Proper trim length for rifle cases

S

souther33

New member
ever since I have started loading I have always heard that the rule of thumb is to trim all rifle brass .010 shorter then SAAMI max length. but why? is there a certain reasons why MUST loaders do that.
personaly I trim all my brass .010 shorter because not all my brass is the same length and I like uniformity. but if my brass was SAAMI length then would I not see less throat ware.
 
While there may be a more profound answer, possibly all that is being said is just to allow for some additional expansion room before trimming needs to be considered again. Just a rule of thumb type of thing as you mention. When it comes to trim length, probably everyone has their own rule of thumb. I don't trim often but when I do I don't pay much attention to exact case length but rather to squaring up the case mouths and getting the cases the same length as you do.
 
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I have always heard that the rule of thumb is to trim all rifle brass .010 shorter then SAAMI max length. but why?
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Because most reloading manual recommend the 0.010" shorter length as the "trim to" length.

For maximum length, on your rifle, it may allow a longer length, but you need to measure and determine YOUR maximum length. Since most folks don't take this extra step, trimming when they reach or exceed (after sizing), trim then. The key is to avoid the case mouth pinching the bullet due to it contacting the end of the chamber neck. That can spike pressure.

Regarding shorter, the RCBS X die tells you to trim 0.020" shorter than SAAMI max to start with. Unless you have a cartridge with a very short case neck, I never worry about trimming slightly shorter than suggested. Case neck engagement with the bullet affects neck tension as does the amount of interference fit for bullet seating.
 
TRIM

Hi the reason to trim your brass is for better accuracy of your round you have to measure the lands in your rifle with a bullet comparator to measure the ogive . and you go from there for more Info . google Hornday Reloader .
 
No there is probably no such math formula known to man, but since you are bringing up an entirely new subject, rather than just going off on a related tangent, you should open a new thread on the subject matter.
 
the reason to trim your brass is for better accuracy of your round
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No not really . Now most competition shooters do trim every time . I how ever know of a few guys that only trim when needed . Meaning they trim once to minimum then don't trim again until there cases stretch to max length . Usually many loads later when cases are sized and worked very little . Those guys load and shoot little tiny groups . So I'd say trimming is not a must for accuracy .

you have to measure the lands in your rifle with a bullet comparator to measure the ogive . and you go from there
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Sorry I really don't mean to be picking on you but that measurement has nothing to do with trim length but could effect accuracy .

Generally you want to trim the cases to the recommend trim length because if the case neck is to long on a short spec chamber . When the gun is fired the neck can be pushed into the lead/throat of the barrel pinching/crimping the bullet . This can cause a pressure spike resulting in nothing good .

In the pic below you can see that there is an area ahead of the chamber and before the rifling that the neck if to long could be forced into pinching/crimping the case
dUX4Y4.jpg
 
If cases are too short a dreaded carbon ring can form in the area of the chamber immediately between the end of the case and the leade which will adversely affect accuracy. Removing that ring can sometimes be really challenging, and often is not removed by the usual cleaning regimen.

Speaking for myself only, and only in those chambers in which it matters to me, I use those leaden plugs sold by Sinclair to determine my maximum chamber length, and then cut to .005" shorter than that, in effort to minimize the formation of that carbon ring.

For general use, I trim to the lengths specified in the manual. It is just simpler that way. Generally speaking, the weakest point in my shooting is me, not the ammunition.
 
but if my brass was SAAMI length then would I not see less throat ware.
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Less? Not a chance. Very few know where the end of the chamber is located.
I want to cover all of the chamber possible, I form cases for wildcat chambers, the forming and fire forming process shorten the case as much as .045". To solve that problem I use longer cases, one chamber has a neck length of .217", some claim the 300 Win Mag has a short neck at .268+/-, if .268" is short .217" is very short.

F. Guffey
 
ever since I have started loading I have always heard that the rule of thumb is to trim all rifle brass .010 shorter then SAAMI max length. but why? is there a certain reasons why MUST loaders do that.
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It isn't a "must" requirement. Simply put, the "trim to" length of .010" less than SAAMI max is a safe, convenient, generally accepted length to trim to and not have to trim after every firing/resizing cycle. If you want to trim your brass more often, you certainly may.
 
as far as i know use the trim lenth in the manual ex. .308 win 2.005

you want uniformity for precision accuracy but for loads needing less precision a .005 bumper in either direction is within a safe zone.

i have never heard of trimming .010 below manual case lenth
 
i have never heard of trimming .010 below manual case lenth
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there is the 'trim to length' and the 'X' RCBS die with recommendation, they suggest starting by trimming the case neck .020". The illusion is the 'X' die stops case length from getting longer.

F. Guffey
 
Reloading

Hi there is a site called Hornady Reloader A guy that has been reloading for over 35 years . I suggest that you check him out about Trim Length . it might surprise you of his remarks on Ammo reloading I have done a lot of reading on this . and I,am new at this game . now every time i listen to some one i get a very different story . and the guy that calls his self Hornady Reloader .make a lot of sense . if you take a Modified case to get a reading from your lands .to provide consistent used by many shooters to check uniformity of bullets from base to ogive which is critical to accuracy .this method allows direct comparison of your loads as you set up your bullet seating die for the correct bullet free travel jump . please give me your take on this as i said I,am new at this and as soon as i think i have every thing down some thing comes up and there goes all my research . thank you TRAPPER1
 
Trapper :

I use the Hornady OAL gage that uses the modified cases . It's a helpful tool but not always needed . I use it because it's quick and easy and even though a don't . I spend money on reload stuff like it grows on a tree in my back yard .You can just crimp the neck of a fire formed case and set a bullet in the case sticking out as far as it can with out falling out . You then genitally chamber the round and as the bullet hits the lands it will be pushed back into the case . You then carefully remove the cartridge and measure . Now that way takes some practice because to much primp and you just jam the bullet in the rifling . To little crimp and the bullet can move on extraction and not give you the correct measurement .

FWIW and this may just be me but your posts seem to lump two different things together as if they are the same thing . Trimming the case or case length is not the same as cartridge over all length (COAL) or over all length (OAL) . The case length or trim to length refers to the case only with NO bullet seated . It is a measurement from the head/ bottom of the case to the mouth/top of the case . COAL or OAL is the measurement from the head/bottom of the case to the tip of the seated bullet in the case .

Hope that helps
 
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I trim every time, 308 caliber. Max case length is 2.015 I trim my cases to 2.012 need room so the case can expand to release the bullet. Same length same neck grip on all your rounds. I try to make every round exact. Throat wear will always happen, mostly from heat & use. Don't let your barrel overheat, clean it after shooting, fouling causes pressure problems. This last sentence will start a s_ _t storm. I always start a shooting session with a clean rifle & never had a problem.
 
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I trim every time as well but to 2.005 . I never really thought of trimming longer . If I did I'd likely trim to 2.010 .
 
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