COL?

[jsthntn247]

Alright guys, I got a question about letting your groups determine your seating depth. If your groups are close together but horizontal how do I need to adjust my seating to help this out? Here is a 4 shot group from my 25.06 shot a 100yds. My max COL is 3.248 and this load was shot at 3.145, which is way off lands. I have been told to decrease my COL even further, if so how much should I try?​

 

[Gene]

Generally, increasing overall length will tighten groups. It sounds as though you are measuring from loaded cartridge base to tip. This is not the best way to do it. Get a Hornady Lock N load guage, read instructions and use it. Learn how to determine when the bullet is touching the lands. There are many sources for this information.

 

[Mikecr]

Generally, increasing overall length will tighten groups

Why would this be Gene?

jsthntn247, seating adjustment affect on grouping is an abstract. Nobody can predict anything about it. And for all we know this could be a scope, bedding, bullet, bag, target, lighting, mirage, wind, or recoil issue.

For seating adjustments, the standard described in any book is to start near or against the lands, and work back from them in fairly large steps(5-10thou). Then repeat in an area of best potential, with fine tunning adjustments(~2-3thou). But there are no guarantees of anything one way or another.
We are all on our own here.

 

[jsthntn247]

The length that I stated, 3.248, was the max COL determined from the ogive for this round in my rifle. I started with 3.145, which is the length of my factory hornady ammo, and my best group is the one in the pic. From there I increased my col to .3.238 and 3.228 and my groups opened up to about two inches. I had heard when you get horizontal stringing in your groups, that you decrease col, but I didn't know how much to try. So, I backed off .01 and .02 from there and loaded some last night and will try it today.

 

[Mikecr]

Wish I knew..

If there is someone who could even guess about 'adjusting out' horizontal, I'm thinkin Jason Baney over at 6mmbr.com/accurateshooting.com.
He's a 1Kyd competitor at Williamsport, who has done some testing with meplat trimming to reduce vertical. This left him with the remaining horizontal, and if it were me, I would have then worked on that.
You might ask him, if I remember right his handle is near JB_1000

 

[Gene]

Why would this be Gene?

For seating adjustments, the standard described in any book is to start near or against the lands, and work back from them in fairly large steps(5-10thou). Then repeat in an area of best potential, with fine tunning adjustments(~2-3thou). But there are no guarantees of anything one way or another.
We are all on our own here.

I shoot long range with four different competition rifles. In my experience and that of most competitive shooters, settling OAL at the lands or even further in, produces better accuracy than jump. Even David Tubb does this with the 6XC. There is no rock fast rule on this. When jamming bullets, the pressure goes up. If you understand pressure signs, you will know when to stop. For the guy loading his deer rifle, some jump is probably better.

I have tried it both ways, and jam always produces better groups. The choice is yours. Jump them .005" or .010", then jam them the same distance. Form your own conclusions. Every rifle is different.

 

[Mikecr]

Even David Tubb does this with the 6XC. There is no rock fast rule on this

That's right, there is no rule. Even one slightest difference changes everything.
MY 6XC, from a Tubb2000, shoots 105VLDs best at .085" off, and 105Lapuas best at .005"off.
My 6.5WSSM in a 16.5lb LG, shoots 139Laps best at .008"off (and NOT 6 or 10thou!).
Both 6br/95VLDs, and 223/50FBs of mine, also do best .005"off.

I adjusted all from .1"off to .01"into.
But so far with my guns, I have never seen touching as best.
I'm thinkin that would just be too easy.

I've seen implications over & over where anything could be made to shoot -jammed.
That's probably true, every gun I have will shoot there.
But good enough a rule, is rarely best.

 

[lever-hed]

In a .25-06 I don't see how your OAL to ogive is 3.148", that has to be a tip dimension. I'm running 2.710 OAL to ogive in my gun and that's .020" off the lands. See Gene's first reply, use a comparator to measure..
To try to address your issue, I don't see how seating depth would directly translate to horizontal stringing (it might), but, horizontal is the last thing I worry about when shooting for groups. There are too many variables, especially wind. If your groups were spread further on the horizontal I would be apt to worry, but it looks decent for that powder. Shoot 4 or 5 shots for a better representation ..IMHO. And, move further out..