Painted bases

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  • Last Post 26 October 2015
mtngun posted this 25 October 2015

Some background:  this gun/load combo has been struggling with a leading problem.   Recovered bullets appear to suffer etching, melting, & gas cutting at the base.  I wanted to see if painting only the base would stop the gas cutting.

I drilled a scrap piece of wood so that only the bases of the bullets protruded.  

Lubed with Rooster HVR and loaded in a 357 mag with a health charge of WC297.   The picture was supposed to say “only the bevel base was painted." :P

Bullet fired into water -- engraving is crisp, edges of engraving are sharp (except for light skidding at the front band), no gas cutting, no etching.

Results are encouraging so far but I need to do more comparison tests before I jump to conclusions.  If the trend continues I'll write up an article for TFS.

Why paint only the base instead of the entire bullet, as most people do?   To isolate the problem.

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John Alexander posted this 25 October 2015

It looks like there is a lot of skidding by the unpainted bullet.  Am I seeing it right?  Why would painting the base have such a dramatic effect on skidding.  Why are the edges of the land marks rounded on the unpinned what is your theory on that? Fantastic pictures.

John

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mtngun posted this 25 October 2015

Well, it seems like if 10 different people look at a bullet recovered from the water tank, they have 10 different interpretations.   :D

Obviously we cannot crawl inside the barrel and watch what happens, so some guesswork is required to interpret what we see on the recovered bullet.

What some people are calling “skidding” I am calling “gas cutting.”     I don't call it “skidding” unless it is most pronounced on the front band.      When it is most pronounced on the bottom band, I assume it is gas cutting.

Alternatively, it's possible that the rounded edges of the engraving are due to lead building up in the corner of the grooves (I've verified with a bore scope that there is build up in the corner of the grooves when leading occurs).

Once the corner of the grooves is filled with lead deposits, the next bullet that travels down the barrel will get gouged by the lead deposits, leading to gas cutting, which leads to more lead deposits.   Lather, rinse, and repeat.   

As for why the painted base seems to make such a difference, I'm guessing it functions as a physical barrier that protects the base from the hot gases so that it doesn't melt.     Ditto hi-tech coating, ditto powder coating, ditto gas checks.     Or at least that's the theory, which needs more testing before I can say it with confidence.

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mtngun posted this 25 October 2015

The bottom of a recovered painted bullet.   Unfortunately, most of the color washed out in the photo so it's hard to see the white paint.  So you'll have to take my word that most of the bottom of the bullet still has paint, but it's burnt off in spots, particularly around the edge. 

The ding on one side is due to impact inside the water tank.

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mtngun posted this 25 October 2015

BTW, I haven't seen the slightest bit of yaw on recovered bullets since switched to the “snug slip fit freebore” and 1-diameter or nearly 1-diameter bullets.    So the yaw problem seems to have been solved, but the freebore throat created some new problems, mainly velocity variation, that I'm still wrestling with.  

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John Alexander posted this 26 October 2015

Wider land marks at the front of the bullet = skidding is logical. Just what you would expect.   

Wider “land marks” at the rear = gas cutting-- also logical. But it is very neat and tidy gas cutting that looks more like a wide land mark than something melted away.

I don't have anything better to offer but it does make you scratch your head.

Thoughtful cast bullet shooters often remark that there is a lot we don't know.  We don't even have a clue what we don't know until we start looking at recovered bullets.  John

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gnoahhh posted this 26 October 2015

Interesting.

I think though, that if I were operating at nigh 2000fps I would have gone straight to a gas checked bullet. Have you experimented with epoxy coated bases at more sedate velocities, in terms of accuracy & leading?

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mtngun posted this 26 October 2015

No, I haven't anything with coated bases at “more sedate velocities.” This was my first test with coated bases, hopefully more will follow so we can see whether there is a general trend.

I keep blowing up my water tank so that is slowing down the tests. :D

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