs ~.014-.015". I usually turn mine down to about .013-.014" just to clean up the high spots.

I just checked a couple of 3 times fired pieces of un-turned Norma 6.5x284 brass and they measured .293 loaded and .297 fired. So, it appears my chamber neck is cut about the same, but the necks are slightly thicker on the Norma samples that I happened to measure which resulted in .004" expansion vs .006".

Regardless, you've hit on one of the trade-offs between better concentricity and even neck tension vs working the brass. ...hence, tight neck reamers for avid competitors.

I've been using a bushing that's ~.002" under sized rather than .003". Others may be better qualified to speak to that. But, I think you can count on about .001" of spring back and you need about .001" for neck tension.

In any case, you're likely working it a lot less than a standard die would be doing for the same piece of brass.

-- richard

 

[rsbhunter]

Thanks for your reply, it makes me feel better about the amount of expansion....I might try using good brass instead of factory.The brass (Rem factory) was necked turned very lightly, not even a full cut, more like just knocking off the high spots....i'm guessing on the bushing sizes to go 0.289 and 0.288 to cover the range.....rsbhunter