What 308 neck bushing?

[Jmccracken1214]

Im running 169 smk in alpha brass, when I measure the neck of a loaded round, I get .334

I see people saying subtract .001 and .002... so, should I run a .332 or .333 bushing?

 

[ChrisGarrett]

Never shot Alpha brass, but you seem to be in the ballpark.

I’ve collected a lot of bushings for flexibility’s sake, mostly off of EBay, so look there and have a few on hand.

Chris

 

[Threadcutter308]

.002" under.

 

[Baron23]

And what spring back would you expect after using a .002" under bushing? Curious, I don't use bushing sizing dies but understand that there is some spring back....no?

 

[Threadcutter308]

And what spring back would you expect after using a .002" under bushing? Curious, I don't use bushing sizing dies but understand that there is some spring back....no?

Well......this may be a rabbit hole you don't want to follow me down.

I neck turn

I've never worried about springback. What I have found (consistently) is that .001" does not offer enough neck tension and .003" is too much.

To answer your question though, I haven't found there to be any springback, at least the way that I do it. I specify the neck diameter on the reamers that I have made. Usually, the neck diameter (of the reamer/chamber) will be .003" larger than the loaded round neck diameter, taking into consideration the turned neck wall thickness of the brass.

So, for .308W, turned brass neck wall thickness of .0135" is a total of .0135" + .0135" + .308" = .335"
I would therefore use a .333" button (.002" under).

Don't waste your money on a .001" under button. Not enough neck tension, never will be.

edit; FWIW, I'm not a fan of neck sizing without also turning the necks. Turning cleans up the necks and makes the neck wall thickness far more consistent than if the brass has not been neck turned.

 

[spife7980]

Im running 169 smk in alpha brass, when I measure the neck of a loaded round, I get .334

I see people saying subtract .001 and .002... so, should I run a .332 or .333 bushing?

If you are not using an expander ball or mandrel then go with the .332.

If youre running an expander ball or mandrel then go with a .330-.331 so that the expander then has some interference fit so the expander can overcome any spring back.

 

[Jmccracken1214]

If you are not using an expander ball or mandrel then go with the .332.

If youre running an expander ball or mandrel then go with a .330-.331 so that the expander then has some interference fit so the expander can overcome any spring back.

Ok.
I’ve got a set of rcbs match master dies I haven’t used yet, I was going to leave the expander ball in

 

[rustyinbend]

Might not be a popular process, but I've found that sizing "down" (more than recommended) with neck bushings, and then expanding "up" with the right mandrel to get the right neck tension ... works better for me than just trying to pick the .001-.002 sized-down neck bushing alone. I usually go down in the bushing .004-to-.005, and then bring it back to the right neck tension with my set of mandrels. This process improves concentricity and lets me more accurately manage my neck tension. Note: If you're going to try to do this, you absolutely positively MUST anneal after every firing and before sizing. YMMV (of course). BTW ... friends don't let friends neck-turn.

 

[Rocketmandb]

Might not be a popular process, but I've found that sizing "down" (more than recommended) with neck bushings, and then expanding "up" with the right mandrel to get the right neck tension ... works better for me than just trying to pick the .001-.002 sized-down neck bushing alone.

100% agree here - and I've proven it in my Mandrel Musings thread.

I usually go down in the bushing .004-to-.005, and then bring it back to the right neck tension with my set of mandrels.

I actually found that trying to right-size the bushing against the mandrel size works best. I try to have the least amount of "work" being done against the brass by the mandrel. I still want to engage the mandrel, just not by a large amount.

 

[jmornoinf]

I use a .335 bushing and mandrel to get to .336.5 on Lapua 300 PRC brass.

My loaded 300 PRC is around .338 loaded