For the past couple of years I've wanted to build a left hand rifle (actually have it built is more correct) in 300 H&H.
First off, I've never done this before and I've got a lot of questions.
Question #1 - What action length is needed? Would a RUM action length work if I decide to go with a 700? If I go with a Model 70 action, will I have to go to a 375 H&H length action? It is my understanding that a 300 Win. Mag. action length is too short. Correct?
Question #2 - Since I'm leaning toward Remington or Winchester, what cartridge should the initial rifle be chambered for so that the bolt face has the proper dimensions?
Question #3 - Concerning bbl. length, what is the optimum for this cartridge?

Thanks for all the responses you make.

When I get it completed, I'll try to post some photos.

Thanks
Ken

Ken,
The .300 H&H is the .375 H&H necked down with a little more shoulder.
You'll need the long action. Base diameter is 0.532".
Go with the mod. 70 (just my preference). If you do not need a super
dooper fancy receiver use a nice m98 and have a competent 'smith open it up.
Use a 26" barrel or longer if you want.

Roger's pretty much on. 375 length action, magnum bolt face, 26" barrel. - Dan

All Mod. 70 actions are the same lenth with one exceptions and we won't worry about that one as it doesn't apply here.

You have to pull the block out of the shor and med lenty magazines and change the bolt stop. but it is a little easier to use a 375 lenth action..I prefer the pre-64 action...My 300 is a 30-06 openned a bit for the 300 H&H...I opened the ejection port a bit in back. You can do that with a file, dremmel tool or a tough fingernail.

If you are set on a Remington 700 or a Win 70 action you need to know a couple things to shop for a donor rifle.ALL Pre,64 Model 70's are the same length,only bolt faces,magazine boxes/followers and bolt stops differ.They can be changed/modified.The push feed Model 70 and the newer "Classic" controlled feed models are made in two lengths.It's easiest to find one originally chambered for 300 Weatherby,300 H&H,375 H&H or 7mm STW.They will have the proper 3.60" mag box.If you are buying a Remington,all long action 700's have a 3.70" magazine.Just get one with a .532" bolt face,ie: any belted magnum from 264 Win Mag to 416 Remington.From there it's a simple rebarrel.I would suggest NOT buying one in 300 Win or 300 Weatherby because if you do you will see no need whatsoever for a 300 H&H , unless it's nostalgia which is worth(?) different things to different people.

Just find a Rem 700 in any magnum caliber (such as 7mm .300W etc.) and put a new barrel on it. Done.

Unless you have a strong preference for the Winchester, Dan in Wa has a point. Any 700 Remington originally chambered for a belted magnum is the easiest (and cheapest) conversion, with no work on the bolt or magazine needed.

On the other hand, if you object to the time-bomb trigger/safety and the fallible extractor on the 700, you'll have to spend some money on most Winchesters (other than the more recent ones originally chambered for the long belted cartridges listed in a post above.)

Winchesters made for the short magnums will have to have considerable, but not impossible, magazine and bolt stop work. In the pre-64 factory versions of the .375/.300 H & H, they moved the magazine FORWARD and milled off some of the feed ramp (which left only a marginal amount of steel behind the lower - right - bolt lug). A better approach is to lengthen the magazine to the rear and leave the feed ramp alone.