Thread: Deformed Rims

Came across this article, it's exactly what’s been happening to me, wonder how many of us have experienced this issue and do you have simple & effective way of dealing with it. Have used Wilson chamber headspace gauges, easy to use and have proved to effective, this issue is many affecting my 223, Laupa Brass, ADI basically the lot.


I think all of us have seen this at one time or another. You push your case on to the shell holder on your press and the case seems to not want to go it. Once you get it in, it’s a tight fit and will not rotate freely on the case holder.

What I have found is this is caused by firing a hot load which caused by a more than normal expansion of the case head. The pictured case has no ejector swipe/mark. The rim is distorted not during actually firing but when you do full length sizing. I lube my case with Imperial, but even then sometimes it takes more effort when the slight case head expansion requires more effort to pull the die off the case. When this happens, the shell holder pushes down harder on the rim and distorts it so that the rim is now slightly wider in diameter. You can see the shape of the case holder in the first photo on the top of the rim.

If you place the sized case into a Wilson case gauge, it will not fit completely in since the rim is now over sized.

Now this case be easily fixed by running the rim around a sanding stone chucked into a Dremel drill and it fits now in both the case holder and case gauge just like normal.

BTW, the expanded rim does not affect how tight a case sit in a rifle chamber because at the rear of the chamber, the rim is not supported by the chamber because the rear of the chamber is chamfered to allow the extractor to sit and grab the rim when the round is loaded.

hmmm S&B was a shocker for it in .308
one of the milserp .223 headstamps used to do it a lot so I binned all of them and kept the others that dont...never thought to try sanding tiny bit of outside of rim....

Originally Posted by flock

Came across this article, it's exactly what’s been happening to me, wonder how many of us have experienced this issue and do you have simple & effective way of dealing with it. Have used Wilson chamber headspace gauges, easy to use and have proved to effective, this issue is many affecting my 223, Laupa Brass, ADI basically the lot.


I think all of us have seen this at one time or another. You push your case on to the shell holder on your press and the case seems to not want to go it. Once you get it in, it’s a tight fit and will not rotate freely on the case holder.

What I have found is this is caused by firing a hot load which caused by a more than normal expansion of the case head. The pictured case has no ejector swipe/mark. The rim is distorted not during actually firing but when you do full length sizing. I lube my case with Imperial, but even then sometimes it takes more effort when the slight case head expansion requires more effort to pull the die off the case. When this happens, the shell holder pushes down harder on the rim and distorts it so that the rim is now slightly wider in diameter. You can see the shape of the case holder in the first photo on the top of the rim.

If you place the sized case into a Wilson case gauge, it will not fit completely in since the rim is now over sized.

Now this case be easily fixed by running the rim around a sanding stone chucked into a Dremel drill and it fits now in both the case holder and case gauge just like normal.

BTW, the expanded rim does not affect how tight a case sit in a rifle chamber because at the rear of the chamber, the rim is not supported by the chamber because the rear of the chamber is chamfered to allow the extractor to sit and grab the rim when the round is loaded.

Some more detail or a link to the article would help understanding.
Regards Grandpamac.

Have been giving a quick touch up with a fine file, usually just a small but persistent bur that cause the grief, no problem firing them without a touch up but I'm in the habit of checking them with wilson gauge for head space, one in 15 always causes a problem, doesn't fully engage.

https://forum.accurateshooter.com/th...uence.3906096/

Originally Posted by flock

Have been giving a quick touch up with a fine file, usually just a small but persistent bur that cause the grief, no problem firing them without a touch up but I'm in the habit of checking them with wilson gauge for head space, one in 15 always causes a problem, doesn't fully engage.

https://forum.accurateshooter.com/th...uence.3906096/

Thanks for the link @flock,
I don't think that the rim deformation is due to hot loads. Any load hot enough to expand the rim is nuclear hot and would likely expand the primer pocket beyond further use or worse. I have had the problem with .223 brass in my M700. The problem was traced to tight cases from neck sizing being shaved by the extractor. Some of the shavings got behind the extractor and caused problems until they were cleaned out (thanks Jeremy). The rifles chamber is tight and the standard CH full length die produces cases with the right amount of chamber bump so I could have saved myself the trouble. The cases were only ever fired in the M700 so the problem was not from a previous rifle. Cases for my T3 .223 are sized with the + .002 Redding shell holder ant these chamber tight in the M700.
Regards Grandpamac.

Read the 2nd paragrpah of the article. Causation seems to be work hardened brass. Annealing would have prevented this issue at the source. 2C.

I get 1 out of every 5 brand new cases of 7.62x39 Lapua Brass having to force/tight fit into shell holder and I am using the shell holder that came with the Lee dies. Other case brands where fine.