30 BR Neck Turning of Doughnut

[ChrisNam]

I've just progressively necked up 6 BR brass to 30 BR and noticed a doughnut on the outside of the neck, propably where the 6 BR shoulder became part of the 30 BR neck. Should I remove this doughnut when neck turning the 30 BR brass?

 

[ChrisNam]

i've accidentally posted this thread 3 times. My appologies. Lets use this one and hope Moderator delete the others

 

[6Dasher]

There's an entire article on the 30BR on the 6mmbr.com site Might want to check that.

 

[AlNyhus]

I've just progressively necked up 6 BR brass to 30 BR and noticed a doughnut on the outside of the neck, propably where the 6 BR shoulder became part of the 30 BR neck. Should I remove this doughnut when neck turning the 30 BR brass?

There is no way a case will chamber unless you turn the 'bump' off. The 'bump' measures around .336 in most cases..if you indeed have a 30BR 'Robinett' reamer with the
.330 neck diameter, it's obvious you're going to have problems.

Simply set up your neck turner to just remove the 'bump' while not touching the neck. Do this on all your cases before proceeding to the next step.

After doing this, take a very light 'skim' cut of the neck. Next, seat a bullet and measure the diameter of the neck over the base of the bullet...that's where the pressure ring is,on a flat based bullet) and it will be a bit larger in diameter that when you measure the neck over where the shank of the bullet is.

Now you can adjust the neck turner in small increments and repeat this process until you get the neck diameter exactly where you want it. Yes, you will sacrifice a couple of cases and bullets until you hit it correctly, but that's the deal.

Once you have the neck turner set up to give you the desired dimension, do not touch or adjust it. Now, do all your cases and you're ready to go.

Additionally, I would not recommend going below .0015 total neck clearance and I run my 30BR a bit looser than that. I would recommend .002 total neck clearance as a minimum. Remember to use the fattest bullets you'll shoot in the gun when setting up your final neck clearance so you don't get into trouble when you try a bullet with a big pressure ring later.

And make darn sure you know what the reamers neck diameter is. A Cerrosafe cast of the chamber is always a good idea if you have doubts.

 

[bbeyer]

Chris, I shoot a lot of Randys 30 booooolets and the majority are closer to .309 than .308.

 

[ChrisNam]

Al, thank you very much for the advise. I've started the process and will let you know.