buddy had a rem 660. What's the best way to make 350 Rem Mag.

Had and build several 350s; great round. You can make brass from any belted mag, but 338 WM is a good choice. No matter what you will have to trim, of course.
Now, the unknown is the OD of your chamber neck; that will make the decision for you on whether you have to neck ream/turn. No matter what brass you use you are making necks from shoulder meat.
Except 6.5 Rem Mag.
I actually made some out of 375 H&H that had thin shoulder walls so the 350 necks worked fine as it.
But is it not hard to make.

if it were me, i'd likely use 458 winmag brass - i used to have plenty around, bet there's some in a bin somewhere in my shop

https://visionammo.com/product...s-350-rem-magnum-25/

WHEW - spendy

https://www.youtube.com/watch?v=Tx_DzlVwuyE
(not me)

https://www.24hourcampfire.com...n/983548/type/thread

Using .458 will be a stretch. Ok, not a stretch; more like a shrink. A huge one.

I just made 50 from Norma 264 mag brass. Took some time I had to neck turn them all. I would try the 338 win mag brass if I had to do it again

In this day and age of rifle brass prices, I think I would have sold the .264 brass and used something else!

Hip

Use the thinnest brass you can find. They use to recommend Winchester. Maybe Hornady, now. Redding made a trim die, or you can Zip-Cut the top off a cheap 7mmRM die.

For a proof of concept , I used a tubing cutter, resized and trimmed a once-fired a 7mmRM case.They recommend new cases. But I was able to buy some Aussie Bertran , so never bothered.

I trim brass off in my lathe. Fast and easy.

Start with 7mm Remington Magnum, then trim with one of these:

https://elite3ddesign.com/prod...g-brass-case-trimmer.

I make mine from 300 Win Mag Norma New brass. Cut them to 2.175", simply run it into the 350 Rem Mag die, trim to 2.170, chamfer, de-burr, load and shoot. Works fine. I use Frankford Arsenal spray lube and deposit a little Redding Imperial Die Wax inside the case neck with my fingertip, run the case into the die in 4-5 steps lowering the ram and rotating the case 90* each time Out of 100 I only had 3 shoulders fold over.
cwhuntsalot

quote:

Originally posted by loud-n-boomer:
Start with 7mm Remington Magnum, then trim with one of these:

https://elite3ddesign.com/prod...g-brass-case-trimmer.

I have two of those. One for making 300 Savage brass from 308 and one for making 8x57 from 06. It takes like 10 minutes to set it up and cut off 50 cases. Excellent tool and very affordable.

I'm not experienced in this kind of shortening but wonder if it might be better to form the new shoulder and then cut off the case.

I formed the shoulder first then shortened in a trim die

quote:

Originally posted by sambarman338:
I'm not experienced in this kind of shortening but wonder if it might be better to form the new shoulder and then cut off the case.

There probably isn't space in the die to do this.

I ran them into a trim die to forming the shoulder then cut off. If your using a f/l sizing die to form u will likely need to remove the decapping assembly first

U can use the seating die to form as well