A rule of thumb?

[NYDAN]

I seem to remember reading on this forum someone mentioning a "rule of thumb" concerning the direction to go when looking at your groups. Trouble is I can't remember what was mentioned or whether anyone else would agree. I think it went something like:

1. If you have horizontal groups you should try increasing the powder charge.
2. If you have vertical groups you should try decreasing the powder charge.

Are there any such rules of thumb concerning powder charges and/or seating depths? And if there are any such rules of thumb, do you experienced shooters actually utilize them? Or, do experienced reloaders believe that every rifle and combination of components is a unique case and rules of thumb don't apply?

 

[OU812]

The shape of the group tells all. If the groups is a large equilateral triangle, seat the bullets out a 1/4 turn on the die and repeat until the group shrinks. If the group is 2 together with the 3rd out there, seat the bullet deeper in the same manner, a 1/4 turn at a time and the group will shrink.

 

[woods]

The shape of the group tells all. If the groups is a large equilateral triangle, seat the bullets out a 1/4 turn on the die and repeat until the group shrinks. If the group is 2 together with the 3rd out there, seat the bullet deeper in the same manner, a 1/4 turn at a time and the group will shrink.

This is what I've heard. IOW large group move closer to the lands, flyers move away from the lands. Of course, there are no 100% set in stone laws that govern all rifles and loads

 

[Osprey78]

A good friend of mine and also a pretty exerienced reloader said to me that if you have vertical groups, it's because there may be slight variations in powder charge equalling the up and down groupings.

If you have horizontal groups your charges are most likely pretty equal, as the are on the same vertical plane.

 

[Sas874runner]

Dan I thought it was the other way around but that post was about 3-4 months ago abd have thought about reloading info...say non stop since then. Vertical stringing can also be related to a bedding issue.

 

[Darkhorse]

Never heard those theory's but now I'm thinking.....
All my test loads are weighed with a powder trickler, no powder charge variations.
Have seen firsthand what stock warpage or poor bedding can do to group size.
Also some barrels have stress in the metal, like my Browning .300 and will start to string shots to the left when it gets too hot.
I glass bedded this M700 early this year and barrel is free floating. Here is a 3 group test page that seems to bear out the seating depth theory. Take it for what it's worth....

 

[DrMike]

I've certainly observed such dramatic changes in accuracy with relatively small changes in seating depth. That is pretty dramatic, Darkhorse.

 

[jmad_81]

interesting to see that much change with such a little seating depth change. Good to know.

 

[Elkman]

When I first started loading my Tactical, 308, groups were consistently in the mid .400's. When AOL was reduced "shorter" than factory AOL, group sizes were reduced by 1/2. Same components, just seated em deeper.

 

[joelkdouglas]

I also see quite noticeable changes in group size based on seating depth. I almost would say powder charge is mostly inconsequential, just pick a near max charge (after working up safely) and adjust seating depth. Heresy, I know, but just what I have noticed.

 

[Darkhorse]

I think it has everything to do with barrel oscillation. This rifle has the Remington factory magnum contour barrel. It is bedded the first 2 inches of receiver then free floated. Due to the diameter of the unsupported barrel the oscillation is greater than say, a varmint contour. Or even a barrel with original Remington " 2 bumps", which probably serves to dampen barrel movement somewhat.
When we change seating depth we change where in that oscillation the bullet leaves the barrel. Same as changing powder charges.
I've done a lot of work with the Browning "BOSS" in my .300 mag. With a barrel tuner I pick the load I want, test for pressure, then tune the "BOSS" to find the node. Seating depth changes are not really an option as the magazine length controls OAL by the tune of around .080.
With a standard barrel I pick several loads I'd be content to use with a chosen bullet, then work with seating depth and charge weight to find the node.
Some velocity's may not be able to be achieved accurately with a single powder. In that case a powder change is in order. For example with the 150 BT I haven't been able to find a sweet spot with either 62. or 63.grains of IMR 4350. It seems the sweet spot is around the 3000 FPS mark with this combo.
Here is another target. Notice the POI change with only .005 difference in seating depth.
The more I search for perfection the more complicated this becomes. If not, it would become boring.

 

[SJB358]

I also see quite noticeable changes in group size based on seating depth. I almost would say powder charge is mostly inconsequential, just pick a near max charge (after working up safely) and adjust seating depth. Heresy, I know, but just what I have noticed.

I have noticed about the same Joel. If I have room to tweak powder charges and my load is consistent across the chrono, I will work seating depth to tweak. I will usually work towards the upper end of what the cartridge should produce then work heavily with the bullet. I haven't been disappointed too often.

 

[ElmerThud]

I also see quite noticeable changes in group size based on seating depth. I almost would say powder charge is mostly inconsequential, just pick a near max charge (after working up safely) and adjust seating depth. Heresy, I know, but just what I have noticed.

I have noticed about the same Joel. If I have room to tweak powder charges and my load is consistent across the chrono, I will work seating depth to tweak. I will usually work towards the upper end of what the cartridge should produce then work heavily with the bullet. I haven't been disappointed too often.

And the same again with this. Scotty knows well and helped considerably with propellant data when I was developing my load for the 110gn AccuBond. First I managed with his help to sort out an appropriate charge & then messed around for ages with a seating depth until it worked properly. Seems odd I didn't have the same issues when setting up for the Sierra Prohunter 100gn bullet...that development period was very short.

I hadn't heard about the 'vertical' & 'horizontal' groups requiring differing seating or propellant charges, not something mentioned in my earshot in the UK. I simply regard a barrel more or less like a 'tuning fork'...it just has to vibrate the same every time.

'Concentric' case resizing with correctly adjusted headspacing and finally utilising a Lee Factory Crimp die has worked wonders and although I still wobble occasionally, at least I know my ammo. works and I get consistently low ES when I check MV with my chrono.

 

[tim629]

280AI with 140 BT using 60 grains of RL-19

when I first started loading this rifle I seated the bullets between 3.335-3.340 had good results so I just stuck with it.

read this thread and decided being a new reloader I had to play with seating depth and see the changes for myself.

I did change the set-up of the bag a bit between the 2 loads which I believe is the reason for the change in point of impact, but now going to have to retry the 3.335 load and also see if my rifle will accept something just a touch longer and see if I can shrink that down even more, although I'm very happy with the 3.335 group so thinking time to see how it does at longer distances and on groundhogs. also quite pleased that the point of impact is about 1/2" higher than my 160 AccuBond load so no need to play with the scope