I trim cases when they exceed maximum specs for the case unless I have a gun with a match chamber and neck.
I did a brass fail test.
.308 and I had 4 cases a winchester a remington a Lapua and a federal.
I loaded them at the range with a scooper and did not trim until I seen slight rifling marks on the case mouth.
That was at .036" past max trim length I believe. Full length sized each time.
Now here is an eye opener.
Measure how far you set the shoulders back.
I found out I was getting case head cracks in my winchester cases after 8 reloadings and I was setting shoulders back .008".
I had no idea I was setting them back that far. After fixing that issue and setting them back only .002" at the max my winchester cases lasted 14 reloads with full length sizing.
Cases grew much less at each firing when you do not set the shoulders back as far.
But a semi auto may not like that.
Accuracy was sub moa from short trim until the case got into the lands.
I do not trim unless I want everything spot on and trying to get all bullets into the same hole.
www.okshooters.com
Look at the 4 shot group in post 3 and it had a winchester case with a case head crack line forming.
Those 4 mixed cases were on their 14th firing not trimmed.
.308 and I had 4 cases a winchester a remington a Lapua and a federal.
I loaded them at the range with a scooper and did not trim until I seen slight rifling marks on the case mouth.
That was at .036" past max trim length I believe. Full length sized each time.
Now here is an eye opener.
Measure how far you set the shoulders back.
I found out I was getting case head cracks in my winchester cases after 8 reloadings and I was setting shoulders back .008".
I had no idea I was setting them back that far. After fixing that issue and setting them back only .002" at the max my winchester cases lasted 14 reloads with full length sizing.
Cases grew much less at each firing when you do not set the shoulders back as far.
But a semi auto may not like that.
Accuracy was sub moa from short trim until the case got into the lands.
I do not trim unless I want everything spot on and trying to get all bullets into the same hole.
.308 Winchester More brass testing
At it again. Going to shoot/reload 4 different head stamped cases until they all fail. So i have Varget measured into a 454 Casull case This gives me 42.1-42.5gr of powder as I tested it on a beam scale. But only using the 454 case no scales. Brass is Winchester , Remington, Federal and Lapua...
www.okshooters.com
Look at the 4 shot group in post 3 and it had a winchester case with a case head crack line forming.
Those 4 mixed cases were on their 14th firing not trimmed.
I measure every time. I do not trim unless they exceed SAAMI max.
In the time it takes to measure them, I can run them through the trimmer. If they get trimmed, fine, if they don't I guess they didn't need it, but it's all the same time.
This right here. I use a WFT for .223 and .308. Each case is in and out in just a few seconds, regardless of how much it is or isn’t trimmed.
New or range pickup straight wall brass, I clean, resize and trim to uniform length. Done.
On bottleneck, before 1st loading and again when marks are seen on neck. If 1 gets trimmed, the entire batch gets trimmed.
On bottleneck, before 1st loading and again when marks are seen on neck. If 1 gets trimmed, the entire batch gets trimmed.
Same here. I have probably 10K .223 cases in reserve from range pickup. Every one gets ran through the trimmer I built just as fast as they can be measured.
Don't even pick them up any more after firing. Probably never shoot up what is in reserve.
Every so often when getting bored, I'll run a couple thousand through the trimmer and put them away with a note inside that they are ready to size, prime, and load.
I have at least two unopened boxes of Lapua 308 brass and A BUNCH of mixed headstamp I acquired at an estate sale, but I’m still using the same couple hundred Lapua I started with in 2006. They’ve never been cleaned or trimmed, and I can’t even start to tell you how many times they’ve been loaded. My loads are relatively mild, and as long as accuracy is good, I’m going to keep doing what I’m doing. 
