Less velocity with more powder?

[JCB]

I have been working on a .308 load with Varget and 178g Amax's. Today at the range, I had prepared five loads ranging from 44.0 grains up to 44.4 in 0.1 grain increments. Brass was virgin Winchester. CCI 200 primers were used. All shots were loaded to same seating depth. The thing I found interesting is that the average velocity (5 shots for each loading) went down with each increase in powder.

Grains Avg E SD
44.0 2645 60.10 24.53
44.1 2644 35.78 16.34
44.2 2632 37.81 16.27
44.3 2607 36.48 17.08
44.4 2582 38.31 16.09

I was hoping to get a bit more velocity than what I am seeing. Is it common to see velocity decrease with an increased charge weight?

 

[Sean the Nailer]

Re: Less velocity with more powder?

Tighter packed cases, to which there is less powder being ignited upon detonation of the primer, or,
Possibly the wrong cases were marked in the order of charging them?

This is using the analogy that if a case is far to 'under-charged' then too much powder can be ignited too soon, spiking the pressures to "grenade" status.

I'm sure others will chime in here.

Merry Christmas

 

[JCB]

Re: Less velocity with more powder?

Thank you for the help. I'm certain the cases were marked correctly as they were labeled and packed as completed. It must be the tighter packing of the powder in the cases that is the issue. Would switching to a magnum primer potentially help with the issue?

 

[bricktop]

Re: Less velocity with more powder?

Did you have them indoors, then take them outside to shoot? Perhaps the cartridges and powder got colder over time as your shooting went on.

 

[JCB]

Re: Less velocity with more powder?

They were indoors, approximately 68 degrees and the outdoor temp was 54 degrees. I was at the range for just over an hour.

 

[bricktop]

Re: Less velocity with more powder?

Maybe the powder scale drifted as you were loading them? Was it an electronic one?

 

[colt933]

Re: Less velocity with more powder?

What kind of chronograph do you have?

Was it partly cloudy - sometimes it was sunny and sometimes it was cloudy?

My chrony piece of crap varies a lot depending on the consistency of ambient light.

But I suggest if you're at about 2600fps with 178AMAX with good accuracy, you are done. I was just tweaking my charge with some brand new Winchester brass and was getting right at 2600fps with 178AMAX, CCI200, and 44.0gr Varget in a 700P. I get the same velocity with 42.8gr Varget in LC Match cases. This load is sub-MOA in ever rifle I've ever tried it in.

You might get more velocity with 4064 or RL15 if that's what you're after.

 

[JCB]

Re: Less velocity with more powder?

I did use a RCBS Chargemaster. Looks like there are lot's of variables.

 

[JCB]

Re: Less velocity with more powder?

The Chrony is a Shooting Chrony Beta. On the velocity, you are probably right that I am about where I should be. It's a Remy 700 varmint with a 26" barrel. I thought to have such a long barrel the velocity seemed a little low.