brass trimming
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QuietTexan
Well-Known Member
Are you asking why wouldn't cases get longer? Because if you size them correctly and measure your chamber to know how long it is, cases don't always grow to the point they need to be trimmed. If you don't want to try it yourself you can go to YouTube and watch several videos of the same case being fired 10+ times with zero trimming needed. This is especially common in modern case designs with sharper shoulders than the old machine gun cases.
Why DO cases grow is a better question. Excessive resizing and using an arbitrary minimum spec for case length are two reasons why people trim more often than they otherwise would need to if they worked on those two things.
Also, does the length of the case neck actually matter so long as it's not hitting the end of the chamber? What's more important: the length of the neck, the length of the neck that's sized, or the size to which the length of the neck that is sized is sized to?
I get that it's comforting to a lot of guys to do the same things every time, but really if you stop doing it you might be surprised at how rarely you actually get to the point it's required.
Why DO cases grow is a better question. Excessive resizing and using an arbitrary minimum spec for case length are two reasons why people trim more often than they otherwise would need to if they worked on those two things.
Also, does the length of the case neck actually matter so long as it's not hitting the end of the chamber? What's more important: the length of the neck, the length of the neck that's sized, or the size to which the length of the neck that is sized is sized to?
I get that it's comforting to a lot of guys to do the same things every time, but really if you stop doing it you might be surprised at how rarely you actually get to the point it's required.
srogerson
Well-Known Member
Shooting 5.56 out of an AR needs to be sized and trimmed every time, in my opinion. Especially if it'll be used in multiple guns. YMMV.
You trim every time to get the cases to be the same as possible. If that's not important to you, then that's cool. It is to me.
QuietTexan
Well-Known Member
You're missing the core point of why do the cases grow and become different in the first place - that's the real question. If you're starting with high quality, uniform brass why are you having to de-uniform them by trimming some and not others? If only some need to be trimmed and not others, either the variance is being introduced by the resizing steps, or the brass if of poor quality to begin with so why waste time with it. It's very important for cases to be uniform, if they start that way and end up in difference places, the odds are very good there's a flaw in a step where inconsistency is being added. Excessive sizing, cutting to an arbitrary length, and trimming new brass are all ways inconsistencies are added to brass.
Don't look at it backwards and say "get the cases to be the same as possible"; good cases START that way, and inconsistencies get added along the way. You said why wouldn't cases grow, my question is why DO they grow when they're expanding to the same dimensions every firing.
ARs don't really have a place in this discussion, that action has no camming power and when loaded for functionality will best chamber minimum spec cases. That's prioritizing function over precision and case life, and not relevant to discussing how brass shouldn't grow over multiple firings when you remove excess resizing from the process.
Don't look at it backwards and say "get the cases to be the same as possible"; good cases START that way, and inconsistencies get added along the way. You said why wouldn't cases grow, my question is why DO they grow when they're expanding to the same dimensions every firing.
ARs don't really have a place in this discussion, that action has no camming power and when loaded for functionality will best chamber minimum spec cases. That's prioritizing function over precision and case life, and not relevant to discussing how brass shouldn't grow over multiple firings when you remove excess resizing from the process.
Bruce Treloar
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I believe cases stretch when the chamber is not cleaned properly after the use of solvents and put away oil. I use a thin wooden dowel with a split one end to hold a patch, then rotate this in the chamber. During firing the case expands grabbing onto the sides of the chamber preventing excessive back thrust on the bolt face. If the chamber has left over oil in there the back thrust is much greater, resulting in case length variation.
srogerson
Well-Known Member
I trim AR brass, so I thought it might have a place in the discussion of buying a trimmer. My bad.
QuietTexan
Well-Known Member
No worries, I trim AR brass also, but that's not the point being made. It's a different end goal than being described for precision brass. I trim the heck out out of 300 BO and have a bucket of the stuff I run until necks crack, but precision and accuracy aren't the name of the game there.
Donneric
Well-Known Member
I use a Wilson with the micrometer mostly to trim formed 300 BO brass to length instead of filing to length off the top of the form die which destroys files pretty fast. I have a long reloading bench so that station stays set up all the time. I do 10-15 cases and walk away to different projects. I don't see a power trimmer in the stars for me. Annealer yes but not a trimmer.
