hammered54
New member
I've acquired a large bag of 308 brass (once fired) and it seems that 95% of it is still near factory lengths (2.015) most over....so...why trim to 2.005 when i could trim it all back to 2.015?
trimming brass
- Thread starter hammered54
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hammered54
New member
I've already sized it...why trim all that brass off when I can just trim it back to Saami spec.
Matt.
edited for Scorch
Matt.
edited for Scorch
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hammered54
New member
no one is arguing here....did you read my post?
and you are correct...I can do anything I want....
and you are correct...I can do anything I want....
This is simply a question of "pay me now, or pay me later".
If you just trim it back to max spec NOW, most of it will be over that the next time you size it, and you will have to trim it again, THEN.
If you trim it back to less than max spec length (the usual standard is 0.01 shorter though there are some rounds where 0.005 is the recommened trim) then you can get two or three or perhaps even more firing/sizing cycles from your brass before it grows back to max spec length and needs more trimming.
SO trim just enough and have to trim every time, or trim a bit more and then only need to trim half or even a third as often during the life of the case.
Your call.
I think you are asking why do people choose -0.010” from nominal. I believe most do it because most reloading manuals say that.
I measure my chamber length with a tool from Brownell’s. It allows me to know max length in my gun. Then I trim 0.010”-0.015”. I know my trim accuracy to be about +/- 0.001”.
I could trim 0.005” back from max easily, but to what benefit?
If it expands to a point of contact, that is just another drag point on bolt open. If too long initially, bolt close will be hard, but the bigger issue is it is likely to cause a pressure spike.
Why run as long as possible? Who knows? I know I want to maximize neck to bearing surface contact. I also want to minimize carbon deposits on the neck of the chamber to prevent accuracy and pressure issues.
I measure my chamber length with a tool from Brownell’s. It allows me to know max length in my gun. Then I trim 0.010”-0.015”. I know my trim accuracy to be about +/- 0.001”.
I could trim 0.005” back from max easily, but to what benefit?
If it expands to a point of contact, that is just another drag point on bolt open. If too long initially, bolt close will be hard, but the bigger issue is it is likely to cause a pressure spike.
Why run as long as possible? Who knows? I know I want to maximize neck to bearing surface contact. I also want to minimize carbon deposits on the neck of the chamber to prevent accuracy and pressure issues.
hammered54
New member
thank you Nathan.
Matt.
Matt.
Nathan:
Now that is worth a thought, good of you to go to the length (pun intended) to answer.
Flip is a number of recommends by Unclenick to trim shorter than spec (which I do).
The logic is as long as the lenght is consistent, then the hold will be as consistent as your setup allows.
I have targeted mine to be below max and align with my anneal so its a combined process of case maint.
I do use an excellent (best in my take as well as a number of others) carbon removed cleaning (Carbon Killer 2000) - only barrel cleaner is a new one from the factory.
Now that is worth a thought, good of you to go to the length (pun intended) to answer.
Flip is a number of recommends by Unclenick to trim shorter than spec (which I do).
The logic is as long as the lenght is consistent, then the hold will be as consistent as your setup allows.
I have targeted mine to be below max and align with my anneal so its a combined process of case maint.
I do use an excellent (best in my take as well as a number of others) carbon removed cleaning (Carbon Killer 2000) - only barrel cleaner is a new one from the factory.
I probably went too long, but that is how. Think about it.
Now should we ask the age old question……
Is it better to control datum circle to neck opening length or case base to neck opening length? There are 2 types of trimmers one must choose from….hmm?
The manuals all show base to neck opening, but they also show die instructions that leave CBTD under max length…hmmm.
Then of course shout I trim fired cases or sized cases?
Now should we ask the age old question……
Is it better to control datum circle to neck opening length or case base to neck opening length? There are 2 types of trimmers one must choose from….hmm?
The manuals all show base to neck opening, but they also show die instructions that leave CBTD under max length…hmmm.
Then of course shout I trim fired cases or sized cases?
If you trim to recommended you could trim prior to sizing. However there is no guarantee, based on the method used to resized and thickness of the brass in the neck and shoulder, than when sized it will grow evenly around the mouth of the case and it could end up inconsistent.
As far as trimming for consistency, I would think trimming from the shoulder, or rather the point of headspace, would be more consistent. However most bullets are seated based against the base of the cartridge, so it could theoretically give inconsistent seating within the neck.
I'm sure this is all hashed out, or the precision shooters haver their stances on the issue. I don't know how to answer it. Perhaps some of our wise sages will enlighten us. I for one would very much like to learn the answer(s). I have the feeling we are headed down a very deep rabbit hole.
As far as trimming for consistency, I would think trimming from the shoulder, or rather the point of headspace, would be more consistent. However most bullets are seated based against the base of the cartridge, so it could theoretically give inconsistent seating within the neck.
I'm sure this is all hashed out, or the precision shooters haver their stances on the issue. I don't know how to answer it. Perhaps some of our wise sages will enlighten us. I for one would very much like to learn the answer(s). I have the feeling we are headed down a very deep rabbit hole.
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Friend of mine reloaded the same Federal 308 Winchester case 57 times with max loads for Sierra 168 HPMK's, full length sized each time setting shoulder back about .001 inch. Trimmed the case back about .010 inch every dozen reloads. All shots went into a three eighths inch group at 100 yards.
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This is not a rabbit hole. It does not get any simpler in reloading.
1. You trim after sizing.
2. While it probably does not matter a great deal, the goal is consistent trimming a round to fit the chamber (neck area in this case)
3. You trim to keep the case lenght from getting too long for the chamber (neck)
4. If you want to get exotic you can measure the neck and trim to that spec.
Or you can just trim to max spec or the trim length.
1. You trim after sizing.
2. While it probably does not matter a great deal, the goal is consistent trimming a round to fit the chamber (neck area in this case)
3. You trim to keep the case lenght from getting too long for the chamber (neck)
4. If you want to get exotic you can measure the neck and trim to that spec.
Or you can just trim to max spec or the trim length.
Yes you trim after sizing because sizing can lengthen the brass too.
The only ones I don't do after sizing is my 350 Legend because the Lee length trimming stem won't go in the brass after sizing. (I think there may be a dia. problem with it.)
Think about it, aside from things like expander ball dragging in the necks of bottle neck cases, what sizing does is squeeze a brass tube (closed at one end) SMALLER in diameter. This results in the "tube" getting LONGER.
You trim after you're done making it longer. Its that simple.
You trim after you're done making it longer. Its that simple.
The primary reason for trimming is to avoid letting a long neck extend too far into the chamber and cause the case to be too long to let the bolt close. The 0.010 limit above SAAMI is the solution to avoid that.
I have tried 2.017 with one of my .308s because I got lazy and and didn't trim that case. The bolt wouldn't close.
There is another effect of not keeping consistent cartridge OAL if you are a precision reloader.
An added 0.002 inches in trim length increases the velocity of the round by about 1 fps.
Shooting a cartridge with the exact same seating depth with a variation of 0.010 would mean that you would have a difference in 5 fps in muzzle velocity.
Considering that you get a variation of about 7 fps, at least, from differences in powder/primer detonations with all else equal, another 71% variation could mess up accuracy a bit, if you were a precision shooter.
If you are averaging over 0.5 inch groups, you probably wouldn't notice the difference.
I have tried 2.017 with one of my .308s because I got lazy and and didn't trim that case. The bolt wouldn't close.
There is another effect of not keeping consistent cartridge OAL if you are a precision reloader.
An added 0.002 inches in trim length increases the velocity of the round by about 1 fps.
Shooting a cartridge with the exact same seating depth with a variation of 0.010 would mean that you would have a difference in 5 fps in muzzle velocity.
Considering that you get a variation of about 7 fps, at least, from differences in powder/primer detonations with all else equal, another 71% variation could mess up accuracy a bit, if you were a precision shooter.
If you are averaging over 0.5 inch groups, you probably wouldn't notice the difference.
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