Understanding Rifle Proof Pressures

[Hunter-Habib]

I saw a 7x57 mm Mauser today - The " Alpine " Model of the " Fire Arms Co. England " . What struck me as unusual , is that the rifle is proofed for a pressure of only 18.5 Tons Per Square Inch . Unless I'm very wrong , this amounts to only 37000 PSI or 2551 BAR ( I tried to do an online conversion ) . Isn't this very low for most modern 7x57 mm Mauser ammunition ?

I'd appreciate if anybody here could shed any light on this topic . Here are some photos for clarification .

 

[PHOENIX PHIL]

I'd want to know the date of manufacture of the action. Early 7x57's did not have the strength of today's actions. What I've read about this manufacturer is they sporterized Mauser's in various calibers in the 50's-70's. The original rifles were confiscate presumably from the battle fields. This could easily mean you have quite an old action.

I guess it is also possible that pressure was in terms of an English or long ton which is actually 2240lbs not 2000lbs. That increases the number to 41440 PSI. But I've no idea if that is true or not.

 

[Hunter-Habib]

I'd want to know the date of manufacture of the action. Early 7x57's did not have the strength of today's actions. What I've read about this manufacturer is they sporterized Mauser's in various calibers in the 50's-70's. The original rifles were confiscate presumably from the battle fields. This could easily mean you have quite an old action.

I guess it is also possible that pressure was in terms of an English or long ton which is actually 2240lbs not 2000lbs. That increases the number to 41440 PSI. But I've no idea if that is true or not.

Very good point . Now that I think about it , the action is a DWM 1908 military surplus Mauser 98 action . The rifle itself was built in 1965 , so it fits right within your estimated time frame .

 

[Bob Nelson 35Whelen]

I saw a 7x57 mm Mauser today - The " Alpine " Model of the " Fire Arms Co. England " . What struck me as unusual , is that the rifle is proofed for a pressure of only 18.5 Tons Per Square Inch . Unless I'm very wrong , this amounts to only 37000 PSI or 2551 BAR ( I tried to do an online conversion ) . Isn't this very low for most modern 7x57 mm Mauser ammunition ?

I'd appreciate if anybody here could shed any light on this topic . Here are some photos for clarification .
View attachment 413874View attachment 413873View attachment 413872

@Hunter Habib
When the No4 SMLE is converted to 7.62x51 it is proof tested to 20 tons from memory and this is marked on the bolt head with 20t.
I think the British measure bolt thrust not chamber pressures but I may be wrong. 20 ton is well under the 80 odd thousand PSI chamber pressures proof loads .
Bob

 

[Hunter-Habib]

@Hunter Habib
When the No4 SMLE is converted to 7.62x51 it is proof tested to 20 tons from memory and this is marked on the bolt head with 20t.
I think the British measure bolt thrust not chamber pressures but I may be wrong. 20 ton is well under the 80 odd thousand PSI chamber pressures proof loads .
Bob

Thanks for suggesting this possibility , Bob .

 

[Shootist43]

Hunter-Habib, have you tried doing a search on what a British marked 18.5 T converts to in PSI? There are differences in the systems of measurement used by various countries. Once you get that sorted out you may wind up needing to convert CUP pressures to PSI.

 

[425SCHADE]

Not an answer per se, but I have a barrel here removed from a Parker Hale (commercial M98 action) in 7mm Rem Mag stamped 19.5 tons. If the 7mm Rem runs around the 62,000 PSI mark a quick reverse calc. gets you 58,820 PSI for your 18.5 tons.

 

[425SCHADE]

I needed to know, a quick search turned up this info referring to the British proofing system ( here in regards to Lee Enfield's)


"18.5 tons or tsi (45,000 cup or 49,000 psi U.S. measurement) is the normal operating chamber pressure and "NOT" the pressure the rifle is proofed at, the Enfield was proofed with two proof cartridges at a pressure between 23 to 25 tons or tsi. One "DRY" proof round was used to proof the barrel and one "OILED" proof round was used to proof the bolt and receiver. The oiled proof test round was used to seat the locking lugs and bolt head, after proofing the Enfeild rifle was checked with a .067 headspace gage. If the bolt closed on the .067 gage the rifle failed proof testing due to excessive bolt lug setback. Please note that any oil or grease in the chamber or on the cartridge case will cause twice the amount of bolt thrust to be delivered to the bolt face. The oiled proof round also simulates combat conditions like firing in the rain with wet ammunition or water in the chamber and bore."

 

[Bob Nelson 35Whelen]

Hunter-Habib, have you tried doing a search on what a British marked 18.5 T converts to in PSI? There are differences in the systems of measurement used by various countries. Once you get that sorted out you may wind up needing to convert CUP pressures to PSI.

@Shootist43
Art trying to convert PSI to cup is fought with danger. The only conversion I have come across is 52,000 cup is close to 62,000 PSI.
They don't convert well.
Bob

 

[Hunter-Habib]

Thank you everybody ( @PHOENIX PHIL , @Shootist43 , @Bob Nelson 35Whelen & @425SCHADE ) for your very educational insights . 58820 PSI sounds more normal for a 7x57 mm Mauser than 38000 PSI .

 

[mark-hunter]

I still have doubts. Uk follows CIP standard, and this 18.5 tsi, still seams a bit low to me.
@425SCHADE
Could you provide some links or references, for yours above?

 

[Hunter-Habib]

I still have doubts. Uk follows CIP standard, and this 18.5 tsi, still seams a bit low to me.
@425SCHADE
Could you provide some links or references, for yours above?

Now that I just did the calculation again with English Tons . 18.5 English Tons Per Square Inch amounts to 41440 Pounds Per Square Inch . That's still quite low for 7x57 mm Mauser .

 

[mark-hunter]

Standards for 7x57:

Max CIP 56.565 PSI
Max SAAMI 51.000 PSI
Max CUP 46.000 CUP.

Brits should be under CIP.
We need to decode stamps and proof marks on that rifle.

One possible reccomended action may be to send a question by email to birmingham and london proof houses.

 

[Shootist43]

Here is a QuickLoad simulation for a 7 x 57 Mauser.

 

[jwp475]

@Shootist43
Art trying to convert PSI to cup is fought with danger. The only conversion I have come across is 52,000 cup is close to 62,000 PSI.
They don't convert well.
Bob

The formula PSI = -17,902 + 1.516 x CUP is useful if you have data published in CUP, and want to compare with data published in PSI, Or, if you're like me, and have instrumented one or more rifles with strain gauges, you might want to use published CUP data to set an approximate limit for your loads in PSI.

Copper units of pressure - Wikipedia

en.m.wikipedia.org