How Important is 1/10th of a Grain?

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AZ_M&P

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I'm fairly new to reloading, and I'm curious how important 1/10 of a grain is (provided I'm not at or over the Do Not Exceed).

The reason I'm asking is I'm using Lee Auto-Powder Disks, and I'm finding that with some powders I can throw a charge spot on, but with other powders it varies by as much as 1/10th g either way.

One of my carry guns is a .40 cal M&P Pro Series, and I'm making loads for it using Bullseye. With a 165 g FMJ RNFP the Lyman manual tells me I need to be between 4.8 and 5.4 g. The Lee disk for this charge in Bullseye recommends 2 different disk holes. Problem is one occasionally throws a 4.7, and the other occasionally throws a 5.5 (mostly 5.4 which I don't want to shoot on a regular basis. I use this gun for training, putting about 200-400 rounds through it, so I don't want to be at the upper end of the scale.

I sort of solved my problem by using a step drill to modify another hole on the disk by partially enlarging the lower end of the hole. Now I'm throwing a consistent 5.0-5.1 g. I'm happy with this, but I'm wondering - Is this acceptable or do I need to be dead nuts on?

Thanks for any advice guys, you all have been super helpful so far.
 
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Yes, but Alliant says you can go to up 5.8 with a 165 gr GDHP so all I am saying is that your max load will vary on what data source you look at and the "exact" bullet you are using.

Just be careful with those fast powders like Bullseye in the 40 SW. Better yet if you have or can find, use a slower powder in high pressure rounds.
From what you say, you should be fine. It also depends on how deep you are seating the bullet and your COAL.

Speer says 5.3 to 5.8 for the 165gr FMJFN or the GD.
 
Read the directions that come with almost all powder scales and you will find that your powder scales will only read + or - one tenth of a grain accuracy. So, your measure may throw say, 5 gr charges everytime of a particular powder. However, your scale may give you a weight that varies plus or minus one tenth of a grain from the 5 grains thrown. The bottom line is with reasonable loads a variation of one or two tenths of a grain doesn't make any practical difference.
 
The only time 1/10gr matters is pushing über fast powders in small volume/high pressure rds. Anyplace Else, matters a lot less.
 
Nice fix and . . . even though you now know the rest of us wouldn't be too concerned about your reported variations . . . it was still the smart thing to do.

Dunno if you are aware, but Lee makes an Adjustable Charge Bar that should work well at the ~5gr mark. For $10 it may be worth your while . . . though maybe with shipping you might want to tack it on to some other order lol.
 
1/10 grain isn't even worth noting, much less being concerned about. I tried using some SR7625 to load 38 specials and found it unsuitable due to extreme position sensitivity. Tested with a chronograph the velocity ranged from 400 fps with the barrel pointed down prior to firing to 700 fps with the barrel pointed up prior to firing, a 300 fps swing in velocity. BTW, the 400 fps shots felt like shooting a 22 LR and werent much larger.

Thing is that the velocity didn't have much effect on the accuracy or the point of impact on the target, from a rest at 45 feet I was shooting cloverleafs at both velocities and the POI was within 1/2 inch between the two. Yeah, further out I'm certain the slow movers would exhibit a lot more drop but the point is that at handgun defense ranges huge velocity swings don't have much effect where the bullet hits. So don't be a bit worried about a variation of 40 or 50 fps, shooting offhand you would have to be some kind of Robot to notice any difference.
 
Wow... without a doubt some of the most knowledgeable guys around! I felt sort of stupid asking the question but I really appreciate your explanations and responses.

Thank you all!
 
AZ_M&P said:
Wow... without a doubt some of the most knowledgeable guys around! I felt sort of stupid asking the question but I really appreciate your explanations and responses.

Thank you all!
Click to expand...

Better safe than sorry and good to note that not all powders behave the same in your measure especially when you get to very small quantities.
For example a 0.2 grain variance when throwing a 2.0 grain load is a 10% variation which could be significant but the same 0.2 grain variance on a 20.0 grain load is only 1%
I am generally less concerned about the variation when I am in the middle of a range than at either the low or high end of published data.
 
scooter123 said:
1/10 grain isn't even worth noting, much less being concerned about. I tried using some SR7625 to load 38 specials and found it unsuitable due to extreme position sensitivity. Tested with a chronograph the velocity ranged from 400 fps with the barrel pointed down prior to firing to 700 fps with the barrel pointed up prior to firing, a 300 fps swing in velocity. BTW, the 400 fps shots felt like shooting a 22 LR and werent much larger.

Thing is that the velocity didn't have much effect on the accuracy or the point of impact on the target, from a rest at 45 feet I was shooting cloverleafs at both velocities and the POI was within 1/2 inch between the two. Yeah, further out I'm certain the slow movers would exhibit a lot more drop but the point is that at handgun defense ranges huge velocity swings don't have much effect where the bullet hits. So don't be a bit worried about a variation of 40 or 50 fps, shooting offhand you would have to be some kind of Robot to notice any difference.
Click to expand...

I never gave much thought to position sensitivity until I had a discussion with other shooters about alternative powders. Since some are significantly more or less dense than others, certain powders would fill the case to a greater degree. In a long case like a .38 Special it could mean a lot. It's interesting that you've tried to see how much of a difference there was in speed and how it affected shot groups. I would have thought there would be a bigger difference. Next time I take a trip to the range I'll see what it does at 25 yards with a bench rest.

As far as a powder difference of a tenth of a grain, I pretty much ignore an amount so small. When I reload I occasionally weigh a large number of powder throws in a row. I can be off by that much on numerous throws and, as long as I'm within that range either way, I consider it OK. As others have also pointed out, unless you have a very expensive scale, most are only accurate to a tenth of a grain.

Another interesting point, at least to me, is exactly how much unburned powder leaves the barrel. Years back, after a very busy night of shooting at an indoor range, we were cleaning up and someone commented on it. We picked up all the brass and then swept the remaining "dirt" into a small pile. We very carefully lit it with a match and I was surprised to see the pile of unburnt powder go up in flames. I suppose it would depend on how fast or slow burning the powder and barrel length as well.
 
I meant to ask in my orginal post.

What scale are you using to weigh your charges??

Is it a electronic or a balance beam type? Your variation could be with this!
 
I used to use an RCBS powder-trickler to get .223 rifle loads on the money. It didn't make any difference at all concerning accuracy...but then again I was target shooting with a Ruger Mini-14. :D
 
Rule3 said:
I meant to ask in my orginal post.

What scale are you using to weigh your charges??

Is it a electronic or a balance beam type? Your variation could be with this!
Click to expand...

I'm a longtime bowhunter who's pretty anal about the weight of everything - and I never got close enough with a beam scale to be happy.

I have what I suspect is a mid-range (in quality) digital scale, but I never thought about the scales accuracy abilities. I do know that if I run the ceiling fan on high when I'm using the scale it's sensitive enough that the air movement won't allow it to settle! I need to have the fan off to use the scale.
 
AZ_M&P said:
I'm a longtime bowhunter who's pretty anal about the weight of everything - and I never got close enough with a beam scale to be happy.

I have what I suspect is a mid-range (in quality) digital scale, but I never thought about the scales accuracy abilities. I do know that if I run the ceiling fan on high when I'm using the scale it's sensitive enough that the air movement won't allow it to settle! I need to have the fan off to use the scale.
Click to expand...

If you are anal, than ditch the digital scale and get a balance beam scale. There in lies you problem.

Unless you spent big money and bought a scientific, legal for trade electronic it's not gonna be accurate.

Most electronic are only accurate =/- .2 grain when they work correctly.

Most beams are made by Ohaus who has made them for 100 years. They work, do not shut off or die from bad batteries.

Powder measure or a scale is the most important tool in reloading.
 
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