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Post by ET on May 31, 2011 21:18:21 GMT -5
Okay I might be losing it but am going to pose a few questions to the sharp minds on this board. Obturation is the process where bullet expansion occurs from the force applied to it. Now if the force is applied to the base then the most degree/amount of expansion should occur here. Does the expansion take on a cone form with the largest expansion point occuring at the base? What affect do you think this would have on bullet flight? Would it aid for a stable bullet flight if proper RPM is present? I’m running out of Tylenol trying to get a grasp on this and any helpful comments are appreciated.  Ed |
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Post by rossman40 on Jun 1, 2011 0:42:54 GMT -5
It can not expand too much because of the bore. It is not going to come out like a badminton birdie. Now how much it puts a squeeze on the sabot is another question, that would depend on the thickness of the sabot and how tough the material is.
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Post by edge on Jun 1, 2011 7:42:02 GMT -5
I doubt that there is much obturation except sabotless. More with thin jacketed bullets or plated bullets and probably zero with a Barnes in a sabot with most loads. I suspect that enough bullets have been recovered from deer that we would have seen some strange looking bullets. IMO, your sabots are moving too quickly off of the powder to have enough pressure to distort the bullet very much. Clearly the bullets would have some evidence of four "ears" where it extruded into the slots between the petals OR recovered sabots would show that the plastic was severely stressed and basically sealed up the slits. Most recovered sabots show the evidence of the rifling and the bullet expanding would have to leave the same type of evidence...IMO  edge. |
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Post by Dave W on Jun 1, 2011 8:29:06 GMT -5
I think edge pretty much nailed it.
I have a couple 250 FTX bullets that were recovered in deer. The bullet peeled back so far but only a portion of the bearing surface was affected. Very little expansion at the base of the bearing surface and though I don't have the tools to measure the bullet properly, the calipers only went to .453 and this was only for one spot. I guess it is possible some jacket material washed off inside the animal and bone could have influenced the oblong feature.
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Post by rossman40 on Jun 1, 2011 11:10:03 GMT -5
We probly only need a few hundreths (.0001") to do the job. It could be more but the bullet may "snap back" after the pressure is off just like when you resize one. Trying to measure it on a recovered bullet would be tough. Recovering one without distortion from impact is almost impossible. Can't stand down range with a butterfly net. I have tried measuring sabot petals but is the difference caused by obturation or wear by friction?
We do see something happening, I think the successes of the thin jacket bullets like the BE and the 4500 Hornady and even comparing the XTPs to the thick jacketed XTP Mags and then results from soft lead cast and plated bullets which may over obturate and distort.
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Post by edge on Jun 1, 2011 12:01:25 GMT -5
I am pretty sure that dave d. gets great accuracy from the Barnes all copper bullets and if the thinly jacketed bullets are not grossly expanded there is no chance the all coppers are doing anything...IMO .
edge.
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Post by 10ga on Jun 1, 2011 14:43:50 GMT -5
Such fun, such fun! Some think the bullet gets a eliptical shape as the base moves and the nose dosent and then the middle "expands". Obviously the hardness/toughness, of the bullet etc... will make a difference. Also the "speed" of ignition. Buddie who shoots long range BP cartridge uses PB about as soft or pure as possible for bullets. Harder bullets will not obturate enough to properly catch the rifleing. Slower powders same thing. The "explosive" BP and soft bullets. Just some insight. Not hijacking the thread as this applies. 10 ga
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Post by Richard on Jun 1, 2011 16:00:48 GMT -5
I am definitely in Edge's corner on this one. The Jacketed bullets may slightly expand which might help to seal the bore. On the other hand, the copper bullet do not. I can see this as part of the reason they will drill a sabot more easily. Just today, I fired two five shot groups with a duplex and the 200 SST's at between 2750 and 2775 fps. No problem with the SST's...........then started on a group with the 195 Barnes? First shot 2770............second................a sort of strange "bang" a chrono reading of 2450 and nothing on the target? Obviously a blown sabot!...........End of group  Richard |
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Post by ET on Jun 1, 2011 17:58:55 GMT -5
My thanks to all for your comments that gave a little better overview of the term “Obturation”.
Ed
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Post by youp50 on Jun 1, 2011 18:30:33 GMT -5
Rather stout duplex loads, in my 50, under a RCR and a 250 XTP routinely show missing sabot petals.
Obtruation weakening the base of the petals?
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Post by dannoboone on Jun 1, 2011 18:56:22 GMT -5
Rather stout duplex loads, in my 50, under a RCR and a 250 XTP routinely show missing sabot petals. Obtruation weakening the base of the petals? Unless it's a very stout load, my .45 with 200SST's does about what is generally accepted to the sabot. But when shooting the Barnes, I have yet to find more than a sabot base. Yet the accuracy is superb. ?? Probably no obturation with the Barnes and maybe a little with the SST. Too much thinking about it would cause me to think I was losing it, too. ;D ;D |
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