Possibly the primers

[longrange772]

Took two loads to the range after doing a ladder test, 6.5CM and 7-08. Standard ladder test using min-max powder range in .2 gr increments. Analyzed the data and found what appeared to be flattest spot. Worked up loads for each.

6.5CM
39.1 H4350
CCI 200 primers
140 gr Hornady Match HPBT
Velocity 2593 with SD = 4.7

7-08
44.6 H4350
WLR primers
150 gr ELD-X
Velocity 2709 with SD = 13.4

Same tools were used to throw and weigh the changes and same container of powder was used. I am wondering if the primers may explain the delta. Have you ever experienced dramatic SD consistency between brands? Unfortunately, don't have a big primer supply right now to re-run tests.

 

[pell1203]

So what's your question? Speeds seem consistent for powder and caliber loads.

 

[longrange772]

I have an SD of 4 on one load and 13 on the other.

 

[Anb618]

Stop worrying about SD. Just find the velocity you’re looking for, then test your OAL. Settle on the widest node you can find at an accuracy level that’s acceptable to you.

 

[pell1203]

I have an SD of 4 on one load and 13 on the other.

longrange772, if you were to run the same test again the SD results could completely flip on you. Just not enough data to be statistically significant in my opinion.

I am not very familiar with 7-08 loads but for 6.5 CM you are at one of the low speed nodes. You might try 41.5 grain of H4350 instead at an OAL of 2.81-2.82" as it is a well known medium velocity node (about 2680 fps). There is also a higher velocity load of 42.3 to 42.6 grains of H4350, depending on the rifle, that shoots well in most 6.5 CM rifles.

Note: Velocities above are for a 24" barrel'

 

[Rocketmandb]

Have you ever experienced dramatic SD consistency between brands?

Big? No. Present? Yes.

With that said, it's more likely that you don't have a solid load for the 7-08 than that the primers are the source of the SD discrepancy - or that you don't have a statistically valid sample size.

Question: how many shots in the groups that got you your SD info?

I now like to run triple ladders in a relatively narrow band that gets me in the realm of the velocity at which I want to shoot. I look for a combination of low ES/SD and grouping across the three ladder tests at each load. Then I validate said load(s) for that/those combination(s) over a minimum of 20 rounds. Then I do seating depth.

Also, if you're not shooting at extreme ranges for your rifle, ES/SD is not as important (within a realm of reason, of course) as grouping. The farther out you go, the more significance it takes on.

 

[longrange772]

20 shot sample size. Only did single ladder. Range is from 1000-1500 yards.

 

[MarkyMark007]

try to swich primers and try new load developement with new primer. maybe other primer will tune at different load.
choose which will give the best ES/SD and groups.

 

[Mike Casselton]

OP,
What is your expectation with these loads?

You obtained 4 SD with the 6.5 and 13 with the 7-08.

You're dealing with TWO different cartridges and expecting what appears to be exacting results.

If you got a 13SD with both would you be happy?

I'm still trying to wrap my head around what you're really trying to accomplish.

BTW, as pointed out above in post #5 you're shooting a very mild load.
41.5 of H-4350 is a pretty standard load.

 

[MarkyMark007]

I think if he want, he can have SD of 4 with both cartridges...

 

[Mike Casselton]

I think if he want, he can have SD of 4 with both cartridges...

Maybe, maybe not.
The second go-round might be better, might be worse.

I'd be very happy with 4 SD but I wouldn't really complain about 13 unless I'm stretching them way the hell out there.

What I wouldn't be doing is expecting exact results from two different cartridges.

 

[RegionRat]

I have an SD of 4 on one load and 13 on the other.

Longrange772, sometimes the search ends quickly, and sometimes it doesn't.

It generally helps to research what recipe previously worked out best for other folks and try those components and recipes first, but sometimes it only takes a slight difference in your rig/bbl to cause a different combination to be the best for you.

You did well to try H4350, it is one of the best for temp stability and generally well behaved.

For all we know, you could try a different brand or model of component and find that SD value you want, but then again there are no guarantees.

You may find the primer wasn't best, or your barrel wants a different powder or bullet to run its best. Even brass prep can play a role.

The 7mm-08 is still a very popular design for silhouette shooting due to the magical balance of enough energy to know down the 600 yard plates and not so much recoil to cause fatigue. It is also pretty good at hunting. Again, you are doing well with 7mm-08.

If the performance you have isn't good enough for your purpose, I am sure you will keep looking and do fine.

When you said "flat spots" did you mean speed or vertical spread?
You didn't mention the accuracy or precision performance you found, or what your goal is in terms of distance or precision?

 

[longrange772]

Trying for single digit SDs for both cartridges. Don't expect them to be the same but closer since using same powder, throw, and scale for both. Been working with 7-08 for a while to get single digit SDs. 2nd attempt on 6.5 CM was hitting SD of 4. Reading LItz's book "Applied Ballistics for Long Range Shooting" not a big difference, holding other variables equal, between even 10 fps SD and 20 fps SD inside 600-700 yards. I have been stretching out more past 1000 yards lately, so I know these differences show up more. Target is IPSC sized target. Of course, these differences may get lost in the noise if I don't do my part consistently.

By "flat spots" I was referring to speed. I have been working more on getting lower SDs for consistent velocity right now before starting to play with seating depth. I am ensuring my seating depth is consistent, however, for these loads.

 

[MarkyMark007]

Trying for single digit SDs for both cartridges. Don't expect them to be the same but closer since using same powder...

what is the reason to believe, that if you use same powder you will have same SD ??????????????????????????????????????????????????????????????

do you even know from which things ES/SD came from ?