Reamer Free Bore Recommendation

B

Ben H

New member
I’m getting ready to order 25-06 and a 338-06 reamers from JGS.

How many tenths over nominal bullet diameters should I spec the free bore diameters?

Thanks in advance,
Ben H
 
I would specify, "not less than" 0.0005" over the nominal caliber and many top smiths will recommend 0.0008 to 0.0010" over the nominal caliber: for 25 Cal., 0.2575"" minimum, up to .02580". A reamer which is too small to fully clean-up the groove diameter is undesirable. The"not less than", is over-kill, as most reamer makers specify diameter tolerance @ minus zero, plus 0.0005", but I like the specificity of having stated, "not less than 0.2575", give them their tolerance, and smile. RG
 
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R.G.
You are spot on with freebore diameters. All my 6mm (PPC and BR) recent reamers have a .244" freebore diameter. I have two 6mm point up dies that make a bullet diameters just under (like .0003") .244", and it also works just fine with bullets made from another point up die that are .2432" diameter. I was a bit concerned that gas would leak around the bullet before it engaged the groove diameter with the clearance in the freebore, but after seeing some the ultra high speed video of a rifles firing, holy cow !!! gas starts coming out of the barrel well before the bullet exits. So I guess any leakage in the freebore is no big deal if leakage also occurs while the bullet is going down the barrel.

FWIW
Steve Kostanich
 
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