.458 muzzle threads

[generalzip]

planning to chop and thread my m70 safari to 19 or 20” and thread for a suppressor. Anyone know the proper thread pitch? My 375 ruger is 11/16x24 and there’s plenty of shoulder to mount my suppressor and it’s doesn’t loosen anyone know the muzzle diameter of this rifle in 458wm at 29”?

I’d imagine 5/8x24 is too small. 3/4x24 may work but not sure if enough shoulder would be left. Would be conveinent if 11/16x24 was the proper thread pitch as that’s what’s on the suppressor for my 375 now so would be an easy swap.

 

[generalzip]

I read the muzzle is 18.4mm, or .7244" diameter @ 24 inches. This leads me to believe it may not even be possible to thread for a suppressor as 3/4" is not even physically possible and 11/16" threads would not leave the require .100" major thread diameter to barrel wall distance required. 5/8x24 likely would not leave enough wall thickness for a round of this pressure and recoil and would likely snap off at some point....hmmm

Really curious if anyone threaded a m70 safari express 458 win mag successfully for a suppressor and if so how was this accomplished. Only idea I could thick of is perhaps threading a muzzle brake on 11/16" threads and torquing it down and rocksett. Then use a ASR or other QD mount on a suppressor to attach the suppressor and verify alignment. Downside is this adds length and weight to the setup. However, this may solve the issue with shoulder possibly, especially if shims are used.

 

[Riflecrank]

What are the outside diameters of the barrel at 20" and 19" from the breech face ?
I have several .458 WIN MAG, one .458 B&M+ and even one .458 Lott rifle (Like Jack Built not SAAMI) that have been threaded 5/8"x24 tpi for muzzle brakes and thread protectors.

Others I have are 11/16"x24tpi in .45-70, .454 Casull, 45LC, 44RM and 357RM.
Meant for suppressor use.

I just measured a barrel from a factory contoured M70 Classic Stainless (.375 H&H) that has same muzzle diameter as you state above. Mine is a JES rebore to .458 WIN MAG.
I was fondling it just now so easiest to reach with calipers.
I think same contour was used on the .458 WIN MAG factory M70 Classics.
20" diameter is 0.775".
19" diameter is 0.790".
18" diameter is 0.805".

11/16" = 0.6875"

Cut it to 19" and thread it 11/16"x24tpi.
Thread protector cap for it does not have to be a "slim line."

I have a Griffin Bushwacker 46 and adapters ("Taper Mount Silencer Mount") for both 5/8"x24tpi and 11/16"x24tpi.
Those adapters screw onto muzzle and work as a "minimalist muzzle brake" (better than porting)
without the suppressor screwed onto them.

I never gave a thought to the can breaking off the end of my barrel. But I will now.
11/16"x24tpi is better.

 

[generalzip]

So I don't have the rifle in hand but I did some research...

I have a Ruger 375 Ruger FTW 22" that works perfectly with my suppressor. 11/16x24. According to the internet the Alaskan model is .77" at the muzzle @20". So stands to reason it's likely around .75" on my 22". I never felt there was not enough shoulder. The can actually stays very tight and is one of the few rifles I've ever owned where a DT does not back off when shooting even 10+ rounds.

Supposedly the 24" Win M70 Safari Express from the only article I found online is 18.4mm or 0.7244in at the muzzle @24". Lilja (god bless their soul) has listed all factory profiles and even the taper rate of the Winchester Safari. 0.012" per inch of barrel.

https://riflebarrels.com/factory-contours/

Therefore, we can surmise at 20" the barrel is roughly 0.768 @20" and 0.774" @ 19.5". Based on the fact my 11/16" threads work well on my .75" Ruger in a high pressure high recoil rifle, it stands to reason that a 0.768 or 0.774" muzzle diameter should work fine on the 458 win mag so long as you chop it to at most 21". I think I'm going to cut mine to 19.5" as half an inch makes no difference in velocity and with a suppressor should swing like a 26" barrel. I've hears because Winchester uses the same barrel profile for all Safari rifles, the 375 are front heavy @24" and the 458 are rear heavy at 24". Therefore chopping to 19.5" and adding a suppressor should balance things out nicely and will length wise be similar to a 27" barrel which is long, but not totally unwieldy especially considering the benefits of the suppressor with adding weight, reducing recoil, and reducing sound.

 

[generalzip]

What are the outside diameters of the barrel at 20" and 19" from the breech face ?
I have several .458 WIN MAG, one .458 B&M+ and even one .458 Lott rifle (Like Jack Built not SAAMI) that have been threaded 5/8"x24 tpi for muzzle brakes and thread protectors.

Others I have are 11/16"x24tpi in .45-70, .454 Casull, 45LC, 44RM and 357RM.
Meant for suppressor use.

I just measured a barrel from a factory contoured M70 Classic Stainless (.375 H&H) that has same muzzle diameter as you state above. Mine is a JES rebore to .458 WIN MAG.
I was fondling it just now so easiest to reach with calipers.
I think same contour was used on the .458 WIN MAG factory M70 Classics.
20" diameter is 0.775".
19" diameter is 0.790".
18" diameter is 0.805".

11/16" = 0.6875"

Cut it to 19" and thread it 11/16"x24tpi.
Thread protector cap for it does not have to be a "slim line."

I have a Griffin Bushwacker 46 and adapters ("Taper Mount Silencer Mount") for both 5/8"x24tpi and 11/16"x24tpi.
Those adapters screw onto muzzle and work as a "minimalist muzzle brake" (better than porting)
without the suppressor screwed onto them.

I never gave a thought to the can breaking off the end of my barrel. But I will now.
11/16"x24tpi is better.

Thank you very much for this info!

I would not be worried about the shoulder diameter on a fired rifle. If you've shot it a bunch and never had a baffle strike you're good to go. If you shoot it and it's not coming loose then you're golden. Nothing to worry about.

The wall thickness of the barrel itself is way more of a concern in my opinion. 458s recoil HARD. And that can on the end is heavy. That's a lot of force and moment being applied to those little threads. Having the can tight helps a lot to spread the load along the shoulder. But if your can come loose, even a tiny bit, that energy get imparted on the thread/shoulder junction. Enough shots like that will fatigue the metal significantly and introduce dislocations in the lattice structure of the steel. Over time it will become brittle and could catastrophically fail. Otherwise, it could simply plastically deform and cause baffle strikes. This is why its important to tighten the can down. I'd even recommend tightening with a wrench snug before use when you're operating on the edge like this.

For a muzzle brake I wouldn't worry whatsoever. They are light, don't capture as much gas, and are typically torqued down tight and never come loose. You won't have any issues even with 5/8". For a suppressor, I'd think you're on the edge. 458 socoms use 5/8" threads sometimes FWIW, but mine was a 11/16". Not sure if anyone has had issues with them or not.

Thanks again for the reply and figures you posted. Very helpful and hopefully useful for someone else reaching a similar project.