Berger Bullet method of find best seating depth

[ptf18]

Fellows. I was using the Berger Bullet method of finding the "optimum" seating depth. Berger's suggestion is to shoot 2 sets of groups with 3 rounds per varying seating depths. Starting with (thousands) +10, then -40, then -80 and finally -120 into the leade. The cartridge details are irrelevant. Same load used thru out, etc.

I "found" that the +10 group shot very well AND that the -120 group shot very well.

Is this a in-normality? What is the likelihood of this occuring?

 

[Fotheringill]

I thought it was six rounds 40 apart except for the first @ 10 into the lands per Berger.

As to the results above, I would try it again with 6 rounds each and remember, there are a few weeks (or days) more of narrowing it down more. I.e. -110 might be the best or -45 or whatever.

 

[bsekf]

I don't think your results are unusual. Now you have to tweak the powder and charge and maybe the seating depth a very little. According to Berger, you have found the seating depth/depths for that bullet/barrel combination.

Let us know how the tweaking goes.

Bill

 

[Zero333]

Nothing weird with finding 2 different CBTO's that shoot good.

 

[dmoran]

@ptf18
Very common to see just that. There are multiple seating nodes (same for powder). Finding which one is more accurate or best suited for your intentions should be your next step. Doing so by running refined increments of seating depths on each side of those found.

Depending on your intentions and desires, but having a good node at a big jump from the .120-Off, can play well for clip/magizne feeding scenario's and for not wanting to be in the lands. On the other hand, the .010-In node area, likely would offer less pressure do to the increase in capacity behind the bullet, with room for more powder yet.

That Berger method you used is very "course". Don't be surprised if you find more seating nodes yet, in refined tests.
Good Luck

 

[mikecr]

From Berger:
Load 24 rounds at the following COAL if you are a target competition shooter who does not worry about jamming a bullet:
1. .010 into (touching) the lands (jam) 6 rounds
2. .040 off the lands (jump) 6 rounds
3. .080 off the lands (jump) 6 rounds
4. .120 off the lands (jump) 6 rounds

Load 24 rounds at the following COAL if you are a hunter (pulling a bullet out of the case with your rifling while in the field can be a hunt ending event which must be avoided) or a competition shooter who worries about pulling a bullet during a match:
1. .010 off the lands (jump) 6 rounds
2. .050 off the lands (jump) 6 rounds
3. .090 off the lands (jump) 6 rounds
4. .130 off the lands (jump) 6 rounds

Shoot 2 (separate) 3 shot groups in fair conditions to see how they group. The remarkable reality of this test is that one of these 4 COALs will outperform the other three by a considerable margin. Once you know which one of these 4 COAL shoots best then you can tweak the COAL +/- .002 or .005.

So you can see here various coarse increments can be tested. Berger somehow believes sweet spots are 30 to 40thou wide, but I have never seen that with ANY bullets, not even with Sierra or Lapua.
Best coarse window is maybe 5-15thou wide, and you have to narrow to this 1st before shifting to fine adjustments.
So if 120 off is good, narrow further with testing at 100, 110, 130 (get it to 10thou of best). Then move to powder testing and once you have that node, fine adjust seating (about that coarse best) no more than 2thou at a time to shape grouping for best.
Then log best CBTO, and don't even think about changing that with this bullet in this barrel (for it's accurate life). With best off the land (OTL) seating, I've never seen best change (with same lot bullets).

Also, be sure your coarse seating testing is done with powder backed down & away from any expected powder node that you'll be living with. Sometimes you can't avoid it, but you really don't want to come into or out of a powder node in the middle of your seating testing, making you think things are what they're not. This seating testing can be done while fire forming new brass, which should be done anyway before powder testing, so it's not like your wasting any barrel life here.

 

[Willow]

As others have reported, nothing unusual at all - my 180gr VLDs like a jam and also shoot just as well with a 40 thou jump.

 

[dcali]

It’s normal, or common at least. In my experience with the Berger method, the seating depth is cyclical and the pattern repeats every .100-.120. I haven’t done it a ton, but that’s how my .308 has reasponded. It seems like somewhere less than .020 or so and around .120-.140 seem to work well for my rifle.

 

[shb]

What's the best way to determine the distance to the lands, or over all chamber length for lack of better term?

 

[eric n]

What powder were you testing?
I have seen .010 in and .040 out shoot similar with varget and 8208xbr in .223 and varget in 6br and dasher.

 

[powderbrake]

What's the best way to determine the distance to the lands, or over all chamber length for lack of better term?

Use a Hornady Lock & Load OAL gage, or better yet, use the Wheeler method.