300 WM Dangerous game calibre rebarrel (Advice Welcome!)

[Aiden204]

howdy fellas. I hope this is posted in the correct thread. I recently picked up a Zastava LK M70 at a gunshow & was incredibly impressed with it. Upon further research I realized these guns came left handed. After a week of searching one popped up for sale here in Canada and I quickly purchased it. It's chambered in. 300 WM


My question is on the topic of Barrel Rechambering. I'm not overly sure on what calibre to pick? Ideally I'd like 458 Lott but I'm not sure how easily that will be done as I do not know if the magazine will fit the longer OAL of the 458 Lott Specifically. (if anyone has one handy and can measure that would be great)

I'm not a recoil sensitive person, in fact I'm becoming quite the fan of the "larger" calibres.

currently my collection is as follows
Zastava 9.3x62
Pre 64 Model 70 in 375 H&H
Double rifle in 450/400 3inch NE
Custom 458 WM
BRNO ZKK-602 in 500 A Square.

The gaps in my collection are obviously the lack of 416 (Although 450/400 is. 410) & anything between 458 WM & my 500.

is there an easy choice for a calibre to pick that won't be a huge pain to chamber in this rifle? Oddball stuff is ok assuming the reloading components are available in the US. I'm in Canada but regularly import

 

[Aiden204]

also I'd measure my 9.3 but I work away from home. My 300 is also not here yet and I can't find a definitive answer online.

I know the rifle comes in 375 H&H as well, I'm not sure if the bottom metal or much of anything (besides feeding rails I guess?) is much different between the 375 & 300 WM. If a 458 Lott would fit that's most likely the way I'd go as I have many 458 Lott cases and am already setup for 458WM reloading. This being my first dedicated lefty DGR I'd ideally want something larger than 375H&H as it may end up being my most used rifle my big bore collection & I enjoy the larger calibres.

 

[Delloro]

The Lott is based on the 375 H&H. I have a mark X in 375, and the receiver ring was notched for it.

I suspect you would need to do the same for a Lott. The bottom metal will be different, too.

 

[Inkgardener]

416 Taylor is interesting…

 

[Wyatt Smith]

416 Taylor is interesting…

I agree.

 

[Aiden204]

The Lott is based on the 375 H&H. I have a mark X in 375, and the receiver ring was notched for it.

I suspect you would need to do the same for a Lott. The bottom metal will be different, too.

is there somewhere you can pickup a new larger bottom metal or are they generally custom made? I'm fairly new to this custom work

 

[Aiden204]

416 Taylor is interesting…

yeah I'd looked into the Taylor, although as I'm planning to head to Africa in the future the idea of potentially losing my ammo on the way - combined with finding correctly head stamped brass has made me pause that idea for now. ballistically it does make a compelling case regardless. I can't imagine the higher pressure being an issue either with a true CRF action.

 

[Ontario Hunter]

404 Jeffery. I built one on a standard length Czech 98 Mauser. The cartridge can fit without carving into the receiver locking ring or changing the ejector. Of course the bolt face had to be opened, bottom metal changed (I used 416 Rem bottom metal) and I modified the feeding rails, loading ramp, follower, and extractor. You might be able to keep the bottom metal and follower but the rest of the changes would probably be required no matter which of those other calibers you're considering. 375, 416, 458 Lott would all require carving into standard action locking ring. Actually, I think the Lott cartridge might be too long for modifying a standard action.

Edit: 300 Win magazine box would be too short for 404J. Way too short for 458 Lott!

 

[Aiden204]

404 Jeffery. I built one on a standard length Czech 98 Mauser. The cartridge can fit without carving into the receiver locking ring or changing the extractor. Of course the bolt face had to be opened, bottom metal changed (I used 416 Rem bottom metal) and I modified the feeding rails, loading ramp, follower, and extractor. You might be able to keep the bottom metal and follower but the rest of the changes would be probably required no matter which of those other calibers you're considering. 375, 416, 458 Lott would all require carving into standard action locking ring. Actually, I think the Lott might be too long.

404 Jeffery has always seemed awesome. I don't suppose you'd want to make it happen on another M98? (Or can point me to a good smith who can do the work here in Canada)

 

[Delloro]

is there somewhere you can pickup a new larger bottom metal or are they generally custom made? I'm fairly new to this custom work

Yes magnum bottom metal can be found, but it won't be cheap. You are time and money ahead finding a 375 H&H to start with.

 

[Aiden204]

Yes magnum bottom metal can be found, but it won't be cheap. You are time and money ahead finding a 375 H&H to start with.

I fear by the time I find one that's left handed I may be better off just biting the bullet on the magnum bottom metal

 

[dgr416]

The 416 rem mag is awesome one of the most versitle big game cartridges .I have 4 of them working on 5 .I trusted it as my DGR for 12 years in Alaska .There is no game on earth I wouldnt take with it .Its recoil is not bad and its power is awesome !

 

[mooze]

416 Ruger?

 

[Ontario Hunter]

404 Jeffery has always seemed awesome. I don't suppose you'd want to make it happen on another M98? (Or can point me to a good smith who can do the work here in Canada)

I'm getting old.

Lilja in Plains, MT made my rifle barrel and Dennis Olsen also in Plains reamed, threaded, cut, crowned, and mounted it. Thousand bucks US. A local machinist opened the bolt face. Gave him a hundred Canadian. Bottom metal from Blackburn for $400. Iron sights used off ebay $150. Used stock from Gunbroker $200. Bluing for $150. Follower from NECG for $80 (I think). Timney trigger $80. Parkwest 3-position Model 70 safety & shroud at $200. Two Winchester crossbolts off ebay at $80. I put it all together and modified rails, ramp, and follower to cycle 404J. Picked up Warne QD rings on sale for $65. Found a very low discontinued Weaver base for $10. Scope new from ebay at a shamefully low price.

Acquiring a 98 Mauser action is the cheap part. Do you have one?

 

[Choupique]

Anything can be done with enough money and time.

Your rifle is set up for "short" magnum cartridges (magnum bolt face, .30-06 length action) so the .458 win family of cartridges will be the easiest to rebarrel to. They will only require a barrel and maybe some feed lip work.

.458 win
.416 ruger
.416 Taylor

 

[Badboymelvin]

425 Express...?
It's the .300WM necked up to .423" and gives the same ballistics as the 404 Jeffery.
I have one and love it
My rifle is a custom build, but uses a Zastava action.

 

[Ontario Hunter]

425 Express would indeed be quick and easy. Also has the advantage of belted case with shoulder vs 404J has no belt and very tapered shoulder ( = tricky headspace). Ballistically it's supposed to be same as 404 and uses the same bullet. The downside is headstamped brass is almost nonexistent. That can be a problem if going to Africa with the gun. Using 300 Win brass doesn't match the gun and that can be a problem ... if the airport cops actually bother to look at headstamps.

 

[Schüler Jumbo]

.416 Ruger. Reloading brass is somewhat scarce but available and factory ammo is available if needed.

 

[Ontario Hunter]

I would think getting the feeding rails just right for a straight taper case like 425 Express would be tricky. It's the reason why Jeffery Co went with sloping shoulder when they designed 404. The more constricted shoulder area of feeding rails helps ensure cartridges feeding from magazine make that final jump onto the bolt face at the right time/place. I suspect this is the reason why 500 Jeffery CZ rifles from the factory very often (universally?) have feeding issues. It took me almost three days gently carving on the extractor, rails, ramp, and follower before my 8mm Mauser action would reliably cycle 404 cartridges. Finally, I had to relieve some spring tension on extractor and that got her over the hump. Two gunsmiths told me that build was impossible but I knew Jeffery had done it. Standard action 98 Mauser was all they had to work with when cartridge was designed. Dennis Olsen even refused to tackle modifying the rails etc. But he may have been too busy. Getting the feeding right is an art form for sure. Remove too much metal and the action becomes expensive scrap metal.

I guess the one slight/maybe drawback to 425 Express is its belted case. Sometimes belted cartridges don't stack and/or feed as smoothly as non-belted. Or so the story goes. My experience is limited. I only shoot 30-06 and 404. Both are not belted. Most modern magnum designs have now dropped the belted design (e.g. Winchester WSM and Remington RUM were both designed from 404 case ... almost ... both have slight differences in rim diameter).

 

[Delloro]

I fear by the time I find one that's left handed I may be better off just biting the bullet on the magnum bottom metal

Bottom metal, even used, is hundreds of dollars.

Thread 'Mauser 98 .375 H&H Bottom Metal'

Apr 30, 2025

I’ve got a pretty nice trigger guard and hinged floor plate not being used, and I’m sure someone on here can put it to work. I believe this was originally from a Remington 798. It is all steel and gloss blued. The magazine box was factory extended to 3.7 inches and it was originally designed to stack .375 h&h. Let me know if I missed something, or you need more measurements. Im located in the D/FW metromess.

$275 shipped to an established member (and a bit less if you’re local)

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New Blackburn will be $500 US, unfitted, unblued, may or may not fit your stock, action will have to be modified to work with it. It i$ po$$ible, but you will pay for it.

I cannot imagine a gunsmith charging less that $1000 to convert a std length 98 to accept the longer cartridges.

For the rifle you already have in hand, your most realistic choices are the 416 Taylor or the 425 Express.