Seating depth variation/tolerance?

[BringBackThe80s]

How much variation is typical when seating bullets?

I am using 2 Hornady Custom dies with micrometer top and 1 Redding Competition Seater die (also micrometer), all in a Hornady Lock-N-Load Classic press. If I set a seating depth and just load 10 or 25 rounds and only check them with the comparator afterward, then I find variations of 1-3 thousandths plus or minus. (More variation when seating compressed loads, less when there's ample space.) I have found those variations with 4 different .243/6mm bullets and at least 3 different .308 bullets. To deal with the variability, I often back the micrometer off by ~2 thousandths before first seating each bullet, then measure BTO and dial 1 to 4 thou more as needed to seat within a half-thousandth of my intended BTO.

So, how much variation is typical when seating a bunch of rounds without measuring every time a round leaves the die?

What +/- tolerance do you require for seating depth (BTO)?
+/- tolerance you accept

 

[6mmBCC]

I have two RCBS presses, an old RS and a RockChucker. I use only the Redding Comp Seater die micrometer for my precision loads and my RS press that is 50 years old. I have RCBS and Hornady dies also. What I have seen is seating very dependant on the bullet. I have tested by measuring bullet base to ogive and with. I see very little variation. Ogive to tip is a different story.
I measure mine loads with RCBS precision mics. I can load 50 rounds and won't have .001 variation with the Redding Comp seater. I just went through and measured 30 of my 260 Rem loads woth a 105gr Sierra Blitzkings and they were +- .0005. I don't think 1 or 2 thousandths makes much difference when you are seating more than .010 off the lands. That is the important measurement is ogive to lands. Where it becomes important is when you get closer than .005. I don't load anything between. 005 to the lands. If I want to be in the lands like I am fireforming a wildcat or AI, I push it well into the lands. If say my brass headspace sizing varies .002 - .003 long and my bullet get seated .002 long then I risk being on the lands and off the lands when on the short side trying to seat at .005 off the lands. On my most very accurate rifle, my seater stem is lapped to the bullet I am using which is usually a Sierra bullet. It gives a little more contact on the bullet. I have multiple seating stems for each die/cartridge for each bullet I am using. I have chronographed a lot of loads and I generally get an increase in velocity closer that .030 off the lands and a spike when you touch them. That is highly dependant on the powder too and if you have a leade of 1°30"or something different.
One caution with Redding dies and Comp seater, you don't use a compressed load or you risk cracking the seater stem. The other important factor I think is more important than 1 or 2 thousandth on the seating depth is runout. This is my thoughts and the way I do my loading.

 

[SDHNTR]

Seating depth doesn’t matter much to begin with. Variation of a few thou seating depth does not matter at all.

 

[mlevimadden]

Mine on a cheap Lee press with a redding micrometer seating die are usually +/- .001 base to ogive. No way I would mess with adjusting the micrometer for each individual bullet (or even measure every single CBTO) when I'm loading 200 rounds.

I'm usually loading .030 off the lands, so I wouldn't sweat +/- .002 variance. I'll measure the first few rounds and then every 10 or so after that when I'm doing a big batch to make sure nothing is out of whack.

 

[BringBackThe80s]

I'm usually loading .030 off the lands, so I wouldn't sweat +/- .002 variance. I'll measure the first few rounds and then every 10 or so after that when I'm doing a big batch to make sure nothing is out of whack.

Yeah. My AR is limited by the mag, and my Ruger 243 and Tikka 308 both have such long throats that getting closer than 30 thou off the lands would mean having well under 1 caliber of bullet shank in the case neck.

 

[BringBackThe80s]

Seating depth doesn’t matter much to begin with. Variation of a few thou seating depth does not matter at all.

Interesting. Quite a few precision reloaders point to seating depth as one of the largest factors in keeping groups tight. I have not tested that principle, or even done very much seating depth work, and have thought maybe that was why my most of my better load workups are good for 1 to 1.25 MOA (measured over time or in groups of 10-20 shots; those same loads will usually print 5-shot groups about 50% smaller) instead of consistently shooting the 0.5 to 0.75 MOA 10-20 shot groups I am looking for.

 

[EdP]

A variation of + or - .001 from my desired CBTO is typical for me. The variation comes from tolerance in the press mechanism, specifically the pivot pin connecting the ram to the lever. Seating technique is critical. I check every load and can adjust .001 shorter with a bit more force on the lever.

Some of my rifles seem to be sensitive to seating depth and others not. Even in those that seem to be sensitive I don't think a few thousandths makes any difference and my checking every load is probably a waste of time.

 

[huntnful]

Bullet manufacturer (consistency of the bullet itself) and variation in your neck tension is likely what’s affecting it (harder tension and the bullet forces further into the seating stem before seating into the neck) not your dies.

I’d say your variance is more on the normal side.

And you’re very likely not shooting a system that precise enough to distinguish a +-.0015 in depth variance to begin with.

 

[Slick8]

I'm a believer in seating depth but just like powder charge you should have a window of .003-.006" where the rifle is happy.

As stated above, a large variance of .003 is likely from neck tension or crushing powder.

I'm a bit anal about my loading techniques so I strive for NO more than .001 and even that bothers me a little...

I take an extra step by running my brass through a mandrel die with a dry lube. I believe this is key to consistency.

I also use LE Wilson inline with an arbor press or Redding Micro adjustable dies.
FYI, if you go down the arbor press and inline die rabbit hole, you'll love them.