Help me understand this-Velocity is going down??

[xsn10s]

My best guess is that since the powder is compressed it's just having a tougher time igniting. That's just a guess. During load development I've seen decreases in velocity with small increases of powder. Could be a larger ES in that charge if we loaded five rounds for more data.

 

[QuietTexan]

The physics are E=mc2, and I'm not being a smart ***. The energy goes somewhere, it's either consumed by expanding the brass for bullet release, build up of pressure, bearing surface drag, or wastes by continuing to burn outside if barrel.

The energy does go somewhere.......

This is often why when adding more powder the velocity steadily drops until it bottoms out and stays there….this is bad juju and should be avoided at all costs as a pressure excursion can happen at ANY time doing this. The 243 is notorious for this phenomenon.

You get to find out which part takes in a little too much of the energy when it goes boom


243 Win is a very overbore cartridge. We tend to not think about it, but 243 Win, 22-250, 25-06, 270 Win, those old school chambers are pushing a lot of case volume compared to bore area. You can make bad things happen in small bores fast, even with smaller cases. 25-06 is on par with 7RM and 300 RUM in terms of being "overbore"

6.5CM is more on par with the 30-06, it should be (and in my experience is) somewhat forgiving.

 

[RUFFIAN R - NY]

what weight bullet you using ???? which / whos ????

 

[RUFFIAN R - NY]

any psi sighns ? brass / shoulder stretch ? primers used ?

 

[DocGlenn]

what weight bullet you using ???? which / whos ????

143gn Hornady ELDX

 

[DocGlenn]

any psi sighns ? brass / shoulder stretch ? primers used ?

No heavy bolt lift, no obvious issues with brass, using CCI large rifle primers

 

[RUFFIAN R - NY]

I don't use Hornady brass , but their bullets from time to time. How many times reloaded ? Inspect for " doughnuts " at the neck / shoulder area and remove with a reamer !! I use 4350 also but with Rem 7 1/2 primers with 40.4gr and 130 gr match VLD Target # 26403 inside Peterson brass. Also RL 15 35.7 gr with the 130 gr and Federal 210 with the large rifle primer Lapua brass. What speed you trying for ??? I don't push my loads besides am using a 28 in tube and your's is a lot shorter ! Tried the heavier 140's but like the 130 better at least for me. Am not a fan of compressed loads. Am only target not hunting with this round or would go to a larger case 6.5 .

 

[xsn10s]

41.5gr got me 2623 fps, SD 6.09, but when I went up to 41.7, the speed DROPPED to 2609 fps, SD 13.01???

What's the ES for both?

 

[DocGlenn]

I don't use Hornady brass , but their bullets from time to time. How many times reloaded ? Inspect for " doughnuts " at the neck / shoulder area and remove with a reamer !! I use 4350 also but with Rem 7 1/2 primers with 40.4gr and 130 gr match VLD Target # 26403 inside Peterson brass. Also RL 15 35.7 gr with the 130 gr and Federal 210 with the large rifle primer Lapua brass. What speed you trying for ??? I don't push my loads besides am using a 28 in tube and your's is a lot shorter ! Tried the heavier 140's but like the 130 better at least for me. Am not a fan of compressed loads. Am only target not hunting with this round or would go to a larger case 6.5 .

I was really just trying to duplicate the factory load since it shoots well in my rifle (2609 fps) and I got that plus a little, so I'm happy with the 41.5 since it is sub MOA out of my rifle. I was just surprised to see the velocity drop with an increase in the amount of powder, and I was looking for a reason that was happening (which I got thanks to the previous replies). I'm just trying to get a good hunting load that will work out to 400 yards, and I've got that at this point. Thanks!

 

[DocGlenn]

What's the ES for both?

The ES on the 41.5 was 36.94. It was 37.34 with 41.7.

 

[xsn10s]

The ES on the 41.5 was 36.94. It was 37.34 with 41.7.

I'd argue then that both loads weren't that far off from each other. If more shots were included into the groups then the average velocity might represent the increase in charge more accurately.