Seating depth adjustments

[KMW1954]

This is a new aspect for me as when I was shooting a target 223 with 69gr class bullets the seating depth didn't really seem to make of a difference.

I am believing this is going to be a bit different with the 6mm bullets.

Currently I am using the Lapua Scenar 105 and am about .005" off touch. Next bullet I have on hand to test with is the Barnes Match Burner 105gr, which I have not loaded any of these yet.

I understand some bullets are more conducive to jump or jam but I have no clue which ones are which. I have also come to understand that .003" movement is the most used.

Would like to hear everyone's thoughts or advice!

[grayfox]

I don't chase lands in an AR, nor actually, in any of my rifles. AR's mostly you cannot do that anyway, limited to maybe 2.280 give or take.
As with most AR platforms, the mag length has a lot to do with how much depth range you have. If using a bolt action that uses a non-AR style mag you have more wiggle room... like maybe the howa mini.
For me, and I think for most bullets, except those being used by very ocd competitive shooters (ie, high-grade, high BC match bullets), bullets can have up to a +/- 0.003 or even 0.005" just in their oal due to... well, whatever. Some folks compensate by using the BTO method; but for the rest of us, OAL is what we have to work with.
So. In these circumstances +/-0.003" is a pipe dream.
As well, there are some very much/very VLD bullets with long secant ogives, but let's set those aside for a minute. That leaves us with more traditional tangent or hybrid ogives. The only VLDs I shoot are within AR mags so I can't chase any lands.
An article from a while ago in the PRS shooter's blog-line discussed seating depths "at length", so to speak. What they found out from some pretty extensive testing is that most bullets do their best over the longest period of time (think throat wear) by seating 0.060-0.090" off of lands. You can read their research and results in their series of articles.
I have used that approach for most of my shooting and find it an accurate theory. I may not get the one-holers (I'm not quite that good anyway, lol) but for loads I have tuned right they tend to be 0.75 down to 0.50" on a good day (I- as the shooter- am the weak link in all of this).
Once I have found the powder charge I want to dial in, I vary seating depth by 0.010" and shoot for groups -- one of them will be tighter than the others. I go with the OAL that has the tightest results.

Using a seating delta of 0.010" allows for some natural variance in the bullet oal, plus allows a group size to be - more likely than not - outside the SD "noise" of everything else.

This is what I do. Others with a lot more expertise may weigh in on their methods. But this is one I can follow pretty consistently.

[KMW1954]

Again thanks. This is not an attempt to chase the lands but to tune for the smallest group. I am one that does seat bullet using the BTO method and seldom measure to COAL.

In my case in the target league in which I compete we are mostly shooting at .5MOA X-rings for scores. So .5MOA or larger isn't going to win anything. During this league we shoot from 100-300yds.

[CZ527 Guy]

Let us know what you discover. Generally many offerings do well with considerable jump with the 6mm ARC Barrels and bullets can vary what they like. Anxious to hear what works for you with what bullets. Is this a bolt action or a gas gun?

[KMW1954]

Let us know what you discover. Generally many offerings do well with considerable jump with the 6mm ARC Barrels and bullets can vary what they like. Anxious to hear what works for you with what bullets. Is this a bolt action or a gas gun?

This is a bolt with a Shilen 28", 4 groove, Bull profile. Not threaded.

From NSS. It was off their shelf! Had it in 3 days.

[grayfox]

I got a barrel from them once back when, it was a good one.
Also, wasn't knocking "ocd" types just describing one group of shooters. If your competition is 0.5 moa max, the 105 lapua ought to do well, I've gotten that from my 6 creed Bergara (26" barrel) with that 107 smk load.
Keep us posted on how it does, as to temperature stability, Xbr might be a choice for you, or even maybe varget with that length and a bull barrel.

The discussions I've read on bullet shape vs seating sensitivity, those with a tangent ogive are reported as more forgiving, the longer, sleeker vld (secant) ogives less forgiving. The scenar appears to be a tangent ogive whereas the scenar-L is secant. So your pill looks to be the tangent style (as is the 107 smk btw).
I think I'd expect a node at around 2800 or 2900 from a 28" barrel.

[KMW1954]

So far I have shot load ladders with 6 different powders; A2460, Benchmark, BL-C2, Lever, TAC and Varget. As these are all powders I have on my shelf. The Scenar's were provided by a shooting buddy that bought them back during the pandemic. He purchased 1k. He sold them to me at .20c a piece. He only shot about 50 of them.

Of what I have loaded and shot the best results have come from the Lever, A2460 and then the BL-C2. The Varget didn't come together until almost Max load.

This 6mm is brand new to me. Never shot it, never loaded for it so it is a new learning curve.

[grayfox]

But (face it!) it's a fun and addicting learning curve.
My thinking, a good bolt action gun is a good bolt action gun, regardless of the caliber. The difference you're feeling is that in the bigger diameters there are more possibilities and more combinations.
Like I posted in your other thread, a rifle is a mechanical system, no more and no less. The pipe diameter may be larger but it's still a pipe attached to a powder-energy-projectile movement system. So the theories and basics ought to apply regardless.
The scenar is good bullet no question. Good idea to start with what you have.

---

Lever is honey to the 6Arc-bee!

[popgun]

Like mentioned, secant/VLD are generally more jump sensitive, tangent and hybrid not so much. My experience with 6 ARC and 6x47L is that tangent bullets respond well seated into the lands. The 109 hybrids I use in the 6x47 work well .015" off the lands/jump and 108 ELDms and Berger 108 Targets do best .006 to .010" into the lands. My best load for 6 ARC is the 90gr Berger Target .004" into the lands and they fit the case well. The bearing surface does not go below the neck and shoulder junction. Shooting 300 yards and in I wouldn't be to concerned with a high BC bullet, speed of a lighter bullet will make up for a lot of that.

[KMW1954]

Shot today, Scenar 105 over LEVER, CCI400, Starline brass.
From L to R; 27.5gr, 27.9, 28.1, 28.4, 28.7, 29.0...

The 28.7 the outlier was the first shot and I dropped that one. The 29.0 the outlier was the second shot and I felt the rear bag move. Overall I am pleased with what I am seeing. Still have lots of room to play. Hornady Bolt data lists 30.8gr LEVER as the max and I am a long way from there. Thinking of doing a 27.7 to 28.5gr in .2gr intervals. Also expanding the 28.7 up to 29.9 in .3gr intervals.

Target should be rotated 90* so shots are at top position.

   

[popgun]

Nice! The first three look like it's in a good node without much POI shift.

[KMW1954]

Thanks, Have to totally agree. Very curious to see what is up higher. Also to try these at 200 and 300yds.