Expander mandrel on primed brass?

[setter]

I am going to try using an expander mandrel for the first time and I'm still new to reloading. I did a search in this forum and found a lot of good info. However, when someone asked: "The expander mandrel is the last step before seating the bullet?" and the reply was "Yes", that made me wonder whether I should take that statement literally since that didn't make sense to me. Wouldn't that be difficult with powder in the case since otherwise that would be the last step before seating?.
I have some primed brass and would like to use the expander (before proceeding with adding powder). Could there be pressure build-up when using the expander mandrel since the case is 'sealed' with the primer in place and wouldn't the mandrel actually create an air tight seal at the neck at the same time? Could that either cause the primer to pop out or loosen, and/or cause the case to bulge out?

 

[David_h]

You should be fine either before or after priming. The air is a compressible fluid so no worries on pressure from inserting a mandrel. Yes, I'd avoid using a mandrel after the powder charge is filled; those mandrels can be quite long.

 

[Hugnot]

No powder in case & no decap pin on expander.

I very cautiously wipe the inside of the neck with a slightly moistened small wad of paper towel or Q tip with Hornady One Shot lube & cleaner being careful not to get any of that stuff on the primer. After cleaning neck insides I place the primed cases neck down in the loading block. My reasoning is that the One Shot will facilitate passage of the expander thru the neck and cleaning the insides of the neck will remove all or part of the nitrate salts and other acidic deposits formed by powder combustion that will cause corrosion stuck bullets.

Just be real careful not to mess up primers with the One Shot - a blast of One Shot into the case will probably kill the primer for some time.

 

[stazmania]

The displaced air from the expander pressuring the primer is something to consider. I have new, primed brass that I was thinking about running through a SAC sizing die with an expander, to be sure of uniformity. Checking the primers after sizing would be a good practice. Thanks OP

 

[lancetkenyon]

Run them through the expanding mandrel. Primed or unprimed. No difference. I have done 10s of thousands each way.

NEXT time, run them through BEFORE priming. I think the comment of "last step before seating" should have been "last step before loading" (priming, charging, seating).

 

[RegionRat]

+1
Even if you consider that the starting pressure in the case is 14.7 PSIA, and you are squeezing the volume of the mandrel down into the tight neck, you won't hit the type of pressure that can affect a normal case, with our without the primer in place.

In theory, if that compression causes a primer to move, you have bigger problems.

Try it with your case, mandrel, and bare hands just to satisfy yourself some day.

 

[MagnumManiac]

Just a word on new brass and neck condition.
I run all new brass through a custom neck die and then through a mandrel before doing any loading. Necks on factory brass NEED to be sized IMHO.
I have found factory neck specs incorrect for precision loads, it is always too tight on interference.

Cheers.