Straight 284 Brass Thinning?

[JPB4BAMA]

I'll admit that I'm probably a bit gun shy on this topic after some bad experiences in my 223 AI. I have recently acquired a straight 284 Win along with a decent supply of 3&4X Lapua brass. During my brass prep after my first outing I notices a few with bright rings above the web. Scoping and then cutting one confirms that there is some brass thinning. The brass is bumped 0.0015 from the as fired which measures +0.001 from a whidden headspace tool. I am quite confident this is also the history of the brass as well other than the initial firing and I can only assume that it was at or just a bit below the SAMMI minimum??
So the question at hand is this: How much of this is the result of the first firing, does it stabilize and when is it time to actually get concerned.

Unfortunately I have no tools to actually measure the thinning so those numbers I can't provide.

 

[Deleted member fkimble@charter.net]

Looks like where the brass thins down during manufacturing. I would consider it normal.

Frank

 

[Zero333]

4 x fired with a hot load would do that.

Remember, once you see pressure signs you're actually above 70,000 psi of chamber pressure. You can easily be shooting a 70,000 psi load and not know it till the 4th firing.

I had this happen with 308win Lapua brass shooting 155 Scenar's at nearly 3,000 fps from a 24" bbl. By the 5th firing the primer pockets were very loose and most of the brass was harder to extract.
For the first 3 to 4 firings the thing was a laser. Then on the 5th firing it was not grouping as well and had the other issues.

 

[JPB4BAMA]

4 x fired with a hot load would do that.

Remember, once you see pressure signs you're actually above 70,000 psi of chamber pressure. You can easily be shooting a 70,000 psi load and not know it till the 4th firing.

I had this happen with 308win Lapua brass shooting 155 Scenar's at nearly 3,000 fps from a 24" bbl. By the 5th firing the primer pockets were very loose and most of the brass was harder to extract.
For the first 3 to 4 firings the thing was a laser. Then on the 5th firing it was not grouping as well and had the other issues.

 

[JPB4BAMA]

Sorry, should have noted that in the original post. Not even close. 50.3gr H4350 giving me 57kpsi at 2780fps. I wish it was that simple, but as i stated I'm a bit gun shy as I has some Brand New Starline 223 actually come apart on the mid pressure initial loads, so I'm hoping fkimble is correct and I'm just over reacting, but also putting this out just in case anyone else has seen it and I need to be concerned.

 

[SKWERLZ]

Normally occurs if overly sizing case or on initial firing of virgin brass in a bit longer chamber with no steps to hold base on boltface solidly to ensure proper fireforming.

It’s not a pressure thing.

 

[Deleted member fkimble@charter.net]

Starline had a bad batch of 223 brass that may have been your 223 brass problem. Do a search on here for more info.

Frank

 

[Rook 6]

ALL brass thins to some extent with use. Excessive headspace, which you don't seem to have, can speed up the thinning process. If that were my brass, I would consider what you are showing as normal and acceptable. I took a small piece of stiff-thin wire, formed a small triangle on one end for a bit of a handle, bent the other end 90 degrees and perpendicular to the handle and sharpened the bent end to a point. I check a small sampling of cases from a lot I fired by gently dragging the pointed end along the inside wall of the case to determine if the ring is getting deep and cause concerns for case separation. Since my dies are custom made to my chamber reamer, I generally toss the brass before web thinning is an issue. Checking by scraping isn't really quantifiable, but it is a data point that can warn you about potential case separation.

 

[Zero333]

I found some Starline brass that had less H2O capacity than most in 223/5.56, 308win and 9mm Parabellum / 9x19mm

 

[Ernest T]

I'll admit that I'm probably a bit gun shy on this topic after some bad experiences in my 223 AI. I have recently acquired a straight 284 Win along with a decent supply of 3&4X Lapua brass. During my brass prep after my first outing I notices a few with bright rings above the web. Scoping and then cutting one confirms that there is some brass thinning. The brass is bumped 0.0015 from the as fired which measures +0.001 from a whidden headspace tool. I am quite confident this is also the history of the brass as well other than the initial firing and I can only assume that it was at or just a bit below the SAMMI minimum??
So the question at hand is this: How much of this is the result of the first firing, does it stabilize and when is it time to actually get concerned.

Unfortunately I have no tools to actually measure the thinning so those numbers I can't provide.

You really need to get the correct tools to measure case thickness. They are not overly expensive. I get 20 reloadings out of Lapua brass without excessive thinning of the case wall.

 

[Doom]

The internal view is dirty but as best I can see there is no thinning other the normal thinning that occurs in the base region.

 

[Henryrifle]

The internal view is dirty but as best I can see there is no thinning other the normal thinning that occurs in the base region.

Agree. No issue with that brass.

Hank

 

[Rset]

You really need to get the correct tools to measure case thickness. They are not overly expensive. I get 20 reloadings out of Lapua brass without excessive thinning of the case wall.

How does measuring a case neck have any bearing on the issue being discussed?

 

[Ernest T]

How does measuring a case neck have any bearing on the issue being discussed?

Aren't we talking about thinning brass?

 

[JPB4BAMA]

I should have posted this photo earlier, but the quality is a bit less than I would have liked doe to my incompetence with the teslong borescope. It clearly shows thinning and insipient tensile failure in the thinned area. Now this is the very worst case of the lot and will not be used (probably not unless I want to test if and see if it fails just for data purpose). Again it is rather high up the case wall as compared to my experience with 223, but does appear to be right at the transition between the thicker web and the nominal case wall.
Also being lucky to have obtained 200 of the only remaining straight 284 Lapua cases on the planet, I will dissect one of these and see what that location shows prior to firing, and will also look at one after it's initial firing. So if anyone has recommendations on how I should load that one case I'm open to suggestions. I typically run at about 90% of my target load for fire forming and case head hardening. So if anyone has good ideas please chime in.
Just for reference I'm also attaching the cut case that I referred to with Starline 223 with the very first firing also at about 90% load pressure. This is why I became very attentive to my case inspection every time.

 

[Sandstorm]

Get some new Lapua brass my friend.

 

[JPB4BAMA]

Get some new Lapua brass my friend.

I did. Basically the last 200 cases on the contiinent