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Siamese Mauser Action

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19 January 2015, 08:49
Siamese Mauser Action
I am looking to buy a Siamese Mauser Action, bolt and trigger, complete with the magazine and bottom plate. I have a couple of questions about re-barreling one of these. First Would a 450 Marlin work? I know they have been made into 45-70's. I know the 30-40 Craig and the 303 Britt. both work as well. What else is there in between. Say 338 and up? Ever since I first read about these actions I have wanted to build a Thumper on one.
19 January 2015, 17:04
the marlin cartridge that you question would be feasible in a standard mauser. the " unique domain" of the Siamese is the ability to use rimmed cartridges. therefore the 348 Winchester, 303 brit, 444 marlin, 45/70 and all of the various wildcats that use those cartridges are viable to some degree. I have actually rebarreled them to 348 Winchester, 375/348. and 450 Alaskan all for the same client.
19 January 2015, 22:09
My mistake, for some reason I was thinking that the 450 was the same as the 45-70 except for brass thickness now I remember the wide belt that it sits on. or head spaces on. Also I remember back when Virgin Valley Custom was in business next door to Bullberry. They had a whole line of their own cartridges based on the 45-70. I also have read about .45 Basic. This is modern full length .45 brass equivalent to the 45-120 3 1/2. I think something the same OAL as 30-06 in say .350, .366, or .375 and maybe even .400 or .416. It all sounds like a lot of fun for me.
19 January 2015, 22:40
What Max said.
No point in using a Siamese for a belted cartridge; save those for the big rimmed stuff. Just use a standard Mauser.
20 January 2015, 09:23
I have two, one in 45-70, and the other in 30-40 Krag. I've seen a couple in 7.62x54R as well.
21 January 2015, 02:58
Idaho Sharpshooter
A 45-90 will fit and feed with a little fussing by a good gunsmith.

The 45-120 is actually the 3 1/4" case, and they are usually available from Buffalo Arms.

It would also make a really neat 50-90 or perhaps the shorter 50-95 as used in the M1876 Winchester lever rifles.

I often wish I had one...
25 January 2015, 18:04
I have a Siamese in 375/348 Improved.Very similar to a long necked WSM case. With 270 gr bullets mine developes ballistics very close to the 375 H&H.
26 January 2015, 21:31
O.K. Mine is a .35/.348 rebore by Mr. Ackley (well, the shop) hisself. Per Powley the performance approaches .358 Norma... Kicks like it too.

Actions spring is 93 mauser size??? 98 don't fit. Learned that by trial and error.

.348 was made on the 50/70 rim. Larger than .45/70. As suggested, you go read about the single shot buffalo guns and your only limit is length. I thought about .45/90 but never got there.

There is a .375/.348 Imp that rivals the factory .375 H&H. H&H did not load hot to keep pressure down in HOT parts of the world. Etc.

Mike Bellm ( did a line of 'cats on the .444 case, .444 shell holder and .308 dies... There is some variation... Luck.
09 March 2015, 06:00
D Humbarger
Don't forget to consider the 38-56.

Doug Humbarger
NRA Life member
Tonkin Gulf Yacht Club 72'73.
Yankee Station

Try to look unimportant. Your enemy might be low on ammo.
09 March 2015, 06:53
Will the .500 Nitro Express 3" work?
20 March 2015, 18:47
its about a 3" max oal cartridge length action ..

(sigh) a 45/120 is right at FOUR inches long when loaded with big game bullets (woodleighs) ..

a 500NE 3" is about 3.8" .. most 416-600 caliber heavy hunting bullets are .800 from end of case to nose.

use this for RIMMED carts only -- 30-40, 303, 348, 45/70 .. a 45/90 is PUSHING the max length ..

and no, it's not just chop it up and make it longer, due to slanted magazine ....

within the rounds that fit it, this is a EXCELLENT action... trying to exceed that envelope, unlike most other actions, it VERY hard and STRONGLY advised against...


opinions vary band of bubbas and STC hunting Club

Information on Ammoguide about
the416AR, 458AR, 470AR, 500AR
What is an AR round? Case Drawings 416-458-470AR and 500AR.
20 March 2015, 19:21
I have a different idea for your project. Years ago I read about someone who had converted a couple of those into a .25 Krag with classic American styling and a .256 Jeffreys with British styling. I've always thought those two chamberings would suit the action very well. Nothing wrong with the big bores though.
06 May 2015, 20:26
Remarks made me think. The .405 WCF is a blown out .30/40 Krag case or .303 Brit. Slightly longer. Big thumper in medium pressures, circa 45K cup. Probably slightly stronger brass than .45/70 or .348. I wouldn't "hot load" any of these. I have seen it suggested that it should be considered in the strength of a early 93 Mauser... I am not that conservative, especially since these thumpers are not going to be fired all that much.

#2). The .30/40 Krag, full length Improved case by Mr. Ackley and per Mr. Ackley necked to .25 has exactly the same capacity as the .257 Roberts Ackely Improved. .257 Ackley Imp rivals the .25/'06 with all but the heaviest bullets. You want a long range rifle in 6mm, .25, or 6.5mm ... Not the biggest but that means better barrel life... !! Enjoy.
13 May 2015, 17:23
The 450 Marlin was designed as a way to safely hot rod a 45/70 type cartridge without the risk of being used in a weaker 45/70 action so if the action is a strong one you can load 45/70 to 450 Marlin specs. I have 2 Siamese Mausers in 45/70 & the are fine fifles.

"If a law is unjust, a man is not only right to disobey it, he is obligated to do so." - Thomas Jefferson
23 November 2016, 05:37

Why no a 50/110 Winchester express?
24 November 2016, 05:21
Idaho Sharpshooter
that would work too...