Variations in bullet seating depth

[Howa 9700]

Not sure if this is normal, or if I'm doing something wrong.

So goal was a case overall length (COAL) of 2.830. So went through the trial and error process adjusting seating depth to get to that length, then ran 2 or 3 more and they were all the same.

Then comes #4........and COAL is now 2.822. Then a few more and one might now be 2.838. The average remains 2.830, but with variations as much as +/- 0.008.

Lee press, which does not cam over. Ram runs up to make contact with bottom of the die........which is a positive stop that never changes.

Only source of variation I can think of is the bullet itself, which in this case was a Hornady Interlock, which do not all measure the same. Since these are exposed lead tips, they don't all look or measure the same.

My concern is correlation of COAL to accuracy. But as long as seating depth is the same.....perhaps any variation in the tip finish doesn't matter? Assume they will all behave the same regardless of the minor variation in COAL?

This sound right or am I missing something?

 

[MEHavey]

The variation is in bullet length itself: base to exposed lead tip
But the seating die is likely seating using the ogive anyway.
Bottom line: don't worry about it.


.

 

[jmorris]

Only source of variation I can think of is the bullet itself, which in this case was a Hornady Interlock, which do not all measure the same.

Sounds like you’ve got it figured out already.

If the base to tip is different on your bullets (not surprising at all),

Measure them from a datum along the ogive.

Now that they read the same, use that reference to set your seat die. That won’t make your OAL numbers any more consistent (because the bullets are not the same) but the barrel doesn’t really care about the tip of the projectile.

 

[Nature Boy]

To reinforce what’s been stated above, BTO (Base to Ogive) for a more accurate measurement of seating depth consistency.

However, don’t be surprised if you still get variation as the manufacturer has a tolerance on the ogive as well, some more than others.

Hornady interlocks are hunting bullets, not match bullets. You won’t find the same consistency with them as you would with a Berger VLD

 

[Howa 9700]

That would help with my next step / concern, which was how I was going adjust the seating die to alter seating depth in small EVEN incremental steps when I didn't have a consistent depth to start with. My dies don't have micrometer adjustments on them.

Where did that ogive jig thingy come from?

 

[jmorris]

That one was given to me by a friend but it’s a Sinclair.

https://www.brownells.com/reloading...r-hex-style-bullet-comparators-prod83792.aspx

You can also get them that attach to the caliper but need different inserts for various diameters.



If you just want to see if your equipment is mechanically repeatable, you can remove your seating stem and use it. As that’s the “datum” that’s important anyway.

 

[jmorris]

My dies don't have micrometer adjustments on them.

Most of my dies also do not have micrometer adjustment, I can precisely adjust them with this little fixture I built though.



If you don’t have a dial indicator or a way to make something to hold it, this might work for you.

https://www.amazon.com/Digital-Magn...sprefix=digital+height+gauge,tools,176&sr=1-8

 

[Blue68f100]

You can also use a small caliber cartridge brass slipped over the bullet that contact the ogive. Used like the specialty tools Jmorris displayed. This will give you a reference to compare with. It will let you know if your getting consistent seating depth.

 

[Slamfire]

Phillip Sharpe was right that the real safety measurement, is the depth of the bullet in the case. That is because pressure is directly related to case volume. You can see in his book: Complete Guide to Handloading Mr Sharpe used depth in case instead of OAL in his reloading tables. However, it takes too long to figure out how much of the bullet is in the case, and no one reloads that way.

I am going to tell you, keep the bullets off the lands. Seat them deep enough such that when the cartridge is fed, particularly in auto loaders, the bullet is clear of the throat. It is a particular bugger to eject a round in a 1911 that is jammed in the lands. A number of times the force required to rack the slide has been greater than my hand strength. Then I go looking for a table to hang the muzzle over and press down on the recoil plug. Incidentally, that's when I found guide rods are a solution to a problem that does not exist, and they create more problems than they solve.

 

[GeoDudeFlorida]

You can also use a small caliber cartridge brass slipped over the bullet that contact the ogive. Used like the specialty tools Jmorris displayed. This will give you a reference to compare with. It will let you know if your getting consistent seating depth.

Yup. A .32H&R mag case works great for .308. Bell the mouth using an M-die for .303Brit/7.62R/7.65Arg/7.7Jap. 8mm Mauser (7.92x57mmJS) is a little trickier but I've used modified case necks cut off of scrap .303Brit cases before and they work pretty good. As long as the inside diameter is right and it's long enough and flat enough on both ends to get good measurements anything that matches the ogive will work.

 

[Dirkmc3]

Get a comparator...best 34 bucks you will spend.