In the process of bullet seating(308 win), I have noticed a variation in oal between cartridges. This difference can be as much as + or - .005". The brass has been trimmed to the same length and checked with calipers. Anyone have an idea of what might be the cause?

Your bullets are different lengths. The benchrest shooters sort their premium match bullets by ogive length because they all vary.

Fjold is correct.

Take a look at Converting from OAL to ODL and the issue will be resolved.

The OAL will still vary and that is fine because we need to be concerned about the distance from the Ogive-to-the-Lands remaining constant.

Best of luck to you.

If you're using a conventional soft point, the points will be flatter on some than others from beating around during shipping. This will cause this much variation, but has no effect on the distance from the bullet to the rifling which is the critical dimension.

Fact of the matter is, variations in bullet lengths from base to tip with in reasonable boundries (say, +/- 0.005") is totally insignificant. What one needs to look at is the length of the bullet from base to ogive-that is the point at which the forward section of the bullet first reaches bore diameter (.243, .284, .358 etc.). This is measured with a bullet comparator. Infact, when making load notes, instead of recording OAL, I record OACL (over-all comparator length) as it is the more significant dimension-barring any magazine-length restrictions, of course. Having said that, I have run into differing OACL's when loading heavily compressed charges even with sufficeint neck tension (.222 Rem).

I had an old rcbs rockchocker press that would produce inconsistent OAL. The pin at the bottom of the ram would work itself out a little over time and would change the OAL if I didn't watch it.

http://www.sinclairintl.com/cgi-bin/category.cgi?catego...em=09-600&type=store

That should fix your problem or let you see you don't have a problem.

Molar1:
What the other guys said about bullet length. Get the Stoney Point gages to measure to the ogive. I'm probably too anal about seating depth but I always "rough" seat my bullets about 0.005" to 0.007" too long then measure & dial each one in to what I want. Yeah, this is probably not necessary & is more time consuming but I do this for my rifles anyway.
Bear in Fairbanks