Velocity and Barrel Heat.. Maybe?

[KeeblerArmy]

Probably a reloading issue, maaaaybe a rifle issue but who knows.

Just got a Bergara MHR in 6.5 Creedmore and am doing a a load workup for it based on the components I could find. That thus far is consisting of
130gr Hornady ELD
IMR 4895
New Lapua Brass
Fed match large rifle primers

All charges were loaded on a RCBS beam scale.

I had 3 groups of 5 at 42.4-42.6 grains. I thought I was going to have a node in there... but I think I need to back off a little bit. More on that later

Either way, I shot those groups round robin. So a 42.4, then a 42.5 then a 42.6. In theory I should have a nice sine wave on that sequential shot graph. Instead you see a down trend in velocity and then things getting really wacky.

The only variables that I can think of that were changing were barrel heat and fouling. The gun is new and has less than 50 rounds through it. I did notice some mirage I *think* right about where the graph gets wonky so I gave it some more time to cool. I wouldn't expect heat to cause things to fluctuate THAT much though!

Any theories on what might be going on there?

 

[Doom]

I’m not a creedmore shooter but when I saw 4064 your load struck me as high, based on what I see others loading with slower powders. I checked both Hodgdon and Sierra and both topped out below 40 grains. I suspect your are overpressure but I am thinking 4064 is just too fast to get repeatable results with the 130 grain bullet.

 

[KeeblerArmy]

I’m not a creedmore shooter but when I saw 4064 your load struck me as high, based on what I see others loading with slower powders. I checked both Hodgdon and Sierra and both topped out below 40 grains. I suspect your are overpressure but I am thinking 4064 is just too fast to get repeatable results with the 130 grain bullet.

OOPS!! My bad. IMR4895

4064 rolled off my tongue because that’s what I use for .308. I couldn’t even find good data for 4064

 

[TheOfficeT-Rex]

That graph is terrible to read. Could you not just plot all like charges on the X axis, and then you would have a visual of velocity and extreme spread.

Yes, you would get a sine wave, if not for natural variations in velocity.

 

[Doom]

Sierra shows 38grs for the 130TMK at 2.810” COAL with Hornady brass. Hodgdon shows 37 for a Nosler AB at 2.750”COAL. Same Brass.

 

[KeeblerArmy]

That graph is terrible to read. Could you not just plot all like charges on the X axis, and then you would have a visual of velocity and extreme spread.

Yes, you would get a sine wave, if not for natural variations in velocity.

Sure, I can post that when I get a chance later

I posted the graph I did because time was a component, at a certain point the velocities got wild and I was wondering what could cause the sudden shift

 

[Supersubes]

I could show you some IMR 4064 data, but it’s an even worse choice than IMR 4895 is.

 

[TheOfficeT-Rex]

I was wondering what could cause the sudden shift

Did you do any chrono testing beyond/before this? You may not be in a node, you may just be observing the SD variations of these charge weights.

 

[KeeblerArmy]

Did you do any chrono testing beyond/before this? You may not be in a node, you may just be observing the SD variations of these charge weights.

I took a stab at a satterlee (sp?) test and thought I was onto something.. but I think the SD’s threw that theory

however while doing the round robin shots, I noticed that the lower 2780 ish velocities clover leafed. So I’m going to try and play in that velocity range next