Seating depth adjustments
#2
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.
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Messages In This Thread
Seating depth adjustments - by KMW1954 - 10-19-2024, 08:41 PM
RE: Seating depth adjustments - by grayfox - 10-19-2024, 11:22 PM
RE: Seating depth adjustments - by KMW1954 - 10-20-2024, 12:23 AM
RE: Seating depth adjustments - by CZ527 Guy - 10-20-2024, 01:44 AM
RE: Seating depth adjustments - by KMW1954 - 10-20-2024, 06:23 AM
RE: Seating depth adjustments - by grayfox - 10-20-2024, 08:55 AM
RE: Seating depth adjustments - by KMW1954 - 10-20-2024, 02:46 PM
RE: Seating depth adjustments - by grayfox - 10-20-2024, 03:10 PM
RE: Seating depth adjustments - by popgun - 10-25-2024, 07:37 PM
RE: Seating depth adjustments - by KMW1954 - 10-26-2024, 04:24 AM
RE: Seating depth adjustments - by popgun - 10-26-2024, 01:21 PM
RE: Seating depth adjustments - by KMW1954 - 10-26-2024, 01:35 PM

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