Powder Density and Load Estimate

[merbeau]

I currently am using 3.2 grains of Universal Clays for a Magtech 148 gr LWC for my 38 Special that I use for Bullseye competition.

The first purchase of Universal Clays I used the Lee Loader VMD formula (powder opening (0.34) / powder charge (3.2 gr)) equaled 0.10625. After weighing I did find 0.34 to produce 3.2grains of powder. The inverse of 0.10625 equals 9.37 grains in1 cc and if divided into 3.2 produces an opening of 0.34 which is correct.

The second purchase using the same opening produced a powder charge of 3.0 grains for a VMD of 0.1133 which means this powder is more dense?

Taking the inverse of 0.1133 equal 8.826 grains in 1 cc and then dividing 3.2 grains by 8.826 equals 0.36 powder opening to produce 3.2 grains. My original opening of 0.34 according to this is 3.0 grains which is exactly what I optained when weighing the charge.

My question is do I reduce the charge of 3.2 grains downward to account for a denser batch? If so, would 0.1133 - 0.10625 / 0.1133 which equals 6.2% or 0.2 grains reduction?
Thanks

Robert

 

[Titegroups]

I'm a bullseye shooter also. Powder density is going to vary from batch to batch, IIRC 16% is the allowable std. As long as you load what you intend to use for a single match from the same batch you should be fine. Some people have a natural tendency to make things more complicated than practical, I use to suffer the same problem.

 

[rsrocket1]

No, if your first batch weighed in at 3.2g and your second batch weighed in at 3.0g, your second batch is less dense [\B]. You are supposed to load according to weight, not volume so you need a larger volume of powder in order to get the 3.2g needed to launch your bullets. If you used the same opening, you would be shooting a lighter charge.

Would it matter? Probably not unless you need to make a minimum power factor. If you had an autoloader, it may not cycle, but with a wheel gun, you probably wouldn't notice unless you were already so low that you would risk a stuck bullet.

If you want to keep the 3.2g load, you would need to increase the volume by 6.7% with this new batch of powder. I assume you made about 10 measurements to ensure you are really measuring out only 3.2g.

 

[merbeau]

Thank you Titegroups and Rsrocket1 for replying

A few clarrifications:

Statistics: I use 20 single powder measurements for my analysis to ensure enough degrees of freedom. The powder throws for each opening are very consistent. For example, of 20 throws only two (2.9 and 3.1) were outside of the 3.0 charge.

Load itself: This 3.2 gr load produced a 1.5 inch group out of my SW 52 from a Ransom rest at 50 yards. The group opens up when moving to either side of that load so obviously I am looking for consistency. Some people would probably call me OCD.

The recipe from my manual provides a charge from 2.9 grains to a maximum of 3.8, so my 3.2 grain load is on the lower end.

So if I understand correctly, the current load would need to be increased by 6.7% or 0.2 grains to keep current with the first batch. So this load should be at 3.4 grains? That would correspond to an opening of 0.37 which I do have and will check the charge thrown with this opening.

Thanks again

Robert

 

[rsrocket1]

You want to use the correct volume setting to give you 3.2g, not 3.4g. Of course, if you are using something like the Lee Disk measure or some other non-continuous powder drop, then you would need to shoot a few dozen at 3.0 and at 3.4 to see which is more comfortable to you. I seriously doubt that opening up groups at 50 yards is going to affect your Bullseye scores when shooting off the rest.

If you are OCD and you insist, then drop the 3.0 from the measure and trickle up on the scale just like the bench rest rifle guys do. If it makes you feel more confident, then do it. After all confidence plays a big part in shooting. I shoot skeet and it's a little like putting in golf or free throws in basketball. If you "think" something's off, you'll miss even if it really doesn't matter.

 

[merbeau]

Ok, I started playing around with a few other openings on my loader and found one that will throw a 3.2 grain charge conistently. I called Lee and Hodgdon technical support. Both said to load by grain and look for 3.2 grains. The guy from Lee indicated the VMD is to make sure that shooters with loads at or near maxium will not overcharge. He did say the wording was a little confusing.

Your are correct about confidence. Going into a match with some uncertainty will definitely affect your scores.

Thanks again

Robert