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Post by bestill on Mar 9, 2015 19:13:17 GMT -5
Does a smooth form land rider truly swell into rifling and how much. Any bullet recovered. And at what pressure. Lets say a 300 match hunter for reference.
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Post by 7mmfreak on Mar 9, 2015 19:34:02 GMT -5
I personally have my doubts but have never recovered one so I cannot say. I know that term gets tossed around here, quite a lot, but it is one I have always been skeptical of.
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Post by lwh723 on Mar 9, 2015 20:57:09 GMT -5
It absolutely swells to fill the rifling. I've recovered lots of jacketed bullets that clearly showed engraving. As I recall, deadeye also shot 40cal 195BX's into a 50gallon drum of water and they showed obturation.
I just googled material properties of copper, and the yield stress number I found was 9Kpsi. So hit that with 40-50Kpsi load, and something has to give.
For some reason, once in a while, I think bullets don't swell, and I think those are the ones that keyhole on the target. Recently had a customer with keyhole issues using 250 SST, but not issue with 250BE? Velocity was comparable between the two (and these were 2800FPS loads, so good pressure). Told him to use a wad, and he got his accuracy back with the SST. How he could get 2800 FPS and keyhole is beyond me, but some things are still a mystery.... Maybe barrel geometry or something?
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Post by cr500afx on Mar 9, 2015 21:01:30 GMT -5
I recovered these two 250 TEZ land riders after penetrating seven water filled milk jugs, stopping in the eighth at 2777 fps and 50 yards. After several attempts, I came to the conclusion that there is NO measurable obturation, atleast on the copper solids.  |
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Post by hankinsrfls on Mar 9, 2015 21:28:34 GMT -5
Solid copper bullets are not going to obturate nearly as good as the copper jacket bullets. The lead in the copper jacket bullets is what actually swells forcing the copper into the groves. The BE bullets have super thin and softer copper jackets than does the SST bullets, therefor making the BE much easier to obturate, also explaining why they are so much more accurate than the SST. Not saying the SST is not accurate because I have shot several groups with them under .5 at 100 yards, but those groups don't come as easy as they do with the BE.
The match Hunter bullet has a jacket thickness of .028 (I think) compared to the BE at .015 (I think) making them a little harder to obturate, but they still do to some point.
Think of a water balloon, what happens to it if you drop it on the floor. The side walls expand and it will burst. This is caused from the sudden stop in motion. Think of the bullet the same way. The lead being the water and the jacket being the balloon, now the difference is,, the bullet starts motion so rapidly that the lead expands forcing the copper jacket into the groves until either the groves are completely full or the strength of the copper/lead combo exceeds the force behind it. That's why I like a fast burning powder. Get the pressure up as fast as you can to safe limits, and the results will speak..
If these bullets did not obturate to pick up the spin then we might as well start ordering our barrels with a .450 smooth bore and see what we get....
By the way, cr500afx.. Those are some beautiful mushrooms....
Jeff Hankins. |
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Post by edge on Mar 9, 2015 21:37:48 GMT -5
I recovered these two 250 TEZ land riders after penetrating seven water filled milk jugs, stopping in the eighth at 2777 fps and 50 yards. After several attempts, I came to the conclusion that there is NO measurable obturation, atleast on the copper solids. Apparently there was enough for that bullet to be kept going in a straight line, which it would not have done without spin. It may swell some but not enough to cause permanent deformation. A lot has to due with whether it is fully annealed or not. edge. |
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Post by cr500afx on Mar 9, 2015 22:22:58 GMT -5
I recovered these two 250 TEZ land riders after penetrating seven water filled milk jugs, stopping in the eighth at 2777 fps and 50 yards. After several attempts, I came to the conclusion that there is NO measurable obturation, atleast on the copper solids. Apparently there was enough for that bullet to be kept going in a straight line, which it would not have done without spin. It may swell some but not enough to cause permanent deformation. A lot has to due with whether it is fully annealed or not. edge. Very good point. That kind of explains why this duplex load gets better as the charge is increased. As Jeff says, "get the pressure up fast" I haven't had any luck in recovering a jacketed bullet in a measurable state. I may try recovering an SST and a bonded shockwave at 300 yards in the milk jugs. Might be interesting. |
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Post by edge on Mar 9, 2015 22:51:13 GMT -5
From the old board, a 2008 thread on obturation dougva.proboards.com/thread/5922/obturationTwo years ago I would not have thought that the bullet could possibly expand inside of the bore. That was before I shot a buck and recovered the bullet. Now there is a fair difference between what I shoot and what you might shoot. First, the bullet was a 8mm 150 grain Sierra ProHunter from my modified Savage ML-II. Velocity was over 3,000 fps, and the sabots were rigid PVC. Below is a picture of an uncut sabot with pristine bullet and the one recovered. Notice the shape of the cutout in the sabot and the mirror shape of the bullet.  Recovered bullet from the base. Note the slight protrusions where the bullet expanded into the saw cuts. The bump in the center is the mirror of the drilled sabot.  Pristine bullet and recovered to show how much it expanded in the barrel ( notice the saw cut remnants).  I changed the design after recovering this bullet, and switched to the solid base AccuBond. edge. |
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Post by 7mmfreak on Mar 10, 2015 4:01:10 GMT -5
I agree that due to the impulse that overcomes inertia and friction there will be some swelling. That engagement of rifling is what let's it spin for sure. I don't know that it swells enough to completely fill the bore; a 1:1 copy.
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Post by Deleted on Mar 13, 2015 7:19:55 GMT -5
Don't you guys remember my thread "Catching Bullets"?
About 3 years ago I set up a 25 gallon storage tote filled with water at my 100 yard target and shot a land rider 300 grn .451 MH into it.
The bullet was fully engraved with rifling.
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Post by bestill on Mar 25, 2015 13:07:18 GMT -5
Is there pics of a copper jacket smooth form bullet out there that has been recovered showing the amount of obturation?
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Post by Dave W on Mar 25, 2015 13:47:51 GMT -5
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Post by smokeeter on Mar 25, 2015 16:32:10 GMT -5
Here's a pic of a solid copper ( probably the hardest bullets to obturate) I modified the bullet by concaving the base and the bullet was only sized to the bore not FF sized. It definitely engraved as seen in the pic, which means it obturated. I now FF size my bullets and this seems to better insure obturation , no more keyholing.   |
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Post by bestill on Mar 26, 2015 6:25:04 GMT -5
How bout jacketed bullet(parker) with out base modifications.
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