Bullet seating problem


August 21, 2003, 11:06 AM
I have found that during the bullet seating process for 9mm in win brass in a lee single stage press with lee 9mm carb dies. I am having a problem with getting a consistant (sp??) seating depth. It will very as much as +- .010 is this normal or have I done something wrong in the setup of the seating die? Oh just in case you need to know I am using 115gr FMJ that i am seating or trying to seat at 1.120 and can get 1.110 through 1.130. Anyone have any ideas.?

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August 21, 2003, 01:48 PM
Just make sure it's tight in the press and the locking ring is tight. Then measure the length of the bullet just to be sure.

Steve Smith
August 21, 2003, 03:14 PM
Pistol bullets are exactly known for their dimensional accuracy. Check 20 or 30. .010" won't matter in a pistol anyway.

August 21, 2003, 07:36 PM
In 9mm, especially as you approach maximum loads, 0.010" can make a big difference! Seating depth is the most important thing, so measure those bullets and see if you can account for the OAL difference.

Steve Smith
August 21, 2003, 08:08 PM
I can see it making a difference with hot loads, and I apologize for my generality. I do think that standard dies and bulk pistol bullets can account for about .010" variation on average, though.

August 21, 2003, 09:18 PM
It's always interesting to measure a few factory-made cartridges to see how their dimensions vary...

August 21, 2003, 09:23 PM
FWIW ..... let me mention something I have had happen ..... not a Lee problem per se ...... any seating and crimp die I'd say.

Over time I have gad alox type lube build up inside die ... enough to slightly alter the seating depth ..... now and again, a round will come out of die, finished, but with large glob of lube on it's nose.

Seems useful to check with a toothpick periodically to remove build up.

If you don't use alox type lube then this is prolly irrelevant.

9mm is IMO one of most critical for OAL being such a high pressure round .... and so variations are more importrant I'd say, to try and control.


Meat to say ... one other thing ..... if case bell mouthed quite wide .. generous flair . the the speed of seating can have effect . the ''intertia'' of ram thrust can seat a tad more or less .. depending on ''vigor'' of operation.

August 22, 2003, 05:20 PM
thanks for all the posts. I have card. dies so I dont have to worrie about lube build up. But the "vigor" could very well be my problem. I may need to do controlled thrusts instead of trying to make a assembly line out of it. (i am new to reloading) and I may need to back off my case flaring also. I will check them out tonight.

Smokey Joe
August 23, 2003, 12:22 AM
When I load cast bullets (using carbide dies) there is a crud buildup in the bullet seating die, but not (obviously) from brass sizing lube. The crud comes from the lube for swaging the bullets, and from the lube grooves on the bullets. A little always works its way into the seater die. And as it builds up, it changes my seating depth. I just adjust for this as the reloading goes along, unless it gets really bad.

The answer for me has been to take my die to my gun cleaning station after every session, disassemble it, and clean it with solvent. Annoying, but it works.

You do want to be careful with seating depth, as the amount of room for the powder to expand when it begins burning varies with changes in how far down the bullet's back end intrudes into the case. Change that room, and you change your pressure, and therefore your bullet velocity. Change bullet velocity, shot to shot, and there goes your accuracy. In extreme cases you could cause a dangerous overpressure.

You also mentioned case mouth belling. You want to bell your case mouth as little as will allow your bullet to sneak into the case undamaged. Less belling means less working of the brass when you crimp your bullet. Less brass working means less splitting of cases and more reloads per case. BTW, you also don't want to crimp the cases any more than necessary, for the same reason. However, heavy loads and heavy bullets require a heavy crimp.

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