Seating depth variance/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?

 

[Clancy]

With Bergers and customs, I’ll see .0015 extreme spread over 50 rounds with a Wilson seater. Sometimes less. If it’s any more, I anneal.

I only load in batches of 50, so that’s as much data as I can give at ONCE, but it’s always the same variation so I guess my sample size is entire barrels??

 

[BringBackThe80s]

I anneal after every firing.

 

[BringBackThe80s]

With Bergers and customs, I’ll see .0015 extreme spread over 50 rounds with a Wilson seater. Sometimes less. If it’s any more, I anneal.

I only load in batches of 50, so that’s as much data as I can give at ONCE, but it’s always the same variation so I guess my sample size is entire barrels??

Is that .0015 above and .0015 below (in which case the shortest round would be seated .003 deeper than the longest round)?

 

[Clancy]

I anneal after every firing.

An arbor press is one tool I think everyone needs. It’s the first thing I tell people to buy when I help them set up.

 

[kyotekiller25]

I have found the same, and do the same as you. Set it longer by about 10 thou and gradually get it down to where I want. Very frustrating because when I measure the bullets ogives, I'm seeing a max of around 3-4 thou on a box of eldms, and most are within 1 or 2. It just makes the bullet seating process miserably slow...rcbs single stage press and Forster ultra micrometer seaters.

 

[Clancy]

Is that .0015 above and .0015 below (in which case the shortest round would be seated .003 deeper than the longest round)?

No that’s .0015 total.

Like last night I loaded some BRAs and they were 1.7945-1.7955, .001 extreme spread.

The only way I know to do this is a combination of good bullets, good dies, annealing and not wet tumbling. I run a nylon brush in the neck a couple of times right before priming. I want that carbon in there.
If you’re annealing every firing, you might try an Iosso nylon brush in a drill. Don’t get carried away just a couple of zaps on the trigger.

 

[BringBackThe80s]

No that’s .0015 total.

Like last night I loaded some BRAs and they were 1.7945-1.7955, .001 extreme spread.

The only way I know to do this is a combination of good bullets, good dies, annealing and not wet tumbling. I run a nylon brush in the neck a couple of times right before priming. I want that carbon in there.
If you’re annealing every firing, you might try an Iosso nylon brush in a drill. Don’t get carried away just a couple of zaps on the trigger.

I stopped wet tumbling 2 reload cycles (2 firings) ago. Are you suggesting the brush in order to smooth out the carbon buildup in the neck?

 

[BringBackThe80s]

An arbor press is one tool I think everyone needs. It’s the first thing I tell people to buy when I help them set up.

I've been thinking about going that route. Not really where I want to spend my shooting/hunting budget at the moment, but I don't know how else I can get tighter seating tolerances than I am now.

 

[243winxb]

How much variation is typical when seating bullets?

Maximums .005" single stage. .010" Progressive.

 

[BringBackThe80s]

Maximums .005" single stage. .010" Progressive.

That would definitely make seating depth tests, moving in .003 increments, meaningless when seating depth tolerances are 3 times the size of the test increments.

 

[Clancy]

I stopped wet tumbling 2 reload cycles (2 firings) ago. Are you suggesting the brush in order to smooth out the carbon buildup in the neck?

Just the burned carbon from annealing. It’s a little more coarse than the generic version.

 

[quest450]

less than .001" I use custom bullets, I get maybe 2-3 rounds per 100 are off by a thou loading for a match, Micron seater, arbor press (AMP) and to get an accurate reading I use comparator like the one from Accuracy One, if you are not shooting benchrest I think 3-4 thou will not make that much of a difference IMO.

 

[CharlieNC]

Where on the bullet are you measuring seating depth (ogive) vs where is the bullet contact by the seating die (near tip)?

 

[BringBackThe80s]

Where on the bullet are you measuring seating depth (ogive) vs where is the bullet contact by the seating die (near tip)?

Ogive. I use the Hornady bullet ogive comparator on Frankford Arsenal digital calipers. I check zero and/or rezero the calipers frequently during any reloading session.

 

[JFrank]

Seating stems make contact on a different spot than your ogive comparator, if you have variances in the bullets nose geometry as many non custom bullets have than you may be seeing that. Another aspect to consider is that a measurement taken with a caliper and ogive comparator can also be manipulated by how much pressure you apply resulting in inconsistency.
I also like and use the Accuracy one comparator that gauges off the shoulder rather than the base of the case, they are not subject to those pressure variances.

Just a couple thoughts…
Jim

 

[urbanrifleman]

Too much neck tension.

 

[piie]

Have you just measured your bullets before seating them with the same comparator you measure after seating?

 

[BringBackThe80s]

Have you just measured your bullets before seating them with the same comparator you measure after seating?

No. I thought the point of measuring BTO instead of COAL was to avoid lands-to-ogive variance caused by bullet manufacturing tolerances. (So my assumption is the comparator has the same inside diameter as the lands.) But since bullet location is set by headspacing off the sholder, I guess to measure consistency of depth within the throat, your comparator would also have to measure shoulder to ogive instead of base to ogive.

Regardless, I'll run a box or two of new bullets through the comparator and see what I find.

 

[urbanrifleman]

If you aren't using an arbor press seater, none of your data would be valid (not to say you didn't).

My guess is that you are crushing your bullets.