doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 10 bore Reproof Pressures

My question may be answered more easily by our brethren in the U.K. but I was wanting to know if a 10 bore chambered for 3 1/4" is proofed at the same pressure as a 3 1/2" magnum ten??
Thanks, standing by.
Terry

Terry, if no one on the board is able to answer your question drop a note to the Birmingham proof house. They've been very polite with me answering questions and I'm sure will be with you also.

Hi Joe, thanks, I was going to go that route as Plan B. Hope all goes well on your expedition. We are trying to improve the weather...

Dont have that info to hand but I will check on my list at work tommorw and report back .

Thanks Gunman, I am considering rechambering a heavy 10 that is already out of original black powder proof due to bore size but has lots of barrel wall thickness and a heavy action but currently appears to have a chamber measurement somewhere between 2 5/8" and 2 7/8". Chamber is also hard to measure as it appears to be slighty undersize and my chamber gauge seems to be stopping short of the forcing cones.I may take/send the gun for nitro-proofing eventually and wondered if the 3 1/4" chambering would be done at a lesser pressure??

My understanding is that proof charges now are 25% higher than the maximum pressure developed by any load available for the chamber length/pressure.

There are two kinds of prof - Standard and Superior.

Superior is for magnum loads, Standard for non-magnum.

So, a 12-bore 70mm Standard Nitro Proof will be for non magnum loads.

A 12-bore 70mm Superior Nitro Proof is for magnum loads.

For a 10 bore, rules will be equivalent.

Hi Dig, Thanks for the input. I would assume that there would only be one level of magnum proof for a 3 1/2" 10 as there is modern ammunition available which is likely loaded to maximum pressures. The question becomes whether there is an option of standard or magnum proof for a 3 1/4" chambered gun. The plot thickens....

Terry, I must be missing something. Are you talking about rechambering the gun, since you state the current chamber length is shorter than that? If so, why would you rechamber at 3 1/4", since 10ga shells are either longer or shorter than that? It's interesting to note that the SAAMI service pressure standard for both the 3 1/2" and 2 7/8" 10ga shells is 11,000 psi.

I can't speak to the English proof rules, but SAAMI pressure standards for 2 3/4" and 3" shells are the same in 12 and 20 gauge, and for 2 7/8" and 3 1/2" 10 gauges. Because of this, it would seem to me that the same proof loads would be used for the longer chambered guns as the shorter one. Am I mistaken in this?














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For some reason I got confused and have the pressures for 8 bores . All bores are proofed at the same pressure for that bore irispective of chamber lengths for instance 12 bore 2%1/2 " and 2&3/4 " are proofed at 950 bar for a max sevice load of 740 bar all 3" are now classed as magnum or "superior" and will be proofed at 1320 bar. 8 bores if new would be proofed at that ,however as they are considered in the UK as an obsolete caliber ans as there is no commercialy loaded cartridges available the Birmingham poorf house will re proof at 850/900 bar for a maximum service pressure of 680 bar .This is because most 8's would not stand the higher proof pressures ,not so much the barrels but the old actions are not strong enough to withstand the back pressre.
As 10 bore cratriges are available , 10's 3inch plus would be proofed at 1320 bar .
Please note that as they CIP have once again changed the metod of measuring the proof pressures it is not possible to make a direct traslation to other systems of measurement .