Magnafluxing a Part to Determine Its Strength

Discussion in 'Gunsmithing Forum' started by jd45, Dec 18, 2011.

  1. jd45

    jd45 New Member

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    Hello to all & Merry Christmas! I have an Armi San Marco mfg'd Colt SAA replica I bought thru EMF several years ago....'93 I believe. Recently I handloaded some cartridges to take to the range & velocity test. I used 8.5; 9.0; & 9.5grs Alliant Power Pistol under a .455" 250gr SWC. Groove diameter is .454", also chamber throats. The 8.5 & 9.0gr loads worked fine....I got 820s & 870s from the 5-1/2" bbl. When I fired one round & one only of the 9.5gr load, I knew I'd gone too far. The clock read 1450-something; recoil was severe & I had to drive the case from the chamber with a wooden dowel. Is there a way aside from a visual inspection, such as I mentioned above, to check whether the cylinder has been weakened to an unsafe-for-further-use condition, so even if I were to just fire factory-level .45 Colt ammo, it could possibly let go at some point? I'd appreciate any insight you might be able to share. Thanx, jd45
     
  2. kenhesr

    kenhesr New Member

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    Realistically, probably not. Magnetic particle and dye penetrant would be great for finding out if you had created a crack in the cyl. surface.

    Ultrasonic testing would be more appropriate for finding subsurface flaws in the metal but can be costly unless you have access to the equipment & technician.

    By weakened I assume you are concerned that you have stretched the fired chamber of the cyl beyond it's yield point.

    Visual inspection might be the best way to go. If you have a precision vernier caliper you could measure the concentricity of the fired chamber against the normal ones and overall dimensions of the cyl.

    IMO a 100% test that would stand-up in a court of law would involve sectioning, polishing and a microscope, (destructive testing). Good luck, Ken
     

  3. danf_fl

    danf_fl Retired Supporter

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    If you know someone in the hospital, try ultrasound.
     
  4. jd45

    jd45 New Member

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    Thanx guys....I guess I'll use my vernier caliper very cauciously & see how the chambers compare. Wish I'd had the foresight to mark the chamber I fired the hot load thru. jd45http://cdn.firearmstalk.com/forums/images/smilies/biggrin.gif
     
  5. jd45

    jd45 New Member

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    BTW Ken, can you enlighten me as to just what the term "yield point" means? Inquiring minds want to know. Thanx, jd45
     
  6. kenhesr

    kenhesr New Member

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    Yup jd, I won't get too deep into it but think of the chamber walls of the cyl. Every time you fire a rd the brass case pushes outward & the steel chamber wall flexes outward.

    The pressure makes the steel stretch. With a normal rd it stretches to a point and returns to normal when the pressure lowers.

    Now with a very hot load you can stretch the steel PAST the point where it can return to normal, (yield point). It just stays in the new shape, (bulge).

    With the permanent movement of the metal it gets thinner in these areas. Even with no visable damage it can set up a stress riser situation. Think of the old metal coat hangers. If you went slow it could be bent back & forth many times before it broke.

    Take a file and make a small mark on the metal hanger. Now when you bend it just a few times it will break. Why, because you have created a stress riser when you filed the mark. The stress is now focused at that mark and it will break easier than normal.

    Same thing in your cyl walls if you have stretched them past the yield point.

    Thats why I thought maybe you could check the chambers from the inside looking for a bulge in one of them.

    This is probably more than you cared to know jd, I can get longwinded! Ken
     
  7. danf_fl

    danf_fl Retired Supporter

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    If you have more of those 9.5 loads, you may want to double check the charge.
    That seems like a large jump for .5 grains.
     
  8. jd45

    jd45 New Member

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    hanx for the explanation....it was very enlightening. As far as the other 9.5gr loads, I only made up a total of 5, and after I saw what the first one did I pulled down the other 4. Don't wanna accidently run another of those thru the gun, I can tell you! jd45
     
  9. jd45

    jd45 New Member

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    Dan, before I seated the bullets in the cases for each of the three charge weights, I looked into the mouths of all 5 cases for each charge, to make sure that after I poured each weighed charge in the level was the same. I'm thinking I reached a critical point pressure-wise with that weight bullet & the burn rate of that powder that was over the safe limit. I don't think I'd've had the same result if the bullet weight had been say, 200grs, instead of 250. I'd be interested to hear your thoughts on it. Thanx, jd45
     
  10. jd45

    jd45 New Member

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    kenhesr, I measured all chambers with the vernier, first one way & then 90 degrees from that. All measured about .485" both ways. Next, I'll have to do a real close & thorough visual inspection, I guess. jd45
     
  11. danf_fl

    danf_fl Retired Supporter

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    I'm glad you clarified that. Just wanted to make sure that the scale did not slip up.
    Did you find the charge that works with your firearm?
    I've seen where people work up max loads and never consider that a lower load will (sometimes) produce better results in accuracy.
     
  12. jd45

    jd45 New Member

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    Dan, the 9.0gr load was real close to factory velocity , as I said in the 870s, however I didn't load enough to also test for accuracy at that time. When spring comes around I'll have enough ammo stored up to see how it shoots. It's an outdoor range. Thanx, jd45
     
  13. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

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    Pressue is not always linear. Add some powder, get an increase in velocity. Add a little more get some more velocity, or get a LOT more velocity (and pressure). Pressure spikes happen. That is why you are well advised to not exceed book maximums and approach those maximums cautiously.
     
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  14. jd45

    jd45 New Member

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    I think you hit the nail squarely on the head........pressure spike is apparently just what it was. I was in uncharted waters going a full half grain past the 9.0 charge. I just thank God I didn't blow the gun up or injure someone. Thanx, jd45