Go Big or Go Home Range Day |
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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I checked and rechecked the bore and found nothing out of the ordinary, yet. The lands and both grooves do not show any signs of damage either. I'll figure it out eventually...
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Offline Points: 6539 |
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This shows up only on of the rifles, correct? Were these a new batch of bullets by any chance?
Not every bullet hole showed the pattern, so it might be an occasional bullet with an uneven jacket thickness. There only appears to be one small area on the bullet that gets the jacket scrapped off. The amount of lead that is leaking out I would have thought those bullets would go wide from imbalance.
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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This group came from my All Black Long Branch with the 2 groove barrel. The bullets in question came from a batch that I loaded a few years back using the .312" GRAF BTHP's and the N202 powder. As I stated earlier in this thread, I checked the chamber where the rifling starts and checked the grooves and lands forward to the muzzle and found no trace of anything unusual. Actual cleaning of the barrel just brought out the normal fouling you normally have.
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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I might have accidentally found the reason as to why the bullets are leaving swirl marks britrifles and more likely than not, it's my fault.
You mentioned that those pistol bullets might have been damaged in the bore and then you also mentioned thin walled rifle bullets, specifically the Sierra brand. I pulled a bullet from that batch and saw something that would possibly contribute to the swirl marks. It is also my assumption based off of what I saw that the bullet was damaged prior to entering the bore. I used to crimp the case as the bullets were seated. After pulling the bullet, I can see a definitive deformation in the ogive that can and would strike the rifling hard enough to remove enough outer material to allow the core to melt away from the heat build-up from the excessive friction caused by that deformation. I have ten of the crimped cases left. Then next time out I am going to fire ten rounds of uncrimped cases first and then the remaining ten rounds of the crimped cases and I bet I see swirl marks from those bullets...
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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Ah HA! you may have hit the nail on the head. I never crimp unless there's a specific crimping groove in the projectile. What I do instead is to very slightly reduce the expander ball diameter, usually by spinning it in a power drill & polishing firmly to a mirror finish with a very fine abrasive. This increases neck tension without distorting the projectile at all.
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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I too have slightly reduced the expansion ball. When I used the crimp die I pretty much added too much of a crimp. I no longer use a crimper and haven't in years.
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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I will know for certain if this is the reason the next time I go to the range even though I'm certain of it now.
My issue now is digging out six boxes of loaded Norma brass that I originally crimped years ago. I know I'm going to find the same thing. I'm going to have to find an extremely clean container to catch all that N202 powder in...
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Offline Points: 6539 |
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I bet that is it. The interesting part is it appears that only a fairly small area of the jacket is getting opened up, possibly because of the two groove barrel. If the worst part of the crimp hits one of the lands, the jacket cracks/breaks thru. If the jacket was perforated in two spots on opposite sides of the bullet you would see two spiral trails on the target.
I’m amazed that those bullets even hit the target at 200 yards let alone grouped at under 2 inches. Years ago I used a light crimp with the Lee Factory Crimp die on the 174 SMK. The thin jackets deform easily. I stopped doing this and did what Shamu did by sanding down the expander ball in the FL sizing die and also bought a -0.001 mandrel for my Lee Collet sizing die to increase neck tension. |
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