Can someone possibly explain this to me?

[71GTO]

I have been reloading for a heavy barreled Savage Axis II in .223. Before starting I acquired a good array of gauges and tools to try and produce safe and accurate ammo. I used 50 pieces of new Lapua brass and reloaded with Benchmark and 53gr SMK's, shot them through the Axis, FL sized making sure that the shoulder was bumped .002" on each. I have done this a total of 3- times. I have read many posts on THR, which say that it can take up to 3- reloads of new brass before the brass will conform to the actual size of the chamber. I was meticulous with making sure that all 150- loads were as close to each other in charge weight and dimensions, as my equipment and gauges would allow. I used a Hornady comparator to measure the length (headspace) of each piece of brass and also the ogive to base of each completed cartridge. The good news for me is that all 50 of these were grouping (5-shots) at an average of .730" at 100 yds. with my all stock rifle.
I'm hoping someone can explain why there is up to a .006" variance in the headspace measurement of the 3-time fired pieces of brass (50 total), which were fired from the same chamber with
(as close as possible) same loads? The ambient temperature only varied by 6-degrees over the 3-days that I shot these. Is the .006" difference a problem or am I concerned about the wrong issue with making accurate reloads? Thanks for taking the time to read this post.

 

[kalielkslayer]

Sounds like initial accuracy is there. .006 difference is your question but I don’t have enough experience to answer it.

But varying your distance off of the lands may even shrink that some more, as well as minor variations in weight charge.

I’ll be waiting for the experts to chime in.

 

[ericuda]

Good shooting and those groups are fantastic. You are only off by not much more than a human hair. Not sure how much more accuracy that you expect. I would vary powder a bit each way a bit and see if that has any effect but me I would be happy shooting that load.

 

[Dale Alan]

How consistent were the unfired brass ? If I am understanding , you have a total of .006" growth from new brass to 3x fired ? If so , some of that growth can be from undersized new Lapua brass .

 

[Walkalong]

I'm hoping someone can explain why there is up to a .006" variance in the headspace measurement of the 3-time fired pieces of brass (50 total), which were fired from the same chamber with
(as close as possible) same loads?

Double check your measuring first.

Mixed brass? Some soft, some hard? Some full loads, some light?

I usually have all the same cases fired with the same load withing .001 of each other. .006 is way too big a spread.

 

[71GTO]

How consistent were the unfired brass ?

As I explained there is a difference in headspace measurement of .006" between the 50-pieces. The longest pieces are 1.452" and the shortest 1.446". The biggest percentage of them are at 1.451 - 1.452". Thanks

 

[243winxb]

Take a sized piece of brass that chambers with a crush fit. The bolt takes just a tiny bit of extra effort to close, lock down.
Measure head to shoulder datum, no primer seated. Record measurement.

Put a used/fired primer in the empty piece of brass. Pull the trigger. Extract and remeasure head to datum. Did it change? Shorter head to datum?

The firing pin strike can set the shoulder back .006" If pressure is not high enough, the bass may not fully expand to the chamber again on firing.

 

[Walkalong]

As I explained there is a difference in headspace measurement of .006" between the 50-pieces. The longest pieces are 1.452" and the shortest 1.446". The biggest percentage of them are at 1.451 - 1.452". Thanks

I thought that was your fired cases?

 

[AJC1]

Sizing consistency can be improved by annealing and dwell time in the die. If I want the best consistency I dwell in the die for 20 seconds. Neck variation can change your lengths if using an expander ball.

 

[Reloadron]

In detail exactly how are you measuring? What gauge or gauges?

Ron

 

[Hugger-4641]

I'd be willing to bet all the brass wasn't much closer than that when new unless you sized and trimmed it first, which I wouldn't do to new brass either. Shoot a few more times until it is needed to trim length and I bet that variance will shrink.

 

[Bazoo]

Well, differences in brass thickness, barrel temperature, and different pressure rounds (working up a load) could all cause that difference in headspace. And as mentioned, differences in annealing.

Weigh the brass between the long and short and average and see if there is a corresponding difference.

Honestly I think you are looking too close in an area that don't matter much. That said, I don't load for precision rifle, just for hunting and plinking and casual target work.

 

[jmorris]

As I explained there is a difference in headspace measurement of .006" between the 50-pieces. The longest pieces are 1.452" and the shortest 1.446". The biggest percentage of them are at 1.451 - 1.452". Thanks

Using your rifles chamber and stripped bolt as a go/no go gauge how are your results compared to the method in this video? .006” could take you through all three conditions unless the cases are all over or under.



You couldn’t get the “bolt drops half way” condition with brass that is being sized .006” different from one another. If all your cases are achieving that condition and your measurements vary by .006” your tools or method of measuring are at falt.

 

[AJC1]

.

Using your rifles chamber and stripped bolt as a go/no go gauge how are your results compared to the method in this video? .006” could take you through all three conditions unless the cases are all over or under.



You couldn’t get the “bolt drops half way” condition with brass that is being sized .006” different from one another. If all your cases are achieving that condition and your measurements vary by .006” your tools or method of measuring are at falt.

I'm betting they are all below chamber length.

 

[Walkalong]

Sizing consistency can be improved by annealing and dwell time in the die. If I want the best consistency I dwell in the die for 20 seconds

Or a second time back up in the die.

 

[dcloco]

Not sure, but believe 50,000 + psi will form that brass to your chamber on the first firing.

Not sure where the three times to fire a piece of brass to actually conform to your chamber arrived at. Was there a technical resource quoted or provided?

 

[Reloadron]

The longest pieces are 1.452" and the shortest 1.446". The biggest percentage of them are at 1.451 - 1.452".

On another note your numbers don't seem to agree with the .223 Remington chamber specifications. Normally a fired case expands to fill the chamber and then it shrinks about 0.001". The SAAMI specifications for a .223 Remington chamber are 1.4636 Min and 1.4736 Max. This is why I asked earlier how you were taking your measurements? The .223 Remington cartridge dimensions are 1.4666 - 0.007" so 1.4596 Min and 1.4666 Max. Most new factory ammunition comes out of the box right around 1.4636".

Most of this really matters not but you should be able to take a lubricated fired round and resize the case using the die manufacturer's instructions and the die should return the case to nominal. Now if you just want to as they say "set the shoulder back" then you should measure a fired case and resize it to about 0.002" less than you started with. The resized case should chamber easily in the rifle it was fired in. Your cases should not be coming out with a 0.006" deviation. Unless you are not measuring all cases in an identical manner with accurate gauging. Especially since you mentioned Lapua brass.

Ron

 

[AJC1]

Not sure, but believe 50,000 + psi will form that brass to your chamber on the first firing.

Not sure where the three times to fire a piece of brass to actually conform to your chamber arrived at. Was there a technical resource quoted or provided?

The most common reference for this is for custom dies to make sure they have grown to chamber demensions. This also assumes full pressure loads, which is exactly that an assumption.

 

[Dale Alan]

Not sure where the three times to fire a piece of brass to actually conform to your chamber arrived at. Was there a technical resource quoted or provided?

Experience is the best teacher . It's real, sometimes takes more firings .

 

[Dale Alan]

New Lapua brass, on a SAAMI scale...started at -2 and grew to +4...initial growth as high as .006" . Maybe ?

 

[ms6852]

Many of the technical features can be achieved that are mechanical in nature such as brass thickness, length , weight, and the same thing with bullets weighing the same and having the same length, but after the first cold bore shot, every thing changes unless you are willing to wait 10 to 20 minutes to assure the barrel reaches the same temperature as your first cold bore shot, the six thousands of an inch difference at this point can be the human element causing those variances. Even though Lapua brass is top tier, if you want to have more consistencies I would anneal each piece even though they have not been fired so that it can conform the the size of your chamber easier.

 

[Walkalong]

Not sure, but believe 50,000 + psi will form that brass to your chamber on the first firing.

Not sure where the three times to fire a piece of brass to actually conform to your chamber arrived at. Was there a technical resource quoted or provided?

No, just experience. It's not a large difference, but it's there. It's why neck sizing only gets to the point where you have to full length size after a few firings.

 

[AJC1]

No, just experience. It's not a large difference, but it's there. It's why neck sizing only gets to the point where you have to full length size after a few firings.

Which is how I believe you should size before getting a custom die but I've never had that confirmed or seen it spoken.

 

[DownEaster]

Are you measuring your headspace on these fired pieces of brass with the spent primers still installed? I have found I get much more consistent measurements if I knock the spent primers out with a universal de-capping die.

 

[dcloco]

No, just experience. It's not a large difference, but it's there. It's why neck sizing only gets to the point where you have to full length size after a few firings.

Brass never quits changing.....when under pressure.