Trying to decide on trim length......308.....

[TheGidds]

So my fired brass is measuring overall length of 2.009" to 2.017". Sampled 27 cases after FLS. Trying to prep these for load development, so would it be best to trim all to the same length (2.009") or just Chamf&Debur and go with lengths as they are. I don't have my measured chamber length with me at the moment but if I remember correctly it was over 2.022".....

From what I understand the recommended trim to length is 2.005".

Thanks in advance !

 

[madmixerman]

I would trim all to the length of the shortest brass.

 

[Dusty Stevens]

If your trim length is 2.005 and you have a case that measures 2.017 youre way way past the trim stage and into the danger stage.

 

[TheGidds]

If your trim length is 2.005 and you have a case that measures 2.017 youre way way past the trim stage and into the danger stage.

I think 2.005" is the published recommended trim length. I haven't trimmed yet but I understand where you were going..... .012" growth would be dangerous....thanks for the input.

 

[DngBat7]

If your trim length is 2.005 and you have a case that measures 2.017 youre way way past the trim stage and into the danger stage.

Dusty, What makes it dangerous? I having been needing to know this. I always figured if your brass is to long, your bolt simply won’t close??? Where is the danger?

 

[msinc]

Dusty, What makes it dangerous? I having been needing to know this. I always figured if your brass is to long, your bolt simply won’t close??? Where is the danger?

I think the danger is the idea that if a case has "grown" that long then it had to come from somewhere. That somewhere might be getting thin. The term "grown" is bad and misleading...cases get longer because the brass moves...they really do not grow as in make new material. Typically the area just forward of the case head, the front of the "web" is where it thins out and if it gets thin enough, too thin that is, then you can suffer a case head separation and that is bad.
The other "danger" is that if the case mouth is so long that it interferes with the chamber then you can have a pressure spike and that is another thing that is never good. Might not damage anything the first time, but you don't want that to happen very many times.
It is important to have a "trim to length" and use the same cases in the same rifle if you are not going to trim them to the suggested length. If several cases that are minimum length or less are fired and leave a carbon deposit it could interfere with cases that are fired later which are longer. Carbon build up or beginning of the throat, either one can cause a bad pressure spike if a case can interfere with it.

Edit: This forward flow of brass has always been a concern of reloaders. P.O. Ackley designed his "improved" line of cartridges with a 40 degree shoulder to help stop that forward flow of brass. Obviously, there is way more to Ackley Improved cartridges, but that is one aspect.
As far as the bolt not close...I mean, if it has .010" interference then probably no...but if it has .003-.005" the bolt will cam over and curl the case mouth right tight into the bullet and then it will have a pretty substantial grip.

 

[alinwa]

I think the danger is the idea that if a case has "grown" that long then it had to come from somewhere. That somewhere might be getting thin. The term "grown" is bad and misleading...cases get longer because the brass moves...they really do not grow as in make new material. Typically the area just forward of the case head, the front of the "web" is where it thins out and if it gets thin enough, too thin that is, then you can suffer a case head separation and that is bad.
The other "danger" is that if the case mouth is so long that it interferes with the chamber then you can have a pressure spike and that is another thing that is never good. Might not damage anything the first time, but you don't want that to happen very many times.
It is important to have a "trim to length" and use the same cases in the same rifle if you are not going to trim them to the suggested length. If several cases that are minimum length or less are fired and leave a carbon deposit it could interfere with cases that are fired later which are longer. Carbon build up or beginning of the throat, either one can cause a bad pressure spike if a case can interfere with it.

Whuhhh-BAMMMM!!!!!

 

[JFrank]

If your trim length is 2.005 and you have a case that measures 2.017 youre way way past the trim stage and into the danger stage.

If memory serves my 308 max case trim length is 2.015

 

[msinc]

I think what Dusty is trying to say here is that if you started out at 2.015" and saw it stretch to 2.017" that would be one thing...but if you trimmed once to 2.005" and see 2.017" stretch that is a lot....something is going on here that is not right, do it again and you are probably going to suffer a case head separation.
Most cartridges have a tolerance range on the trim spec of plus .010" minus 0". The chamber {if it is a SAAMI} allows for more. You can of course go shorter, it doesn't really do any good or harm. Some people trim minus .010" just so they can skip a trim. Cases have to get pretty long before you have interference. It's that stretch/forward flow that causes all the problems.
Spend time reloading for an M1 Garand or M14 and you will learn all about it...the Garand is a violent action that typically stretches cases .008" on extraction. It doesn't run too well with tight headspace so the general rule was to load your cases 2 or 3 times and toss them. All that stretching and growing will leave a thin web for sure.
Bolt guns are different, I only bump my shoulders back .001" under minimum headspace length and I set all my chambers at go minimum. I can feel the bolt cam over on the go gauge. This way I have as little as possible forward flow and stretch.

 

[Howland]

As far as the bolt not close...I mean, if it has .010" interference then probably no...but if it has .003-.005" the bolt will cam over and curl the case mouth right tight into the bullet and then it will have a pretty substantial grip.

Or think of it this way. You can be working with a known good and safe load, but if even a few cases have a neck length too long, those cases will in effect get a super crimp. Even if your load with in spec case length is well within pressure tolerances, add that super crimp and you can easily far exceed safe pressure.

 

[Lefty Trigger]

I watch all my lengths and when they approach 2.010 I trim all back to the 2.005. When they get too long my trimmer is peeling off chunks and has a tendency to "grab" the brass.

 

[Martin52]

.......would it be best to trim all to the same length (2.009") or just Chamf&Debur and go with lengths as they are. I don't have my measured chamber length with me at the moment but if I remember correctly it was over 2.022".....

From what I understand the recommended trim to length is 2.005".

Thanks in advance !

Sinclair make a simple plug to measure for a particular chamber, it takes the guess work out of how much to trim.

 

[msinc]

Sinclair make a simple plug to measure for a particular chamber, it takes the guess work out of how much to trim.

Works like a charm...I cheated though, when I did it I drilled a hole in the back of a sized empty case and looked with my borescope. I tried trimming to exact chamber fit vs. trimming to minimum but I saw no difference or advantage/disadvantage. Either way, you want to keep the bore free and clean of carbon buildup. Still, it's always nice to know how far you have to go with a given chamber.

 

[DngBat7]

Sinclair make a simple plug to measure for a particular chamber, it takes the guess work out of how much to trim.

Best 5 dollars I spent.

 

[NorCalMikie]

If you think your chamber measures 2.022", then you have a ways to go at 2.017" before you have fit issues. As suggested,trim them all to the shortest length then, think about using different dies to control the length.
Shoulder bump dies will keep the length from growing.
How many times fired and resized? Pushing the shoulder back too many times will contribute to case head separation. (they're getting ready)
That length that keeps coming back when resized had to come from somewhere and that's mostly right above the case head. Get yourself a broken case extractor tool and be ready.

 

[JFrank]

A reamer print would tell you exactly what length is max