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Do you want to calculate how safe your gun is?

Discussion in 'Shooting Related Threads' started by dverna, Sep 29, 2009.

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  1. dverna

    dverna Active Member

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    A chamber failure will occur when hoop stress exceeds the yield point of the material.

    A chamber is a thick walled cylinder and the link above provides a way to calculate hoop stress. Maximum stress will occur at the inside radius so you put that number in to calculate the max stress. A 12 ga chamber is about .80". ID in the formula

    Measure your barrel/monoblock OD and input that as your OD. (say 1.2" in this example)

    SAAMI lists the max pressure for a 12 ga at 11,500 psi. For a safety factor of 2 you would use a radial pressure of 23,000 psi. For a safety factor of 3, 34,500 psi. Without a barrel obstruction, it is unlikely we can produce more than 20,000 psi (if I correctly recall the testing that Bowen did). You decide how much pressure you want to contain. I will use 23,000 psi in this example

    Hit the "calculate' button and what is the max pressure? (59,800 psi)

    Using 4140 steel, yield will occur at about 60,000 psi. Other barrel steels will be different - example - 416R stainless, some rifle barrels use this, has a yield point of about 130,000 psi. You may be able to get the material spec from the manufacturer of your gun.

    Does the hoop stress exceed the yield strength? If yes, you have a problem.

    In this example, we have a safety factor of 2 using 4140 steel with a max chamber pressure of 23,000 psi.

    Pressure vessels normally are designed with a minimum safety factor of 3. Airplanes (subject to intensive inspections) are in the 1.5-2 range.

    Note, in the example above, if the OD was increased to 1.5" the safety factor is about 3.

    Don Verna
     
  2. sliverbulletexpress

    sliverbulletexpress TS Member

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    Don thanks for the info. I think 4130 is used more often in guns but I could be wrong.

    All of this discussion of gun blow ups need to include the simple fact that when you have a catastrophic event like we've seen pictured the pressure far exceeded the strength of the metal. Not just a little bit, a lot more, at least in my thinking and it looks like you've proved that scientifically.

    Now the question is why the extreme pressure? Many are dismissing reloading errors but why are all the reloading guides so adamant about not exceeding or changing anything about their recipes if there was no real danger in doing so?

    Would they mention the risk of injury and even death if there was no danger? That would seem to run off some potential buyers for no reason if not correct. CYA I know, but going too far can cause problems too but that is for a business lawyer to discuss, I'm just asking?
     
  3. hmb

    hmb Well-Known Member

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    Powder detonation = extreme pressure.

    Changing their recipe = powder detonation.

    Powder detonation = danger.

    You asked, I answered. HMB
     
  4. Borderland

    Borderland Member

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    guerini uses 42CrMo4 which interchanges w/4140 in U.S. common terminology
     
  5. 221

    221 Banned User Banned TS Supporters

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    Being made of 4140 does not mean much.....it just tells you what it's ingredients are....how it's cooked is what matters.....I've got some 4140 that wouldn't make good anchors......I also have some 4150 that will go over 60HRC
     
  6. KENENT1

    KENENT1 Active Member

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    221 is correct on his post....what or how is the steel treated...I have seen bolts rolled in bars of steel, when you turn them they break out...too hard and it's brittle and breaks....there are soo many possibilities for flaws, everything would have to be x-rayed to be sure.

    even a rough finished turn will break before an identical piece with a smooth finish...


    tony
     
  7. Mapper

    Mapper Member

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    After a previous discussion of guns blowing up, I miked the sidewalls of my trap guns and a couple of old doubles, all 12 gage, in the chambers. I used a ball mike. At.152, the sidewalls of my K32OU were the thinnest. Some were hard to get a good number, like my old Ithica SBTs, but my model 12(nickel steel( was .195 and my 31T was.211. Seems like they are making barrels a bit thinner now. I have no idea what analysis steel a Flues SBT is, but they are really thick. As they are, they are just numbers without steel type and heat treat information.
     
  8. KENENT1

    KENENT1 Active Member

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    my .50 tompson center muzzle loader, I can fill the barrel full of powder, the unburnt powder burns as it goes out the barrel, gives a good kick, but the powder can only burn so quick, the rest goes out the barrel.


    tony
     
  9. PerazziBigBore

    PerazziBigBore TS Member

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    A quick call to Simmons will yield some very interesting facts about barrel steel.. Those who have cut them on a lathe will quickly tell you.. many barrels are made from seamless tubing.. I've seen barrel made from 1018 on up.. Perazzi still drills from solid stock their barrels.. Some barrel makers use forgings.. some just run tubing thru a CNC and screw it into their mono-block.. To this point.. I agree with the entire thread.. 221.. you made a very valid point.. the best of steel can be destroyed by improper heat treatment..
     
  10. 1100 REMINGTON MAN

    1100 REMINGTON MAN Active Member

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    I had a friend of mine a aircraft mechanic told me many years ago about aircraft engines and why a part costing hundreds of thousand of dollars would fail because it came from a rock and has no common sence. With all man does to mfg. steel, test it insp it . It still thinks like a rock and with man involved there will always be a flaw some time no matter how smart we think we are. No matter if it is a gun or an aircraft engine. some time things just go wrong no matter who is the Mfg.
     
  11. JerryP

    JerryP Active Member

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    KENENT1, You state, "there are soo many possibilities for flaws, everything would have to be x-rayed to be sure. "
    How do gun manufacturer's deal with this. Shouldn't every gun be x-rayed?
     
  12. KENENT1

    KENENT1 Active Member

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    JerryP, there are several independent labs that do nothing but check chemical and mechanical properties on steel for aerospace and aircraft manufacturers.....maybe some of the thinner barrel guns should be x-rayed....who knows.


    tony
     
  13. Dennis DeVault

    Dennis DeVault Well-Known Member

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    This is a good post and many good points have been brought up. The fact that Italy uses SAMMI for their testing is good but doesn't prove much. The problem with the test is that you are pushing a piston through an open ended cylinder. Another factor foreign made steel is very different than that of domestic made steel. ASTM numbers may be the same but the treatment of that steel is very important. Heat treating of steel is as much art as it is science. Another factor that is being overlooked here is the barrel design. You absolutly cannot have sharp corners in pressure areas. If you have a sharp corner it sets up a stress riser and no matter how good the steel is it will fail when introduced to pressure. Amother factor is the chemical content. How much Manganese is in the steel. Manganese will raise tensile and yeild strength but gives a false sense of security. Manganese does not like heat and will run from heat that will create stress risers that lead to cracking. Manganese does not like to be cold work as well. Another overlooked area is heat, what happens to a good grade of tool steel when it is introduced to 1100 to 1200 degrees of heat when a rib is silver soldiered in place. There are many many varabiles to consider and it will take a long time for any lab to determine the cause of a faliure. I have spoken with HP White on several occasions and they have told me it is difficult to determine a problem after the incident has already occured. Just a little fuel for thought and my humble opinion.

    Dennis DeVault
     
  14. dverna

    dverna Active Member

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    Hoop stress is not affected by having one end open. A cylinder is a cylinder.

    Devault raised some good points and that is why a safety factor is used when designing any part.

    FEA analysis can address most of the affects of sharp corners etc. This is beyond the scope of barnyard mechanics or this post.

    The point was to make us think. There are hydraulic hoses in daily service at 4000 PSI. Yet we suspect barrels are blowing up with normal loads at under 11,000 psi.

    I fear the reloader far more than I fear the assembly of my trap gun.

    Don Verna
     
  15. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    I fear both and for good reasons. Some people should never attempt reloading shotshells let alone rifle cartridges.

    I also fear the misuse of heat in working metals too! I call those "Monday" fixes. Too much heat and the molecular structures change becoming more tightly bound together creating "hardness" losing it's flexibility to expand and contract. As Dennis pointed out above, heating spots for adding ribs to 1100-1200 degrees will change the relationship, molecular wise, in the parent metals. Too hard and metal can and will shatter like broken glass instead of flexing and contracting when subjected to the sudden impact of outside forces!

    Hap
     
  16. Too Bad

    Too Bad TS Member

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    Dennis, how do you make your barrels and what are they made from? How is the barrel attached to the mono block? How is your rib attached to the barrel?

    Thanks,

    Richard Luckett
     
  17. Dennis DeVault

    Dennis DeVault Well-Known Member

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    Hi Richard,

    The barrels are made from 4340 vac melt steel from the Timken Company. The material is heat treated and then cyrogenic stress releived. The barrels are a solid bar and the barrel is completely machined inside and out. The tensile strength rating of the material when heat treated is 158,000 tensile and 135,000 yeild. We use the monoblock method of assembly. We use an adhesive that was designed for me back in 1991 by the Loctite Corporation. The rib is attached by a collar on the front of the barrel that is held into place with the same adhesive and the back of the rib is held in a dovetailed slot on top of the monoblock. The adhesive allows us to make all the componant parts to exact dimensions and then assemble the parts with no heat. The only heat that our barrel sees is the bluing process. With the adhesive the entire joint has 100%, there are never any voids or areas of the joint that do not have adhesive. The adhesive is tough enough that after the assembly process they are blued and the bluing does not penetrate the adhesive. When Loctite did the initial testing of the barrels and adhesive joints we were told that after 2 million cylces it would take 85,000 PSi of pull pressure to break the joint apart. There are many ways to attach barrels to monoblocks but this method works for me and I do not want to change a process that works. Thnak you for the question,

    Dennis Devault
     
  18. Too Bad

    Too Bad TS Member

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    Dennis thank you. Very clear explaniation.

    Richard Luckett
     
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