Home Forums Hunting & Shooting Custom Rifles & Wildcats 300 Win Mag on a Magnum length action?

Has anyone built a 300 Win Mag on a 3.600" length action? If so, what kind of increase in case capacity could one expect over a standard length action? I have a Win 70 Classic donor in 300 Weatherby and started thinking...

I haven't done a 300 win mag that way, but I do have a 7mm rem mag that I essentially did that way by using a 375 H&H magazine box/follower/bolt stop. I run 145 Barnes LRX's at 3.5" and it turned it into a whole new round.

Putting the magazine block in place was the dumbest thing Winchester ever did, they should have made every long action 3.6" like Remington did.

A 9 twist 300 win mag running some of the heavy bullets available now would be very nice. More magazine length is never a bad thing.

Yes.. The extra length of action means bupkis as far as case capacity. You still have a .300 WM case. And you STILL hafta keep pressures within safe limits.. Duh....

Your donor is already chambered to a bigger 300.

I assume that you'll want the bullets seating out further than standard and you'll have longer throating than standard...

You can figure the extra capacity by calculating the extra distance the bullet is seating out. There's formulas that others have worked out as to how much extra velocity. I don't think you'll be getting a lot of extra velocity. Having said that, I think the extra magazine length is a good thing, not just for velocity but more for accuracy if you're thinking long range shooting- where that would make some difference that is of value, in my opinion..

(Accuracy due to being able to adjust seating depth to obtain a "sweet spot".)

I should be easy to rechamber 300 Weatherby to 300 Super, or as Jarrett calls it the 300 Jarrett.

http://www.jarrettrifles.com/pet-calibers.html

Yeah, but I have a s***load of 300WM brass, and I’d rather not deal with the Weatherby freebore.

So, for kicks and giggles, why not just set the barrel back and rechamber without the freebore? You'd have the Weatherby additional power without the freebore. Sell the s***load of 300 WM brass and buy half a s***load of Weatherby brass and you're good to go. I like the 300 WM, but the Weatherby is a step above, IMHO.

Bob

The loony solution go weatherby then build a long 7 Masburn to use up the 300 win brass. Problem solved.

My .300 WM Ed Brown Damara has a mag length 3.6" box and Ed throated it to utilize the longer box. You get a bit more case capcity but not enough to make a notable difference.

I just like the way the rounds look and how bullets fit the neck. Having more bullet down in the case doesn't change performance that much. I just like having more freedom to seat bullets to fit the throat, even high ogive, longer bullets. A 3.6" box is less confining than a 3.4" box.

If I was going to build a .300 WM from scratch, I'd go 3.6", throated to fit the bullet I was going to use. M-700 mag actions are 3.6". If the box is blocked for 3.4", remove the block.

DF

Damara.

. Aint that the truth. Guy wants to fu ck up an already good thing...

The .300 Wby does kill stuff pretty dead. Here's an example of what it can do with the 180 NPT.

First shot at 125 or so wrecked the boiler room. He ran, second shot hit his spine, dropping him on the spot. He was a dead elk running after the first hit. I wanted to stop him before he hit the woods and I did.

DF

That is one huge Elk!

Partition cut him down to size. Lots of good eating.

DF

Well, I dunno about that - the Wby action was headed towards becoming a 7mm MSM anyway, but that project is on hold for right now. I'm thinking that I'd like to build a 300 WM around the 200 grain AB for its high BC and thought that the magnum length action might be of benefit with the long AB. If that works out, I might not need to build a MSM anyway. Seems like no one can give me a number as to how much case capacity might be gained, though.

And then I thought some more (often a dangerous thing)...I could have a 30 Nosler barrel installed on one of my standard magnum actions and keep the Wby action and the s***load of 300 WM brass for the MSM project. Hmmm....

Good thinking on keeping the 300WM brass for the 7MSM build. You are definitely on to something there. As for the 30 Nosler, well, that may be a good cartridge. But, what will it do that the good ol 300WBY can't? I'd look into which one has better availability: cost of ammo and reloading components and weigh that out.

If I was building a 300 Win I’d def want the 3.6”box for bullet seating.

I used a Magnum P64 action for my 7 Mashburn Super for the same reason. No reason to not have some flexibility.

I give up. Why not keep it a .300 Weatherby in the long action?

The driving factor in the .300 Win Mag case design was keeping OAL short enough to fit in standard length magazines. Hence the short neck, as Winchester hurried to beat the performance of the .308 Norma (lots of folks, me included, believe the .300 Win Mag would have been what is now the wildcat .30/.338 based on the .264/7mm Rem Mag/.338 family of cases).

And for those who do go the .300 Win Mag route in long actions, there is still redemption. It’s an easy rechamber, as the .300 Weatherby will clean up a .300 Win Mag chamber nicely.

Yes, and in my opinion certainly not worth a hunting build. I just reached 3k with a 200-gr bullet but so what..?
It’s right up there with “improving” the 35 Whelen which I did also.