Thoughts on Extreme Velocity Spread and Fixing it

[Dougfirtree]

I'm curious how others tinker (or don't) with high ES. I'm trying to make a decision about whether to stick with a loading project for a while longer, or if I should just start over with different components.

The quick version: I'm trying to work up a new practice load for my 7mm-08. I'm playing with 139 SST's and Big Game powder. I've got one load (46.5 grains @2.8") that is showing some promise in terms of groups at 100 yards. It's a little over an inch and normally, I'd play with COAL now and see if seating the bullet deeper shrunk those groups a bit. However, the ES of velocity is all over the place; well over 100fps.

Have you ever fixed a high ES by tinkering with COAL? Or is that something you've only improved with different powder charges, different components, etc? I guess I don't totally understand the factors that cause a high ES (aside from the obvious one of component consistency).

 

[golfer]

Maybe try a crimp?

 

[p_ham]

Change powder charge or change powders all together. Keep your load density above 80%.
Make sure your primer pockets and flash holes are uniform/ deburred.

 

[Addicting]

What primers? If they are Winchester that’s your problem.

I shoot big game in my 7mm08 with Fed 210m and my ES is in the teens.

 

[Addicting]

Also what chronograph?

 

[Dougfirtree]

What primers? If they are Winchester that’s your problem.

I shoot big game in my 7mm08 with Fed 210m and my ES is in the teens.

Primers are CCI 200's. The chronograph is a Competition Electronics Pro Chrono Pal. I wondered about the chrony as it was sunny out and the spread seemed kind of ridiculous, but I fired some factory .22 ammo through it while I was there and the velocity was right where it should be, ES of about 20...

 

[Addicting]

Was the barrel allowed to cool in between shots?

I’ve had ball powders react funny when shot in strings from the heat. Progressively faster depending on how long the loaded round sat in the chamber before it was fired.

Do you have any loaded rounds where you could measure the brass?

The brass stretches and the necks can get varied in length. Some dies have a crimp feature separate from the seating depth adjustment. Your die could be set close enough that some are crimping and some are not depending on neck length.

 

[Seamaster]

Sometimes a large ES is not very evident on target at 100 yards. If you shoot the same load at 300 yards you may not be very happy. I have seen fellows load their cartridges a bit long to the point where any inconsistency in length may be the difference in a jam, a touch, or a small jump. If that is not the problem it may just be a powder choice issue, or two different lots of the same powder. Figuring out this type of problem is fun, but can be a bit expensive.

 

[Dougfirtree]

Was the barrel allowed to cool in between shots?

I’ve had ball powders react funny when shot in strings from the heat. Progressively faster depending on how long the loaded round sat in the chamber before it was fired.

Do you have any loaded rounds where you could measure the brass?

The brass stretches and the necks can get varied in length. Some dies have a crimp feature separate from the seating depth adjustment. Your die could be set close enough that some are crimping and some are not depending on neck length.

I let the barrel cool between three shot groups. Never got even close to hot and velocity jumps were random, not getting faster as the group was fired. I use Big Game for my hunting load, so I'm guessing that's not it.

Good point on the necks. I hadn't thought about that, though I did measure the brass before this load and it was on the short side of acceptable. Hmmm... I do appreciate all of your thoughts here. I'm kinda leaning towards trying a different powder for this load. Wish I could find H 4895. I use that for some other rifles. Maybe I'll go back to Varget, but I like the idea of using fewer powders and buying them in larger quantities...

 

[Addicting]

Big game recently switched manufacturers and went from the red label to a green label. There is quite a bit of difference in between the two. The red seemed better than the green.

Lastly, I would decopper your barrel, shoot one fouling shot, and shoot that promising load again. If you still end up with the same result then ditch it in favor of a different powder.

 

[Addicting]

Also how many firings on the brass and it’s all the same manufacturer?

Do you feel different individual pressure when resizing the batches batches?

Some are normal and others are slightly harder?

 

[morgaj1]

Neck tension can have a big impact as well. The suggestion of a crimp is a good one. I use the Lee Factory Crimp die.

 

[Addicting]

Neck tension can have a big impact as well. The suggestion of a crimp is a good one. I use the Lee Factory Crimp die.

That’s is where my mind went with the previous post. If his brass has several firings on it I’ve had the brass turn hard at different rates. Some got sticky and you could feel the difference in the seating die expanding the neck.

Annealing the brass may resolve the issue.
@Dougfirtree

 

[JLS]

This is by no means a statistical sample based on n=5, but I tested some handloads today with no crimp, 1/8 crimp and 1/4 crimp with a Lee FCD. I found adding the crimp reduced spread on the velocity, the best being 1/4 turn.

 

[winmag]

I don’t think this helps to explain that huge of an ES but something to consider. Nosler notes the most accurate powder tested, as well as the most accurate charge weight, for each cartridge/powder/projectile weight combination. Interestingly, Nosler defines “accurate” in this context as “lowest velocity standard deviation”, not group size. At long range lowest velocity standard deviation definitely does equal accuracy, but not necessarily at short range.

Anyhow, they do note Big Game as the most accurate powder tested for 140gr class projectiles in the 7mm-08, but the most accurate charge weight for Big Game is their starting load at 43.5gr. I would be interested to see if the ES decreased if you decreased your charge weight. And even if it does, I’d still change powders, because who wants to give up that much velocity for accuracy?

Regardless, #1 I'd rule out chronograph issues. I chased my tail for a while with inaccurate optical chronographs when trying to shoot over snow. I was wasting trips to the range (free time is a premium these days) so bit the bullet and bought a Labradar. #2 if I can’t find accuracy (group or velocity spread) I change powder. If that doesn’t work I’ll give up on that projectile in that rifle. I’m confident enough in my case prep and loading that if it’s not accurate then I know it’s just a combo that my gun doesn’t like. This hasn’t happened often.

 

[JLS]

Annealing the brass may resolve the issue.

I’ve never annealed brass. It’s such a rabbit hole to go down.

I did however have a good opportunity here. I have 15 cases that are in loads 4-7ish. I just shot them. I annealed them and will re shoot with the same charges and same crimp and see how they stack up. I know it’s not a statistical sampling, but I might be able to glean a little info from it.

I used a torch and cordless drill per Steve at Hammer. I heated until I could see a blue line start to form below the shoulder.

 

[Addicting]

I’ve never annealed brass. It’s such a rabbit hole to go down.

I did however have a good opportunity here. I have 15 cases that are in loads 4-7ish. I just shot them. I annealed them and will re shoot with the same charges and same crimp and see how they stack up. I know it’s not a statistical sampling, but I might be able to glean a little info from it.

I used a torch and cordless drill per Steve at Hammer. I heated until I could see a blue line start to form below the shoulder.

View attachment 278386View attachment 278387

It’s a start but very easy to ruin brass that way. That is how I started and quickly quit messing with it. Consistently is key and you just can’t get it with a drill. I Spent the 200 on a Annealzee set up. Best money on reloading I’ve spent.

No more hard necks, every stroke of the press feels the same. ES and SD single digits / low teens over long strings.

Worth every penny.

 

[std7mag]

Essentially everything and anything to do with the cartridge can have an effect on ES/SD.

Cases are all from the same manufacturer and the same lot?

Case prep being first on the list.
Primer pockets uniform.
I run the flash hole uniform/deburr tool in from the primer pocket.

Size, then trim.

Trim length. It's ok to be slightly short as you have mentioned, but they all need to be the same length.

Deburr flash hole inside of the case.
Chamfer & deburr case mouth.

You said your loading to 2.8", and may seat deeper.
Did you measure your magazine?
Do you know your distance to the lands with THAT bullet?
With a 140gr Nosler Ballistic Tip my COAL was 2.895" for 0.020" off the lands.
I've found cup & core bullets shoot well 0.02-0.03" off the lands. VLDs and mono's are a whole different beast.

As @p_ham said, load density of at least 80%.
Loads above about 104% lead to other problems.

Magnum primers sometimes will help settle erratic ES/SD with some powders.

 

[elkfanatic]

Annealing the brass and using a separate expanding mandrel to get consistent neck tension dropped my es from mid 30's to single- to low teens in my 300 win mag. Brass prep is just as critical as loading powder and bullets.

 

[cahunter805]

Lots of good advice given above already.
What reloading dies are you using? Are you FL sizing? Neck sizing? Are you lubing necks while sizing? Prepping brass?
100ES is pretty high. Did you chronograph the other test loads? Were they all this high?
Sometimes just a little less or more powder or a primer change can really help also.