I’m relatively new to reloading, I’ve reloaded about 400 rounds for my 7mmRM and just started with my 204. I’m a bit OCD when it comes to reloading and I started with an RCBS supreme kit, read the manual front to back, minus the load data as it’s a bit boring, if I don’t have the cartridge.


My main question or rather concern is in regards to powder measurements. I have a RCBS digital scale and when I load I notice that to achieve the desired weight in tenths of a grain usually means one granule or half of a granule difference to make it to my desired weight. I know that I’m not achieving that precise weight down to the 100<SUP>th</SUP> of a grain. So how much difference should a “heavy” load i.e. 20.11 grains versus a “light” load 20.19 grains make in the final accuracy in the cartridge?


Am I just being overly obsessed?

Yup, you are. :)
A weight difference in powder charge of 1/10th of a grain makes absolutely zero difference in terms of accuracy and trajectory. It's just too small a difference, given all the other variables in reloading and shooting.
Many benchrest shooters don't even weigh charges. They have very accurate measures set to throw the weight of poder they know is the right load, and leave it at that. They know that even in a super accurate rifle, a 1/4 grain variation in powder charge is meaningless.

Your RCBS scale won't show hundredths of a grains. It should resolve only 10ths of a grain. Only lab type scales have resolution of more than one place after the decimal point in grains. However, if you accidentally are using the scale set to read in grams (gm) instead of grains (gr), you would then get two decimal places after the decimal point. There are 15.432 grains in a gram, so 20.11 gm = 310.345 grains. Too much to fit in a 7 mm RM case, so I don't think you are doing that. I am just sounding a warning to be careful what units the scale is set to so you don't get an accidental overcharge.

The reason 0.1 grains is all you can see on a typical loading scale is that it is too small to matter in all but the highest accuracy benchrest guns firing at very long range in zero wind conditions. I saw recently there was a new world record five shot group for 1000 yards that was under an inch. If you get up into that precision range, get the Acculab VIC123 scale from Sinclair. It is a stripped down lab scale and resolves 0.02 grains and has a price tag of about $300.

The best practice, though, is to find a load that is accurate over a range of powder charges so it doesn't matter so much. Catching a barrel in the right part of its harmonic vibration will allow that. Dan Newberry's optimum charge weight site is all about that idea. He qualifies only loads that perform equally over a range of 0.6 grains of powder (±0.3 grains from nominal) and perform well in a variety of different guns. It is an interesting idea. You can read about it and how to develop your own, here. (http://home.earthlink.net/%7Edannewberry/dannewberrysoptimalchargeweightloaddevelopment/index.html).

The effect of a change in powder weight of 1/10th grain is minuscule. To nitpick, the actual effect is dependent on the speed of the powder and the size of the charge; it might have a detectable effect in a pistol load of, say, 4.6 gr but not so in a rifle load of 40 or so grains. But in the real world, the change in velocity would probably not be greater than the random variations with any powder charge.

Bud W
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I think I'll go see the doctor and get some OCD pills for when I reload.

Thanks for the replies and I think I'll go read about creating my own loads. I felt fairly confident that small changes in the weight of the charge would make very little difference especially when I was using 72 grains of RE22 with a 110 grain hollow point. But with my new 204 using around 20 grains of BLC-2 the percentage change in 1/10 of a grain goes up alot faster. I'll be shooting some of those 204's this Saturday so we’ll see how it goes this time. I've noticed in the past that when I load near the bottom of the power range or starting loads my POI accuracy is all over the place and as I raise the load up the groups will tighten up a bit, some powders go all over the place, H1000 being one of those.
For my own education I started with IMR 4350 because the book told me that was a very popular powder for my rifle. Unfortunately for me, the book and my rifle had never been introduced. So I went with H4350 and oddly enough it seemed a little better. Then the OCD kicked in and I began to wonder what would happen if I used that really slow H1000 powder, and what about that RE22. It appeared to me that my rifle liked middle of the road powders. So I will continue to mess around with these loads, as long as the “boss” doesn’t begin to feel too abandoned.

Actually, for any such digital readout the accuracy is what's stated (the item's specifications), plus or minus one count. That's as good as anything digital gets.

I doubt if we could tell any difference in accuracy for most cartridges with charges varying by .3 gr., or more, if the load is well worked up to begin with.

I prefer to discuss it in terms of percent of the total charge, rather than absolute weights, because a couple tenths of a grain make a whale of lot more impact on the 10-grain charge for a .22 Hornet as compared to the 120-grain charge for some mega-magnum!

As a general rule (to which someone can and does always report an exception), a variation of a half-percent in charge weight will go unnoticed among all the other variables. In some rifles and loads, a full percent of the charge will make very little impact.

In your desired 70-grain (approximate) load, that means being 0.3 off shouldn't make you quiver with dread. If you had as much as 0.7 variation from charge to charge, you might want to try to improve it, but only if test-firing shows that it does affect the accuracy and/or velocity more than you'd like.

My abbreviation manual got lost, or I forgot where I put it.
OCD?
As for charge weight, I used to throw charges of H4831 for my .300 Win Mag. As the powder measure couldn't throw the full charge weight, I dialed it back to half a charge, and did it twice. The best I could do with this Mauser actioned rifle with a factory barrel was six shots in .6 inches at 100 yards, a couple of times (six shots because that was two magazine loads).
Best chronograph results were only an extreme spread of under 10 fps the couple of times I checked.

Al,
Obsessive Compulsive Disorder.

DiRL,

The guys are right. I was thinking in terms of your 7 mm RM, and not smaller rounds. Some really little guys, like .32 S&W or even the .25 ACP have full charges in the ballpark of only one grain, so a tenth can make some serious difference there. Even in the .45 ACP, I've had as little as 0.2 grains of Bullseye prove critical to accuracy and proper functioning. Still, if you can find a load that is not very sensitive to charge, it is your best bet for consistent performance. I had an accurate .308 load for the 155 grain Sierra Matchking using Scott 3032 that didn't change 100 yard group size at all over a very wide charge span of 2.5 grains in Remington cases. Alas, Scot's extruded powder plant in Scotland burned down and was never rebuilt, so their excellent rifle powders are no longer available. Their 4065 was the best all-around .30-06 powder I had ever found.

Ranger335v,

There are actually strategies to reduce error in the least significant digit (abbreviated LSD, if that isn't a trip?). It can be made to approach ±0.5 LSD rather than ±1 LSD. In the case of the VIC123, for example, its display rounds up from an internal measurement precision that is ten times the displayed precision. It further averages 10 of those higher precision internal readings before updating the display, which reduces the probability of a display error by another factor of 10. I have no idea whether the less expensive plastic load cell scales are using these approaches, but I expect they are at least doing averaging? I remember looking at a 16 bit A to D converter once that averaged sixteen readings internally before updating the output. That allowed it to provide 18 bits of output, even though the two least significant bits (LSB) were created mathematically rather than by native resolution.

Unclenick, There are days I have to teach math to some of my co-workers who are mathematically challenged. For a brief moment I think I'm pretty smart.

Then I read one of your very thorough and descriptive post's and realize I'm only slighter smarter than my fork when it comes to math.

Fortunatley I know enough math to handle 99.5% of what I need.

Then if I need help, I call somebody.

Sriously U-N thanks for helping us mortals out.

The most important feature of my RCBS scale is the safety.

If you haven't already, give Winchester 748 powder a try in your .204. Also, if you really get into the .204 loading, RCBS makes a competition seater die that has a bullet insert window in the body of the die, so no more pinched fingers.

Good luck and happy shooting!