i just received a 58 cal rifle 42 inch green mt barrel, flint the touch hole was drilled the correct place for the pan but it ended up drilled into the preach plug,there is 1/2 inch of plug on tang side of hole,,plug was removed and the plug filed down to the touch hole,so it will fire,,,,,i was told to shoot lite loads,,,what would be safe loads in this barrel,,,was told 80 gr 2f is ok,if so what about 3f??? this would be shooting patched round balls, :thumbsup: THANKS just want to be safe, :hatsoff:
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- Thread starter brubincam
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You should have no problems with any reasonable load. Many original guns had plugs of only 3/8". What you describe was not at all uncommon, and still isn't. This is often done in order for the lock fence to be even with the end of the barrel at the breech. A half inch of plug thread is more than enough for safety.
I'm making a few assumptions here so take it for what it's worth.
First, I'm assuming the thread is a 3/4-16 UNF
Second, I'm assuming the material around the threaded hole is about than 1 1/8 across.
With threaded fasteners, the length of engagement, or nut height is such that the bolt will break before the threads shear or strip when under load. (In other words, threads of this length can take more load.)
Looking at the American Standard for the Regular nut height for a standard 3/4-16 thread says it should be .455-.524. Notice that your 1/2 of threads meets this criteria.
The Minor Diameter of this thread is approx .672.
This .672 diameter, when used in a steel with an ultimate tensile strength of 57,000 PSI (12L14 material, common to BP rifle barrels) gives a failure strength of 20,216.375 pounds.
For a 3/4 diameter thread to be loaded to this amount, the gas pressure in the gun would have to be greater than 45760 PSI. Using a safety factor of 4 (life/death), this would limit the chamber pressure to 11,440 PSI.
Looking at the Lyman BP Loading book under .58 caliber guns they don't list any FFFg loads however they do say that 140 grains of GOEX FFg creates about 9,100 PSI and 140 grains of Pyrodex Select gives about 8,500 PSI when loaded under a .570 diameter round ball.
It's only when shooting the heavy Minies like the 510 grain Lyman #575213 with Select or GOEX FFg that chamber pressures get into the 11,000+ range.
Based on all of this and using the 15% reduction number that's always tossed around when talking about FFFg I would say you should be safe using up to 120 grains of FFFg powder under a patched round ball.
First, I'm assuming the thread is a 3/4-16 UNF
Second, I'm assuming the material around the threaded hole is about than 1 1/8 across.
With threaded fasteners, the length of engagement, or nut height is such that the bolt will break before the threads shear or strip when under load. (In other words, threads of this length can take more load.)
Looking at the American Standard for the Regular nut height for a standard 3/4-16 thread says it should be .455-.524. Notice that your 1/2 of threads meets this criteria.
The Minor Diameter of this thread is approx .672.
This .672 diameter, when used in a steel with an ultimate tensile strength of 57,000 PSI (12L14 material, common to BP rifle barrels) gives a failure strength of 20,216.375 pounds.
For a 3/4 diameter thread to be loaded to this amount, the gas pressure in the gun would have to be greater than 45760 PSI. Using a safety factor of 4 (life/death), this would limit the chamber pressure to 11,440 PSI.
Looking at the Lyman BP Loading book under .58 caliber guns they don't list any FFFg loads however they do say that 140 grains of GOEX FFg creates about 9,100 PSI and 140 grains of Pyrodex Select gives about 8,500 PSI when loaded under a .570 diameter round ball.
It's only when shooting the heavy Minies like the 510 grain Lyman #575213 with Select or GOEX FFg that chamber pressures get into the 11,000+ range.
Based on all of this and using the 15% reduction number that's always tossed around when talking about FFFg I would say you should be safe using up to 120 grains of FFFg powder under a patched round ball.
