My once fired brass and headspace question

flyingtorpedo

I just finished my first "batch" of 8mm mauser reloads. My brass was unfired Remington and used 34.5gr IMR4064 with a horndy 170gr bullet and a CCI LR primers loaded to 2.850" When I got the brass I rounded out the mouths and put it in my LE Wilson Cartridge Headspace Gage ,http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=345548. The brass was between the two "steps" for min and max so I was good. I was cleaning my once fired brass and after I sized one I checked it in my gage again and it was below the minimum step by a tiny amount-you have to look close to tell. I then checked the rest of the lot-without resizing them at all- and they all went below the minimum. The bolt was no harder to close than if the chamber was empty. I took an unfired Remington case that measured between the min and max and made a dummy round loaded to the same 2.850", cycled it through a couple of times and after I checked it with my Wilson gage again and it was still between the min and max. I also had a few squib loads but as far as I could tell the primers looked the same as the ones that fired properly. There isn't any signs of pressure and the reloads had less recoil and noise than the remington 170gr factory ammo I've fired previously. So what exactly is going on to cause this? Thanks.

Pearyw

I looked in a couple of my manuals and it looks like your load is about 20% lower than the recommended starting load. Hornady manual showed a starting load of 42.2 gr of 4064 with a 170 gr bullet.

B17-P51

The brass will get shorter on the 1st firing as it expands to fit your chamber. If you neck size, you will have a perfect fit in that chamber only.
This is good as you will not overwork the brass and will have no headspace problems. The brass will grow SLIGHTLY with each subsequent firing and MAY need trimmed in 5 or so firings. Downside, if you have 2 of these caliber rifles it may not fit the other one.Full length sizing will lengthen the brass slightly and reduce the life of the brass a little as it will stretch with each firing and be reformed in the die each time.

flyingtorpedo

I only have one rifle in this caliber. I'm using the "wimpy" lawyered down data from my Lee book right now. I also have the JS data in my Lyman book but I'm just plinking with it right now so I wanted something lighter. I'm going to neck sizing these as well.

B17-P51

You can Pseudo neck size with your full length die by smoking the neck and shoulder of lubed, fired case over a candle flame then running it into the FL sizer till the shoulder just kisses the die. You will know this when the soot begins to disappear. Leave about a full turn of clearance between the die and shellholder initially then screw down an eighth of a turn each time you run the same case into the die until there is an impression in the soot. Set the ring with the case in the die and you are set to go.The whole process takes about a minute and you will never have any problems with headspace and your brass will last almost forever.

JustC

factory brass almost always becomes shorter on it's first firing in a non min-spec chamber.

jonk

I wouldn't worry about it. I will say though that that is a very mild load, and Lee's data is just wrong. It isn't so mild as to be dangerous though (detonation).

I personally use 38 gr of 4064 with a 185 gr bullet for pre-98 actions, about 45 for 98 actions (with about 48 being max).

I do recommend neck sizing only if for one gun though- either with neck dies or a full length die screwed in just enough to size the neck and not push back the shoulder. Just gotta play with it to realize this.