Seating depth

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Iamduck82

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Newbie reloading question.

I'm using Redding Type-S dies with micrometer and am having an issue with overall seating depth. Not sure if this is critical but it's messing with my head.

I'm using Lapua brass and SMK match kings. OAL of each projectile and casing in the batch are within 0.001 of each other. But when I go to seat the bullet I use the same amount of pressure and the OAL of the batch of rounds varies with greater degree then the variation in case and projectile length.

Example goal OAL is 2.800 out of a 5 round batch I'll have 3 within 0.001 of each other then the third and fourth will seat 0.003-4 deeper.

I think it's operator error but does a variation of 0.003-4 make a critical difference?
Any suggestions on how to maintain consistent seating depth?
 
That's what my thoughts were but everything was secure. If it came loose it would have backed out not gone deeper. I'll try another batch today and see if I can repeat the issue. It was fairly late in the day and could just be me.

How will a variation of 0.003-4 affect the rounds performances?
 
Take a close look at the meplets (tips) of the SMKs. Are they all consistent or do some have small burrs and inperfections. Since the seating die seats the bullet using the ogive and you are measuring off the meplet, any variation in the dimensions of the bullet is going to show up.

You can either buy a bullet comparator and check, or simply not worry about it. SMK are very tolerant wrt to seating depth, you are not likely to notice.
 
Ive found that when I seat my bullets that if I dont use the same downward force/speed all the time, I dont get the same seated depth of my rounds. Im just using regular RCBS dies though.
 
One to 4 thou will make no difference at all.
If there are burrs or any imperfections on a MATCHKING, take 'em back where you bought 'em. They're defective.
 
Your seating die will push on the shoulder of the bullet, not the tip. The dimension that matters is the shoulder of the bullet to the start of the rifling. I typically seat the bullet to be about 20 thou off the rifling.

The MatchKing bullet folds the jacket over an empty cavity to form the hollow point. It is an excellent bullet but the style of construction means that there is a significant variation in the length of the bullet, forward of the bullet shoulder. This variation means absolutely nothing in shooting performance except that handloaders measure OAL and then get concerned about the variation they see.

The variation is in the bullet - not your loading technique. Sierra Match bullets can vary about 20 thou, within one box. Hornady vary about 10 thou. SO if you measure OAL to the tip of the bullet, you will see these meaningless variations.

If you want to measure how consistent your seating depth, you need to put a collar on the round that sits down on the bullet shoulder. I use one because it allows me to switch bullets and come up with a new OAL for the new bullet that gives me the distance from the rifling I want.

I make my tool from a piece of barrel that has been touched with the throating reamer, so it replicates the throat of the rifle. It sits on the shoulder (ogive) of a VLD or a round nose bullet and allows me to measure from the top of the collar to the base of the case so I can load any bullet to the "jump" I want.

COALTOOL.jpg
 
If necks get workhardened unevenly, that has caused depth variation for me. The ones needing more ram handle pressure to seat likely to end up longer.
Annealing has always fixed this glitch.
And my loads shoot better with even bullet pull.
 
Measuring the OAL from the tip(meplat) to the base of the case is a sure way to drive yourself to drink. Measure only from the base to the ogive and I'm sure they will measure much more consistently.
 
The reason is the base to ogive length varies. I buy in bulk and my first process is the measure base to ogive and separate in one thou increments. In a lot of 1500 bullets, I have found variations up to 10 thou. I then sort those lots into overall lengths in increments of 3 thou. Then I trim the meplats and re-point. What is happening to you is the variation in base to ogive so your seater picks up on the ogive and seats accordingly. so what you have is 4-5 thou difference in the base to ogive. As far as accuracy is concerned, it depends on what you are trying to achieve. Generally it won't make much difference unless you are a highly competitive long range shooter
 
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