What dimension to full size brass to

[timelinex]

So I decided to start full sizing my 338lm. I was looking for advice on what dimension to full size to. All the dimensions I used are stripped to just the .01 or .001 place, to make it easier to read.

My virgin brass was 0.016". My once fired brass was 0.022-0.024. My twice fired brass ended up being around 0.0275.

So with my once fired brass, just neck sizing, the brass went in smoothly. However after firing the ejection was rough. It was doable, but I would definitely have to use some muscle. I ended up sizing my 1x fired brass to 0.021-0.0225 (depending on the piece it seems like it varied slightly, I assume thats normal).

Interestingly enough, both of the NS and FS brass ended up being 0.0275 after the second firing, however the previously FS brass was a smooth ejection. <span style="font-weight: bold">I am assuming that the shoulder wasn't the problem but other areas of the brass was?</span> The NS only brass actually looks like it was ran through a sizer, in other words my chamber was sizing it on extraction!

<span style="font-weight: bold">So should I continue bumping the shoulder back .001 from the first firing, or should I bump it back .001 from that maximum dimension that comes out on my second firing?</span>

 

[MitchAlsup]

Re: What dimension to full size brass to

This is where having the tools to measure the position of the shoulder come in (Hornady dial caliper attachment or RCBS case micrometer).

It is also where having the tool to measure the diameter at the case web expansion comes in (4 digit micrometer--or 0.0001 inch capable measurement device).

It is not about how much to push the shoulder back, but where the shoulder ends up that counts. It also maters how wide the case web ends up.

 

[timelinex]

Re: What dimension to full size brass to

I do have the tools... That's why I'm asking and included measurements. My question had to do with which figure to go off from. The 1x or 2x fired

 

[jdgray]

Re: What dimension to full size brass to

If it chambers easy, and after firing, you get hard bolt lift, thats a sign of overpressure. If the bolt is stiff on chambering, now you need to bump the shoulder a few thousands. I would measure a case that chambers a bit stiff, and use it for a base to measure with.

 

[timelinex]

Re: What dimension to full size brass to

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jdgray</div><div class="ubbcode-body">If it chambers easy, and after firing, you get hard bolt lift, thats a sign of overpressure. If the bolt is stiff on chambering, now you need to bump the shoulder a few thousands. I would measure a case that chambers a bit stiff, and use it for a base to measure with. </div></div>

Ok thanks. On my next firing batch I will bump the shoulder based on the 1x firing dimensions. With the new brass the bolt drops with just the weight of my fingers, while with the 1x fired dimensions it does not. So I assume that means there is contact.

The slightly stiff bolt doesnt happen with the new brass, or the 1x fired full sized brass. Only with the NS brass, so thats why I was more inclined to think it was a sizing issue somewhere rather than pressure. I understand the brass expands to the walls upon firing, but brass sized smaller before firing will rebound to a smaller size than larger brass.