Throwing charges, weight variance

[Pharmseller]

I use an RCBS Uniflow dispenser to throw charges for my .223. I check weigh every 15th charge or so.

My goal is 23.5 grains but some are 23.4, some are 23.6.

So the question, how much impact does plus or minus 0.1 grain potentially have on accuracy?




P

 

[mtnbound]

I would not be concerned with a .1 of a grain.

 

[Castle Rock]

FA

 

[OXN939]

Disassembled and weighed the components of a partial box of Federal factory stuff I had a few years ago, out of curiosity. Charge weights variation averaged around .3 grains, with an outside spread of half a grain between the min and max I measured. So, for whatever it's worth, everyone getting good results with factory ammo is likely doing so despite a relatively large variance in charge weight compared to what most of us tolerate when handloading.

I always get it gnat's ass to the tenth since I'm mostly loading for hunting rifles, but a lot of loads are probably more tolerant of charge weight variations than you'd think. BLUF, one tenth not likely to affect anything.

 

[EdP]

I loaded some 280AIs yesterday. 55.5 gr IMR 4831. .3gr/55.5 x 100 = .5% How much of a difference do you think 1/2% is going to make? You can do the math for .1gr with your .223 load. I think it will be less than 1/2%.

The above is why developing a load ladder in .2 grain increments doesn't make much sense to me.

 

[waspocrew]

Definitely not enough to make a notable difference at all.

 

[Pharmseller]

I loaded some 280AIs yesterday. 55.5 gr IMR 4831. .3gr/55.5 x 100 = .5% How much of a difference do you think 1/2% is going to make? You can do the math for .1gr with your .223 load. I think it will be less than 1/2%.

The above is why developing a load ladder in .2 grain increments doesn't make much sense to me.

Thanks to all who took the time to reply.

I particularly liked this way of looking at it.

0.1/23.5 = 0.0043 (rounded up). So less than one half of one percent.





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[Mojave]

50-80 FPS.

 

[MikeDeltaFoxtrot]

If your margin of error is .1 grains, you won't know the difference.

 

[11bar]

Sling some powder and go shoot. I think there should be an emphasis on precsion but don’t get to hung up on it. People for the most part can’t shoot better than the ammo anyways.

 

[JF_Idaho]

.5% +/- @2700fps would be around 27fps

 

[TaperPin]

One full grain of varget in a 223 makes roughly 100 fps difference in velocity - it’s not a big stretch to assume 1/10th gr will make roughly 10 fps difference. Not much of a difference for short range use under 500 yards.

 

[JF_Idaho]

One full grain of varget in a 223 makes roughly 100 fps difference in velocity - it’s not a big stretch to assume 1/10th gr will make roughly 10 fps difference. Not much of a difference for short range use under 500 yards.

Just did 23-24gr varget yesterday under a 75eldm 150fps difference.

Should be said that with rounding to 1/10gr +/- you are getting up to 3/10 variation in charge weight.

So in that scenario roughly 45fps.

 

[TaperPin]

Just did 23-24gr varget yesterday under a 75eldm 150fps difference.

Should be said that with rounding to 1/10gr +/- you are getting up to 3/10 variation in charge weight.

So in that scenario roughly 45fps.

I was just going with chrono data from nosler with 77 gr bullet - 22gr to 23gr was 100 fps and 23gr to 24gr was another 100 fps. An additional 10 fps variance from average isn’t much (20 fps addition to extreme spread). I don’t see how it triples.

 

[JF_Idaho]

I was just going with chrono data from nosler with 77 gr bullet - 22gr to 23gr was 100 fps and 23gr to 24gr was another 100 fps. An additional 10 fps variance from average isn’t much (20 fps addition to extreme spread). I don’t see how it triples.

It triples because it round to the tenth. So until you're over .15 it doesn't round to .2
.15 over plus .15 under equals .3

 

[EdP]

In the interest of more detail, I went back and looked at my load development records for the 280AI. I had a load of 55gr and a load of 55.5 gr that I could compare. The avg MV for the 55.5 gr load was 16 fps faster than the 55 gr load. That 1/2 grain is .9% of the 55.5 gr load. A straight line interpolation for .3 grains would suggest a difference in MV or 9.6fps. It's not nothing but it's not much to worry about either.

 

[seand]

Unless your loading technique is extremely dialed in, you likely won’t see any meaningful difference in Velocity SD’s with +\- 1/10 gr vs weighed charges. Assuming a significant enough sample size to get reasonably accurate SD’s.

 

[IAm_Not_Lost]

The first question would be what are you using to weigh and verify the charges? With the basic pocket digital scales I see an occasional variance of about 0.1gr

Secondly, a total variance of 0.3gr would potentially lead to a velocity swing of maybe 20-50fps, depending on what cartridge. It won't specifically affect accuracy, but it could change long range elevation impacts a tiny bit. You're talking 600 yards and further generally.

 

[Koda_]

My guess is it will affect your Standard Deviation more than your average velocity or 100yd POI. I would think this matters at long range...

 

[Vern400]

Out at 300 yards you'll probably never see that.
400 to 500 yards starts to weed out problems.

If you really want to know, load 10 identical shells meaning every single thing perfectly identical including the powder charges. Run about 10 of them across the chronograph and get your SD and ES.

Then do it with the ones with the thrown charges. The difference will be the answer right?

I have to be careful with my RCBS charge master to let it warm up long enough. If I don't, it will have a zero shift of about 0.1 grain after some minutes of use. My loading room is out in the barn and it's not temperature controlled. And it only reads one decimal point so there's got to be 0.1 grain just in rounding error even if 100 charges say 50 grains right?

I'm still getting SD of 7 or nine and a 10 shot string. That's way better than I am at shooting. Your 223 might be a little more sensitive because my charge weights exactly twice yours. Once again, it's not too bad.