.458 Remington Ultra Mag

[Never Been]

I've been tossing around ideas for the Model 70 Classic in 300 RUM I have, and remembered a gun my brother owned briefly back in '09 or so and that I had a dummy round still on hand.

A guy had it built for a dangerous game hunt on a R700 (I know, the horror). It had this cheesy single stack plastic mag extension that would dump all the rounds every time you fired. I fired it once from standing and really wasn't too bad for a 9ish lb rifle, but it was braked. Anyways, it sure looked good and fed well in the M70 action!

I was a little suprised to not find more on it while searching last night. I found one reference to a .458 RUM and another for a .458 Super Cat. I'm assuming a bit more power than necessary and lack of properly headstamped brass is at least partially to blame.

 

[John Wasmuth]

There are companies that do custom head stamped brass.

 

[Riflecrank]

Where there is a will, there is a way.
Build it and the way will come ...
Is there a way to slip "45/" in front of the "375 RUM" on the headstamp with your own bunter or stamp?
Call it the "45/375 RUM" and put the terminal part of the SAAMI .458 WinMag throat onto it.
This could be done with an existing SAAMI .375 RUM reamer simply run into a barrel already chambered for the SAAMI .458 WinMag. Use the .45-pilot on the .375 RUM reamer with live pilot.
Use the SAAMI .458 Lott reamer to extend the chamber neck to 2.800".
Or get your custom reamer made, throated as you please.
Look to Quality Cartidge for proper headstamp.
IIRC, Atlas group were recently making RUM brass again, they are made up of guys who split off from Remington R&D in Elizabettown, KY.
Peterson makes highest quality stuff including a blank headstamp H&H basic wildcat tube.
Have they started making RUM basic too ?

I have done similarly to create a .458/.416 Ruger and a .458/.338 Lapua Magnum Unimproved.

Whitworh MKX M98 .458 WinMag had a ringed chamber from the factory reamer chatter/chips or whatnot. QA issues can happen.
The .416 Ruger reamer cleaned up the chamber rings. Now I have smooth chamber walls and an excellent throat.
A .458 Lott reamer was used to extend the chamber neck to 2.58" from breach face.

A custom-barreled CZ 550 Magnum 460WbyMag with long cylinder shank 26" barrel with muzzle ports
was whacked off by 3" at breech and re-chambered to .45/.338 LM. I call it the '.458 Ted Williams Thumper" due to personal issues.

I also have a ".500(.490-bore)/.338 Lapua Magnum Improved" also called the "12.7x68mm Magnum" that was co-developed with a fellow riflecrank in Germany. Custom dies from Hornady.
Custom reamer from Dave Manson.
It was done on a Winchester M70 Classic Stainless 300 RUM donor rifle.
Sunny Hill bottom drop floor plate and McMillan stock to match.
It retains the factory windowed RUM sheet metal magazine box. Works a charm.

Above are all the "Lapua Cats" I have rifles for.
.500 (not .510):

The .458/.375 RUM would be excellent in that combo.
It would have about identical case capacity as the .458/.338 Lapua Magnum Unimproved.

 

[Riflecrank]

I used to get Jamison/Captech International blank basic cylindrical brass for .338 Lapua Magnum.
Could just neck them down and anneal so the "Improved" versions (.500 and .510) had no risk of split necks and could be left a little longer, no shortening on fire-forming.

Blank basic cylindrical RUM brass would be great for a .458 RUM, but there should be no split neck problems with .375 to .458 neck-up of .375 RUM.

"Anneal before necking up and after necking down" for previously fired brass.

With new brass I would just neck up .375 RUM to .458 RUM and fire-form.
Then go hunting. Start regular annealing after every three firings including that initial fire-forming.

 

[Never Been]

I did see ADG is making .375 RUM brass, one could make an excellent double duty long range/dangerous game rifle with such high quality components readily available. My real problem is that I'm left handed, and although I can shoot right handed and appreciate the relative ease of selling right handed rifles, I really just want a left hand 550. When I finally get bored of day dreaming the RUM will go down the road.

As a side note, I thought I remembered reading issues with the M70 and using Lapua based cartridges? Something about the tenion not having enough meat if I'm not mistaken. Long Rifles Inc. opens up the threads when they blueprint the action and it supposedly helps to alleviate the issue. What has your experience been?

 

[Riflecrank]

The tenon: Given my experience with one .338 Lapua Magnum wildcat in an M70 Classic rifle, no problems.
To enlarge the barrel threads would require the action be bored out for the larger threads.
Add barrel steel, take away the action steel surrounding the barrel.
Sounds no good.
It is known that the Winchester Custom Shop built a few .416 Rigby rifles on the M70 Classic action.
They had to stretch it for that one.
I had two of the .500/.338 LM Improved (12.7x68mm Magnum) rifles built.
One was on a BRNO ZKK 602, forerunner of the CZ 550 Magnum, same barrel threads.
The minor diameter of those threads is same as the major diameter of the M70 barrel threads.
The M70 .500/.338 LM stayed with me.
The other got re-barreled to .408/.338 LM.
Hello, my name is Ron.

 

[Never Been]

Thanks for the info Ron, I hope someday I have your appetite and budget for all of those varieties of recoil!

 

[Inline6]

I did see ADG is making .375 RUM brass, one could make an excellent double duty long range/dangerous game rifle with such high quality components readily available. My real problem is that I'm left handed, and although I can shoot right handed and appreciate the relative ease of selling right handed rifles, I really just want a left hand 550. When I finally get bored of day dreaming the RUM will go down the road.

As a side note, I thought I remembered reading issues with the M70 and using Lapua based cartridges? Something about the tenion not having enough meat if I'm not mistaken. Long Rifles Inc. opens up the threads when they blueprint the action and it supposedly helps to alleviate the issue. What has your experience been?

The parent case of the 338LM is a 416 Rigby.

 

[Never Been]

Thanks Inline6, but I was speaking in reference to this;

With new brass I would just neck up .375 RUM to .458 RUM and fire-form.

Though not in the context of necking up to .458 but rather just building a .375 RUM. Think about it, a low power scope sighted in with solids and another higher power scope with something like the 260gr Accubond and you could have all of your bases covered. Availability of ammo in the event yours gets lost would admittedly be a bit spotty though.

 

[michael458]

I did a 2.5 inch RUM case instead of the full length for a RUM action...... Mine is called the 458 B&M EX. I did 2.5 inches primarily so that I could load full nose projection CEB Raptors, with Talon Tips installed, and work through the 3.6 inch magazine limit......

As a side bonus, one I did not realize at the time, is that you can take any RUM case, cut it to 2.5 inches and form it to .458 or .500, I have both 458 and 500 in 2.5 inches. Now, my 500 MDM is a full length 2.8 inch RUM case, for the RUM action, brass has to be made from 375 RUM brass, I have not ever been able to use anything but 375 RUM to get there. With the 2.5 inch case you can use any RUM, such as 300 RUM .......... This is a pretty big bonus feature, as for many years there has been no 375 RUM brass available.

What is the big deal about using Raptors with Talon Tips? From 125-150 fps added velocity at 50 yard impacts, which is rather substantial. Yes, you can do it as a single load with the longer 2.8 inch case, but that won't work through the magazine, which was my goal.

Now, no doubt, the full length 2.8 inch case would be a big big hammer, no question about it.

My rifle has a 20 inch barrel and at 2.5 inches I run 450 CEB Solids at 2400-2450 fps under 64000 PSI. A matching 420 Raptor with Talon Tip at 2520 fps at 62000 PSI.......... This is plenty, and more than enough to get the job done.

I recently loaded some shelf ammo for the rifle and had a lot of leftover 480 gr CEB Solids from test days, I loaded those to 2325 fps and matched POI with a bunch of leftover 425 gr Lehigh at 2520 fps. Making good use of left over bullets.........

 

[Riflecrank]

Oh, yeah, I forgot to mention michael458, aka Doc M of MIB (McCourry Institute of Ballistics).
He will tell you all the ins and outs of wildcatting the RUM cartridge case.
Be careful about mentioning to him that you might build a simple .375 RUM rifle on your M70 Classic.
He has no use for any rifle of .375 "rat" caliber, except for blowing out the brass to .500 MDM.
As for me, I think the idea of a .375 RUM M70 Classic is a swell idea.

I will add this: A .375 RUM reamer will not clean up a .375 H&H chamber on an M70 Classic unless you set the barrel back.
It has to do with the shorter neck and narrow shoulder on the .375 H&H so that the longer-necked .375 RUM will end up with a deformed, compound neck-shoulder juncture.
However the CIP .375 Weatherby Magnum reamer will clean up a .375 H&H chamber with no set back.
However that might leave a tiny trace of the .375 H&H leade-only throat leading into the .375 Weatherby throat.
I have found that to be no impediment to accuracy or velocity.
Pedal to the metal there!
But it is still a "rat rifle" according to Doc M.

Actually, I prefer the .375 WbyMag to the .375 RUM.
Both will do 2800 fps with a 300-gr bullet in a 26" barrel.
The Weatherby factory load with 300-gr Nosler does about 2740 fps in my 24" rifle: 5000 ft-lbs

With the .375 WbyMag you can fire standard 300-gr factory .375 H&H ammo of 2530 fps MV
and only reduce it to 2430 fps MV from the .375 WbyMag chamber, with excellent accuracy.
It will land 3" lower at 100 yards compared to the .375 WbyMag factory load with 300-gr Nosler Partition. That is how it worked in my "rat rifle."

So the full-power .375 WbyMag load is zeroed for long range, 3.0" high at 100 yards,
and the .375 H&H factory 300-gr ammo is dead-on at 100 yards, same rifle & sight settings,
and recoil is reduced for quick follow-up shots in case a wounded rat charges you.

And .375 H&H factory ammo is more common than .458 WinMag factory ammo wherever you go on this planet, if your ammo is lost in transit.
One planet, two rifles: .458 WinMag and .375 WbyMag
That combo done with same +3.6" magazine boxes on the rifles, same bolt throws, is good backup.

 

[michael458]

OMG @Riflecrank ..............After all that BS and 375 I am about to puke

One planet, two rifles: .458 WinMag and .375 WbyMag

No No No........... One Planet Two Calibers... 458 and 500......... The end........

Good use of 375RUM brass, make 500 MDM or even 458 RUM...... The End.

Good use for 375HH Brass, make 416 Remington, 458 Lott, 470 Capstick, cut and trim 458 Win, even 358 STA, I always keep stock 375HH for those purposes.

The only 375 allowed on the Compound is 375HH Brass and 375 RUM brass and only to make something worthwhile........ That is all its good for............ End of Story.........

 

[Never Been]

358 STA was my first "big gun". I had a Browning A-bolt in 300 Win that I rebarreled with a Douglas. I kind of wish I had it back, but I keep in touch with the guy I sold it to and I still have a soft spot for that chambering.

We'll see how the gun does in the classifieds. Building high dollar right handed rifles is always a safer bet, but I have a lead on a left handed Montana in 300 RUM that I'm thinking seriously about.

Michael, do you have any experience with the ADG .375 Ultra Mag brass? Supposedly they make their brass a little thicker so I wonder if that would complicate the kind of stuff you do or compliment it.

 

[Jim Golden]

Oh, yeah, I forgot to mention michael458, aka Doc M of MIB (McCourry Institute of Ballistics).
He will tell you all the ins and outs of wildcatting the RUM cartridge case.
Be careful about mentioning to him that you might build a simple .375 RUM rifle on your M70 Classic.
He has no use for any rifle of .375 "rat" caliber, except for blowing out the brass to .500 MDM.
As for me, I think the idea of a .375 RUM M70 Classic is a swell idea.

I will add this: A .375 RUM reamer will not clean up a .375 H&H chamber on an M70 Classic unless you set the barrel back.
It has to do with the shorter neck and narrow shoulder on the .375 H&H so that the longer-necked .375 RUM will end up with a deformed, compound neck-shoulder juncture.
However the CIP .375 Weatherby Magnum reamer will clean up a .375 H&H chamber with no set back.
However that might leave a tiny trace of the .375 H&H leade-only throat leading into the .375 Weatherby throat.
I have found that to be no impediment to accuracy or velocity.
Pedal to the metal there!
But it is still a "rat rifle" according to Doc M.View attachment 593325View attachment 593326View attachment 593327View attachment 593328View attachment 593329

Actually, I prefer the .375 WbyMag to the .375 RUM.
Both will do 2800 fps with a 300-gr bullet in a 26" barrel.
The Weatherby factory load with 300-gr Nosler does about 2740 fps in my 24" rifle: 5000 ft-lbs

With the .375 WbyMag you can fire standard 300-gr factory .375 H&H ammo of 2530 fps MV
and only reduce it to 2430 fps MV from the .375 WbyMag chamber, with excellent accuracy.
It will land 3" lower at 100 yards compared to the .375 WbyMag factory load with 300-gr Nosler Partition. That is how it worked in my "rat rifle."

So the full-power .375 WbyMag load is zeroed for long range, 3.0" high at 100 yards,
and the .375 H&H factory 300-gr ammo is dead-on at 100 yards, same rifle & sight settings,
and recoil is reduced for quick follow-up shots in case a wounded rat charges you.

And .375 H&H factory ammo is more common than .458 WinMag factory ammo wherever you go on this planet, if your ammo is lost in transit.
One planet, two rifles: .458 WinMag and .375 WbyMag
That combo done with same +3.6" magazine boxes on the rifles, same bolt throws, is good backup.

I really like .375 Weatherby, and it's what I built my custom Enfield "Hannibal" on. Mine has a 30" barrel, and some guys have said it's too long. But I see lots of pictures on here of guys with suppressed rifles that are longer than mine. I get 2889 ft/s with 300gr bullets. I don't plan to use anything other than 300's in it. I've put about sixty rounds of .375 H&H out of it and they shoot just fine. No trouble hitting the target with them, and they do kick less. Now I just need to take it to Africa

 

[michael458]

A worthy Thread, a Worthy Caliber/Cartridge and it has degenerated into some sort of 375 worship?
How does that work?

Lets be clear, 375 is nothing, zero, notta, is not worth a sentence written on it, it is a waste of my typing skills to even address this and have to type those three numbers together. It is the most universal useless good for not one thing on this planet, that many others will do much better. Universal means this "Not really good at Any One Thing"............... OMG........ I would not give 50 cents for every 375 of any sort ever made in history of the world........Enough...... There are plenty of 375 worship threads here, far more than any other subject, I often refer to this forum as the 375 Worship Forum....... just go there and worship this POS caliber elsewhere, it is making me want to puke ........ I don't go to a 375 worship thread and even speak about anything, I let you that worship at the alter of 375 have at it, with no disturbance on my part....... I expect the same............ Now, out with the 375 crap...........

Rant over............. Now, what were we speaking about, oh yes, something about 458s............ Magic Starts at 458 Caliber....................

 

[Riflecrank]

This is going to make michael458 nauseated, but that too shall pass:

1. Cut off one inch of the breech end of the Winchester M70 Classic .375 H&H barrel that was 24" long.
2. Re-thread for an early CZ 550 Magnum action having no billboard on the left side of action
(had serial number "AHR 50001" and was found at Great Northern Guns in Anchorage, AK circa turn of the century).
3. Chamber with .375 RUM reamer, timing sights to proper alignment, at proper head space.
4. Send to highly skilled engraver to erase the "H&H" and engrave "RUM." Like magic.
5. Cerakote metal.
Voila !
A 23"-barreled .375 RUM !

That is one way to turn a .375 H&H into a .375 RUM: Set the barrel back.

Shoulders only above. Necks and throats not shown, but wouldn't that be interesting ?
Not meant for michael458, of course.

 

[Forrest Halley]

How come you didn't use that engraver on the Lott?

 

[hoytcanon]

I'm assuming a bit more power than necessary and lack of properly headstamped brass is at least partially to blame.

Just have a brass peen made. I made one for my .375 WSM, so that I would have properly stamped brass when travelling abroad where that could possibly be an issue. A friend put me onto it from a custom project he had done.

The process to make the new brass stamping, is to make a 3/8" (.373") rod insert, which I clamp in a vice seated on the anvil bar, sleeve the casing over the rod, landmarks by the primer pocket guide, then whack the peen with a mallet. The brass flows better than you woukd imagine to push out the existing stamping and flow to create the new stamping.

 

[Forrest Halley]

Just have a brass peen made. I made one for my .375 WSM, so that I would have properly stamped brass when travelling abroad where that could possibly be an issue. A friend put me onto it from a custom project he had done.

View attachment 594963

The process to make the new brass stamping, is to make a 3/8" (.373") rod insert, which I clamp in a vice seated on the anvil bar, sleeve the casing over the rod, landmarks by the primer pocket guide, then whack the peen with a mallet. The brass flows better than you woukd imagine to push out the existing stamping and flow to create the new stamping.

This is very cool! What a beat concept. One question: does this tighten the primer pockets at all? You got me thinking about that with the peening of the case head.

 

[hoytcanon]

This is very cool! What a beat concept. One question: does this tighten the primer pockets at all? You got me thinking about that with the peening of the case head.

Not in any significant way, the load distribution from the peening is bearing on the rod which is dead flat with a very slight bevel... the path of least resistance for the brass flow is for the bunt to distribute the brass into the old stamping, if the first "square" blow doesn't fully eradicate the old stamp you can feel the bottom of the new stamp to strike again. If necessary a 320 grit emery rub down will remove the old stamp shadow.