Minimum FB for .308 factory ammo

[X Count]

Hi Everyone,

I know SAAMI spec is correct answer BUT for a rifle that will be fed handloaded ammo for 99.5% of its life what would be the minimum FB that would still accept factory ammo like federal gold medal Match or similar.

 

[LVLAaron]

Will you want to keep rounds at mag length? (2.8 overall)

 

[X Count]

Factory ammo should fit mag length so if the throat is suitable for factory ammo then mag length should take care of itself?

I don't have any bullets in that 175 / 185gr range to seat to mag length and test. Only have 155.5 and 200 hybrid which probably aren't very reflective of a typical factory ammo

I'm concerned that if I plunge a 0 FB reamer and then extend the throat to suit a 155.5 seated to mag length the throat will still be too short for 168 / 175gr factory rounds.

 

[NorCalMikie]

HS Precision rifles are known to have pretty long free bore. .050 isn't out of the question and still deadly accurate.

 

[tobnpr]

would be the minimum FB that would still accept factory ammo

SAAMI freebore is .090.
You want a chamber with less freebore? Why?

I'm concerned that if I plunge a 0 FB reamer and then extend the throat to suit a 155.5 seated to mag length the throat will still be too short for 168 / 175gr factory rounds.

I own several .308's with SAAMI chambers and have no issues with seating light jump (.020) with 175's.
CBTO (cartridge base to bullet ogive) is what you're referring to- and it's going to vary not just by bullet weight, but type of ogive as well. No way to know other than making up a dummy round and using a comparator to find out.
Unless you're building the rifle for ONE, specific bullet I'd use a SAAMI reamer.

 

[SKWERLZ]

Standard FB is pretty good for a mag fed 308, especially with factory ammunition

 

[LVLAaron]

90 freebore - you should be able to shoot most (not all) 200 grain and below bullets without a ton of fuss. It wont be ideal for say, a berger 200.20x but it can be done.

If you just want a "do all" rifle, saami is fine.

 

[X Count]

SAAMI freebore is .090.
You want a chamber with less freebore? Why?

Because majority of shooting will be done with 110 - 155gr handloaded ammo but would like to be able to use 175gr factory if SHTF.

Maybe I should have worded it more like. "What is the minimum freebore for federal 175gr FGMM?" I'm guessing it's going to be around .070ish