Lapua Virgin Brass short of SAAMI Headspace Length?

[Taxman1002587]

I received a Redding Instant Indicator-Headspace & Bullet Comparator for Xmas. Its labeled 6MM BR Remingtion. Following the instructions for use I measured for headspace 20 virgin Lapua 6mmbr brass cases. 14 were 1/1000 short and 6 were 2/1000 short compared to the length that was established at 0/1000 using the "Set up Gage" (basically looks like go gage for headspacing) provided with the tool. The shoulder angle, datum diameter and length are according to the instructions made to SAAMI minimum 1.1670. Using a Bullet Sorting Stand and .338 caliber insert in the stem of dial caliper and setting the caliper to 0/1000 with "Set up Gage" I remeasured the cases on the Tru Stone base and got the exact same deviations. I was expecting given that the Gage is made to the minimum SAAMI that the readings would be long not short.
Either I am doing something wrong - or the SAAMI Headspace ML is different between REM and Norma - or the brass is short at the shoulder. HELP or ADVIVE Appreciated.

 

[msnations]

If a case isn't at least .001" shorter than the minimum sammi headspace, it can't be guaranteed to go to battery in every chamber...

 

[fdshuster]

Taxman1002587: You're building in complexities that do not exist. Lapua brass is the finest available, load it up and shoot it. All the cases will then be fire-formed to fit your individual chamber. It may or may not fit in other 6BR Norma/Lapua chambers because of the max/min saami tolerences, but who cares?

 

[Taxman1002587]

I don't disagee with you regardig Lapua Brass. It just surpised me that it is shorter then the SAAMI minimum. However I will make sure the first loads are jammin into the rifling so that the base of the cartridge will be firmly against the bolt face.

Thanks for your response.

 

[Ackman]

You're worried about a nonexistent problem. Just load the cases and shoot them.

 

[Rust]

Virgin brass, regardless of maker, must fit in every chamber out there for that case. Becaue of this is must be slightly shorter than a SAAMI minimum spec chamber. Which is also why you see so much talk of fire forming brass to an individual chamber for maximum accuracy.

When fire forming is is usually a good idea to seat the bullets into the lands, using a fair amount of neck tension.

In self feeding rifles, the brass really needs to be shorter than the chamber (slightly) to insure proper feeding, ie so the bolt goes completely into battery since a self feeding rifle has so much less closing force than a bolt rifle. Not that using excessive force to close a bolt is a good idea at any time although a little force is required to close the bolt with hard jam bullet seating. Don't want to rick galling the lugs.

 

[Taxman1002587]

Thanks now I get it. Are body sizing dies (not the full length sizing dies) such as the Redding Body Die and the Scinclair also set up to result in the shoulder/headspace being short of the SAAMI minimum?

Thanks for your help.

 

[NorCalMikie]

The body die resizes "only" the body. No shoulder movement and they don't have any moving parts. At least on my Redding body dies.
And on a custom gun, if you can reset the headspace to the shorter length brass, it won't have to grow much to fit the chamber.
The less brass has to move, the longer the it will last. JMHO.

 

[Taxman1002587]

The instructions included with my Redding Body Sizing Die state "Body dies are designed to full length resize your cartridge case and correctly bump the shoulder position for proper chamber fit without disturbing the neck" - if you go to their web site and look up their Body Dies it says the same thing and adds "For the ultimate shoulder bump control, use these dies with our new Competion Shellholders.

Having extensively used a Redding Body Die in 6.5X 284 I know that they do, if set up properly bump the shoulder.

I am trying to prepare some 6mmBR brass (new gun new round to me) and follow the steps listed in the Article in the Article archives on this web site titled - Case Preparation Complete Guide - by B J Gottfredson. Step 1 says you should use the body die to force the shoulder and body to a standard configuration - as I now know Lapua brass is a couple 1/1000s short of SAAMI min head space if I now do Step 1 I will have to bump the shoulder even further away from the Min headspace - does anyone know how far below the SAAMI Min you should go?

 

[Rust]

You do not want to bump the shoulder back too much on any brass, the brass then has to stretch too much on firing and this leads to weakening the brass and eventually a potential case head seperation.

Fire form a couple of pieces of new brass twice using fairly stout loads with he bullets seated to the lands, only neck sizing to reload. This should give you a pretty fair baseline as to where your shoulder is in the chamber. .0015" to .002" is a good amount of shoulder bump in a bolt rifle. Self feeders (ARs and such) generally should be full length sized with .002" to .0025" of shoulder setback since their bolts exert much less closing force than a turnbolt.

Note that there will likely be other opinions stated as to the amount of shoulder bump, but that's pretty much what has worked for me.

 

[Ackman]

You've got yourself worked up over nothing. Just load it and shoot it and stop worrying.

 

[jo191145]

Taxman
Your die instructions are correct. Your body/ FL die will set back the shoulders. You can't set up that die until you've fired some brass, preferably several times. No need to use it on virgin brass. The important measurment is how much ahead of Saami minimum your chamber is cut. Your body die needs to be set to bump the shoulders .001 back from that measurment.

If your body die will not set back the shoulders on fired brass the headspace is short in your rifle. Not a bad thing really. Or the die came a little long.
With my Savage rifles I headspace barrels to a slight crushfit on virgin brass. Keeps the initial stretch to a minimum. This can eliminate the use of some factory ammo at times. Can't afford it anyway ;D I've seen economy brass .011" under Saami specs. That would be a lot of stretch. It was'nt actually possible to headspace that low in my rifle. The bolt would bind on the barrel stub.

Depending on the specs of that specific lot of brass most FL/Body dies will not bump the shoulders back that far.
Simple solution. I long ago stoned the tops of my shellholders off. Now I can set my dies deeper to size to my specs. When FL sizing my dies do not contact the shellholders. Thats a generic one size fits all setting and not the proper set up for a FL sizer. You have the tools to set up a FL die properly. Now you just need the fired brass. The most material I've needed to remove from a shellholder is .013"

Another attribute of thinner shellholders, My standard necksizers can be adjusted down to create shoulder bump neck sizers without touching the body. Works like a charm.

I'm not advocating you need to do this. Its just an option we should all be aware of if we change our rifles headspace lower than Saami.
FWIW The Redding competition Shellholders are thicker than standard. Completely useless to me but I quess someone figured out a use for them.

Ackman is right. Your brass is perfect virgin brass. Go fire it.
Good to see your paying attention and thinking tho. - Have Fun