Fired Cartridge vs. Loaded Cartridge Neck Size?

[kodiakoutdoors]

I trying to figure out if my numbers are correct before ordering neck die bushings. The cartridge is Winchester brass in .300 WM. A loaded round (HSM) is 0.334" and a once fired case from my rifle measures 0.341", a difference of 0.007. I was going to order a bushing in size 0.333" which is .001" smaller. However, I just came across the following regarding Redding bushing sizes from Redding.

"Redding has found that when you have cases with neck wall thicknesses on the thin side of the SAMMI tolerance, your fired case will measure considerably larger (.006" - .010") than your loaded rounds. In these circumstances, Redding's tests have shown that a bushing .001" larger (than the loaded round) may give you the desired bullet grip."

Since the difference in my measurements fall into this category and if I were to follow Redding's recommendations then I would need to buy a bushing that is .335" (.001") larger than my loaded round.

What are your opinions and what type of measurements are you guys getting from your .300 WM rounds?

Thanks!

 

[cahunter805]

Bushing dies are a great tool. I really like them. Have you measured the thickness of you neck walls?? I would do this first and then do some figureing. I like about .002-003 in neck tension.

 

[Kevin Thomas]

To be honest with you, and save the frustration of waiting for the big brown UPS truck, I'd order all three. The .333", the .334" and the .335" just to make sure. I make it a practice to have at least the one above and below whatever bushing I'm using, just so that I can adjust to varibles in neck thicknesses should I accquire some more brass, or desire a little more or a little less neck tension. After all, the strong suite of the bushing dies is exactly this type of versatility. I always start with the neck OD of the loaded round, subtract .002" and then order one of each .001" in each direction. I go with the steel bushings, as they're considerably cheaper (about half) than the TiN coated. Since I F/L size, I'm lubing anyway, so the extra lubricity doesn't mean much to me.

 

[Mikecr]

The reasoning behind Redding's adjustment is that bushings are limited in the amount they 'predictably' size.
7-8thou is a lot of sizing for a bushing. It causes the brass to fold inward at an angle that results in more sizing than expected. Redding is probably right, and Kevin's advice to cover your range is right also.
Given that you have this situation, if I were you, I'd follow your neck sizing with a Sinclair 30cal neck 'turning' mandrel for desired tension and straighter seating.

 

[kodiakoutdoors]

Thank you all for the great info. I guess neck turning it is. Thanks again!

 

[Mikecr]

Turning your necks will only increase this problem.
Your clearances are already huge.

 

[kodiakoutdoors]

Okay, now I'm a bit confused. I do not have an extensive background on reloading, but I'm trying to learn so I apologize if I my questions are too general.

How is neck turning go to make my situation worse? Not questioning your comment, I just don't understand.

Thanks.

 

[Mikecr]

I guess neck turning it is.

Where did this notion come from?
Nobody said anything about neck turning.

You wondered about Reddings recommended bushing sizing. Then imply that it all comes down to neck turning -as a solution -to what?
I'm saying that your clearances are very high for single bushing sizing, and that's Redding's basis. Neck turning would only increase the clearances further.
That's all

 

[kodiakoutdoors]

Okay I got it. Just another newbie misinterpreting things. Thanks again for the help.