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Author Topic: Jacket Fatigue  (Read 1260 times)

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Offline Al Barnhart

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Jacket Fatigue
« on: April 21, 2009, 05:53:37 PM »
Cant seem to solve this. The Jacket has a ring (stress mark) that looks like it wants to crack right in front base. Its hard to see in the scan but its there. It shows up when pointing up. I think its comming from core seating. I have tried more pressure, less pressure. More lube less lube. The punch size seems ok. I am getting a small amount of blow by so I dont think its too big. I have tried everything I can think of

Any suggestions would be great.

Al Barnhart

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Offline talon

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Re: Jacket Fatigue
« Reply #1 on: April 22, 2009, 05:46:55 AM »
 Al, do you anneal your jackets before core seating? It could be that your jackets are made of an alloy that doesn't take stress well. Not all jackets are formed of the same alloy.There is no springback at the base during seating while all along the sides of the jacket there is. This could be what's causing the 'crack'.  Annealing could solve this problem. I doubt if this condition will affect the performance or reloader handling of the bullet as long as the 'crack' isn't an actual seperation. I've never seen a crack like this before.
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Offline Al Barnhart

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Re: Jacket Fatigue
« Reply #2 on: April 22, 2009, 10:45:19 AM »
They are J4 jackets that are 1.290" long and I am trimming them to 1.125”. The samples I got from the die supplier look great when the jacket is used full length. The only problem with that is a full length jacket makes a 145-grain 6mm bullet. The pic I posted is a 106-grain with about 2/3 of the nose full. Lead all the way to the tip makes a 108.
This mark shows up about half way in the point up process. I have tested this by ejecting it after its half way down and it still looks good. The point-forming die still has room left to go in further. Overall they are a little small. They have a .0001-.0002” pressure ring and the body is .2429” I have tried increasing the pressure in core seating but I end up with the ojive body junction being as much as .0003” over size. I even tried pointing up half way on 50 or so then resetting the punch and finishing pointing up. The stress mark was a lot less but still there on most.

This also happens with a rebated boattail die I have. I’m sure its stressed as I have had a core and BT only eject out of the point forming die and leave the body of the jacket and mostly formed point in the die. What a butt pucker that was.

Al Barnhart
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Offline Smokin7mm

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Re: Jacket Fatigue
« Reply #3 on: April 23, 2009, 03:33:12 AM »
What type of lube are you using?  Also when seating the core how much pressure are you using.  I have had instances when seating a core, if too much pressure is applied it stresses the jacket and seperates.  Granted the seperation is more in the middle of the jacket and usually only during set up when I am determining the adjustment on the core seat die which requires adjusting down a little at a time which cycle the jacket/core several time and if adjusted down too far it stresses the jacket.  I have never seen a stress ring near the base as you are seeing.
Bret
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Offline talon

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Re: Jacket Fatigue
« Reply #4 on: April 23, 2009, 04:17:40 AM »
When I make my 6mm ( .243cal) 118 gr bullets I use a jacket only .942" long and .185 wire 1.125" long. It would seem a jacket 1.125 long would have a deeply set core. I forget if a J-4 jacket has internally sloped walls, but if they do, I wonder if your seating punch is cutting into the sloped ( tapered) jacket wall? This would probably be the case if you are triming the jackets to start with. If so, that would be a problem because you may not be seating your core... the punch is bottoming out on the sloped wall. However, if the heal mics to .2428 ( aprox) after core seating it would appear the core is properly seated. In any case, it wouldn't hurt to section a jacket with a 'seated' core to find out to see if there are any internal signs of a stressed jacket.  J-4 makes superior jackets, but there's always a chance of a bad lot. It would seem that a 6mm jacket 1.29" long is a bit unusual(?).
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Offline Al Barnhart

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Re: Jacket Fatigue
« Reply #5 on: April 23, 2009, 10:22:55 AM »
Talon

You are on the right track with the jacket length. It was way too long. Late last night I trimmed some down to 1.080" and they look great. All detentions look good. I guess the part that got me off track was I still had lead near the tip. probably with a loose core. So this led me to believe that the jacket length was OK. What I believe was happening was, when applying enough pressure to point up the core would move ahead a little and supported the nose. (J4s are tapered inside) Heavy core seating pressure would get me wrinkles at the front during point up and lighter core seating pressure would get wrinkles at the back. Not enough lead for core length.
The funny thing is the point up stroke is a lot smoother now and seems to take less force on the press handle…

Thanks all

Al Barnhart

PS: Talon, check your messages...
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