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Thread: RCBS 500M Weights

  1. #1
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    RCBS 500M Weights

    Here is data from my cast RCBS-500M weights, using pure lead. The average weight was 535.51 grains.



    531.9
    532
    532.2
    532.3
    532.3
    532.4
    532.5
    532.6
    532.8
    533
    533.1
    533.2
    533.5
    533.6
    534
    534.2
    534.4
    534.4
    534.5
    534.6
    534.7
    535.1
    535.3
    535.3
    535.3
    535.3
    535.4
    535.4
    535.5
    535.5
    535.6
    535.7
    535.8
    535.8
    535.8
    535.8
    535.8
    535.9
    536
    536.1
    536.1
    536.1
    536.2
    536.2
    536.3
    536.4
    536.4
    536.4
    536.4
    536.4
    536.5
    536.5
    536.5
    536.5
    536.6
    536.6
    536.6
    536.7
    536.7
    536.7
    536.7
    536.7
    536.8
    537.1
    537.1
    537.1
    537.1
    537.4
    537.4
    537.5
    537.6
    537.7
    537.8
    537.9
    538

  2. #2
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    I was casting up some more of these the last couple of days to go play with my Pedersoli P58 again.

    I re-discovered that this bullet is really a pain in the butt to pour with a bottom-pour pot. Only now I also have a ladle.

    I cast up 19 bottom pour that appeared to have no void. They averaged 536.2 grains.
    I cast up 28 that had visible voids. They averaged 536.4 grains.

    I then cast up 84 using a ladle. They averaged 539.4 - about 3 grains heavier than with bottom pour.

    It looks like there is little benefit in throwing out bullets with voids vs. those without - in fact it may well be that the bullets without voids actually have internal voids that are not on the centerline of the bullet. At least the ones with voids have voids directly at the apex of the core pin.

    But side-pouring using a ladle appears to do away with the voids altogether, at least from the heavier weight.

    Steve

  3. #3
    jonk is offline
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    I get fewer voids with ladle pouring, this is true; however, I do still get voids with a variety of molds. Whether they are on the centerline with the pin or not is debatable; I had one this last nationals that I noted had a void and shot it anyhow... and ruined a target that had a 38 2-x going with one out in the 5 ring. Me? Possibly. The void that was slightly bearing to the left? Possibly. Who knows? I just toss any bullets with voids visible, however I pour them.

    Interesting though, that the weights were so far off the benchmark. 495 to 505 I'd see as normal; much above that and I'd suspect an out of spec core pin or something.

  4. #4
    Kevin Tinny is offline
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    Hello:

    Some thoughts:

    Your listed weights are well within a range that should not materially increase the group size.
    A few grains one way or the other for that weight bullet is not significant at reasonable ranges.

    One thing with weighing: Electronic scales have a tolerance in the form of +/- amount of weight, even if zeroed AND the weight reading has stabilized. So a bullet may weigh more or less by the tolerance another time. For your weight bullet, this can be a FEW GRAINS. Also, in many electronic scales, voltage variations from weak batteries or normal AC fluctuations can cause strange readings. There are relatively inexpensive electronic scales with narrow tolerances and power leveling circuitry.

    The weigh readings appears to show increasing weight. That could be due to mold or metal temperature increases. Unless the mold, core pin, if any and sprue plate are FULLY up to casting temperature, the finished casting can vary in density and size. I dip the leading, bottom edge of my closed mold INTO the molten lead to help it reach proper temperature. I do the same thing with the sprue plate extension. If there is a core pin, as with hollow based designs, its temperature is critical to uniform and complete fill-out. An old trick is to dip it into the metal for a few seconds and hang it in the flame of a propane torch between castings.

    Pure lead flows and fills-out LESS evenly than an alloy containing a slight amount of tin. I use 80 or 60 parts of ABSOLUTELY pure lead to one part of tin, by weight. That small an amount of tin will NOT change hardness enough to reduce skirt expansion or separate in the alloy to cause weight variations. THE NRA's cast bullet experts have confirmed this in their excellent Cast Bullet Handbook.

    The SIZE of the sprue plate hole is often too small for large weight/size bullets. I open mine to around .200" and polish the underside on 600 grit to remove any burrs.

    Lastly, maintain the alloy temperature at 750 degrees to 775 degrees, NOT MORE!
    An immersion thermometer from RCBS or ROTAMETALS will confirm this as pot dials are unreliable.

    I ladle pour most bullets using the side pour technique. It takes a bit of experimentation to establsh a rhythm.

    Finally, sorry to warn you, but RCBS has been reported on forums for quality control issues for sprue plate holes being off center and other irregularities that the Customer Service types said were within specification. Watch that the INSIDES of the handle projections that lay in the block cutouts don't contact the bottoms of the cut-outs. This can put pressure on one side of the closed blocks.

    Thr LEAST influential factor in my black powder target shooting is bullet weight variation. Way more influential were SEATING PRESSURE variations that fractured powder granules, producing velocity variations. The proper use of a chronograph will help isolate these factors.

    What you should look for are flyers outside the normal group or chronograph readings that are over 35 fps different.

    Respectfully,
    Kevin Tinny
    Last edited by Kevin Tinny; 10-24-2016 at 04:26 PM.

  5. #5
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    Your listed weights are well within a range that should not materially increase the group size.
    A few grains one way or the other for that weight bullet is not significant at reasonable ranges.
    Once I determine an average weight, I weigh all bullets and discard any that are +/- .5% of average.

    You are correct that once I started ladle pouring most of the bullets lie within the range.

    One thing with weighing: Electronic scales have a tolerance in the form of +/- amount of weight, even if zeroed AND the weight reading has stabilized. So a bullet may weigh more or less by the tolerance another time. For your weight bullet, this can be a FEW GRAINS. Also, in many electronic scales, voltage variations from weak batteries or normal AC fluctuations can cause strange readings. There are relatively inexpensive electronic scales with narrow tolerances and power leveling circuitry.
    If you are using a reloading scale that cannot resolve with 3 grains, you have a serious problem (for smokeless applications). Any scale suitable for reloading had better be capable of repeatable accuracy to within one-tenth of a grain at least.

    I am using the RCBS Chargemaster 1500 scale, and I find it to be of very good quality and highly repeatable.

    Now sensitive scales are sensitive to their environments. I have heard that ballasts from overhead lights, vibrations, and air currents from air conditioners/fans can cause fluctuations, which is why it is important to avoid these.

    The weigh readings appears to show increasing weight. That could be due to mold or metal temperature increases. Unless the mold, core pin, if any and sprue plate are FULLY up to casting temperature, the finished casting can vary in density and size. I dip the leading, bottom edge of my closed mold INTO the molten lead to help it reach proper temperature. I do the same thing with the sprue plate extension. If there is a core pin, as with hollow based designs, its temperature is critical to uniform and complete fill-out. An old trick is to dip it into the metal for a few seconds and hang it in the flame of a propane torch between castings.
    The appearance of increasing weight is solely because I have sorted the weights numerically. I do not weigh them in order as when casting they become all randomly jumbled together.

    However, I do absolutely now believe that, especially on the low range, weight tracks with mold temperature. When you examine the above chart you will see that the graph is fairly linear except below about 535 grains. When I examine some of the light-weight bullets, I can tell that they were cast cold and there are wrinkles in them that, by eye alone, I would have passed. But clearly there is a significant weight difference. Likewise I suspect that the much smaller uptick at the high end is a result of mold over-temperature.

    I now pre-heat my molds on a propane camp stove before casting.

    Pure lead flows and fills-out LESS evenly than an alloy containing a slight amount of tin. I use 80 or 60 parts of ABSOLUTELY pure lead to one part of tin, by weight. That small an amount of tin will NOT change hardness enough to reduce skirt expansion or separate in the alloy to cause weight variations. THE NRA's cast bullet experts have confirmed this in their excellent Cast Bullet Handbook.
    I cast 99.99% pure assayed lead with a tiny piece of tin solder thrown in the pot. I agree the tin helps with fill-out.

    Lastly, maintain the alloy temperature at 750 degrees to 775 degrees, NOT MORE!
    An immersion thermometer from RCBS or ROTAMETALS will confirm this as pot dials are unreliable.
    That is about what I cast. I use an RCBS thermometer.

    Thr LEAST influential factor in my black powder target shooting is bullet weight variation. Way more influential were SEATING PRESSURE variations that fractured powder granules, producing velocity variations. The proper use of a chronograph will help isolate these factors.
    I do not yet have a chronograph. For a proxy I just look at my group sizes. I require my competition guns to shoot clover-leaf holes off of a bench at 50 yards (25 for my smoothy). I've achieved this with all my guns except my poor Uberti 1858 which I left with Ball Accuracy at the last Nationals to see if he can work his magic on.

    Steve

  6. #6
    jonk is offline
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    Just food for thought: I'm not saying anyone is right here, as differnent gun, bullet, and lube mixes may require differing quality control methods, but after culling any bullets with obvious voids or skirt issues, I tried ONE time weighing them. Shot 30 rounds in 5 round shots of weighed bullets vs. whatever I grabbed.

    No difference at 50 yards. All cloverleaf groups benched. Maybe some slight difference at 100, but all within minute of tile, so I gave up on that.

    Now, for shooting at longer ranges, whether with black or smokeless powder, you betcha, I weigh bullets.

  7. #7
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    For me, it's a mental thing.

    I like to eliminate all variables possible. It's important for me to have 100% confidence in my gun and the load. Otherwise it wreaks havoc with me on the firing line as I start second-guessing my shots and start being tempted to "chase bullet holes" and "correct" my aim. It's one reason I'm not a big fan of spotting scopes or otherwise checking my hits while shooting. There should be no reason to do so if your gun and load is sighted in.

    Steve

  8. #8
    jonk is offline
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    Quote Originally Posted by Maillemaker View Post
    For me, it's a mental thing.

    I like to eliminate all variables possible. It's important for me to have 100% confidence in my gun and the load. Otherwise it wreaks havoc with me on the firing line as I start second-guessing my shots and start being tempted to "chase bullet holes" and "correct" my aim. It's one reason I'm not a big fan of spotting scopes or otherwise checking my hits while shooting. There should be no reason to do so if your gun and load is sighted in.

    Steve
    If I were shooting a glass bedded cartridge gun from a bench, I'd entirely agree with you. As it sits, temperature, humidity, wind, the position of the sun and whether it is cloudy or sunny... I DO chase bullet holes. My guns were sighted in on a particular day with particular temperatures and humidity; these variables may mean that I can shoot pots all day long or miss tiles all day long. If I have a bad bird board, I very certainly look at where I was hitting; usually it's high or low.

    Same gun, same load, shot in 20 degree temps vs. 100 degree temps shows a 80 fps variance in chronograph tests. On a cold day I have to hold high; on a hot day, 6 o'clock. Sun to the right? It artificially illuminates the right side of the sight, and puts shadows on the bird board, meaning I focus on the point of illumination and SHOOT right. Sun right overhead? Illuminates the top of the sight and I shoot low. Sun up, sights up.

    I'd rather hand weigh each charge than each bullet, as I think that variance there is a lot more damning; still, as someone who came to this sport from high power and bench rest shooting, I can't criticize the idea that you weigh every bullet, and just say I never felt the need.

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