Breech design question.

[Cat Whisperer]

Don't make the assumption that the tensile strength is adequate even if it excedes the expected pressures.

It is the repetitive stretching/relaxing that dictates the nature of the steel be adequate to prevent work hardening.  Mild steels (1018 and others) are great for this as are some alloys as 4100 series.

Many of the great-machining steels, as the leaded and stressproof are NOT good in this respect.

[GGaskill]

One more thought on the flat 1" plate and 4 screws design.  It is a good idea to examine the design in the light of a first degree failure, such as one bolt breaking or simply getting loose enough not to carry its load.  How is the additional load going to affect the remaining bolts.  With only three bolts holding, the two closest ones will have to shoulder the load of the broken one, so they will have their own 3925 lbs of tension plus half of the broken bolt's 3925 lbs (a total of 5888 lbs.)  This is now 85% of the nominal strength of the bolt which doesn't leave much for a safety factor.  It will also cause them to stretch more with the possibility of a positive feedback situation causing total failure because of a greater area being exposed to chamber pressure.

All of these numbers are based on the original 3/8-16 by 100 ksi postulated bolts.  Stronger ones would have better numbers.

[Bornsouthern34]

Round stock with a flat spot would probably be the simplest design. By not boring all the way through, the barrel in essence maintains a bit more strength. A simple set screw would work to hold it in place. If you only plan on removing it to clean on occasions it seems like the most expediant design so far. The breech plug could serve as a way to help hold the bar or just sit there for looks.

[Double D]

Take a look at Frank De Haas' vault lock single shot rifle action for some ideas.

[Victor3]

One more thought on the flat 1" plate and 4 screws design.  It is a good idea to examine the design in the light of a first degree failure, such as one bolt breaking or simply getting loose enough not to carry its load.  How is the additional load going to affect the remaining bolts.  With only three bolts holding, the two closest ones will have to shoulder the load of the broken one, so they will have their own 3925 lbs of tension plus half of the broken bolt's 3925 lbs (a total of 5888 lbs.)  This is now 85% of the nominal strength of the bolt which doesn't leave much for a safety factor.  It will also cause them to stretch more with the possibility of a positive feedback situation causing total failure because of a greater area being exposed to chamber pressure.

All of these numbers are based on the original 3/8-16 by 100 ksi postulated bolts.  Stronger ones would have better numbers.

 Yes, I thought about the loose screw problem (no comments about my mental state please )

 After some thought, I've pretty much abandoned the bolted breech idea. It would be fine if properly designed, but if at some point in the future someone changes out the bolts for ones from a lawn chair, it will no longer be safe.