Necking down 300 Win to 270.

[HRM Johnny]

Very interesting thread. Thank you for starting it. Please let us know what you decide; and what the results are.

 

[Frank in the Laurels]

..not sure how long the throat or the barrel would last, that's alot of powder to burn in a .277 bore..might as well just make it a standard 7mm rem mag, .277 vs .284, no animal would notice the difference.. guaranteed.

 

[pacowboy]

I have a custom 7mm-300 Weatherby and inherited a 1960's built 6.5-300 Weatherby. When making brass for the 6.5 using .300 WBY brass I always use the 7mm die first in the resizing. Virtually eliminates crushed cases.

 

[Nimrod]

I sized .300 Winchester magnum cases to .257 Weatherby Magnum in a single pass and had zero issues. I would agree that neck turning would be required unless you go with a custom reamer.

 

[dogz]

If...the 300 WM brass has been shot in another chamber then I'd toss it. If not, then I'd go 7 Mashburn Super. The easiest way to make brass is via the 300 WM route.

 

[1bamashooter]

@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!

I shot Matrix 165s in my stw but I was wanting this one to be my Alabama whitetail "beanfield" rifle. I was pushing 130gr TTSX @3600 and from 0 to 500yds it would flat out lay them down.

 

[1bamashooter]

If...the 300 WM brass has been shot in another chamber then I'd toss it. If not, then I'd go 7 Mashburn Super. The easiest way to make brass is via the 300 WM route.

I've got plenty of both.

 

[1bamashooter]

At the end of the day it is very hard to beat the 270STW, you could but not worth it in my opinion you
already have one nasty barrel burner.
BB

That rifle burned up in a house fire I'd do another if you could find stw brass

 

[Mike Matteson]

If it was me, I would do this. Anneal the cases. Then FL size the case without the expander ball on the end. Then use an expander die to push the inside of the neck out to uniform the inside the neck. Then cut the case for unform length. Then cut neck to unform thickness of about .013th thickness. I do step down several case for different calibers. Some take as many as 4 steps to achieve resizing the neck. That from a 280AI to 6mm necks size. I do anneal in the middle step.
New brass, I cut my cases to length.as the very first thing. Then turn the cases for thickness. If once fired, I anneal first as I stated above. That way the stop on turning the neck stops at the same place each time. Besure where you stop on the neck at the start of the shoulder.
I would purchase the reamer and keep it. That way you can rechamber the barrel at lease once.