New Barrel coming need help with chamber particulars

[treetux]

I have a Broughton 5c .308 barrel coming soon but I am not sure what to do about a Chamber specs.

I have decided to chamber it in .308 after leaning towards 30-06 heavily. I am building it on a long action and plan to shoot 175 sierras in it. So, what is freebore? and how much do I need? I have heard people talk about different angles at the rifling also. Not sure what that means either. This is my first custom rifle so I need help understanding some of the particulars of the chamber. I would like to take advantage of the long action being able to set the bullets out longer,is this an advantage? Does it allow for more powder? Any help would be appreciated.

 

[Steve Blair]

This is a link to German Salazar's Gun of the Week #91 article. Skip down to the paragraph entitled "Match Chamber with 1.5° Leade, Throated for 190s ".

 

[GermanS1]

The .308 has a shorter neck than the .30-06 so you're a bit more limited in how broad a range of bullets you can use while staying above the base of the neck, but it's workable. My .308 has a 0.140" freebore which is perfect for 175 gr. to 190 gr. bullets. The 190 Sierra has to bottom of the shank right at the base of the neck and the 175 is a bit further up but still plenty of engagement.

If the freebore is too short, you'll lose some powder capacity because the shank of the bullet will be in the powder space more. If it's too long, shorter bullets will have a long jump to the rifling when seated and that's not so good for accuracy. You want to see at least half the neck engaging the shank of the bullet on a .308, that's enough to have consistent grip and allow ignition to begin properly.

As to leade angle, 1.5 degrees is standard for .308 and gives great accuracy. The .30-06 standard was 3 degrees and that is not as good, so when ordering a .30-06 reamer I make sure to specify 1.5 degrees. You can go shallower, but I'm not sure there's a big gain past 1.5 degrees. My last two .308 barrels have had 0.5 degree leade angle but I haven't seen any dramatic change.