A Real Head Scratcher-30-06 Headspace Issue

[Chas1]

While I'm by no means new to reloading, this one has got me scratching my head big time. I purchased a Weatherby Vanguard Range Certified (guarantee less than 1 moa) new not too long ago along with 100 new Lapua brass cases. Originally stated load development with IMR 4895 and then the powder shortage set in and I had to switch to IMR-4064 as I was able to get 14lbs of it. Throughout load development I only neck sized. Best load seems to be 49.0grs IMR-4064 with bullet seated .011 off the lands with groups 50% of the time under 1/2 inch and some 1/4 inch and the other 50% around 3/4 inch to just under. In an attempt to get more consistent groups I had already eliminated everything I could think of....EXCEPT headspace as I was only neck sizing, nonetheless I figured let me just check headspace...and man was I in for a surprise.

Of the 100 lapua cases fired out of the Weatherby the cases measure anywhere from .003 to .017 BELOW max headspace for 30-06 using Wilson case gauge along with Wilson case gauge depth micrometer. So I took 8 cases that all had the same headspace and loaded them up and shot them today. Four shot 3/4 inch group and four shot 3/8 inch group @100yds and once again noticed several primers were slightly above flush (having seated them .002 below flush with tight primer pockets. A buddy of mine at the range said you might have too much headspace so measure the case with the primers in them and then measure w/o the primer. The result are as follows: with primer .002 - .004 below max. w/o primers .004 - .012 below max. so at this point I pulled out my Hornady Headspace Gauge and cases measure 2.035 - 2.040 now If I'm reading SAMMI spec correctly max headspace is 2.052 -.007 setting minimum at 2.045. So best case I'm .005 shorter than minimum and worst case .007 shorter. How in the heck is this happening, I thought cases were supposed to stretch to eventually fit the chamber....remember I haven't FL sized any. I'm lost and would appreciate any insights. Thanks.

 

[Howland]

You don't say how many firings the cases have, nor the bullet weight which would tell us whether your 49.0 grain load is toward the top end or bottom end of the charge weight range. Also, while I'm not familiar with the Wilson tool, the Hornady tool is a comparator, not a true gauge. It is used to compare, not give a traceable measurement. Two different tools will give two different measurements.

During load development for 338LM, it took 3 firings before just a couple of cases expanded to fully push the case shoulder to the chamber shoulder. Your cases just might not have enough firings to have fully expanded. The lower the load pressure, the more firings it will take until they are fully expanded.

 

[Chas1]

Sierra 150gr FMJBT and according to Sierra's Load manual starting load for IMR-4064 is 44.9grs and max is 52.1grs so at 49.0 it's not exactly a light load IMO. Some cases on 2nd maybe 3rd firing.

 

[User4302021]

You have a tight chamber. It isn't too tight to chamber a round. It is accurate. Nothing to worry about.

 

[243winxb]

The gauge is to compare fired brass to sized. Not chambers.

Light loads in 30-06 will do 2 things.
1. Expand the case body and make the head to datum & trim length shorter.
2. A fired case may not except a bullet or it will be very snug. The neck has not fully expanded because of low pressure.

 

[Chas1]

Light loads in 30-06 will do 2 things.
1. Expand the case body and make the head to datum & trim length shorter.
2. A fired case may not except a bullet or it will be very snug. The neck has not fully expanded because of low pressure.

Not sure but, would you consider 49.0 grs a lite load if manual min is 44.9 and manual max is 52.1, your thoughts.

 

[MagnumManiac]

I have a 25-06 that is .002" below minimum SAAMI spec. New cases only just fit.
However, no case after firing comes out shorter in head to datum. This is measured with an RCBS Precision Mic.
I believe these give the best actual measurement when used on a tight fitting case of your chamber dimension.
I also have the Hornady set, the 2 do not give the same measurements.
I would fire the same case 3 times with only neck sizing it and see what happens. If it shortens, this is a dead giveaway that there is insufficient pressure to obturate the brass. Reduced loads increase headspace over multiple firings, this can cause bad things.

Cheers.

 

[slikmrc]

It's been my experiance that Weatherby rifles generally have good chambers. I would take a deprimed case and put a piece of scotch tape on the case base and see if you feel any resistance on the bolt close. If not keep adding tape until you do, I figure 1.5 to 2 thou per piece of tape. If this load is weak you should see soot an the case neck and shoulder. Could be undersized brass I suppose, would be helpful to know how fast the load is going. Imr 4064 has always been a great powder in the 30-06, 49 grains should be running around 2850 I would think.

 

[243winxb]

Not sure but, would you consider 49.0 grs a lite load if manual min is 44.9 and manual max is 52.1, your thoughts.

Yes in some rifles. This is why we work up. The 3 grs of powder, to get to maximum, is a lot.

The maximum load is dependent on components. A Sierra 150gr FMJBT needs it own load data, for this bullet. Does Sierra show this 1 bullet or a bunch of 150 gr bullets of different types, with generic load data?

I looked at the Hodgdon website data using IMR 4064, to get an idea of the maximums. Plus other data showing a range of IMR-4064 From 44.2 grains to 53.6 grs.
Most show 52 gr maximum with different bullets.

When neck sizing only, i find the bolt becomes had to close, soon or later. Then the brass must be Full Length Resized. If neck sized loaded ammo has never caused a crush fit when closing a bolt action, the loading is on the light size.

 

[243winxb]

Some cases on 2nd maybe 3rd firing.

Keep firing & neck sizing till the bolt provides a crush fit on closing. This will be a correct head to datum brass measurement of the chamber. When using the FL die, only move the shoulder back about .002" to .004"

 

[Chas1]

I think I'm going to take cases that are .003 - .007 below max headspace and step the load up gradually and see if at some point they start to stretch.

 

[wnc-coyote]

may want to try seating a few in the lands firmly, as one would form AI brass. Doing this will help keep the base of the cartridge firmly seated against the bolt for fire forming.

There are others that know more about this than I, Maybe one will chime in about this.

 

[ThrdKllr]

You can insert a used primer in a fired case just enough to hold it and chamber it and close the bolt. If it's too short the primer will be sticking out not fully seated. The only way you can measure your chamber with a comparator is to measure a go gauge first and COMPARE it to your fired brass.

 

[Chas1]

I ordered a go gauge today so I can calibrate comparator. Good advice.