Case mouth looks rolled after firing.

[Mtstalker]

I just finished firing 200 peices of lapua brass in my 22-250. Went to resize and for fun i tried to slide a bullet into the fired case. It takes a bit to get it going but then after the bullet passed the case mouth they slide freely. If i look it appears the mouth looks almost crimped. I checked length and they were all 1.902" just were i trimmed them before loading. Every one was like this. I ran a sinclair case length guage in a case , measures 1.950" so i know the cases are not to long. Loaded neck dia is .252" and fired neck dia is .255" .002" of neck tension. I dont belive its a carbon ring since i ran a brush with JB's in the neck prior to firing them. Everything chambers great and accuracy is really good too i would like to find out what is causing this.

 

[ireload2]

That is fairly common and turns up when you start paying more attention to your brass. I think it is just spring back of the brass.
Go through 10,000 cases from indoor ranges and you will find a lot of brass like that. Try annealing the case mouth.

 

[T-shooter]

I just finished firing 200 peices of lapua brass in my 22-250. Went to resize and for fun i tried to slide a bullet into the fired case. It takes a bit to get it going but then after the bullet passed the case mouth they slide freely. If i look it appears the mouth looks almost crimped. I checked length and they were all 1.902" just were i trimmed them before loading. Every one was like this. I ran a sinclair case length guage in a case , measures 1.950" so i know the cases are not to long. Loaded neck dia is .252" and fired neck dia is .255" .002" of neck tension. I dont belive its a carbon ring since i ran a brush with JB's in the neck prior to firing them. Everything chambers great and accuracy is really good too i would like to find out what is causing this.

Most if not all the new Lapua .308 brass was like that out of the box before firing. After firing they were ok. Nothing I could really see but the neck mouths were smaller than the rest of the neck. I usually resize new brass and deburr and that fixed them.

 

[Mtstalker]

These were all deburred and sized prior to firing. Problem didnt occur untill after first firing. It doesnt appear to be hurting anything. If i make one turn with the deburring tool they slide right in.

 

[Homerange]

Sounds like carbon ring to me.
Open case necks only and rechamber to check.
Double check measurements.
Soak some rag/patches in solvent and park them in the chamber for an hour. Then use your brush again.

 

[Mtstalker]

Checked for carbon ring with cheap bore camera. There was a bit of carbon there but 5 twists with a solvent soaked brush cleaned it out. I checked my lapua brass from a diffrent load and there fine. It appears to only be the cases loaded with reloader 15? There necks are also covered in soot. Maybe just a coincidence. My other 50 from a h380 load were all fine. Shot all at the same time. I think there was a carbon ring forming but if it was established i dont belive they come out that easy from what ive heard. Is that correct.

 

[dellet]

Maybe a stretch here, but the same type of thing happens in some of the black powder cartridges running smokeless powders.

As I understand the issue, with a slower burning powder you can end up with low pressure in the case, high pressure outside the case. If the neck has not expanded enough to seal the chamber, the higher pressure will blow back and collapse the case. Softer or thinner brass can be more susceptible.

If you have soot/carbon on the neck, it might be possible.

You also see this from time to time shooting subsonic loads, where again it's a low pressure load.