Lapua Brass - 300 Win Mag Headspace Anomalies?

[jguill]

I recently purchased 2 boxes of 300 Win Mag Lapua brass in preparation for a custom rifle being built. I normally follow benchrest case preparation techniques. Before neck turning the 300WM brass I decided to measure the headspace of the virgin brass. Using a Redding Instant Indictor the Lapua headspace was .015" to .017" shorter than the SAAMI minimum. In my past experience with virgin .308 Win Lapua brass the headspace is normally .002"-.003" shorter than the SAAMI minimum.

Because the shoulder is so far back on the 300WM brass I can not FL resize the brass to the same shoulder/neck junction dimension. Therefore I can not get a consistent neck turning shoulder bump cut. I imagine this brass is going to grow like crazy after fire forming and the shoulder and neck are going to move around considerably. This is another reason neck turning seems futile at this step. I can always neck turn after fire forming, however I don't particularly like this option since it requires 2 fire forms before the brass is "ready to go".

Belted cases are notorious for thinning around the web due improper headspace-belt chamber alignment. It seems like the Lapua brass will grow at least 15-17 mils assuming the chamber is cut to SAAMI minimum. Is 15-17 mils of growth something to worry about? Has anyone else seen such large headspace setbacks in new 300 WM brass?

One way to solve this problem would be to cut a custom chamber with a reduced headspace to match the Lapua brass. Since this handloaded brass will be married to this rifle I am not worried about factory ammo/brass chambering issues. Does anyone have comments (good or bad) about this option?

Thanks,
Jarret
Frisco, TX

 

[jb1000br]

The instant indicator only gives relative numbers, not actual distance, how do you KNOW it is 15-17 thou short?

JB

 

[jguill]

Redding provides a calibrated SAAMI minimum brass blank that you use to index the dial indicator to 0. I have used Redding instant indicators on 270 and 308 Wins and they match SAAMI minimums extremely well. I also measured several once fired 300 WM rounds from another factory rifle and they measured +2 to +4 mils over SAAMI minimum, as to be expected. If I were to use the Lapua brass in that gun it would have to grow 20 mils before reaching the shoulder datum.

Thanks,
Jarret

 

[jb1000br]

Gotcha /ubbthreads/images/graemlins/wink.gif

I thought the brass dummy was just for measuring bullet bearing surface /ubbthreads/images/graemlins/wink.gif

Good to know about the saami Dim. I have just been using it to check seating depths...

I would email lapua. Hopefully you still have the box with the lot info on. I bet they will take it back.

try nina:

[email protected]

JB

 

[jguill]

Is the purple stamp located on the inside box cover the Lapua lot #? These two boxes were stamped EFCLLS. I could not find anything on the outside of the box that indicated the lot #.

 

[Jim Hundley]

Jarret,
I use the .300 WM Lapua brass and never had any problems.I prep the brass to benchrest standards,including neck turning.I have never been concerned about the SAAMI headspace,maybe I should be,though!I just run the brass through the FL die with the appropriate expander to match the neck turning mandrel.I have the FL die adjusted to not touch the shoulder,just straighten out any "wrinkles".Trim the brass to length of the shortest and turn.On my good days I am shooting in the .3's and .4's.Yesterday had a 5 shot group in the .5's.My chamber is minimum SAAMI.This accuracy is with 168 Barnes TSX's.Have reloaded some of the brass 5x's or until primer pockets loosen.These loads a fairly warm at 3200f/s.No indications of case head seperation.Hope this helps.
Jimmy

 

[jb1000br]

[ QUOTE ]
Is the purple stamp located on the inside box cover the Lapua lot #? These two boxes were stamped EFCLLS. I could not find anything on the outside of the box that indicated the lot #.

[/ QUOTE ]

Yes, the outside number is the part number.

JB