Neck bushing question...

[crazyhorse]

My rifle is a 300wsm that was built as a "tightneck" on a reccommendation from my gunsmith at the time. Over the last couple of years I've noticed that it was getting passed over for other guns in the safe because turning brass became a pain in the butt.

Getting to the point I had the rifle opened up to a standard 300wsm chamber from the original .336 neck. The neck of the fired brass from the new chamber measures .343. What size bushing do I need to buy for my redding dies to load for the new chamber? Would .342 be to tight? All of my other stuff is standard FL dies but I spent a lot of money on the original set so that I could load for the smaller neck diameter. A new bushing is only about $15, the dies originally cost over $100 so I want to keep using them!

Thanks in advance!

 

[Mikecr]

First Look at it in terms of neck clearance.
what is the loaded neck diameter, of unturned brass, with bullets you intend to use?

For example, if your bullets are true .308", and your neck brass measures 13thou thick, then:
.308+(.013x2) = .334 loaded neck diameters, fitting in a .336 chamber neck, = 2thou of clearance.
You can just seat a bullet & measure with calipers to check.
Still with this example, if clearance is actually 2thou, fired brass will spring back ~1thou from the .336 chamber to ~.335.
You only need 1thou under loaded neck diameter(.334) to grip bullets well, so you downsize necks from ~.335 to ~.332 and they'll springback to ~.333, giving you ~1thou of tension.
The bushing is .332, if you want a little more tension go .331, I wouldn't go more than that.

That is only for this example.
But you can apply the jest of it for what your actual loaded necks measure -vs- fired neck.
Where it turns into trial & error is when your bushing has to size more than 5thou from neck diameters as they come smoking out of the chamber. Such a condition is common, but sets up an excess angle of sizing for the bushing, causing a bit more sizing than predicted(like an extra thou or two). People often end up buying a couple bushings, collect them, they're useful in the future..

 

[crazyhorse]

The brass that measured .343 was from a factory load fired in the newly opened up chamber. The old bushing was for the tight chamber before I had it opened up. I can't size brass until I get the new bushing should I start around .339? I'm confused...

 

[AZShooter]

Are you going to use new unturned brass? Or once fired factory brass? You were not clear on this. It is quite simple: measure the OD of the case neck with a bullet seated. Then subtract .001" and .002" from this number and order those bushings.



I suppose you could order a third bushing that is .003" smaller than neck OD. Depends on how much of the bullet is in contact with neck, neck wall thickness and rifle's recoil.

 

[crazyhorse]

Ok, I think I'm tracking now. I guess it doesn't really matter what size the neck is after the sizing die as it will expand to whatever necessary when the bullet is seated. The OD will then be determined by the wall thickness of the neck. Right?

All of the brass I currently have has been turned to fit the old "tight" chamber. So correct me if I'm wrong that because the neck is thinner than factory brass I will need one bushing for the turned brass and another for standard unturned brass.

Sorry for the dumb questions but bushing dies are a new venture for me.

 

[MontanaRifleman]

Ok, I think I'm tracking now. I guess it doesn't really matter what size the neck is after the sizing die as it will expand to whatever necessary when the bullet is seated. The OD will then be determined by the wall thickness of the neck. Right?

All of the brass I currently have has been turned to fit the old "tight" chamber. So correct me if I'm wrong that because the neck is thinner than factory brass I will need one bushing for the turned brass and another for standard unturned brass.

Sorry for the dumb questions but bushing dies are a new venture for me.

Correct.

I would separate the factory brass from the turned brass and put one lot away until the other lot is no longer usable.