M70 300 WM - Any way to increase COAL capacity?

A

AD5GB

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OK. Got my first Winchester rifle and first belted magnum all at the same time. It was in exchange for a few hours of computer work so, what the heck, right? It's a WalMart grade M70 in 300 Win Mag, 26" barrel, bottom of the line Bushnell 4-12 but looked hardly used. (I have 2 700s I've accurized and the .270 also sports a 27" Krieger bull sporter tube - always been a Rem guy) Well, took it to the range with a box of Remington 180s and proceeded to fire a couple groups less than 3/4" @ 100. Intrigued I was! I'd been mulling over building a 338 Lapua or Edge but thinking the WM is cheaper to work with and could do almost as much I decided to put a little into it. The standard 13-3/4" LOP is a bit short for me though up until now I've just adapted to it. With this level of recoil... well anyway, ordered a properly fitting Boyd's custom stock to replace the plastic one, a Vortex Viper PST, a set of loading dies and a little while later am running 165gr SSTs through the chrony @ 3260 with decent (large-ish 1/2") groups. I'm infatuated with this thing all of a sudden.

I'm wondering though if anyone knows if there's an easy way to expand the magazine length (this is a blind magazine machine) to accommodate cartridge lengths that are a bit longer than SAAMI specs? It really seems to like a little longer than the magazine will allow. I've talked to a couple local smiths and get looked at like I've got boobs on my head or something. :confused:

Thoughts??
 
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Yes there is a way to lengthen the magazine box but you'll also have to move the bolt stop back. The M70 long action is the same regardless if it is a .30-06, .300 Win Mag or a .375 H&H. To convert your M70 to take the longer H&H magazine and modify the bolt stop will cost you a lot of money, it might be cheaper to just trade in your M70 on a .375 H&H M70 and rebarrel to .300 Win Mag.

Just don't forget to change the throat on your .300 Win Mag if you do all the work. Running cases longer than SAAMI specs might cause you to jam the bullet into the lands and create excessive pressures. I'd hate for you to do all that work and then blow up your rifle during testing.

Cheapest way to get what you want is to trade in your rifle on a Savage 110 rifle in .300 Win Mag. Put in a single shot adaptor in the magazine box and ream out a special throat for your longer cartridges. However, that's not what you wanted anyway.

Me I'd just load your current .300 Win mag as long as possible to where they just feed from the magazine and don't jamb the lands, and see what it can do.
 
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old roper said:
With the longer VLD type bullets it's pretty common on a build to have Wyatt box installed and doesn't cost all that much. Main thing is you get longer option over factory box.
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What's all that much? I guess that depends on the gunsmith you get and his shop rate. Here is what's involved to install a longer magazine box in a M70 action. The same thing is involved to install the longer factory H&H magazine box.
 
1, why bother modifying the rifle when ammunition that rivals the 338 Lapua Magnum 250gr lockbase loads are within SAAMI COAL specifications?

2, in case you need said ammunition specification: http://usarmorment.com/pdf/300WM_load data.pdf

3, please note that Mk248Mod1 has a higher MAP rating than a SAAMI spec load, so your brass life will be reduced! Work up at your own risk.

Jimro
 
Thanks much for your responses and thoughts. Much appreciated!

@old_roper:
Thanks for the link and the lead! I was beginning to think I was the only one who thought of something like this but knew it couldn't be true. I'm really a noob with "magnum" anythings though. It's a brand new adventure!

@taylorce1:
Yeah, were I to do it over I'd have started with a rifle plan that was planned correctly from the start - as you mentioned. Also, your suggestion to simply do the best with what it is, is really a good one, for many reasons. This thing seems to shoot very well as it is, for what it is. I've only loaded 165 and 180 SSTs though and not too many of them at that so I guess I really don't know what it's capable of yet. I suppose I can still always return to my plans to build the custom .338 from scratch.

Again, many thanks for your thoughts!!
 
Gun Parts should have a 375 H&H mag box and bolt stop. I have done this before an a 300 M70. It took me about 10 minutes to do.
 
Originally Posted by guv
Gun Parts should have a 375 H&H mag box and bolt stop. I have done this before an a 300 M70. It took me about 10 minutes to do.
Click to expand...

Wow! It would have never occurred to me to try that. Looks like < $50 in parts too. Thanks for that idea!!! :)

Originally Posted by Jimro
1, why bother modifying the rifle when ammunition that rivals the 338 Lapua Magnum 250gr lockbase loads are within SAAMI COAL specifications?
Click to expand...

Well, I guess I'm a bit OCD about getting the most out of my rifles. :o Both accuracy and velocity. With the 300 WM it seems like there's a good bit of bullet jump, even at the max OAL the magazine would allow. In my experience with my other rifles I found they shoot the best groups with the bullets seated fairly close to contact. My .270 (Krieger barrel) actually does its best when I "soft seat" them (powder charge adjusted accordingly) by not using a crimp and allowing the action to seat the bullet on closing. Clearly, I can't hunt like this so I seat them .020" back and factory crimp for hunting loads. My .22-250 is a bit more fussy and it really depends on which bullet I'm using as to how deep it likes them seated. In both these rifles the stock magazine will accommodate any seating depth I choose. Not so with the 300.

Just looking for the most out of this thing and fishing for tips-n-tricks from folks who know way more than I do on the 300 WM.

Thanks a bunch all!!
 
taylorce1,Please read my post again if you can't here it is.

With the longer VLD type bullets it's pretty common on a build to have Wyatt box installed and doesn't cost all that much.

What part don't you understand?
 
Old Roper,

I read and understood your post perfectly the first time. I simply asked how much was "doesn't cost all that much"? Shop rates vary and depending on how many hours it takes a gunsmith is how much it is going to cost. Shop rates are usually around $100 an hour, how much time does it take to set up a mill, make the necessary cuts, clean up, and refinish the action?
 
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