Okay, I have a new to me, Rem 700 Classic 300 H&H magnum that I am having trouble finding brass for. Seems that unless I want to spend $50 a box for factory, I need to handload for it. That was the plan anyway and my dies came in today.
Big problem is that there is extremely little brass for it out there. Since I have a .375 H&H already, I can just buy brass for it and neck down. What's the best process, easiest process for necking down .375 H&H to 300 H&H? I understand the idea, just haven't ever done it so this will be a first.

Starting with brand new brass is a given.

Should I anneal before I begin?

Should I go in one step from 375 to 300 or should I do an intermediate step and if so, what should it be?

Will I have to neck turn?

I figure $28 for Remington cases versus $56 for Nosler per 50 cases is worth the work. Or we'll see once I try for the first time. Maybe. Depends on how much tooling I need to buy just to get started.

New brass comes annealed so I don't think you would need that step. I've never necked down so far so I can't say if you should do an intermediate step. I'd sure get some Imperial sizing wax to lubricate well.

I've necked 308 cases down to 243 in one step and that didn't work out to bad. If you haven't got one of the stuck case removers I'd get one just in case.

I'm sure that some of the folks on here will have done that and give you some advice from the horses mouth so to speak.

I've had really good luck with Remington cases in several different calibers.

Boy - you came to the right place to ask that question, Michael!

The RCBS Special Order Catalog 2001 edition lists a forming die for making 300 H&H cases from 375 H&H brass. Part #15065, Group "D", and was priced at $40.95 back then. www.rcbs.com or Customer Service 1-800-533-5000, 6:30 AM to 4:00 PM, Pacific time.

Boy - you came to the right place to ask that question, Michael!

The RCBS Special Order Catalog 2001 edition lists a forming die for making 300 H&H cases from 375 H&H brass. Part #15065, Group "D", and was priced at $40.95 back then. www.rcbs.com or Customer Service 1-800-533-5000, 6:30 AM to 4:00 PM, Pacific time.


MidwayUSA carries them, $45.99 but they won't have them until June 30...

I have experience both in necking up and down and found that annealing new cases really helped eliminate case failure. I'm not sure, but I would bet that the case forming die set has at least 2 and probably 3 steps. I had tried necking down 30 Rem to 25 Rem and was getting a lot of case failure.....not good! Went to an intermediate 270 die and VOILA! No more case failures. Emery

So maybe I should be looking at necking down from .375 to .35 or .323 or so, then from there to .300?

The forming die you ordered should do the trick, Michael.


When not having a specific forming die, I tend to use intermediate diameter neck sizing dies to neck down from a larger diameter - such as 30-06 cases down to 6.5-06, and .284 Win down to 6mm/284.

Time and patience cures everything. Take your time, don't get heavy handed and reduce a bite at a time. Liberal use of a lube such as Imperial Sizing Die Wax and rotation of the case between hitches in the reducing process aid greatly.

Thanks kdub. Like I said, this is a first time try at necking down so rather than learn the hard way I'd like as much info as I can get. Sometimes information needs weeding or clarification so I keep asking questions. I'm STILL waiting for RCBS to make and ship me my die so I keep looking at that box of brand new RP brass and those factory Federal cases going, " Man I hope I don't screw up too many because this rifle is very nice to shoot", when I look at how much smaller that case mouth is going to need to get.

It's probably the waiting.

I don't believe you need to worry about extra forming dies. I sized a lot of .308 Winchester down to .243, and lots of .30-06 to .270 Winchester, and I only used the standard full length sizing dies for the new calibre.
The only trick that I found, especially since I normally used once fired brass, was to full length size in the original calibre. Since you already have a .375, I would full length size in .375, and then run them through the .300. Be careful about too much (or any) lube on the case neck or shoulder.
Best bet is to size without the decapping pin, and then go back later to size the necks up.
Annealing is only needed after you size, and possibly not even then.
Why not try with some of your fired .375 brass and see how it works out.
Remember, you are not sizing the body at all, just the neck. Should be no heavy duty forming involved here.

Be sure and "ream" the inside of the necks after "necking down", otherwise the increased "grip" on the bullets are going to send your pressures "over-the-top" on fairly moderate loads. I've never necked that far down, but used a lot of match .308 brass for .243 loads in the past (had to neck ream them too).

I'm still waiting on that Form and Trim Die from RCBS. Lucky me, I like a caliber that you have to special order dies for that have to be made first because they normally don't. Oh well.

Thanks Al. I was planning on starting with new unfired R-P brass. Already have that in so it's like I said, the wait is killing me.

Yep, I was curious about inside neck reaming. May need MORE TOOLS! :p