300wsm norma brass vs 270wsm

[muffo]

I'm looking to size some 7wsm brass. So far I haven't found any 300wsm brass in aus. Threw is one site that has it for 220 per 100 but is out of stock and waiting on back order. They do have 270wsm cases for the same price. Would it be that much of a disadvantage to resize 270 instead of 300

 

[RDavies]

Are you shooting a standard 7 WSM chamber? The 270 and 300WSM brass has shorter shoulders than the 7WSM. ( I think it is .038" but could be wrong on the exact amount)

 

[Elkbane]

Muffo,
I just completed fireforming 300WSM cases to 7mmWSM, so perhaps my experience can help you. In order to preven case stretching at the web, I had to back out my 7mmWSM dies about 1/8 turn in order to create a false shoulder on the 300 WSM case neck that was high enough on the neck to make solid "crush feel" contact" with the throat. This took some trial and error, and I stretched 2 cases pretty significantly before I got the die set right. What this does is keep the casehead firmly against the bolt face so that the case expands at the shoulder, NOT just above the webbing. The two cases I ruined showed pretty significant thinning above the web, and the primers were squashed flatter than I've ever seen a primer flattened (primer pocket did not expand - the primer surface just expanded to encompass the whole beveled radius of the entry to the primer pocket).

That being said, as long as you can expand the 270 necks to 30 cal, then neck down to 7mm to create a high false shoulder, I'd say go for it. Or, if you want to just expand to 7mm, then create enough neck tension to get the bullets firmly jammed in the lands to hold the casehead against the bolthead, that would probably work as well. The fireforming load I used was Norma 300 WSM cases, 58.5 g H4831sc, standard LR primers and 162g AMAX jammed 5k into the lands.

Cases came out perfect. It was lot of trouble, but worth it.
Elkbane

 

[chiefkerdog]

Just to let you know I have some used norma 300 wsm and some 270 norma necked up to 30 cal. I dont need this brass any longer. I switched from a tight neck and these cases are neck turned I think to thickness of .0135 . If you can use this brass let me know.

 

[muffo]

I wish I could use the cases but I'm in Australia so I'm not sure about importing cases. I'm running a 313 neck but it is still standard 7wsm. So to do that I just have to get an expander mandrel, expand the necks over it then use a neck sizer to size down to 7mm

 

[Elkbane]

Almost right. Get an expander (I like K&M's) with both a 7MM and a 308 mandrel. Expand the cases to 7mm. Then expand them to 308 (the necks will probably stay straighter if you do it in two steps). Then just use your F/L sizing die, screwed OUT about 1/8 turn to neck down to 7MM. This will leave a small portion of the neck at the neck/shoulder junction at 308 caliber, creating a false shoulder for the chamber's throat to bear against so that when you close the bolt the casehead is tight to the bolt face.

If you use your F/L die, you get a little contact on the sides of the case which help center it up in the die. If you use a neck sizer, the case body will float in the die and the only contact you will get is at the neck - which could lead to more runout on the finished neck.
Elkbane

 

[muffo]

cheers I think I will have to do that seen as I cant get 300wsm