Exactly how important is case trimming?

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Minuteman
    • Oct 11, 2013
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    #1
    Got a rifle shooting in the ones now and as I get further into the round count of the brass I start to wonder when it's going to be trim time.
    It's a 6.5 creed in Alpha brass that's not pushed hard. SAAMI chamber. I flame anneal every couple of firings.
    Question: Will never trimming begin to affect my groups in the future? Anyone here that shoots small groups not trimming?
     
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    #3
    Basic user said:
    Anyone here that shoots small groups not trimming?
    Click to expand...
    I do, most of my brass never gets trimmed . I may trim some to uniform it but I have found most never get long enough to become dangerous . I measure all chambers, there is no guess work on my part . I load for about 15 rifles right now and have not trimmed any in a long time .
     
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    #4
    Eventually, your brass will grow until it impinges on the front of the chamber. After a time, the case mouth will get squeezed, by chambering pressure, around the seated bullet and your groups will go weird. It might take some time depending on how you are sizing and your chamber dimensions but absolutely not trimming is not an option if you are shooting your brass many times. The good news is that 6.5 cm won’t grow that fast. If you have a borescope you can put a piece in the chamber and look at the case mouth in relation to the end of the chamber.

    Here’s a pic of the offending area from a cutout chamber. Once that gap closes up, you need to trim.
    IMG_0584.jpeg
    IMG_0583.jpeg
     
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    #6
    Basic user said:
    Got a rifle shooting in the ones now and as I get further into the round count of the brass I start to wonder when it's going to be trim time.
    It's a 6.5 creed in Alpha brass that's not pushed hard. SAAMI chamber. I flame anneal every couple of firings.
    Question: Will never trimming begin to affect my groups in the future? Anyone here that shoots small groups not trimming?
    Click to expand...
    Typically, yes . . . never trimming can affect your groups in the future.

    Some of that can depend on how well you clean out the carbon ring that builds up in your chamber. As the carbon ring can, as the case length grows, make the case mouth act like act like a crimp on the bullet and that "crimp" can become severe.

    Another way it can have an effect is that as the case mouth grows, the timing of the blowby changes (where the end of the bearing surface passes the case mouth as the bullet moves forward before the bullet fully engraves). This isn't likely an issue for the likes of a factory gun or a gun set up for hunting, but could be an issue for highly precision results.

    Because I load my cartridges long where there may not be enough bearing surface to hold the bullet well, I like my necks to be as long as possible. By doing so, it doesn't leave much clearance for the neck to grow with an issue. So, I trim after every firing/sizing. Also, since I trim to the same length every time, the carbon build up doesn't present any issue like having cases that grow at different rates where they can interact with the carbon ring. But if one is removing the carbon ring all the time, then variations in case lengths is not much of an issue. ;)
     
    #7
    I see. I suppose my main question is, how much of a difference (between each case) will each neck eventually end up at lengthwise, to where it's starting to introduce neck tension variances to the point where groups are opening up. Is that even a thing? Will a neck that's one thou longer have just that much more tension to where it shows up on paper?
     
    #8
    I am in the consistency camp. I trim every sizing. There is a fair amount of variation in case length after sizing in my experience. Some cases trim a lot, some a little and some none. Which is better? No idea I have always done it this way and have good results so I don't change. I figure if I am spending time on concentricity and neck tension I want my bearing surfaces all the same length.
     
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    #9
    Basic user said:
    I see. I suppose my main question is, how much of a difference (between each case) will each neck eventually end up at lengthwise, to where it's starting to introduce neck tension variances to the point where groups are opening up. Is that even a thing? Will a neck that's one thou longer have just that much more tension to where it shows up on paper?
    Click to expand...
    That’s going to take a level of data tracking and analyses that I don’t have time or components to do….like weighing primers and sorting bullets. If benchrest is your thing, enough rounds, with brass length measured, seated and tracked with an AMP press, sent over a chronograph, and shot into a group….might show you a correlation between case length and some other variable or pressure, speed or group size.. The question is, do you want to eliminate variables in your brass prep or not? Varying cases lengths is a variable that’s easy to eliminate with trimming. So…it’s up to you. This is how superstition-level reloading OCD practices start and are perpetuated.
     
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    #10
    ShtrRdy said:
    It's more of a safety issue.
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    This is exactly it. If it grows long enough you’ll pinch a bullet and spike pressures up.

    I trim every time: consistent in my treatment and prevents oversights.
    Ounce of prevention = pound of cure

    A powered trimmer that also chamfer and deburrs makes this a simple task rather than a chore.
     
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    #12
    Basic user said:
    I see. I suppose my main question is, how much of a difference (between each case) will each neck eventually end up at lengthwise, to where it's starting to introduce neck tension variances to the point where groups are opening up. Is that even a thing? Will a neck that's one thou longer have just that much more tension to where it shows up on paper?
    Click to expand...
    To measure is to know. Not all cases grow at the same rate. I do not think the neck tension will vary that much due to unequal case growth.

    Get yourself a reasonable quality caliper and measure your brass after sizing. When any case gets to maximum length, trim the whole batch. If consistency is what you are after, once any case gets out of your imposed limits, trim the whole batch.
     
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    #13
    supercorndogs said:
    I have powered trimmers, but I also have calipers. So I don't trim unless they need it. Usually that ends up being only a few times in the life of a batch of cases.
    Click to expand...
    But what is your definition of “need it”? If it affects groups size? If it changes seating pressure? If it causes variable “neck tension”? If case length approaches or exceeds chamber dimension? If case length approaches or exceeds “book” value for max length? What if there is no “book value” (wildcat)? Do you measure every case every time?
     
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    #14
    I don't trim very often. When it needs it. If you're only bumping your shoulder .001 or .002, it's only going to grow a little over time. You can see how close your brass is to the chamber throat with a bore scope.
     
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    #15
    supercorndogs said:
    I have powered trimmers, but I also have calipers. So I don't trim unless they need it. Usually that ends up being only a few times in the life of a batch of cases.
    Click to expand...
    This is where I’m at. I’m also not shooting bench rest or chasing the last mm in accuracy. My time is too valuable to me.
     
    #16
    Great points here. Just trying to see if I actually need a Giraud or not. Trying to see if that is really a machine for people that shoot a ton of matches a year and each match shoots like 200 or so rounds. But if you guys say that you really only need to even em all out a few times during the length of their service lives, then maybe a manual trimmer would be better for me. I just like measuring off of the shoulder and not the OAL; to me that's by FAR the ONLY way that makes any sense. Are there any manual trimmers that index off of the shoulder?
     
    #17
    Basic user said:
    Great points here. Just trying to see if I actually need a Giraud or not. Trying to see if that is really a machine for people that shoot a ton of matches a year and each match shoots like 200 or so rounds. But if you guys say that you really only need to even em all out a few times during the length of their service lives, then maybe a manual trimmer would be better for me. I just like measuring off of the shoulder and not the OAL; to me that's by FAR the ONLY way that makes any sense. Are there any manual trimmers that index off of the shoulder?
    Click to expand...
    It saves a lot of time once initially set up for various calibers. It makes trimming not so bad lol.
    I went from a drill operated Lyman to Giraud and am very pleased.
     
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    #18
    Basic user said:
    Great points here. Just trying to see if I actually need a Giraud or not. Trying to see if that is really a machine for people that shoot a ton of matches a year and each match shoots like 200 or so rounds. But if you guys say that you really only need to even em all out a few times during the length of their service lives, then maybe a manual trimmer would be better for me. I just like measuring off of the shoulder and not the OAL; to me that's by FAR the ONLY way that makes any sense. Are there any manual trimmers that index off of the shoulder?
    Click to expand...
    Yes, there are a number of options, but I'd look at the Frankford Arsenal Platinum Case Prep Center or something similar. Pretty cost effective, and far better than anything I'd call "manual." The Trim-It II used to be my recommendation, but they appear to be out of business. It's really nice to have something that does it all in one step (trim length plus inside/outside chamfer), but the Frankford or similar will handle your needs fine.

    And to answer some of your other questions, trimming to length is important for safety more than anything (as others have noted). I wouldn't expect a few thou variation on OAL to matter for consistency. However, one think I've personally seen is when the case mouth rolls inwards a bit, it can scrape bullets, and that's a no-go for me, so now I trim/chamfer every firing just to put a clean inner chamfer on. The cases grow each firing enough for the cutter to kiss them (22BR with a moderate load). I'm miles away from the end of the chamber, I only do it to have a clean and consistent inside chamfer.

     
    #19
    Basic user said:
    I see. I suppose my main question is, how much of a difference (between each case) will each neck eventually end up at lengthwise, to where it's starting to introduce neck tension variances to the point where groups are opening up. Is that even a thing?
    Click to expand...
    Theoretically, yes. But to be able to actually measure and see the specific effect means you'd have to isolate it from the many other factors that are at play at the same time. When you look at the size of your groups, you're looking at the results for a combination of things occurring. . . including things like a shooter's skill at managing shooting mechanics, wind reading, adjusting to atmospherics, etc. When precision reloading, all we can do is manage the things we can manage to make things as consistent as possible. Trimming is just one easy thing than can be managed. How far you want to go with that is up to you for what level of shooting you're willing to accept.

    Basic user said:
    Will a neck that's one thou longer have just that much more tension to where it shows up on paper?
    Click to expand...
    No . . . for being such a small difference along with that reason of having so many other factors involved.
     
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    #20
    I see. Thank you guys for all the help. I actually have the Frankfort arsenal all in one trimmer/inside outside chamber station, but only use it for the inside outside operation as I thought the way you adjusted the depth for case mouth trimming was too inconsistent. Maybe I should give that thing another try?
     
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    #21
    ggmanning said:
    I am in the consistency camp. I trim every sizing. There is a fair amount of variation in case length after sizing in my experience. Some cases trim a lot, some a little and some none. Which is better? No idea I have always done it this way and have good results so I don't change. I figure if I am spending time on concentricity and neck tension I want my bearing surfaces all the same length.
    Click to expand...
    I would like to see someone who really has their handloading dialled in take ten cases that are at or just under minimum length and compare them to ten that are at or just over max length and see how it affects velocity or pressure signs.

    Personally I trim when some of the cases in a batch get over halfway between min and max length.
     
    #22
    Rodney65 said:
    I would like to see someone who really has their handloading dialled in take ten cases that are at or just under minimum length and compare them to ten that are at or just over max length and see how it affects velocity or pressure signs.

    Personally I trim when some of the cases in a batch get over halfway between min and max length.
    Click to expand...

    I will say I had about a dozen 300WM that I overtrimmed by mistake setting up a new cutter head on my Giraud. Maybe .010-.015' if I remember correctly. Figured what the hell, lets see what they do. I marked them and shot them the next day at 1000. No chrono or other measurements just whether I hit the MOA steel at the same rate. They performed the same as the rest of the box in terms of hits. If it made a difference it wasn't enough to tell on a 10" plate at 1000. That said, I still trim every firing.....maybe superstition of years doing it that way or just habit.
     
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    #23
    ggmanning said:
    I will say I had about a dozen 300WM that I overtrimmed by mistake setting up a new cutter head on my Giraud. Maybe .010-.015' if I remember correctly. Figured what the hell, lets see what they do. I marked them and shot them the next day at 1000. No chrono or other measurements just whether I hit the MOA steel at the same rate. They performed the same as the rest of the box in terms of hits. If it made a difference it wasn't enough to tell on a 10" plate at 1000. That said, I still trim every firing.....maybe superstition of years doing it that way or just habit.
    Click to expand...
    A 10" plate at 1000 is probably as good as a chronograph so that's good to hear.

    I feel you on the superstition/habit thing. Once you have a step in your reloading process it's hard tostop doing it and produce, at least in your mind, lower quality ammunition.
     
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    #24
    Rodney65 said:
    I would like to see someone who really has their handloading dialled in take ten cases that are at or just under minimum length and compare them to ten that are at or just over max length and see how it affects velocity or pressure signs.

    Personally I trim when some of the cases in a batch get over halfway between min and max length.
    Click to expand...
    How much that trim length effects the amount of interference the neck has on the bullet is one of several factors regarding bullet release. How much trim length matters depends a lot on those other factors.

    If you're just a normal hunter and plinker, it doesn't matter one iota. If you're a high level precision shooter competing at a high level . . . it probably matter a lot, to at least be sure they're consistent???

    Here, take a read:
     
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