Thoughts on muzzle threads for 30cal

[JohnCZ]

Hi all

I have bought a used 2008 Weatherby Mark V Ultra Lightweight chambered for 300 Weatherby Magnum, all the usual things for these rifles, stainless fluted 26" skinny contour No.2 barrel, fibreglass stock etc. and I have mounted a Leupold VX3HD 3.5-10x40 in Talley fixed rings. Weight is 3.5kg (7.7lbs) without ammo or sling, so a reasonably light mountain rifle for the chambering.

The rifle is in good condition overall and Weatherby states that the rifle left the factory with an unthreaded muzzle, the previous owner had it threaded 1/2UNF (1/2"x20). I am wanting to shoot Barnes TTSX 168gr in the velocity range of a very useable 3250fps which the 300Wby will usually achieve without over doing it.

1. What are the thought on 1/2UNF on a 30 calibre magnum? (0.500" looks thin around a 0.308" hole)

My Mauser M12 Expert (thread 15x1) and Blaser R93 30-06 barrels almost looks like a varmint contours in comparison

2. I have been told in the past that shooting Barnes bullets (or all copper mono bullets) through thin barrels can stretch/swell the barrel near the muzzle. I haven't seen this happen and am wondering if this is a real thing or a internet myth/BS?

I will probably put a brake on it (yes muzzle brakes are loud, however being an ex-Arty Gunner I should be wearing hearing protection to save what hearing I have left) for load development and maybe hunting.

Cheers
John

 

[jthyttin]

What's the barrel diameter at the shoulder of the thread? E.g. Ase-Utra specifies that diameter should be 1.5mm thicker than thread (e.g. 15.5mm for M14x1). Older rule of thumb is that spigot threads can cope with 0.5mm shoulder in a pinch (i.e. 15mm for M14x1) and threads w/o spigot need 1mm shoulder (16mm for M14x1).

Here's AU spec, it's in Finnish but quite self-explanatory:

https://www.aseutra.fi/wp-content/uploads/2020/12/AU_piipun_kierteiden_mitoitus.pdf

 

[JohnCZ]

What's the barrel diameter at the shoulder of the thread? E.g. Ase-Utra specifies that diameter should be 1.5mm thicker than thread (e.g. 15.5mm for M14x1). Older rule of thumb is that spigot threads can cope with 0.5mm shoulder in a pinch (i.e. 15mm for M14x1) and threads w/o spigot need 1mm shoulder (16mm for M14x1).

Here's AU spec, it's in Finnish but quite self-explanatory:

https://www.aseutra.fi/wp-content/uploads/2020/12/AU_piipun_kierteiden_mitoitus.pdf

Interesting, thanks.

 

[Ronin]

Have to say I don’t like doing 1/2 unf on .30 cals

Root depth leaves a fairly thin wall ….

 

[Tim.243]

Hi all

I have bought a used 2008 Weatherby Mark V Ultra Lightweight chambered for 300 Weatherby Magnum, all the usual things for these rifles, stainless fluted 26" skinny contour No.2 barrel, fibreglass stock etc. and I have mounted a Leupold VX3HD 3.5-10x40 in Talley fixed rings. Weight is 3.5kg (7.7lbs) without ammo or sling, so a reasonably light mountain rifle for the chambering.

The rifle is in good condition overall and Weatherby states that the rifle left the factory with an unthreaded muzzle, the previous owner had it threaded 1/2UNF (1/2"x20). I am wanting to shoot Barnes TTSX 168gr in the velocity range of a very useable 3250fps which the 300Wby will usually achieve without over doing it.

1. What are the thought on 1/2UNF on a 30 calibre magnum? (0.500" looks thin around a 0.308" hole)

My Mauser M12 Expert (thread 15x1) and Blaser R93 30-06 barrels almost looks like a varmint contours in comparison

2. I have been told in the past that shooting Barnes bullets (or all copper mono bullets) through thin barrels can stretch/swell the barrel near the muzzle. I haven't seen this happen and am wondering if this is a real thing or a internet myth/BS?

I will probably put a brake on it (yes muzzle brakes are loud, however being an ex-Arty Gunner I should be wearing hearing protection to save what hearing I have left) for load development and maybe hunting.

Cheers
John

I am with Ronin on this one, not that I machine barrels but from years of machining parts you need enough (meat) material
for the part to have enough mechanical strength for it to work properly.
like kfc go large lol

 

[JohnCZ]

This is a 26" tube so it tapers considerably at the muzzle, threads measure 0.500" (12.7mm), between the threads and shoulder measures 0.435" (11.0mm) and the shoulder measures 0.575" (14.6mm).
Threaded section shoulder to crown is 0.535" (13.5mm) long, before buying a brake I might look into having it trimmed to the shoulder, re-crowned and a 9/16x24UNEF thread cut. That is the actual factory threading that Weatherby cut for this model.

Cheers
John

 

[jthyttin]

Them silly 'muricans put 1/2" thread even on 9mm (Luger, obviously much lower pressure).

I'd shoot it with no muzzle device to see if it reaches your goals. I'd be kind of wary to cut a 9/16" (14.3mm or thereabouts) thread on 14.6mm barrel. Leaves very little shoulder. And you presumably don't want to sacrifice barrel length for diameter. Some kind of sleeving could be possible but maybe creates problems of it's own. Then again, if you thread brake on once it's much easier on the shoulder than putting a moderator on and off.

You'd want to do load development, zeroing etc. wtih the same configuration you hunt.

 

[JohnCZ]

Them silly 'muricans put 1/2" thread even on 9mm (Luger, obviously much lower pressure).

I'd shoot it with no muzzle device to see if it reaches your goals. I'd be kind of wary to cut a 9/16" (14.3mm or thereabouts) thread on 14.6mm barrel. Leaves very little shoulder. And you presumably don't want to sacrifice barrel length for diameter. Some kind of sleeving could be possible but maybe creates problems of it's own. Then again, if you thread brake on once it's much easier on the shoulder than putting a moderator on and off.

You'd want to do load development, zeroing etc. wtih the same configuration you hunt.

I did think of trimming to get more barrel diameter, however the fluting starts at 3" (76mm) from muzzle and trimming from 26" to 24" increases the OD to just 0.605" (15.3mm). I couldn't see the velocity loss being a drama between 24" to 26" but lots of Vanguard owners with 24" barrels always say they would have preferred the 26". I'll see what it does without a brake first and go from there and maybe trim it just to clean it up at 25".
As a side note, muzzle brakes only here in Australia, we will all turn into super ninja sniper assassins if we are allowed to use moderators when hunting.
Thanks for your input
John

 

[takbok]

I would just use the rifle as is. I don't think it's a safety issue, more just an something that's annoying.

If you shorten the barrel I don't think that 15.3mm shoulder is optimum for M14x1 thread either, although you don't need a shoulder for some brakes that clamp to time them.

 

[Muir]

The company that builds my suppressors cut my Tikka T-3 Lite 308 in 1/2-28. I raised a question about this and they said that they cut many light weight magnums to that pitch with no problems. All my 30 cal suppressors are 5/8-24 so I purchased an adapter. I have had no problems with the 308.

I don't understand the 1/2-20 thread pitch for a suppressor. It is so coarse. When GunSite ordered the new Scout rifles to be threaded 1/2-28, Steyr instead threaded them all 1/2-20. It looked like a hardware store bolt. The Gunsite people were put out. Their custom shop made me a very fine adapter for my Creedmoor to run it up to 5/8-24 which I lock tite-ed into place. ~Muir

 

[Harry mac]

My own .308 is threaded 1/2" UNF.
It's been that way for over 10 years, with quite a few rounds put through it in that time, and still shoots very well.

 

[JohnCZ]

I would just use the rifle as is. I don't think it's a safety issue, more just an something that's annoying.

If you shorten the barrel I don't think that 15.3mm shoulder is optimum for M14x1 thread either, although you don't need a shoulder for some brakes that clamp to time them.

Shooting as is without a brake, found a Barnes TTSX 168gr load at 3300fps which is 1.5 grains under (Barnes published) maximum load. Recoil is stout in a 3.5kg rifle but controllable, more like a hot 300Win with similar bullet weights. The Barnes 168gr TTSX is a good 30cal bullet weight for Aussie game.

 

[takbok]

Shooting as is without a brake, found a Barnes TTSX 168gr load at 3300fps which is 1.5 grains under (Barnes published) maximum load. Recoil is stout in a 3.5kg rifle but controllable, more like a hot 300Win with similar bullet weights. The Barnes 168gr TTSX is a good 30cal bullet weight for Aussie game.

Good to hear - that's a really mean load. Enjoy!

 

[Foxyboy43]

My own .308 is threaded 1/2" UNF.
It's been that way for over 10 years, with quite a few rounds put through it in that time, and still shoots very well.

Hmmm. My .222 and .308 Remmys are the same plus my Steyr Mannlicher Prohunter 6.5x55 SE which has the slimmest barrel I have seen on a c/f rifle is also 1/2 UNF. All have had a considerable number of rounds through them, shoot really well and never had any issues.

 

[JohnCZ]

Update on 168 Barnes load at 100m - three shots no cooling, first two almost touching third drifts off by an inch. Let cool a minute or two between shots and it will do just over an inch off sticks which is great for an ultralight hunting rifle.
Now just have to get it in front of some game.