Velocity Drops with Powder Increase

[Fast14riot]

I've found that testing with weights around your charge weights helps, say a 40 or 50 grain test weight, then add your kernels to check response rate. Also, no fluorescent lights around digital scales!

 

[Twicepop]

It's called............"the law of diminishing returns".

 

[RDRFab_65]

Updates:
I purchased a Gem 20 scale as a cheap test.
First i calibrated both my Hornady scale and the Gem 20 scale. I then tare'd the powder tray on each scale and tested repeated zero by removing and mounting the tray numerous times. Both repeated without issue. So i threw a rough 40 ish grain load and weighed it on each. Both agreed so i duplicated the repeat consistency test; success like the first time. So i pulled kernels out one at a time until i had the Gem 20 reading a flush a number with the hundredths as null (40.90). I transferred to the Hornady scale and it seemed to read low by .1 so i am assuming due to consistency reasons the Hornady is rounding.
I am going to use the Gem 20 on the next load test so i can see when the kernels are closest to the whole tenth desired. Going to be fun collecting more data. Thanks for the information.

 

[RDRFab_65]

1 more picture

 

[Ned Ludd]

Updates:
I purchased a Gem 20 scale as a cheap test.
First i calibrated both my Hornady scale and the Gem 20 scale. I then tare'd the powder tray on each scale and tested repeated zero by removing and mounting the tray numerous times. Both repeated without issue. So i threw a rough 40 ish grain load and weighed it on each. Both agreed so i duplicated the repeat consistency test; success like the first time. So i pulled kernels out one at a time until i had the Gem 20 reading a flush a number with the hundredths as null (40.90). I transferred to the Hornady scale and it seemed to read low by .1 so i am assuming due to consistency reasons the Hornady is rounding.
I am going to use the Gem 20 on the next load test so i can see when the kernels are closest to the whole tenth desired. Going to be fun collecting more data. Thanks for the information.

If you haven't already seen it, there is a very good thread about the Gem20.

http://forum.accurateshooter.com/threads/remarkable-little-scale.3985753/

In post #63, I did a direct comparison of charge weights as measured between the Gem20 and a several thousand dollar Mettler-Toledo analytical balance. The Gem20 fared pretty darned well for a balance that only cost $20. It is capable of very close to +/- one kernel accuracy.

 

[RDRFab_65]

I read that prior to purchase. Im really happy it is working out for me as well. Never know the condition after ace ventura shipping gets their hands on it.
Its very fast at reading change so it should be very nice combined with the trickler.

 

[Fast14riot]

I've found the Gem20 response rate to be quick enough that I can get a good groove going and not have it shut off between charges. I did several tests with known accurate loads in a couple of my rifles and it did improve my vertical dispersion a bit in one, and gave me enough confidence to use it regularly.

 

[RDRFab_65]

I've found the Gem20 response rate to be quick enough that I can get a good groove going and not have it shut off between charges. I did several tests with known accurate loads in a couple of my rifles and it did improve my vertical dispersion a bit in one, and gave me enough confidence to use it regularly.

Thats good to know. Im going to expand the origianl test and see if the gem 20 reduces the velocity variance from one weight to another. This should help determine if the powder is doing funny stuff.

 

[RDRFab_65]

Update: I got another ladder test loaded. I am just waiting for some range time. Hopefully in the next couple weeks.
I should not that the tiny tray that came with the gem20 was a pain in the rear to deal with. The gem 20 has this face plate that has a raised surface in it so i couldn't put a larger tray on it. I removed the face plate and checked the calibration and consistency of reads through a range of powder loads until i was satisfied removing the faceplate was not causing problems. for $20 i was not afraid of ruing this gem20 scale. i zero'd my larger tray on both scales and threw a few random powder measure to check scale agreement and found them to be nearly identical. there was a difference in that the gem20 displays the hundredths digit. it makes it easier to know if i am closer to the target tenth or closer to the next higher tenth.
When reloading my ladder test I used the gem20 and targeted the same near true tenth +-.02 grains. Looking forward to see how just an extra digit changes the velocity variance.

 

[Webster]

I have been reading through the forum and found interesting arguments, but I am not finding anything to help me understand this velocity drop as my grain weight increases.

I performed a ladder test from 40 to 42.8 grains in +.2 increments.
As shown you can see the grain increases but drops a fair amount of fps. I find it hard to believe these are chamber issues and suspect these are ignition issues. I do have some concern that the scale i am using just might not be accurate enough. I do an initial throw then trickle up to final grain weight on a Hornady GS-1500 scale. I can drop anywhere from 3-5 powder grains before the scale registers an increase in weight and sometimes that increase shows .2 grain increase instead of .1 grain increase. So, there is some concern that the refresh rate or accuracy is too low on this scale.
Any thoughts on this topic would be greatly appreciated.

Load Information:
All of the rounds are once fired Hornady brass, full length resized to a .001-.0015 shoulder bump, and the necks are sized slightly under and pushed to final dimension using a -.002" expander mandrel. When loading to final depth, I have noticed a very consistent tension between rounds. Concentricity is between .001-.003" and OAL with comparator is +-.001" max from target depth. I use Lapua Scenar 139 gn bullets for 6.5 CM, Federal 210 primers, and the powder is RL17. I have a 29" Heavy Target barrel so thats why I use the slightly slower burn RL17.

Onw shot group. The chart assumes 0 ES. If you shot a 5 or 10 shot group you might have a ES of 20. That means some of the shots with the same powder charge will be 20 fps above and 20 fps below the mean.