I am very happy with the results Im getting from pre-boring before reaming. On short cases like PPC and BR I now parallel bore to around 0.020" less than the reamer shoulder diameter and deep enough so the bush engages along half its length before the shoulders start to cut. Im consistently getting runout of 0.0005" or less.
When it comes to longer cases I tend to taper bore so that again the bush makes reasonable contact before and reamer flanks make contact with the undersize chamber mouth and before the throat/neck starts to cut. The problem with this though is you have to get the tapered pre-bore very close to the correct size or the neck starts to cut before the flanks are supported. How much do you think that really matters?
I have been wondering what the best way to do longer cases like 6.5x47 or .308? I was considering only pre-boring to maybe half case depth which would be as short as say a BR and then parallel boring again to 0.020" under. Im thinking that with cases like .308 it would be like doing a BR but just continuing in deeper. I appreciate about half of the chamber depth will then be cut with the full shoulder of the reamer but Im thinking the first half pre-bore will have set everything on a true course.
What are your thoughts on this guys?
When it comes to longer cases I tend to taper bore so that again the bush makes reasonable contact before and reamer flanks make contact with the undersize chamber mouth and before the throat/neck starts to cut. The problem with this though is you have to get the tapered pre-bore very close to the correct size or the neck starts to cut before the flanks are supported. How much do you think that really matters?
I have been wondering what the best way to do longer cases like 6.5x47 or .308? I was considering only pre-boring to maybe half case depth which would be as short as say a BR and then parallel boring again to 0.020" under. Im thinking that with cases like .308 it would be like doing a BR but just continuing in deeper. I appreciate about half of the chamber depth will then be cut with the full shoulder of the reamer but Im thinking the first half pre-bore will have set everything on a true course.
What are your thoughts on this guys?
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