I am having a Rem Model 700 300 H&H barrel delivered to replace the barrel on a Model 700 in 7mm Mag. Finding 300 H&H brass is a little difficult but I have several hundred once fired cases in 375 H&H. Since both rounds are based on the same case I am considering necking down some 375 H&H brass to 300 H&H brass. I plan on doing it in 3 stages: Full length size and deprime the 375 cases. Run the cases through a 300 H&H die without the decapping pin and then running the cases through a 300 H&H die with the decapping pin in place. Then check neck thickness and length and trim accordingly and fire form the cases.

In my mind this should work. What are Y'All's thoughts? Doable with normal dies? Or should I have RCBS make me a sizing die from 375-300? Not sure that would be needed. I am curious if anyone has done this and if they ran into any issues.

In theory, it should work. But you will need a step down die or two. You won't be able to go straight from 375 H&H to 30 cal in one step. That's .067", which is a large amount in one step. The shoulder on the 375 is much more forward than the 300 H&H is. Brass length is the same, but after sizing down, the cases may grow and need to be trimmed. Also, you will want to anneal the case mouths on fired brass before sizing down.

https://www.gunbroker.com/item/1040013365

Not cheap, but maybe make an offer?

https://ammoseek.com/ammo/300hh

This seems easier.

I saw 300 H&H within the last week...try Blue Collar Reloading...it seemed like it was either there or Unknown Munitions.

Good luck...necking down and up you can develop a donut (seems to be worse for me when necking up) that neck turning fixes but it's a PIA.

OP,

out of curiosity, what mods are required to a R700 receiver and mag box to convert it from the 7RM with COAL of 3.290” to the .300 H&H with narrower shoulder and COAL of 3.600”?

None the Rem 700 long action receiver can handle rounds up to the length of the 375 H&H. May need to do a little work on the rails for feeding but the action is long enough.

.300 H&H come up quite often , i have seen alot lately, keep an eye out at 24 hourcampf…..myself and a couple friends shoot this caliber and when seeing some available will check if everybody is well- stocked, is usually reasonable too

I find 300 H&H brass regularly on a variety of online auction sites. Occasionally you can get a really good deal.. just be wary of buyers premiums and shipping costs (some of the auction houses will stick it to you).. I picked up 100 pieces of once fired 300 H&H that had already been deprimed, resized, and cleaned a couple of months ago for $26 (shipped to my door)..

You can also find 300 H&H loaded ammo fairly regularly as well on the auction sites..


https://hibid.com/lot/192408567/lee-300-handh-dies-w---50--300-handh-brass?ref=lot-list

https://hibid.com/lot/193787393/ammo---300-handh-brass-only-50-rounds?ref=lot-list