918v said:
What BDS shows in his photos are not bulged cases. They are normal expanded cases.
918v, with all due respect, I believe the OP asked about normal expansion of cases that were fired in Gen4 Glock.
Bobson said:
The 40S&W is a Gen4 Glock 23
I have shot quite a bit of Gen2/Gen3 Glocks and never seen a bulged case like the one pictured on the left. IMHO, that case looks to have been fired out of battery and underwent abnormal bulging that is atypical of bulged cases from 40S&W Glock barrels.
If case bulging occurs like that of the above picture on the right, that's due to the slightly enlarged mouth and chamber Glock did to ensure reliable feeding/chambering. You can see the larger chamber mouth in the comparison picture below. The larger mouth opening does reduce further down the chamber, but especially in older generation Glock barrels, the dimensions are more generous to allow greater expansion of the case wall.
Yes, I would agree that some case expansion is normal from firing, but what I have noticed with factory new ammo/factory level pressure reloads shot in some Glock barrels is that case expansion is more than other factory barrels like my M&P40 and takes more effort to resize them. While reloading, when I come across a case that takes more effort to resize (or one that won't resize fully), the spent primer often shows the telltale sign of rectangle indentation from Glock breech wall face. As I posted previously, I will rotate the case 90 degrees and attempt to resize again. Even significantly bulged cases like the picture on the right above, most cases will fully resize in the Lee carbide resizing die on the second attempt. If the case won't fully resize on the second attempt, I will recycle the case for scrap metal, but that's me. Some reloaders elect to use undersize U-die or Lee FCD and I consider that OK if resizing of cases using these dies are done once and the powder/charge used won't significantly bulge the cases on subsequent reloadings (once you thinned the case wall, no amount of resizing will return the thickness of the case wall back
).
I really think the focus of this thread discussion should be more on what happens to the brass case and prevention of case failure. If a case wall bulges significantly and resized repeatedly, work-hardening of the case wall will make the brass more brittle which may contribute to failure of the case. If the reloads are causing bulged cases, you can reduce the powder charge, switch to a different powder or use after-market barrel with tighter chamber that won't bulge the case. I think that's what the OP's question was about.
Bobson said:
Just trying to figure out whether I'm good to go reloading factory cases fired through these guns.
If the factory loads bulge the cases, resizing once and reloading with lower pressure mid-to-high range load data should minimize the future bulging of the cases.