30 BR

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mtngun
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Location: Where the Salmon joins the Snake

Re: 30 BR

Postby mtngun » Mon Feb 20, 2017 11:13 am

Some thoughts on throat angle. The original 1 degree throat was too long for the 125 - 130 grain bullets to reach the rifling, so as mentioned in a previous post I set the barrel back and recut it to 1.5 degree. Now it turns out that the 1.5 degree throat is a little shorter than I prefer, requiring either seating the bullet deeper than I prefer, or else sizing part of the nose to be a slip fit bore rider.

From my other 30BR thread:
Let's assume that the base of the bullet will be sized 0.3086", and we want the entrance to the throat to be 0.001" larger than the bullet so the bullet can enter the throat without shaving lead or popping off the gas check. The throat will start out at 0.3096" and taper to 0.3006" (the exact bore diameter will vary, but that's a convenient number to use :lol: ), or 0.0045" taper per side.

Let's look at how long the tapered section would be for various throat angles, assuming 0.0045" taper per side:
0.5 degree = 0.52" long taper
1.0 degree = 0.26" long taper
1.5 degree = 0.17" long taper

How do those taper lengths match up with a 125 - 130 gr. cast bullet? When seated 0.13" deep -- which I consider a bare minimum to grip the bullet securely -- there will be about 0.300" of bearing length outside the case, so it looks like a 1 degree throat would be a better match than the current 1.5 degree throat.

In hindsight, the problem with the original 1.0 degree throat is that I simply cut it a little too deep. I may try again after I give the current 1.5 degree throat a fair chance to prove itself.

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mtngun
Site Admin
Posts: 1636
Joined: Fri Feb 01, 2008 5:45 pm
Location: Where the Salmon joins the Snake

Re: 30 BR

Postby mtngun » Sun Mar 05, 2017 2:09 pm

For some reason Idaho weather in early March is cold and windy, so shooting is on hold, but shooting related projects continue. Last time I was not happy with the nose die -- what was supposed to be a .301" reamer for the small end was cutting more like 0.3015", plus the hard bullets were springing back, forcing me to seat the bullet deeper than I prefer. I went through quite a few reamers and dies until I finally got the small end diameter that I wanted.

To complicate matters, Krieger barrels seem to have a tighter bore -- 0.3000"-ish -- than Shilen, which is closer to 0.3005"-ish. So the Shilen's nose die will not work for the Krieger. :twisted: I've decided that it is best to err on the small side for the small end diameter of the nose die, then you always have the option to hone it larger if the need arises.

When the weather cooperates I'll shoot some bullets sized in these new nose dies.
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