Help support WeTheArmed.com by visiting our sponsors.

Author Topic: Do I need to trim?  (Read 4000 times)

cpaspr

  • Senior Contributor
  • *****
  • Posts: 2266

  • Offline
Do I need to trim?
« on: January 29, 2010, 03:25:38 pm »
I used to cast bullets for my father by the hundreds when I was a kid.

A friend loaned me (semi-permanently) his reloading equipment 20ish years ago.  I loaded up some 38s and 357s, and about 40 30-30 and 60 .308s.  Then put the whole setup away.  Shot all the 30-30s then sold the gun.  Still have 39 of the .308s.

Got everything out again a few years ago, but didn't really reload much till a little over a year ago when I brought the setup into the house from the garage.  Then went hog-wild on pistol ammo.

Only recently have I started back in on rifle ammo.

I've loaded up about 50 30-06 rounds, all trimmed first.  So all told, I've loaded less than 200 rifle rounds, and most of those were 20 years ago.

I'm now about to try and develop an optimum load for .308 in my rifle, but before I do, I want to ask - which rounds need trimming and which don't?

I've been told 30-30s don't need trimming, because the cases are held in the proper position in the chamber by the rim, and the chamber is deep enough to not have to worry.

30-06 and .308 are rimless, therefore I assume they need to be trimmed to keep the base of the shell from preventing the bolt closing if the case is too long, as the case seats on the mouth, rather than the rim.  I know there is a term for this, is it "headspaces"?  Like .40 and .45 semi-autos.

Or do I really need to worrry about it?  I think I do, but I don't think I'm the only one with this question.

Oregon

WeTheArmed.com

  • Advertisement
  • ***

    JesseL

    • Gun Mangler
    • WTA Staff
    • Senior Contributor
    • *****
    • Posts: 12451

    • Offline
    Re: Do I need to trim?
    « Reply #1 on: January 29, 2010, 03:41:55 pm »
    Trimming serves a few purposes.

    In rimmed, straight walled cartridges that use a roll crimp (such as most revolver rounds); having a consistent length is helpful in getting a consistent crimp.

    In rimless , straight walled cartridges that use a taper crimp (such as most auto pistol rounds); the case length is what controls headspace.

    In most straight walled cartridges the brass generally won't stretch much with each firing and resizing cycle, so it's rare that it will need to be trimmed except maybe after the first firing.


    In bottlenecked rifle rounds (whether rimmed or rimless) it's important not to have brass that's too long because it may get pressed into the throat of the chamber and effectively overcrimp the bullet, causing excessive pressure. Bottlenecked rifle rounds may headspace on the shoulder (for rimless), on the rim (if they're rimmed), or on the belt (if they're belted), but they all can have problems with over length cases.

    With bottlenecked rounds, there will often be some stretching with each firing. How much depends on how loose the chamber is and how much it gets resized. Stretching can be minimized by only resizing as much as is necessary for maintaining proper headspace and functioning in the gun. For my bolt guns I like to neck size only and completely eliminate case stretch.
    Arizona

    xsquidgator

    • Contributor
    • ****
    • Posts: 1861

    • Offline
    Re: Do I need to trim?
    « Reply #2 on: January 29, 2010, 03:41:59 pm »
    From my understanding, you need to trim all of your 308s and 30-06 cases that are over the max length per the reloading manual.  This is because (as you correctly explained) these cartridges headspace on the case mouth.  An additional possible consequence of not trimming these cases is that they will grow longer with each resizing, pushing the case mouth further towards the rifling.  At some point, if not trimmed, loading one of these untrimmed rounds could jam up some of the case-mouth brass in between the bullet and the rifling, sort of pinching the bullet in more tightly.  If this didn't jam up the action or stop the bolt from closing completely, it could lead to a dangerous overpressure condition when the round is fired.  (EDIT- looks like I was beaten to the firswt post, and that my understanding of cartridge headspacing was incomplete!)

    I trim all my rifle cases each time I size them (all of mine are rimless bottleneck cartridges, no 30-30s yet).  I used to measure them with calipers and then resize the ones that were over the specified length, but... it seemed to me that took as much time as simply trimming all of them.  It's also probably better for consistency and accuracy's sake to have all the cases as uniform length as possible, but I don't know how much or if this actually makes a difference.  I trim them all anyway.

    One last thing: it might not be necessary to trim all your .223 brass, especially if firing it in a 556-chambered gun.  An experienced reloader friend of mine says there's more than enough leade in a 556 chamber to not have to worry about excessive growth of the case.  I don't know if he's right or not about that, but just in case he's not right, I still trim all my 223 and/or 556 brass.

    cpaspr

    • Senior Contributor
    • *****
    • Posts: 2266

    • Offline
    Re: Do I need to trim?
    « Reply #3 on: January 29, 2010, 04:42:59 pm »
    Okay.  Thanks.

    Trim it shall be.  Right now my trimmer is manually operated.  Read:  Tiring.  I'm going to have to think up some way to mount a motor to it such that I can move the base back and forth and leave the cutterhead end constant.  Or move the motor/cutter head assembly together.

    Woo-hoo!  Bubba engineering time ahead!
    Oregon

    THE NORSEMAN

    • To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them. - Richard Henry Lee
    • Moderator
    • Senior Contributor
    • *****
    • Posts: 5071

    • Offline
    Re: Do I need to trim?
    « Reply #4 on: January 30, 2010, 11:22:37 am »
    Fastest way is 3 buckets or cans-  One with the fired brass in it.  Then you use a tool like this http://www.lymanproducts.com/lyman/case-prep/ezee-case-gauge.php  .  If they're short enough, they go in bucket 2, if they need trimmed, bucket 3.  This is for range ammo or plinking ammo only.  If I'm trying for the elusive 1 hole at 100, it's dial calipers, flash hole deburring, weighing each case, etc.
    « Last Edit: January 30, 2010, 03:55:41 pm by THE NORSEMAN »
    This may be considered as the true palladium of liberty. . . . The right of self defence is the first law of nature: in most governments it has been the study of rulers to confine this right within the narrowest limits possible. Wherever standing armies are kept up, and the right of the people to keep and bear arms is, under any colour or pretext whatsoever, prohibited, liberty, if not already annihilated, is on the brink of destruction- St. George Tucker, Blackstone's Commentaries

    cpaspr

    • Senior Contributor
    • *****
    • Posts: 2266

    • Offline
    Re: Do I need to trim?
    « Reply #5 on: January 30, 2010, 02:47:55 pm »
    Thanks Norseman.  I'm not Scots (that I know of), but I am cheap frugal. Money is more important (for this process) than time.  I have the micrometers, and don't mind taking the time.
    Oregon

    RandySBreth

    • Member
    • **
    • Posts: 497
    • Khaaaaaannnnnnn!!!!!!!!!!!!!!!
      • Ozark Outdoor Journal.

    • Offline
    Re: Do I need to trim?
    « Reply #6 on: January 30, 2010, 05:29:27 pm »
    I'm like Norseman on trimming; If it's plinking ammo, I just makes sure it's not over max length, but for maximum accuracy, it's the weigh the cases, trim ALL to the same length, etc.
    Another thing to watch is if you have to trim your cases often, your going to have to ditch them sooner or you'll get incipient case head separation if you try to load them for more than a few load/trim cycles.
    http://www.exteriorballistics.com/reloadbasics/images/reloadingx48x1.jpg
    http://www.exteriorballistics.com/reloadbasics/caseinspect.cfm
    My website: http://ozarkoutdoorjournal.blogspot.com/


    "To be great is to be misunderstood" Ralph Waldo Emerson.

    cpaspr

    • Senior Contributor
    • *****
    • Posts: 2266

    • Offline
    Re: Do I need to trim?
    « Reply #7 on: January 30, 2010, 09:01:55 pm »
    One of my faster "bubba" projects.  I took an old B&D 3/8" high speed drill that I've had for over 20 years that was replaced long ago with quality tools, and clamped the shaft of the trimmer in the chuck.  Held the trimmer flat to a scrap piece of plywood and carefully measured from the plywood up to the side of the drill.  I found a couple of pieces of scrap lumber that when pinched together just exactly measured the same thickness. 

    I cut the two pieces to the width of the plywood, roughly 6", and glued and screwed them to the end of the board.  I then placed the drill/trimmer in position, and screwed down a long track board parallel to the trimmer.  Screwed down a similar board on the other side of the trimmer, then clamped the drill in place with a long section of plumbers tape.  Got it all assembled, set the trimmer to the correct length, locked the drill's trigger in the on position and plugged the drill into a speed reducer I bought for using with a router, to avoid the super high-speed start ups that are hard on router motors.

    Chucked up the first .308 shell and in less than an hour I had trimmed 114 to length.  Not perfect, identical lengths, but close enough for my purposes.  Almost all between 2.005" and 2.010", with just a few down to 2.000".   So much easier and less tiring on the hand.

    Now, on to de-burring.
    Oregon

    Help support WeTheArmed.com by visiting our sponsors.