Necking down a cartridge.

[NMTMarksman]

I reload 270wsm which uses 300wsm brass necked down to fit the 270 bullet. While I have plenty of 270 wsm brass I would like to try my hand at necking down 300 wsm brass.
How is this done and is there anything special I need to do to the brass to make it last long enough to make it worth my time?


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[rushthezeppelin]

Use a really good sizing lube like imperial, you need the best for necking down (or up). Annealing before sizing can be a good thing. Some changes in neck dia might require an in between sizing step, no clue if thats the case for 300wsm-270wsm though. Also might need to turn necks if they are too thick.

 

[Dawico]

Annealing will help the life of the brass.

You should be able to resize it in one step as the difference isn't that much. Neck thickness should be checked but may not be an issue either.

 

[rsayloriii]

Not sure on downsizing, but for upsizing (I convert 270 to 8mm), I find Lee dies are so much easier as they're tapered on the neck sizer.

 

[NMTMarksman]

So what exactly is the procedure for resizing?


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[rsayloriii]

So what exactly is the procedure for resizing?


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Depending on the cartridge you're going from and to, you might have to trim first, but it's pretty simple ... make sure the case is lubed properly then run the case into a full length sizer of the cartridge you're going to. If it won't go easily (you will have to put some pressure on it) then you might need to run it through an intermediary caliber first. For example, I convert 270 to 8mm Mauser. Using a Lee full length sizing die, I can run the 270 brass into the 8mm die, but it won't go all the way in because 270 is longer than 8mm. So, I either have to trim first, or what I do is run it into the die to get the neck forming, trim it, then run it again, trim what is necessary, then run it into the die again. If I wasn't using the Lee die (remember they've got a tapered sizer), and was using the RCBS (they don't have a tapered sizer) then I would have to run the 270 brass into a 30-06 die otherwise I'd crush the mouth of the case. The biggest thing you have to remember is to have the case properly lubed and to NOT force it if it's not going. There will be more resistance, but you shouldn't have to beat on it. Anecdotal ... I was sizing 30-06 the other night and didn't realize I had caught a 270 in there until I was checking all the primer pockets. It sized quite easily.

 

[Dawico]

So what exactly is the procedure for resizing?


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Since the case mouth isn't much different and the length isn't an issue, just lube them up and run them in your die. They probably won't feel much different than sizing your current brass. Like rsayloriii said, if it seems very hard to size then pull it back out and check/ relube it. I don't think it is going to be an issue though.

Big changes in neck size or length are where this gets complicated. Yours should be simple. Just check the neck thickness when you are done. That may not even be an issue.

 

[57K]

If you're going to do this a lot, a step down die might be worth considering along with annealing. The closest dies between .277 and .308 would be .284 (7mm WSM). You'll put less strain on the case-necks by necking down in 2 steps. Is absolutely necessary? Probably not depending on how many cases you're talking about. If it's say 100, I'd be thinking about a 7mm WSM sizing die we're you're not as likely to need to anneal.

 

[dee]

You might have some neck thickness problems depending on your chamber. Also you need to check half of the wsm case's have different shoulder positions to keep from chambering in other wsm chambers.

 

[rsayloriii]

You might have some neck thickness problems depending on your chamber. Also you need to check half of the wsm case's have different shoulder positions to keep from chambering in other wsm chambers.

A full length sizer should take care of that.

Playing "CALL OF DUTY IX: DOUGHNUT WARRIOR" does not make you a "cop". -wakal

 

[dee]

A full length sizer should take care of that.

Playing "CALL OF DUTY IX: DOUGHNUT WARRIOR" does not make you a "cop". -wakal

No it won't.

 

[rsayloriii]

No it won't.

It will move the shoulder. I've converted enough 270/30-06 to 8 mm Mauser to know the full length sizer will form a new shoulder.

Playing "CALL OF DUTY IX: DOUGHNUT WARRIOR" does not make you a "cop". -wakal

 

[dee]

On those they are close enough it won't matter in this case it would be like trying to make 270 brass out of 280. The shoulder is farther forward thus not allowing a bolt to close.

 

[Dawico]

On those they are close enough it won't matter in this case it would be like trying to make 270 brass out of 280. The shoulder is farther forward thus not allowing a bolt to close.

I have made .308 cases out of 30.06 cases. Trim them down and one pass through the FL sizer and trim again. It will work.

Now if the shoulder is back then the OP may need to fire form them to use them.

According to Lyman's 49th the 300 WSM's shoulder is a touch shorter than the 7mm WSM's shoulder. The cases will need to be fire formed for safe shooting. Fire forming is a fairly simple process but I haven't done it so I offer no input on it.

 

[dee]

Fire forming isn't that difficult but can potentially cause problems depending on chamber design verses the case being formed. If there is no pressure on the shoulder or neck area a potential case separation can occure. This is where people create false shoulders or donuts to prevent this. Ackley improved chamber's are a good example as to be done correctly the barrel needs to be set back to get the proper crush on the parent case to prevent case separation that usually occur when the reamer is just ran into the chamber with no set back. It might not happen on the first firing but will happen.