Necking down 300 Win to 270.

[1bamashooter]

I'm wanting to build a 270/300 win to replace a 270stw I lost in a house fire. I've got a 300 and plenty of brass so I figured I'd just build that instead of a 270 WBY or another STW. I necked down the stw in one sizing could I do the same for the 300 or would two be better? Also would neck turning be required after sizing?

 

[Huntaddict]

Why not have a custom reamer made? Since you are already going to have to rebarrel, all you need to do is change the neck specs on the reamer and get a Redding Type S die set and resize only the necks. Done and done

 

[1bamashooter]

Why not have a custom reamer made? Since you are already going to have to rebarrel, all you need to do is change the neck specs on the reamer and get a Redding Type S die set and resize only the necks. Done and done

Sounds like that's what I'll do!

 

[Ol' Red]

That sounds interesting. Following

 

[K.E.C. Darkside]

It may take 2 maybe 3 sizing to go from 308 to 277. Just a couple bushings.
And Maybe need to turn neck's.
Usually do need to. Depends on your reamer dimensions.

I think it's a Great Idea.

 

[Jerry M]

.270 Weatherby Magnum... But have fun!

 

[Lefty7mmstw]

I do 375 to 7mm in 2 steps if I neck down/ blow out 375 h&h to 7stw... I suspect 1 step is possible without much effort as I do 1 step for 30 to 270 with 30-06 brass and it's never been an issue. You don't want to check headstamps on my 30-06 or 270 ammo. I suspect 1/3 of it is the wrong stamp; I simply made the necks what I needed them to be at the time.

 

[tomcat818]

That thing should pack a wallop on both ends

 

[Victor3Ranger1]

Sounds like a fun round

 

[Clem Bronkoski]

I've sized many 30-30 brass down to 7-30 Waters in one pass. I'd suggest 2 passes.

 

[1bamashooter]

.270 Weatherby Magnum... But have fun!

Had one wasn't my favorite but I've already got plenty of 300win brass

 

[fseaman.js]

I new I saw one before.

270 - 300 Winchester Magnum Finish Chamber Reamer-SO19298F

www.pacifictoolandgauge.com

I would recommend neck turning as sizing down makes the necks thick and not uniform.

If it were me...
Anneal
Full size in the 300 Win Mag die but with the expander removed.
Size with a slightly larger bushing to have the ID of the neck 0.279 -+ 0.001
Neck turn to a thickness of 0.015 -+0.001
Final neck size to your favorite 270 ID.

If you have any problems going straight from unexpanded .308 with probably an ID of .300 or less, add a second step in sizing down.

 

[FEENIX]

I'm wanting to build a 270/300 win to replace a 270stw I lost in a house fire. I've got a 300 and plenty of brass so I figured I'd just build that instead of a 270 WBY or another STW. I necked down the stw in one sizing could I do the same for the 300 or would two be better? Also would neck turning be required after sizing?

@Big Jake Duke did this in 2015: https://www.longrangehunting.com/threads/270-300-win-mag-now-feasible.155307/ If you go this route, I would go with a 1:8" or faster barrel twist. I built my .270 AI in 2012 with a 30" Lilja with 1:8" specifically to propel the 165/175 Matrix VLDs. Good luck!