Load dev help

[Pres100]

While working on a starting point for a 6.5 Creedmoor load, I loaded up a starting charge of 37.9 gr and worked up 0.2 gr per round just to get an idea of where velocities would land, pressures, etc. - one load per charge. The charges were carefully weighed on my beam scale - RCBS 505. I know it's not the best scale out there but I have checked against numerous other scales and have check weights that measure the same on other scales. I have also used for years successfully with plenty of other loads.
The results were not as expected and fluctuated in ways I wasn't quite expecting, at least to the level they did. Rifle was a ruger precision (muzzle Brake removed), chronograph was a magnetospeed. Powder was RE-17, bullet was 147 ELDM, brass 1x fired Hornady which was carefully prepped, 70 degrees.

37.9 gr. 2511 fps
38.1 2510
38.3 2549
38.5 2533
38.7 2561
38.9 2542
39.1 2610
39.3 2575
39.5 2630
39.7 2612
39.9 2648
40.3 2669
40.5 2660
40.7 2650
40.9 2683

Didn't expect to see velocity drops of 20 fps for a charge that was heavier (ex. 38.5, 38.9, 40.7) does this seem normal?

 

[Catgunguy]

I have seen this also but want to hear what the pros have to say.

 

[Sheldon N]

Did you skip 40.1?

Looks like there's a lot of variability in the data, but a node seems to exist between 39.9 and 40.7. All those charges span only 21 fps.

 

[Pres100]

Yes, forgot the 40.1, but really trying to figure out why such large drops in velocity. I know I didn't mislabel rounds (they were all loaded and marked on the case) and I didn't rush through charge weighing.... checked each one multiple times.

 

[Jarhead6870]

In my opinion, basing velocities on 1 round is not very good measure of true velocity for a charge weight. Just think of extreme spreads and how they might enter into the picture. One load could be the high of your spread and the next load might be the low of its spread. Since I base my load development around finding the most accurate load, velocities are not important to me until I find an accuracy node and determine the best charge weight. At that time, I load 20 rounds and do a chrono run with a Magnetspeed to find my velocity for my ballistics. Many on this forum, use a Labradar or chrono that is not attached to the barrel and do all of their load work over the chrono. I am more of a steel shooter with the occasional F-Class match for fun so I don't compete at the level as many here and as such, probably don't require as much from my ammunition.

 

[Pres100]

Thanks, I do take into consideration the ES, but hope that it isn't that far apart for 0.4 grains. The basis, of the test was to gain a basic understanding of velocities to look for the nodes and start doing more detailed work up. I guess I just didn't quite expect the velocity reductions in that amount after increasing the charge weight by .4 gr.
I'll just do some further work up with more rounds for data.

 

[Sheldon N]

I would expect that with a 505 scale you've got a fair bit more variability in your powder weights than you expect. At least that was my experience with my old 505 once I compared it to more trustworthy reference scales. That's likely some of the cause of your up/down spikes in the 38.5 - 39.5 range. However, it's not unusual to see a slight downturn in velocity around the node. I got the same thing when load testing for my Dasher, even when weighing the powder charges precisely.

 

[T-shooter]

You might try figuring the velocity necessary to keep the bullet stable for the distance you are shooting and then work the load in that range for accuracy. Most times, the fastest is not the most accurate.

 

[seymour fish]

You might try figuring the velocity necessary to keep the bullet stable for the distance you are shooting and then work the load in that range for accuracy. Most times, the fastest is not the most accurate.

Where is the corresponding Target with shots labeled sequentially ?

 

[Pres100]

I think you may have mistaken T-shooter as the OP - I think he was just making a suggestion. As the OP, I didn't plot impacts as I'm not yet measuring accuracy, only trying to understand basic velocities for powder charge ranges to begin more detailed work up.
I'll have to pick a load somewhere in the range and work up/down with a greater number of rounds for better data. I can then also plot some shots.

 

[Richard Coody]

Just my opinion

Your scale is only accurate to +/- 0.10 at best

Your.load.increments should be 0.30 or even 0.50

I use the OCW or ladder test for load development shot at the longest range.you are.comfortable with. Look for a group of charges with the.least verticle deviation and your max load for that rifle. Your reduced velocity flat.spot would probably show up as a node.on a.target. let the target tell you what is happening. Save the crono for fine tuning.

Next for me is the seating depth test. For many they want to start with seating depth. For me i start off jammed in the lands and look for a.powder charge.