Raised Ring at Base of .223 case?

[Minesweeper3433]

Def appears as though the case markings coincide with the mark in your die in the photo you shared.

 

[WindSurgeon]

Here is my die:

In your photo there's what appears to be something just below (above, when in a press) the radiused mouth that could be the source of that ridge on your brass.

There's a highlight in the pic at that point; is there an edge in your die that's the problem? Even if hard to see you ought to be able to feel it with a straightened paper clip or similar.

Yes, I saw that as well. It was a build up of case lube at that point, but would indicate where the ring is located on the brass.

 

[WindSurgeon]

Posted by Stool

it is possible the oversized brass is just too much for the die..the lip of the mouth of the die is creating the ring...

This would seem to be correct. To know, take measurements on the web area where the ring appears, before sizing . I am guessing its larger than .3789" the maximum SAAMI chamber diameter. If its not to large, try different lube if your using wax. RCBS CASE LUBE-2 may make a difference.

I am headed to the range today with some good brass and will do a post firing measurement later today.

 

[WindSurgeon]

Are you using a standard green box RCBS .223 die or the black box AR series dies that are small base?

I have both, but have been using the green box FL (not small base) lately because I single load these rounds for F-class. I suggested maybe I should always use the small base die, but nobody on this string seemed to react that that would be a solution. What do you think?

 

[243winxb]

.001" off the lands

If this is correct and you didnt mean .010" then the variation in seating may put some bullets into the rifling. Users of QuickLoad claim a rise in pressure as much as 10,000 PSI. Using your maximum (?) loading, over pressure may bulge the web area after 6 firings??

 

[stool]

small base dies are typically used ONCE on brass fired in a chamber other than the current rifle. there are a couple of exceptions..but none for ar's that i know of.

 

[243winxb]

The brass in your photo needs to be trimmed. Its over the 1.760" maximum after FL sizing. But i am sure you know this, just checking.

 

[WindSurgeon]

Already done after I took the photo. Hadn't got to that point in the process. Was in process on this brass when I noticed the "ring".

 

[stool]

triming to a SPEC is silly in precision loading.
find YOUR neck length and trim based on THAT number.
this will typically move your trim to length .005 to .010 longer than spec.
yes it has to be shorter than the chamber neck..but not .015 shorter.....005-.008 is plenty

The brass in your photo needs to be trimmed. Its over the 1.760" maximum after FL sizing. But i am sure you know this, just checking.

 

[WindSurgeon]

A mil spec chamber has a lot of "slop" compared to a match grade . It is made to handle a lot of variance in ammo and function in harsh conditions so our troops can pick up a round and shoot it reliably on the battle field. I trim them just to keep the necks consistent and control what I can control.

I owe you guys a post firing measurement and will do that today. Have not had time this weekend to do it yet. I did a test of 5 shots each from 23.6 to 24 gr Varget under 80 grain Berger VLD's on Friday. 23.9 looks to be the node. Groups got better visually with each 10th of a grain increase. 24 was the max load from Sierra's AR loading manual (its on this site).

For your reading pleasure, here's a good summary of the chambers for the AR15 attached.

 

[jlow]

243winxb is correct. That ridge is caused by the sizing of brass that has been stretched out in the head, most likely due to overpressure.

The .3800 (vs. the .3772 spec number – over by 0.003!) is another clue that supports this.

I went and measure 6 of my Lapua case that recently had pretty stout load for 77 grain bullets (TAC in the 24.2 grain) and with a Mito mic they were:

.37605
.37640
.37670
.37615
.37615

 

[LCazador]

243winxb is correct. That ridge is caused by the sizing of brass that has been stretched out in the head, most likely due to overpressure.

The .3800 (vs. the .3772 spec number – over by 0.003!) is another clue that supports this.

I went and measure 6 of my Lapua case that recently had pretty stout load for 77 grain bullets (TAC in the 24.2 grain) and with a Mito mic they were:

.37605
.37640
.37670
.37615
.37615
[/quote
+1 on this. The head expansion of the case is beyond the die dimension, and it's squeezing the brass down and creating the ring! If you have more than .001" head expansion, your pressure is beyond normal limits, and I would stop shooting that load. Lake City brass will take the excess pressure better than Lapua, but I would reconsider the powder charge and look for a new node lower in pressure.

 

[jlow]

I think your problem is most likely due to your jam which is causing the excessive pressure as the charge weight for that bullet appears to be OK but most here will tell you that jamming can cause excessive pressure and so you cannot go by book values.

 

[stool]

i'm thinking he has a bad chamber..it is ALLOWING the expansion.....

 

[jlow]

Possible but need more info. He did say “Strange that it showed up on these, but not my other brass. I have shot LC in the past without this issue.” So a number of possibility. perhaps he is not over pressure before with the LC i.e. not jamming, lower powder weight. Don’t know – need more info from OP.

Regardless, it is not safe condition that lead to this and his brass is likely toast as the primer pockets are likely very loose now.

FWIW, those numbers I quoted from my Lapua brass was also shot out of a factory chamber and 0.003" difference is HUGE....

 

[BoydAllen]

If the solid part of the head is expanding more than it should, it is a pressure problem. There are several reasons that this could be happening. His load was worked up in cases with larger capacity, and they were at the top pressure with those cases, and over pressure with those with less. If in fact he is seating to what he believes is .001 off the lands, he is probably making contact with the lands, because measuring methods for determining contact are not precise to .001, and seating dies do not generally produce the uniformity of seating, relative to the lands, needed hold that space, even if his measurement was correct. Neck tension could also be a contributing factor, if there is not enough to keep bullets from moving forward as a round is chambered from the magazine. This would work something like an inertial bullet puller. There are several checks that could be done to investigate why this has happened. If you look at my previous post, where I mentioned measuring case diameters at the top edge of the extractor groove, it was suggested to verify an over pressure situation.

 

[jlow]

Boyd, I did check with QL using my own Lapua brass volume and his load and it was not an overpressure at least for mag length and at 60F, however as we know jamming is a whole different matter.

 

[BoydAllen]

If he checks the diameters that I suggested, we will know if the pressure is excessive.

 

[LCazador]

I thought he was single loading, so COL is probably considerably over mag length. Possibly his jam is more than he thinks. I agree his primer pockets must be pretty big by now, but wouldn't one notice that? Three thousands of head expansion could occur over several loadings and one wouldn't notice the expansion right away.

 

[jlow]

Pretty sure he said he was going to "cull the case" in the original OP...