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    • #47248
      Goodsteel
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      I was just brainstorming over our HV bullet catch test. The bullets were swaged down undersized (nearly bore diameter) just in front of the gas check. In fact, the gas checks were barely holding on because the shank had assumed a “dovetail” look.

      I’ve been ruminating on this phenomenon for quite some time since that test. I have assumed that the bullet lube just piled up in front of the gas check, and the pressure became so great right there that the piling up lube created the undersized effect. It has bothered me that the front part of the driving band was not effected near as much as the part just in front of the gas check, but I figured that was just the way things work, but today, I thought of a possible alternative/additional  cause of this effect: Perhaps the pressure is great enough to cause the lube to diesel between the bullet and the wall of the barrel.

      Does anyone have any thoughts on the validity of this theory? Anyone have experience with dieseling different materials (you know, other than diesel fuel)?

    • #47249
      kens
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      if it is getting enough pressure & temp to diesel, then the grease would have melted away or burned up.

      is there any grease left on it?

    • #47250
      Goodsteel
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      I observed no grease left on the bullets, at least not near the gas check, but that is completely inconclusive because honestly, catching a soft bullet traveling at nearly 3000 FPS is like trying to shoot a water balloon out of a potato cannon without breaking it (another adventure I was involved in once. I managed to shoot water balloons about 250 yards BTW….).

       

    • #47251
      kens
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      then how could you use greases of different ignition temperatures?

      different temp greases would light off at different pressures, correct?

      accuracy wouldnt matter here; only lighting off the lube in effect.

      then associate pressure/velocity with ability of the grease to light off

    • #47254
      kens
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      Example for discussion:

      lube of Crisco/Beeswax lights off @ low pressure

      lube of Lyman orange lights off @ medium pressure

      2700 lube lights off @ highest pressure

    • #47255
      Bodean98
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      For there to be dieseling of the lube there would have to be some sort of oxidizer in the lube. Pure fuel nor pure oxidizer will ignite. There has to be a proper mix of fuel, oxidizer, and heat for ignition. Gunpowder is a good example of a compound that contains 2 of the three necessary components for combustion. Not trying to say that the lube is not dieseling but some analasys of the lube would be needed to determine if it truly was.

    • #47256
      Rattlesnake Charlie
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      Interesting Food for Thought.

      I have experienced bottom lube grooves blown dry and not collapsed while lube grooves closer to the bullet nose still contain lube. A head-scratcher for sure, especially if the combo resulted in good groups. More often I have found the bottom lube groove “smashed” closed. The combo worked good as many times as it did not. I have just moved on based on success and failure without delving into the scientific backing. But, now it is cropping back up again. Why? What?

      Bodean98 appropriately brings up that there must be some oxygen from somewhere. Could it be from blow-by from the powder itself? Powder contains its own oxidizer. Does it already exist in our bullet lubes? Things happen under extreme pressure. And, we have created lubes that contain everything including dead cats.

      Everyone with an idea or theory, please post. I’ll try to push this to some of my contacts in the conventional explosives section of the lab.

      I had managed to just go with “it works” or “it doesn’t”. Now the desire to know “why” has resurfaced. Tonight, I’ll probably stay awake thinking about this after my 2 am potty break. Arghhhhhh!!!!

    • #47296
      Harter
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      I do know from my time as a fire fighter that at 1700° everything in the home not metal will ignite .
      As a mechanic having used a spark plug comparator I can tell you that under pressure some solvents that don’t burn well in open air will poof . In talking about carb and brake cleaner with a 90/10 with 50 motor oil at 80-110 psi .
      In terms of raw is it possible , the lube is liquid , often petroleum based with a raised pressure and ignition source .
      The other side is that the pressure may be so high that the oil detonation can’t happen or happens so comparatively slow that it isn’t a factor . I’d have to work some numbers for diesel burn duration vs piston travel time vs the .0007 seconds the average 2700 fps bullet spends in the barrel . Thicker oils with more wax or otherwise solids would burn even slower .

    • #49876
      HangFire
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      I would look at hydraulics reshaping the bullet before dieseling. Rifling displaces lead, lead displaces lube, lube has to go somewhere. It’s going to push back on the lead and on the gas check. The result is a longer thinner cast bullet.

      On that topic, as a kid I used to over-oil my Daisy on purpose, to get it to Diesel. When first over-oiled it didn’t diesel, or do much of anything. There was a sweet spot after several shots when there was not too much oil, and it would fire off, before it cleared itself out, and resumed normal operation.

      Accuracy of the diesel’ed shots were awful, that is, more awful than usual for a 5″ smoothbore that cost $12.

       

    • #49899
      popper
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      First, only vapors burn.  Lube will liquefy (and expand) and flow from pressure.  As the liquid flows to the base it builds up at the GC dam and exerts pressure on the alloy, compressing it.  Larry G. has noted the recovered cast are smaller than bore due to the in-compressibily of the liquid lube – same happens at the base/GC.

    • #49900
      Larry Gibson
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      I would look at hydraulics reshaping the bullet before dieseling. Rifling displaces lead, lead displaces lube, lube has to go somewhere. It’s going to push back on the lead and on the gas check. The result is a longer thinner cast bullet.”

      Agree with HangFire.  I’ve found that lubed cast bullets, even a very low velocity under 1000 fps, all are .002 – .005″ under groove diameter even when .001 – .003″ over groove diameter before firing.  The low end velocities create much less heat and pressure yet the effect is the same….the bullets are undersize.  Can only be from the hydraulics of the lube between the bullet and bore surface.

       

      Larry Gibson

       

    • #49901
      kens
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      Help me wrap my mind around this.

      I understand the barrel lands impress on the bullet and lube, and the extra lead has to go somewhere, but I keep thinking that the end result is a longer OAL bullet, but I cant picture the size going under bore size.

      What am I not seeing?

    • #49931
      Larry Gibson
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      What am I not seeing?

      The layer of lube between the alloy and the barrel/bore surface.  The lube will turn to liquid under pressure.  Liquids do not compress very much if any….hydraulics. It is the layer of lube.

      Larry Gibson

       

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