How much can you gain from Rifle OAL/COAL adjustment?

[LAKEMASTER]

I have been setting My COAL to .015 off the lands.

At some point, some of my recent test loads (walked) on my turret so im Fluctuating ~.020 over 30 cases.

This kinda made me wonder the actual gain of trying different seating depths.


Hypothetically, let's say i have a hunting load that is 1.75 to 2" @ 100y.

If i were to start seating closer to the lands will my groups tighten? What about the opposite direction?

[Hannibal]

There are no hard-set rules here, but generally speaking, setting your COAL to lightly jam the bullet into the lands will result in the most accurate load. Be mindful that this is not a recommended practice if you are loading to near high chamber pressures, as a jam condition will increase pressure. Often the limiting factor is magazine length, unless you plan to load rounds by hand singularly.
And also remember that no loading techniques will compensate for faulty equipment or techniques. But I imagine you know that already.
Hope this helps with your question.

[oldblinddog]

Sometimes well off the lands works best. You have to try it to find out.

[lotech]

Based on my experience with cast bullet rifle loads, Hannibal gave the best advice. There are exceptions to everything, of course, but I don't recall finding best accuracy with cast bullets that didn't at least very slightly engrave when a cartridge was chambered.

Different story altogether with jacketed bullets.

[Crusty Deary Ol'Coot]

One of the better gun writers had a piece a few years back in which he indicated that adjusting the bullet seating depth might have a similar effect on accuracy as that found with the Browning Boss.

Of course as you likely already know, you need to have a solid accuracy "bench mark" from which to work/compare or you'd simply be chasing your tail.

Crusty Deary Ol'Coot

[Love Life]

How much can you gain from Rifle OAL/COAL adjustment?

A lot, or a little, or nothing. You have to test your rifle to find out. I always do rifle load development for non semi-auto rifles with the bullet jammed for powder charge work up. Once I find a nice node, then I'll start working seating depth by progressively seating deeper within a certain window to see if that does any good.

From there its on to testing primers and all sorts of other voodoo. This is after the time spent sorting brass by weight and volume, bullets by weight and ogive, etc.

Sho' am good!!

[Hannibal]

All Voo-Doo aside, seating depth is not going to make a rifle that shoots 2" @ 100 yds shoot 1/2" @ 100 yds.

The barrel is king. No matter what anyone says.

Now, if you can not adequately evaluate your rifle, all bets are off. Which is the primary source for the 'Voo-Doo'.

Clear as mud?

[Love Life]

All Voo-Doo aside, seating depth is not going to make a rifle that shoots 2" @ 100 yds shoot 1/2" @ 100 yds.

The barrel is king. No matter what anyone says.

Now, if you can not adequately evaluate your rifle, all bets are off. Which is the primary source for the 'Voo-Doo'.

Clear as mud?

So true, lol.

[GhostHawk]

In my 2 most accurate rifles, I did pound casts, so I could see what I was dealing with. And then I played with an unprimed case and a bullet. Then slowly seat the bullet until I could close the action without leaving marks on the lead bullet.

Crimped into place, used that to set my dies. Now that system would have the bullet touching the rifling, but not engraved. So I added a quarter turn on my seating die.

Sighting in the rifles in both cases I got cloverleafs at 25, 50 and 100. Well 2 out of 3 at 100. Getting old.
Rifles were both Handi rifle single shots in .357 mag and .444marlin.

The .357 mag are loaded in .360 DW brass as it gets them closer.

But not stuck, they slide free on their own.

I think it takes some diddle work to get there, but from my experience, it well worth taking the time.

[Hannibal]

And then again, it just *might* be that we're paying more attention when shooting those groups.

I do not doubt your results, I simply question the cause. 10 shots on 3 different days will tell the tale.

I find the .357 to be notoriously fickle past 50 yds. YMMV.

[halvey]

In both my Rem 700 VS guns in 223 and 308, seating right near the lands proved the best accuracy. But that's just 2 guns.

[JSnover]

Lakemaster didn't say what he shoots but if it's BP for hunting, I'd load with up to .015" clearance. For target work mine do better with light contact and a wipe after each shot to keep things clear for the nose of the boolit.

[LAKEMASTER]

3006.

And the bullet in question is a ranchdog bullet. It has a 1/4" flat nose

[LAKEMASTER]

3006.

And the bullet in question is a ranchdog bullet. It has a 1/4" flat nose

[country gent]

Seating depth can make a difference in accuracy of a given rifle also with a given bullet. Bore riding bullets that fit the bore well may be a slight exception here. I have "jammed" bullets into the rifling at times ( the load was worked up for this with the bullets jammed into the rifling) the drawback is a ceasefire or wanting to unchamber a loaded round may pull the bullet and leave powder in the action.
What I normally recommend is with a good load start .060 off the rifling and shoot groups adjusting .010 to touching. This shows any improvement and what the bullet barrel combination likes. Seating depth like primer testing is a means to fine tune a load to its very best. Sometime with a very popular bullet ( 168 Sierra MK comes to mind) enough data can be gathered from other shooters to show a trend. IE if you ask 50 shooters how far off they are and 5 say .050 35 say .020 and .010 say touching then you can reasonably test .020 as what that bullet likes.