223/5.56 military neck question

[tstowater]

I'm beginning to wonder if I have been living in a small cave too long and apologize if this issue has been discussed and I didn't find it when I did a search. My question has to do with processing 223/5.56 military brass, in particular, the amount of "stretching" that we have been experiencing in the neck when resizing. Generally, I am finding that commercial brass, 223, 204, etc., the neck will stretch about 2 or 3 thousands during a full length resize. Ex. a 223 commercial Winchester case will go from 1.751 to 1.753 approximately.

The military/range 5.56 Winchester brass on the other hand has been stretching over 10 thousands doing the same process. I will caveat that I was doing the 5.56 with a RCBS small base die and the commercial 223 brass was done on a Dillon carbide die. I don't think that the die was the difference, but not sure what is. I have test measured some of the 5.56 brass pre-resizing and it measured +/- 1.755 and after resizing, the same brass was in excess of 1.765 and some close to 1.770. The brass fits perfectly in a Wilson case gauge so I have a hard time believing that the case itself is being stretched. Would the neck on the 5.56 brass be that much thicker so that it would stretch that much when pulling through the expander ball?

What am I missing? I know that some advocate just using a RCBS X die, but we want the cases full length sized as the shells may be going in a bolt rifle or an AR type.

[ole 5 hole group]

OK, you can look at brass flow in this manner:
When the round is fired the pressure makes the brass conform to the chamber. When you FL resize - you take the now reformed brass and push the shoulder back on the case, some call it bumping the shoulder back a couple thousandths.

When you shoot, you're actually fireforming that case to your rifle's chamber, so the brass is "flowing" or "stretching" to your chamber's dimensions and then will contract about half a frog's hair.

Now when you Fl resize that case you force that extra length gained by forming to your chamber is now going to be "pushed" into your shoulder and neck area. That's why you need to occasionally trim the neck and bump the shoulder.

If you shoot neck sized only reloads, the length of the unfired round was determined by your particular die. If that die is very close to the chamber size you will have very little stretching - exact chamber size is called "custom" and is made by your gunsmith who chambered your barrel. If you use the small base die, you will have a lot of stretching.

Another effect will be thickening the brass in the neck and shoulder area....which can bring about its own problems. If you repeatedly FL size, it might be a good idea to turn the neck, which has an added benefit to make the neck perfectly concentric and the bullet will be perfectly aligned with the axis of the bore.

[tstowater]

I'm still confused. I tried some of the brass on the Dillon this morning and reached similar results. Are the chamber tolerances on presumably non match grade chambered AR's that loose to cause that much expansion/flowing? Second, is there a different approach that I should be taking to get around the stretching? I want to be able to shoot the finished loads in any 223 based rifle so I think full length resizing is necessary. I would suspect that most of these will not be reloaded very many times and could actually be dumped on the first shot. I don't mind the trimming but I just didn't think that the brass would grow that much. BTW, how do the Dillon trimmers get around this issue as I understand that the resizer is an integral part with the trimmer?

[Hick]

I just recently did a detailed study on this. I took 50 cases each of 10 different sets of brass-- each from a different source- some 223 Rem and some 5.56. Drew 20 at random from each set. I FL sized, trimmed all to the same length (1.750 +/- 0.002), then fired them all in my 223 Rem using the same load, then cleaned and resized. Military brass (WCC, LC) did indeed grow a little more than commercial brass (statistically). But-- in terms of velocity variations accuracy and reloading I could not find any significant difference. They all worked fine. The stretch I found for the 5.56 brass averaged from 0.008 to 0.011 for the different sets-- so your numbers don't seem unusual. I assume, though I don't know yet, this will result in those cases not being usable for as many reloads-- but the brass is so plentiful I'm not sure it matters.

[runfiverun]

when an ar type rifle fires a round it is extracting and ejecting it while the case is still trying to grip the chamber walls.
when you resize it your squishing everything back into shape.
all that stretched brass has to go somewhere when you squish it back into shape and the only direction it can go is up in the die.
your brass is getting longer and thinner cause there is only so much of it.

[Lead Fred]

What he said. Nailed it

[Mk42gunner]

Hard to say with you using two different dies for the different brass. I would try a few of each type in both dies, just to see if there really is a difference in the brass or if it is the dies.

Robert

[Pipefitter]

I believe that the Dillon carbide rifle dies are made to the small base specifications, just not marketed as such by Dillon.

[tstowater]

Pipefitter, that is my understanding also about the Dillon carbide 223 dies. Just wanted to eliminate the dies as causing the stretching. What Hick and r5r say makes sense and confirms some of my suspicions.

Sent from my XT1254 using Tapatalk

[ole 5 hole group]

Just wanted to eliminate the dies as causing the stretching. Sent from my XT1254 using Tapatalk

You may have misunderstood - the dies reform your brass cases and that's the same as saying your dies cause the stretching of your brass cases, as they reform your brass case back to SAMMI specs. Using a small base die will cause a tad more stretching than a standard full length resizing die that sometimes needs to be cammed over.

It's your dies that take the now over-sized sammi spec brass case, that is oversized, due to your chamber dimensions and this die squeezes the case body back into sammi specs and brass that stretched into your chamber is then pushed back into sammi spec and that excess brass is pushed up toward the mouth, as it can't go back into the base due to the design of the die. The only way to get around this is to roll size your brass but that method probably over works your brass???

Only if you have a BR tight neck chambered rifle barrel (for bolt actions) are you able to just reload that round without neck sizing or full length resizing - but even there, you will still get a little brass flow and will probably have to touch up the neck a tad by a turning tool and either shave a hair off the shoulders or give the shoulder a slight bump every so often.

[DocSavage]

I pick up a lot of once fired LC 13,14 and 15 brass and find using a standard Redding FL die with a carbide expander cases stretch maybe .005".