RCBS 502 calibration is off

[Kevin1]

I upgraded my scale from the cheap lee to RCBS 502. But the problem is that it’s not calibrated correctly. When zeroed properly, it shows +0.2 grains all the time.

I found this the hard way when 100 loaded rounds weren’t give me the usual accuracy (because loaded with 42.8 instead of 43g). So to get 43 g, I have to read 43.2 g on the RCBS balance.

Not a deal breaker, but a little disappointed at RCBS. My cheap Lee scale was more difficult to use, but the calibration was dead on!

 

[melloyello]

How are you zeroing your scale? Are you setting the zero with the elevation adjustment while everything is on zero and your brass cup is in the holder? Are you checking your zero everytime you sit down to reload? Is your table level? Etc, etc, etc,

 

[Kevin1]

Zeroing every time I use it with the brass cup on the scale (and even checking the zero a couple of time during the session). BTW it would have been nice to be able to lock the screw to not lose the zero so easily (but that’s a different issue).
Since I’m zeroing this every time on my table (and I make sure it stays on the same exact spot), it really doesn’t matter if my table is not perfectly leveled (it would only be an issue if I run out of adjustments).

 

[melloyello]

Again, how are u zeroing it? And what are u comparing it to that is telling u it is .2gr off? If u are comparing to the Lee safety scale, don't.

 

[Kevin1]

I put the brass cup on the scale, put the both poises on zero and adjust the screw until it reads zero. Kinda basic and straight forward.
Once I suspected the calibration was off (+0.2 g compared against Lee when measuring 43 g of Varget), I started weighting a 5 or 6 SMK 175 g bullets. The RCBS was reading 175.2g on the average.

Please let me know if you suggest another way to verify the calibration (as the +0.2g on the SMK might very well be within the range of tolerance of this bullet).

 

[seanh]

just add .2g to your load and move on.

 

[milo 2.0]

just add .2g to your load and move on.

Unless you have scale check weights, you don't know which scale is off. I wouldn't do what seanh said, just add .02, it might get real whacky as the weight rises. Figure out where it's at first.

 

[roggom]

You can not use a bullet as a check weight, you must use a check weight. It could be that your Lee was not properly calibrated in the first place.

You will be able to verify which one was off with the check weight, then rework your load accordingly.


^^^ beat me to it

 

[Continuum]

Perhaps look into getting some check weights. I have a 502 also, and also weighed out 175gr SMKs : ) The zero with no weight might be different than the zero with a 100gr + load. An analogy might be like this IR thermometer I just bought. The manual says (something like) it is +/- 1deg under a certain temp, and +/- 5deg above 600deg. Typically the accuracy and/or precision are a more complex math formula that involves the magnitude of what you are measuring as one of the variables. So as the magnitude of what you are measuring changes, so will the accuracy of the instrument doing the measuring.

 

[seanh]

Unless you have scale check weights, you don't know which scale is off. I wouldn't do what seanh said, just add .02, it might get real whacky as the weight rises. Figure out where it's at first.

absolutely right...don't do as I suggested. I misread the "cup" as a calibration weight.

Get yourself some calibration weights...from there you can properly set the zero.

 

[aloreman]

If 2/10ths of a grain changes your loads accuracy your load isnt in the center of the node. 2/10ths is half a percent of the 43 grains. i promise you that you cant outshoot 2/10ths

 

[Kevin1]

If 2/10ths of a grain changes your loads accuracy your load isnt in the center of the node. 2/10ths is half a percent of the 43 grains. i promise you that you cant outshoot 2/10ths

You’re right.
As you see in this latter test, my accuracy node seems to be between 43g and 43.5g according to Lee scale. With 42.8g I did see more vertical dispersion than expected.
http://www.snipershide.com/shooting...es/103516-savage-10fp-0-5-moa-rifle-pics.html

My next loads are 43.2g according to Lee (reading of 43.4 on RCBS) to make sure I’m in the middle of my accuracy node.
Going forward, I’ll just assume that my accuracy node is 43.2 to 43.7 on RCBS and 43 to 43.5 on the Lee. So basically it’s like the other comment “just add .2g to your load and move on”

From a practical point of view, I don’t really think I need to care about which reading is more accurate.
Not to mention if I find out that the RCBS is off by .2g, I’m not sure if it’s worth the trouble of calibrating it accordingly (not to mention the added cost of calibration weights).

Out of curiosity I might use the sort of calibration weight that came with Lee. It’s a square inch of paper with a known weight (at least it came with something to verify the zero )

 

[Tickle]

I upgraded my scale from the cheap lee to RCBS 502. But the problem is that it’s not calibrated correctly. When zeroed properly, it shows +0.2 grains all the time.

I found this the hard way when 100 loaded rounds weren’t give me the usual accuracy (because loaded with 42.8 instead of 43g). So to get 43 g, I have to read 43.2 g on the RCBS balance.

Not a deal breaker, but a little disappointed at RCBS. My cheap Lee scale was more difficult to use, but the calibration was dead on!

This is the way that I calibrate my 1010's. You can do the same with your 502. 1st: with a good level, confirm the surface that your scale is sitting on is level. 2nd: Place your level on the scale and level the scale with the adjustment screw, don't pay attention to the reading yet, just level the scale. 3rd: With everything level set the (2) poise at zero. Remove all of the little lead weights from the pan holder and put them in the pan. Now place the pan on the pan holder and see what the scale reads. If it is not zero, add or remove some of the little lead weights till it reads zero. 4th: Put the little weights back into the pan holder. 5th: Confirm with a couple of check weights, "I use a 50gr and a 20gr" to see what the scale reads. It should read exactly what the check weights weigh. Now move the (2) poise back to the zero and see if this is repeatable. I use this method with excellent results. If your scale is used there are a few other things that can affect the scale not zeroing but I'm assuming that your's is new.

Hope this helps.

 

[melloyello]

Yes definitely get a check weight. That's the only way u will truly know.

 

[seanh]

get the weight set. I know it seems unnecessary but you'll be glad you got it once you have it.

never have taken the weights out of the scale...not a bad idea though. What I have done is get a paper clip and cut it down...place it at the same place ever time, on the .Xg bracket.

Don't forget that this scale is .1g accuracy...you're only off .1 by that accuracy standard.

 

[aloreman]

Other things to can effect your accuracy such as a temperature difference of as little as 5 degrees.

 

[aloreman]

As long as there consistant scales dont need to be accurate. Ive seen many groups that measure .01 shot at 200 yd benchrest competitions that were loaded from powder throwers

 

[armorpl8chikn]

It does matter if your table is level, I have mine setting on a piece of marble that itself has been leveled on my bench. You need check weights, they sell them for a reason. As has been said .2gr will not matter, I would add UNLESS you are running the edge of an accuracy node. My big rifle "06" has a wide accuracy node of a bit over 1 grain. I could probably load it with a set of Lee dippers and get great results(just making and exaggerated joke there).
Make sure your beam is clean and dust free as well. I clean mine every so often very carefully with a soft bristle brush.