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First time using new brass

Another rookie question.

I started reloading with some once-fired Lapua brass, but I have a limited number of cases to work with, so I ordered a box of new cases. Do I need to resize them before loading? Is the first fire relevant for accuracy, or do I need to fire them once before I can consider adjustments to my load development?
 
I full size new brass before first firing. Don't go crazy stressing about accuracy right away though. Factory brass is often very short (base to shoulder) because they want it to fit in all chambers. After it has been fired, then you can start dialing in the headspace measurement.
 
This will be one of the half dozen different answers you'll get on this subject. My suggestion is to either neck size or run it through a FL die and do as chromatica said, don't bump the shoulder, just straighten the mouth. I've shot some great scores with new brass, it will shoot fine,
 
Another rookie question.

I started reloading with some once-fired Lapua brass, but I have a limited number of cases to work with, so I ordered a box of new cases. Do I need to resize them before loading? Is the first fire relevant for accuracy, or do I need to fire them once before I can consider adjustments to my load development?
The main thing is to get the neck expanded. New brass has super tight neck tension to the point you’ll damage your bullet seating it. Run it over an expander button in your die or use something like this.
 

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Seems to me I get more uniform neck tension (bullet seating feel) with new brass to expand the neck and then run it through the bushing that I want to set up tension with.

Agree, neck tension on new brass can be a variable - but easily rectified with an expander before first use. I pick an expander size that does not require the additional step of sizing down with a bushing.
 
The expander mandrel I like to use is actually a Lee Collet Die. After the case neck rides up on the mandrel, the petals of the split collet squeeze the neck wall against the mandrel. This action can realign necks that have skewed as a result of firing or sizing.
 
I use a Lee Collet Die on new brass to help smooth out the interior of the case neck so that I get easier and smoother seating. And, that helps with getting better performance from virgin brass.
 
You guys weren't kidding about how tight Lapua necks are. No way I could have seated a bullet without risking damage to the case or bullet. I used my full-length seating die just to stretch the neck a bit without actually sizing the rest of the brass, and it made a huge difference. Do you think that would be sufficient for a first time load? My case gauge says once-fired brass is 0.002 longer than the new brass, so I should be in the clear as far as head space.
 
You guys weren't kidding about how tight Lapua necks are. No way I could have seated a bullet without risking damage to the case or bullet. I used my full-length seating die just to stretch the neck a bit without actually sizing the rest of the brass, and it made a huge difference. Do you think that would be sufficient for a first time load? My case gauge says once-fired brass is 0.002 longer than the new brass, so I should be in the clear as far as head space.
It will work fine. As long as you don't have to force the bolt closed.
 
I full size new brass before first firing. Don't go crazy stressing about accuracy right away though. Factory brass is often very short (base to shoulder) because they want it to fit in all chambers. After it has been fired, then you can start dialing in the headspace measurement.
That’s been my experience if the rifle does not have a “match” chamber.

If anything I find factory brass can create way too much neck tension so I tend to consider my first firing to be a fire forming step. If it shoots well, great, but that’s just a lucky bonus. I do not bother to expand the necks unless bullets are seating poorly.
 
I open up the necks of virgin Lapua brass first with a Sinclair "over-sized" expander mandrel that is .001" under bullet diameter, then follow that up by running the cases through a bushing die with the appropriate bushing to yield approximately .002" neck tension (interference fit). In my hands, a die that is already properly set up for brass fired in a specific rifle/chamber will not move the shoulders of virgin brass back at all, so the die re-sizing step really only affects the case necks of virgin brass.

Because Lapua neck are pretty tight straight out of the box, you could also streamline that process by simply using the appropriate expander mandrel to give the desired neck tension in a single pass. However, because brass spring-back works in the opposite direction when necks are opened up with a mandrel from the inside (as opposed to being squeezed down from the outside by a bushing), you will need a mandrel that is about half a thousandth larger than the desired neck tension. For example, a mandrel that is .0015" under bullet diameter will yield a neck tension of ~.002", one that is .001" under bullet diameter will yield a neck tension of ~.0015", etc. 21st Century sells mandrels in .0005" increments:

http://www.xxicsi.com/caliber-specific-expander-mandrels.html

https://www.sinclairintl.com/reload...ls/generation-ii-expander-dies-prod38807.aspx

I have used virgin brass in matches that has been prepared by the above procedures and it shoots very, very well. After the brass has been fire-formed and re-sized with the shoulders bumped back approximately .001" to .002", you may need to adjust charge weight slightly to maintain the same velocity as the internal case volume will be larger after the shoulder has moved, and less energy from the powder charge will be going into expanding the cases on subsequent firings.

One other consideration with virgin brass involves the primers. In my .223 Rem and .308 Win chambers, virgin Lapua shoulders move about .007" to .008" and .004" to .005" on the first firing. Although I have not personally experienced this issue, using virgin brass that has not been fully expanded to fit the chamber can sometimes cause blown primers, even with loads that are not at all over-pressure, due to the "extra room" the virgin case has to move longitudinally within the chamber. Again, it may not ever happen, but it's just something to be aware of.
 
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I second what Ned Ludd said. I recently loaded some 6.5x55 SM for a new rifle build, and used new Lapua cases. The capacity change after firing pointed to a need to use about 0.7 gr more powder (in that chamber and rifle) for second and subsequent firings. This is pretty typical. The Lee Collet/mandrel collet does not expand as much as the Sinclair oversize mandrel used prior to neck turning. The oversize mandrel, for those who don't know, is larger than the neck turning mandrel, which is used for the actual neck turning. I am not recommending neck turning, just pointing out the difference in the mandrel sizes.
 

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