What to do with another Siamese Mauser

BlueFlyer · Jul 10, 2026

When I bought my first Siamese Mauser, it arrived without an extractor.
In my searching for an extractor I found this complete action for AU$200, how could I resist! I then managed to modify another extractor to fit the 416WSM, so I had a spare Siamese Mauser action - what to do?
The action had previously been modified for 45/70, the bolt face opened to .610" and the RH feed rail relieved to allow the bigger rim to feed. I have a 45/70 on a Martini Enfield so don't need another.
With the modifications done to the action all the WSMs are out, but it is perfect for any 348W based cartridges. I have always been interested in the 333 Jeffery, and it would fill a gap between my 280AI and 9.3X64B.
I got PTG to grind up a set of 338-348Ackley Improved reamers.
Sprinter #3 contour 25" long barrel
Rodger Vardy walnut blank - machined to the same contour as my 416WSM.
Now I just have to get all the bits together.

Sarg · Jul 10, 2026

I found a set of .33 WCF Winchester dies in a box of dies I bought & thought it might be a cool build on a bolt or single shot ?

Oh should have read that better, your already doing a .338 on the .348Win case ?

Ontario Hunter · Jul 10, 2026

40-60 Marlin (aka 40-65 Winchester). 45-70 cases can be necked down to 40 caliber. Doesn't somebody make a 40 caliber bullet for big bore or handgun? Finding a reamer might be tricky. I'm sure someone could make a 40 caliber barrel. It would be a helluva challenging project but the end product might be a 404 in disguise. Maybe even better. Something between 404 and 375. Perhaps too close to 405 WCF to really make a difference? I actually have an 1881 Marlin in 40-60 and an Ideal tong tool for reloading. The tool is 40-65 and it casts a slug that's a bit too small diameter. Accuracy not good. I should slug that barrel and have a proper bullet mold made. Yeah, I'll do that this winter. It's a gun designed to kill buffalo and Plains Indians. Wonder what point creep is needed for drawing a tag these days?

BlueFlyer · Jul 10, 2026

Sarg said:
I found a set of .33 WCF Winchester dies in a box of dies I bought & thought it might be a cool build on a bolt or single shot ?

The .33WCF would work perfectly in a Siamese mauser, the .338-348AI is basically a rimmed version of the 338WSM, so a little more poke that the 33WCF. I hope to be able to duplicate the 333Jeffery ballistics.

Sarg · Jul 10, 2026

Ontario Hunter said:
40-60 Marlin (aka 40-65 Winchester). 45-70 cases can be necked down to 40 caliber. Doesn't somebody make a 40 caliber bullet for big bore or handgun? Finding a reamer might be tricky. I'm sure someone could make a 40 caliber barrel. It would be a helluva challenging project but the end product might be a 404 in disguise. Maybe even better. Something between 404 and 375. Perhaps too close to 405 WCF to really make a difference? I actually have an 1881 Marlin in 40-60 and an Ideal tong tool for reloading. The tool is 40-65 and it casts a slug that's a bit too small diameter. Accuracy not good. I should slug that barrel and have a proper bullet mold made. Yeah, I'll do that this winter. It's a gun designed to kill buffalo and Plains Indians. Wonder what point creep is needed for drawing a tag these days?

If your asking about drawing a Tag for a Plains Indian, I’m pretty sure the are off license & protected species in the US ?

Not sure on Canada but I suspect similar or even higher status ?

BlueFlyer · Jul 11, 2026

I clocked up the first 150mm of barrel bore to be concentric with the lathe axis. then went around to the muzzle end with the indicator found the point of maximum runout. No barrel is perfectly straight so you have to work with what you get. The best setup is to have the point of maximum runout at the muzzle on the top side. Then the barrel is shooting up rather than left, right or down. Then back at the breach end put a pop mark so you know where to line the barrel up to the scope mount screw holes (top of the action)
After cutting the threads, this is where the pop mark finished relative to the action mount screw hole.

It was about 1/5 of a turn out. To get it lined up I needed to take 0.36mm off the barrel shoulder (the thread pitch is 14tpi, 0.36 = 25.4mm divided by 14 X .20).
This is where I ended up, with the final rotational alignment for when I do the final torque on the barrel.

Sarg · Jul 11, 2026

BlueFlyer said:
I clocked up the first 150mm of barrel bore to be concentric with the lathe axis. then went around to the muzzle end with the indicator found the point of maximum runout. No barrel is perfectly straight so you have to work with what you get. The best setup is to have the point of maximum runout at the muzzle on the top side. Then the barrel is shooting up rather than left, right or down. Then back at the breach end put a pop mark so you know where to line the barrel up to the scope mount screw holes (top of the action)
After cutting the threads, this is where the pop mark finished relative to the action mount screw hole.
View attachment 776084
It was about 1/5 of a turn out. To get it lined up I needed to take 0.36mm off the barrel shoulder (the thread pitch is 14tpi, 0.36 = 25.4mm divided by 14 X .20).
This is where I ended up, with the final rotational alignment for when I do the final torque on the barrel.
View attachment 776085

What are you using as the protection on the barrel there bud ?

I left slight jaw marks on my .458 Brno last week when moving the front sight back.

Is it rubber O ring/donut ?

BlueFlyer · Jul 11, 2026

Sarg said:
Is it rubber O ring/donut ?

A ring of 3mm alloy TIG wire. Provides a point contact area which allows the barrel to pivot axially without marking the barrel and get the bore lined up. Others have used thick copper wire, it just needs to be softer than the barrel.
At the other end, any tube that can be crushed by the spider screws will do. Using a piece of old steel broom handle for this setup!

BlueFlyer · Monday at 1:45 AM

Chamber and extractor slot are cut and barrel fully fitted and torqued.
I also mounted the scope to see if it cleared the barrel and bolt handle = all good, it fully functions.
Not in love with the bolt handle, but it is functional.

Ontario Hunter · Monday at 2:16 AM

Looks fine to me. Will you be eliminating the screw holes for rear sight? What safety design? Same as the other project?

Velo Dog · Monday at 2:27 AM

Perhaps a Professional Gunsmith could use the Siamese action to build a reasonable Pre-War style hunting Mauser, more or less after the fashion of the somewhat rare and very expensive Slant Box Rigby .303 hunting Mauser.
I had a .303 built on one many years ago but the barrel was way too thick plus the stock was also way too thick and awkward.
At the time I was so broke that I could not pay several hundred or more toward having a proper Gunsmith put it on a diet.
So I sold it.

BlueFlyer · Monday at 3:01 AM

Ontario Hunter said:
Will you be eliminating the screw holes for rear sight? What safety design? Same as the other project?

Yes, I will be filling the rear sight screwholes with screws and filing them down to the surface.
Same safety as the 416WSM, as it will clear the scope.
I am going to leave the barrel slick - no sights as this calibre needs a scope. But I think it will get a barrel band front sling mount.
I need to make the reloading dies next, so I can start to form the brass. It is just neck down to 338 and then fire form. I have run some 416-348 Ackley Improved cartridges from the Martini Enfield through the action and they fed without a problem.

BlueFlyer · Monday at 3:14 AM

Velo Dog said:
use the Siamese action to build a reasonable Pre-War style hunting Mauser, more or less after the fashion of the somewhat rare and very expensive Slant Box Rigby .303 hunting Mauser.

Frank de Haas thought that the 30-40Krag was more suitable than the 303British in the Siamese Mauser, but I am sure that you could get either to work. Unfortunately this action had previously been openned up for 45/70 so it was not suitable for 303 British.

Tintin · Monday at 3:36 AM

nice

for number 3,

a .375 2 1/2” Nitro Express would be cool.

did Cam Hatcher do the stock shaping?

BlueFlyer · Monday at 3:47 AM

Tintin said:
did Cam Hatcher do the stock shaping?

Yes, he has Geoff Slee's original pattern. I don't know of anyone else with a Siamese Mauser pattern in Australia. The Siamese Mauser is not exactly mainstream.

Grumpy gumpy · Monday at 5:18 PM

BlueFlyer said:
Yes, he has Geoff Slee's original pattern. I don't know of anyone else with a Siamese Mauser pattern in Australia. The Siamese Mauser is not exactly mainstream.

I’ve used several of Cam,s stocks, and a couple of Geoff’s from back when he was alive. Sure beats carving out one from a lump of wood, though I’ve still got a couple of blanks and a 6"x2"x8' plank in the shed that are aging .
Are you going to buy a barrel sling fitting or make one. I made the one for my 404 as I didn’t like the look of the pre made ones
Gumpy

BlueFlyer · Monday at 9:33 PM

Grumpy gumpy said:
Sure beats carving out one from a lump of wood,

Totally agree, that getting the stock rough machined is good value for money, as long as you can find a pattern you are happy with.

Grumpy gumpy said:
Are you going to buy a barrel sling fitting or make one

Going to make the barrel band sling mount as they don't take too long on the mill and rotary table. I now prefer the traditional lace on slings as they are very easy to make and are absolutely silent and functional.

Bob Nelson 35Whelen · Wednesday at 8:22 PM

BlueFlyer said:
When I bought my first Siamese Mauser, it arrived without an extractor.
In my searching for an extractor I found this complete action for AU$200, how could I resist! I then managed to modify another extractor to fit the 416WSM, so I had a spare Siamese Mauser action - what to do?
The action had previously been modified for 45/70, the bolt face opened to .610" and the RH feed rail relieved to allow the bigger rim to feed. I have a 45/70 on a Martini Enfield so don't need another.
With the modifications done to the action all the WSMs are out, but it is perfect for any 348W based cartridges. I have always been interested in the 333 Jeffery, and it would fill a gap between my 280AI and 9.3X64B.
I got PTG to grind up a set of 338-348Ackley Improved reamers.
Sprinter #3 contour 25" long barrel
Rodger Vardy walnut blank - machined to the same contour as my 416WSM.
Now I just have to get all the bits together.
View attachment 776027

@BlueFlyer
As you already have a 45-70 and the action is fine for the 348 win why not go big or go home.
450 Alaskan or 50 Alaskan both based on the 348 case and real heavy hitters especially the 50.
Bob

BlueFlyer · Thursday at 4:42 AM

Bob Nelson 35Whelen said:
450 Alaskan or 50 Alaskan both based on the 348 case and real heavy hitters

Yes, they did get considered, but I believe the 338-348Ackley Improved will get more use than the Alaskans would.

Grumpy gumpy · Thursday at 5:52 PM

BlueFlyer said:
Yes, they did get considered, but I believe the 338-348Ackley Improved will get more use than the Alaskans would.

Yes, but you will need all the firepower you can get if you’re charged but one of those pesky rabbits, just remember those huge nashing teeth…that evil stare they give just before charging….the bones of their victims that lay scattered across their killing field….the way they……
Sorry …I’ll take my tablets now…
Gumpy

What to do with another Siamese Mauser

BlueFlyer

Sarg

Ontario Hunter

BlueFlyer

Sarg

BlueFlyer

Sarg

BlueFlyer

BlueFlyer

Ontario Hunter

Velo Dog

BlueFlyer

BlueFlyer

Tintin

BlueFlyer

Grumpy gumpy

BlueFlyer

Bob Nelson 35Whelen

BlueFlyer

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