Adventures in headspace

So I screwed on my new Criterion 223 rem match the other night. I set the headspace pretty close to minimum. Go guage closes fine, but even 2.5 thou of cellphane tape will prevent closure.

Did you know that SAAMI allows a massive TEN thousandths of headspace tolerance in the chamber? It's true. The Forster no-go I have is 1.4666" and that's still 0.007" shorter than max SAAMI spec.

So I'm sizing some brass last night and trying to size it *just so* for this new Criterion's chamber.

My comparator shows the go guage as 1.4565". It's wrong, but since it's just for "comparing" it's OK.

I'm trying to set the headspace for just a tiny bit of squeeze, so I targeted 1.4585" on the comparator. Eventually I got there. In a tray of 50, over half the cases sized exactly to that value. The bolt closes with just a tiny bit of friction, just a very subtle jam, which is exactly what I was going for. This slight interference in headspace should assure that the case centers itself in the bore.

But even though these are all the same headstamp AND they were all fired in the same rifle AND they were all the same charge of the same powder, I still had a ES in headspace of nearly 3 thousandths. The a handful of cases came in closer to 1.4600". One or two were as short as 1.4570. This is with the die locked down, the press a hard stop, and no source of variation other than the brass itself.

Interesting that there is that much variation just in the brass springback.

 

I think we will always get some variation but we can try our best to minimize it. Years ago I was fortunate enough to be invited into the loading room of one of the guys that always wins, always. One of the things I noticed is he used lots of good lube, he moved the press handle slow and when he hit the stop he let it sit there for maybe a 5 count before he slowly raised the handle. Then without turning the case or relubing he repeated the first squeeze a second time giving it a 5 second dwell time. I tried it and it helps for me at least.

Oh and these were dies with no expander ball to pull the shoulder up or make the necks double crooked.

 

Brass spring back and the precision of the press. To reduce that for my LR BR rifles I am ordering a Prazipress.

 

If that is after only one firing, shoot them again before you finalize anything.

 

The force of the firing pin will drive the case forward and the shoulder will center the case in the chamber. You might be at a diminishing returns point.

Trying to read 0.0005" on calipers is beyond their ability. Is your brass all virgin, or do you anneal? Some of the variation you could be seeing beyond the measurement error, could be a function of the history of the brass. The +/- 0.0015" you are seeing isn't that much spread.

 

In my 223 match the HS for fired rounds is within .001 prior to sizing, which is better than I can achieve after FL sizing. As a result I only neck size using the Lee collet after annealing, and the HS does not grow to cause tight chambering. Same case for two barrels. This has not been the situation for any other round, for which FL sizing is required. Take a look at neck sizing only on your 223!

 

Great advice, thanks for sharing.

 

It's not unusual for me to see about .001 to .002" difference in head space dimension in fired cases from the same lot fired of course fired in the same rifle. I don't anneal or use premium brass (i.e. Lapua) so perhaps that contributes to the variability. Also the precision and repeatability of the caliber can be an issue.

I full size striving for a .001" shoulder set back using standard RCBS dies. For the most part sized cases show a set back of between .001 and .002" which works quite well for me.

Since I'm primarily a big game / varmint / predator hunter, functionality is just a important to me as accuracy thus I'm not a fan of neck sizing.

 

Valid points all around. I’m not saying my calipers are accurate to tenths. But the variation in tenths was consistent enough that it rounded to 0 or 5 pretty regularly.

I didn’t mean to imply I have special calipers by showing the 4th decimal.

I very well could be past diminishing returns.

 

It is indeed only one firing so I’ll see what changes as firings accumulate.

 

how are you lubing the cases ? it seems to me like the more even the lube is on the case the more consistent the bump is.. could be some of your difference..

 

what makes you think they will not align on the bullet,instead of the case ?

 

"But even though these are all the same headstamp AND they were all fired in the same rifle AND they were all the same charge of the same powder, I still had a ES in headspace of nearly 3 thousandths."

Mine (.204R using Hornady brass) is more like 5. On average my fired brass is about .003 too long. It's like herding cats to get them all (some too long, some too short) back to somewhere close to optimal.

But worth the effort. I shot these 5 groups of 5 today, 100 yds, waiting for lulls in the breeze.

 

Fguffy said, "Sometimes the press wins and sometimes the case wins," so with that in mind, I screwed the die down so there was zero(0) slack in an RCBS press (yes I over cam), and through annealing, I've reduced my ES on case head space(CHS) to 0.001" or less. I like 0.002' of case clearance. Case lube application is important also, to have a consistent amount applied to each case.

The target tells if you have a good reloading process, rounds stay at the water line. The wind is another factor.

 

when Fguffy speaks people listen!......
Wayne

 

The perceived benefit from sizing cases for an interference fit usually fails to produce any actual improvement. Actually, most of the experts with experience in winning agree that some clearance is necessary though they don't agree on how much. This is one of those things that seems counter-intuitive but has been proved on target with wins and records.

I'll add that in my experience, .223 size cases seem to be more tolerant of neck sizing only than larger cases, but if you're body sizing you should push the shoulder back enough to have some clearance.

 

I shoot the same barrel, and it's very accurate. But I don't FL size the brass, just neck size. After 8 or 10 cycles I'll start getting a sticky bolt on eject and will FL size. I also periodically anneal via salt bath method. 5 to 6 seconds soak in 1000 f salt media.

 

Just one firing will not ussually fill the brass out to the chamber uniformly so this can show up in resizing.

 

Thank you for sharing!... very well put together video.
Wayne