Bullet to bore diameter

[Renton83]

So I am reloading for my Mosin Nagant rifle. I know a lot of confusion surrounds the bullet diameter as many reloading guides and kits call for .308 bullets but many bores are closer to .311. This got me thinking about bullet tolerances. How much can a bullet deform to fit the barrel before you risk damage and a blown barrel. Bore diameter varies a few thousandth on many military surplus rifles but I’ve never heard of barrels blowing.

 

[Englishmn]

I run .314 cast bullets through my mosin.
As long as it's not a solid copper/bronze bullet or a max load the bullet will squeeze down with minimal pressure increase.

 

[Renton83]

My problem is the loading kit I have neck sizes them to 308 so I can’t fit my 303 British bullets in. Hoping the 308 size ones engage the rifling ok.

 

[Englishmn]

My problem is the loading kit I have neck sizes them to 308 so I can’t fit my 303 British bullets in. Hoping the 308 size ones engage the rifling ok.

Ya my rcbs dies came with 308 expander as well I ordered a larger one.
Many times 308 jacketed do ok even tho too small.

 

[Renton83]

So this is the loading die I have, is their any way I can expand the case neck to fit .311 bullets? I tried but the case mouth is just far too tight. I also have a similar die for my 303 British rounds if I can use something from that? It seems the case mouth size is set when I hammer it into the die so unsure if it’s possible to change it after.

 

[Demi-human]

The brass can be expanded to the proper diameter after sizing.

How that is done on a Whack-A-Mole setup, I do not know. My press has an expander die that is pushed into the case mouth.

One could hone out the neck portion of the sizing die, making the size larger. This is a non-reversible change, that should be done carefully to avoid damaging the die. There are die sets that use bushings to control the neck diameter, as well. These use a press though.

The "Brit" die is of the right neck diameter, but I dont know how it could be made to work.

Perhaps a cone shaped bit of steel could be tapped into the case mouth to flare it enough to shove a bullet in. I would be wary of going to far and causing chambering problems, but a little might get the bullet started.
A boat tailed bullet would be easier to get started too, though I know you have some to use already.

Try the three zero eight sized bullets first. They might be fine. Saving a lot of work and worry.