Brass prep question (measuring for shoulder bump)

[Phylodog]

I'm in the process of getting set up to load for my .223 SPS. I've been following the procedure outlined by TresMon in this thread: Link

I've got the tools shown in the first two pics and thanks to member Boone, I have 25 pieces of LC brass fired through my rifle. The brass was virgin when he loaded the 25 rounds for me and I've got 1K pieces of virgin LC that I'll be using for my loads.

I just finished measuring all 25 pieces from the head to the shoulder datum, here is what I came up with:

1.427 5ea
1.43 2ea
1.429 8ea
1.428 8ea
1.424 1ea
1.426 1ea

I'm still learning but I was expecting to see more consistent numbers on the brass. If I average everything out I come up with a length of 1.428". This leaves me with a few questions.

Is it normal to see such a spread over 25 pieces?

I did tumble the brass after I popped the primers out, could that have screwed with the numbers?

Should I set my die to bump the shoulder back .003" from the (1.428") average to 1.425"?

Am I over-thinking this?

 

[QuiggyB]

Re: Brass prep question (measuring for shoulder bump)

You aren't over thinking it. That kind of variation does not seem normal to me. I could be wrong but mine is always within .001. Are you sure you are getting the case consistently square on the calipers each time? If you sorted those out and remeasured some of them do you get the same results?

As I understand it these have been deprimed without case sizing and tumbled right. How did you deprime them?

 

[Phylodog]

Re: Brass prep question (measuring for shoulder bump)

Deprimed them with a decapping die on my Rockchucker press.

I came at the brass a couple of times and spun them a bit to be sure I had everything lined up properly in the calipers. I won't claim it's no possible that I jacked up my end but I don't think I did.

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

I would measure a few pieces of virgin brass from the same lot and see if there is any variances in them. Sometimes brass doesn't conform to the chamber perfectly on the first firing. See what the difference is between the virgin and the once fired at the datum point. If the brass hasn't grown very much by comparing it to virgin, you might want to use a slight bump on the shoulder(.001-.002") and see if it chambers well. After the next firing, check the datum point again and see if you notice that the brass actually got a little bigger from conforming to your chamber. Just a thought...

 

[Phylodog]

Re: Brass prep question (measuring for shoulder bump)

I don't have access to any other brass from the same lot. Boone sent me 25 rounds that he had loaded up and those are what I'm measuring currently. I have a different lot of 1K pieces that I bought but haven't loaded any of them yet.

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

I would measure the new ones you have and do a quick comparison. Might not prove anything but usually LC brass is pretty consistent. Just a thought. If the measurements are close, you'll have a better idea.

 

[Phylodog]

Re: Brass prep question (measuring for shoulder bump)

I just measured 15 pieces of my virgin brass and came up with:

1.422 = 9ea
1.423 = 2ea
1.424 = 2ea
1.425 = 2ea

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

If it were me, I'd set my die up for 1.428. That bumps your biggest piece back .002". The rest are a little smaller and should chamber smoothly. The next time you load, measure the datum point again and see where they all measure. I would think they would all be very similar in size.
What load are you shooting?
Is there any soot on the neck of the brass or is it clean?
Like I said before, sometimes the case doesn't conform to the chamber perfectly on the first loading especially if it's not a fairly hot round.
Hope it helps...

John

 

[Phylodog]

Re: Brass prep question (measuring for shoulder bump)

Don't have a load yet but I plan to start with a 69gr SMK in front of 24.5gr RE15 and go from there. Thanks for the advice.

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

One of my favorite loads with the 223 is 24.7gr of Varget with a 69gr SMK in Win brass. You may have to adjust it down a little with the LC brass. If you ever want to use Varget, just work up to it and see what you think. Good luck...

John

 

[TexIndian]

Re: Brass prep question (measuring for shoulder bump)

One of the most frustrating things for me when I started buying the good tools and measuring devices was the lack of firm, consistent numbers. If I do X and Y, I expect to get Z measurements across the board. But that's not the way it usually happens in my experience. It makes me appreciate a good machinist all the more.

 

[Bayou]

Re: Brass prep question (measuring for shoulder bump)

Here's some data for 10 once fired 308 cases from a R700:

head to shoulder 1X fired

1.625
1.624
1.624
1.624
1.625
1.625
1.624
1.624
1.624
1.624

Remember the chamber dimensions are temperature dependent. A case fired from a cold chamber will measure a bit smaller than a case fired from a hot chamber.

To the OP: was there a wide range in chamber temps for the set of 25 pieces that you posted data on?

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

Bayou,
What is the measurement on a new piece of brass from the same lot that hasn't been fired? My R700 measures a little differently than yours. You know how factory chambers are, no two are alike. Your chamber looks a little tighter than mine.

Thanks.

 

[Bayou]

Re: Brass prep question (measuring for shoulder bump)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Longshooter70</div><div class="ubbcode-body">Bayou,
What is the measurement on a new piece of brass from the same lot that hasn't been fired? My R700 measures a little differently than yours. You know how factory chambers are, no two are alike. Your chamber looks a little tighter than mine.

Thanks. </div></div>

Actually I misspoke. My action is a R700, started off as a 700P. But I rebarreled it with a PACNOR tube in what they call "308 Sniper" which is basically a match 308 chamber throated for a 168 gr SMK bullet. The brass is Lapua. Five new unfired cases all measured at 1.623".

However I do have some data on the factory barrel with Nosler CC cases, for both new unfired and 2X fired. Hope this helps.

Head to shoulder new Nosler Custom Brass 308 Win

no base holder

1.624
1.624
1.624
1.623
1.624


Head to shoulder 2X fired Nosler Custom Brass
308 Win

no base holder

1.626 1.629
1.629 1.629
1.626 1.627
1.627 1.628
1.627 1.628

 

[longshooter70]

Re: Brass prep question (measuring for shoulder bump)

Bayou,
Either you have a really tight chamber and your brass isn't growing at all or your rounds on the first firing aren't conforming to your chamber on the first firing. The reason I say this is the new brass and your 1x brass are the exact same measurement. Generally for me, it takes at least 2x firing and sometime 3x firing for my brass to fully expand to my chamber dimensions.(Depending on the load). That is what I think happened to the OP's brass on his first firing.
My rifle is a R700 PSS DM. The factory data you gave is a lot more inline with what my chamber reads. I'm hoping to have that taken care of soon with a re-build. I'm looking for a good smith now to do it.
Thanks for the info, Sir!

John

 

[Bayou]

Re: Brass prep question (measuring for shoulder bump)

Longshooter70,

Yes it is a tight chamber, that's what a match chamber is really - a tight chamber. I am seeing a slight growth though - on average 1.3 thousandth of an inch: 1.6230" to 1.6243". This is good for reloading, less growth = longer case life. Good luck with your up coming build.

I assumed the OP was talking about once fired brass that's why I posted the first set of 10 cases just to show ho much of a spread there is im my measurements. On the second firing I see very little growth over the first firing in the PACNOR barrel, well less than 0.001", but the increase is measurable if you average several cases. I start bumping the shoulder back after the second firing so I don't have any data on 3X and greater.

Mark

EDIT: I think I see what happened. The first set of data was with Lapua cases in the PACNOR barrel that have a new head to shoulder length of 1.623". The second set of data is for Nosler cases in the factory barrel that have 1.624 for the new length. I think you looked at the new Nosler case and compared to the fired Lapua case to see no growth.

 

[Phylodog]

Re: Brass prep question (measuring for shoulder bump)

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bayou</div><div class="ubbcode-body">Remember the chamber dimensions are temperature dependent. A case fired from a cold chamber will measure a bit smaller than a case fired from a hot chamber.

To the OP: was there a wide range in chamber temps for the set of 25 pieces that you posted data on? </div></div>

Those 25 rounds were fired over the course of 20-30 minutes so there would have been some variation in chamber temps between them.