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Case length ?

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  • Case length ?

    I was thinking earlier today, with all the talk of fire forming cases and bumping shoulders, and bullet distance from lands, I've never heard much said about case length. I know the books give a trim length and a max length, but I'm curious if there is any benefit to matching case length to a particular chamber similar to fire forming and setting oal to fit the specific gun.

  • #2
    in some circumstances yes very much so.
    at the east it keeps carbon from forming in front of the case similar to shooting 38 specials in a 357 mag gun.

    I measure almost every one of my rifles by doing a pound cast of the throat, this tells me all of the critical dimensions I need to know including how long my case necks can really be before causing me any trouble.


    • #3
      If I'm seeing this the same way. If a chamber is cut to accept a longer case then we should take advantage of this. I do agree and have done this. I load for 256 Win mag in a contender barrel. I make cases from 223 and end up with them .030" longer than spec. Does it help with cast boots, possible but it sure doesnt hurt.


      • #4
        Well at least I wasn't crazy to think that. I did find it talked about a little on other forums before posting my question here. Just that some people did it, not what they thought it helped with or anything just that they did it. One way I saw discussed to do it was using a thin piece cut off of a fired case neck, slid over a seated bullet as a spacer and then trimming the case with the bullet in it until the bolt would close, measuring that length then trimming cases a few thousandths shorter than that.

        Seems like pulling the bullet to trim the case that many times would be a pain, but short of making a casting of the chamber, I don't know how else it could be done.


        • #5
          I'm sure there is a benefit, but you'd need to know the exact dimensions of your chamber.. You could do a chamber casting if you haven't had it chambered with a custom reamer. I always like to run them right at just short of max length for a couple of reasons. 1 is it allows me more neck to play with when trying to seat at or near the lands and 2 the longer necks tend to funnel the hot gasses down the bore vs against the throat walls. I didn't come up with this latter theory, I heard it come from John Kreiger's mouth and if anyone knows guns it is him. He explained that is why a 243 W is so much harder on throats than a 6mm BR. So being the cheap guy I am I never trim to min specs .


          • #6
            I've done some more looking into the subject since I got off work a couple hours ago and it turns out that there is a tool made by Sinclair for this measurement. You cut a case short then put it in the end like a bullet, close the bolt on the case with the tool in it, then extract the case and measure. The tool is cheap enough but after seeing it I have an idea on how to make something very similar my self that would work with the hornady oal tool.


            • #7
              In addition to reducing throat erosion, I also think you might gain a little velocity by trimming to the longest trim length possible. You definitely wouldn't want to create a mouth constriction issue, but if the throat is capable of longer, I see no reason to trim them shorter than necessary, as I see it, there's some benefit to doing so.



              • #8
                A longer case neck does make it easier to seat more concentrically. I started loading 30-06, .270 win .308 win, and .244/6mm remington and found the .244/6mm was the easiest by far to get better results with. By far the longest neck of the bunch.


                • #9
                  I use the Sinclair tool to measure length to allow matching case length to that particular rifle.
                  Unfortunately most case makers cut the cases too short so that it takes a while for the cases to lenghten enough to trim for that chamber.
                  "The United States Marine Corps is a drug and I am a recovering addict."

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                  • #10
                    The main rifle I was thinking if this for is my 300 winmag. The chamber is fairly long (around 13 thousandths longer than factory brass if I remember correctly) and the throat is also fairly long, I forget the numbers though. I ended up moving to a different bullet because I had so little bearing surface in the neck, which is already considered to be a very short neck. That's part of what got me thinking, if everything else is longer maybe that is too and any additional neck I could get on the bullet should be an improvement since a lot of people seem to think that the neck is too short already on that round.

                    Another thing that got me thinking about it was when I fire formed the brass a few weeks ago (cream of wheat method) there was a ring of tightly compressed somewhat charred cream of wheat that would fall out of the chamber that was the same OD as the case and seemed to have formed in a gap between the end of the case and..... Something. At first I thought maybe it was the throat but from my understanding the throat is a smaller diameter than the OD of the case neck

                    I'm curious highbc, what about the longer neck do you feel would lead to higher velocity? I'm guessing more friction between the case neck and bullet from the increased bearing surface contact leading to slightly higher pressure before the bullet is released but I may be way off.


                    • #11
                      Originally posted by DesertMarine View Post
                      I use the Sinclair tool to measure length to allow matching case length to that particular rifle.
                      Unfortunately most case makers cut the cases too short so that it takes a while for the cases to lenghten enough to trim for that chamber.
                      That may be due to published trim lengths based on assumptions all chambers are cut to spec and that is very unlikely in mass production.

                      I do same as you. Sinclair calls it a chamber length gauge. I do it once for every bolt action caliber I load. You'll need to "donate" one piece of brass to use the gauge, but once done you'll know your rifle chamber's actual length. I keep a load log for my rifles, note the actual chamber length, subtract .010" from actual length which then becomes trim length for that rifle. I see this no different than finding CBTO measurements for load development and it eliminates unnecessarily trimming brass.

                      In the scenario DM describes, I find the shortest case in a given batch of brass and use it as my trim length until that batch brass grows beyond my determined trim length.


                      • #12
                        Seeing how cheap the Sinclair gauges are I'll probably just buy them for the couple calibers I'm interested in. I did come up with an idea though for a way to make my own tool similar to the method I mentioned in the fourth post. Once I get a chance to make it I'll post some pics of my idea and compare the results to the Sinclair tools.

                        I just wish I had thought of this before I trimmed a new set of brass for my 300 win mag and my friends 270 wsm. I did leave them both somewhere between trim length and max length but now I wish I hadn't trimmed at all until measuring the chambers. Oh well, at least it was only 50 cases for each.


                        • #13
                          I only use i have case gauges is using them for setting the Wilson trimmer's trim length before minor final adjustment. Those minor adjustments depend on the specific rifle being trimmed for.
                          Good judgement comes from experience,
                          and a lot of that comes from bad judgement.
                          Mark Twain


                          • #14
                            Something else to consider on case lengths is neck tension. Some people just load and shoot repeatedly until they need trimming and then trim back to minimum specs. I find it a pain in the ass to do so, but I get more consistency by trimming often and to the same length each time. ( .001" under max) That way I always have a case neck within 1 or 2 thou vs shooting a group one day at max length then at min the next. It probably doesn't matter that much unless you're like me an obsess over small groups. By first fire forming my cases and then only setting the shoulders back .001" during FL sizing they grow slower too.


                            • #15
                              I have some experience playing with case lengths not that I can say the information is of much value.
                              1. Jacketed bullets are not too sensitive to the case length. I accidentally trimmed some cases for an 1891 Mauser in 7.65 Mauser .035 too short. It made little difference in the use of those cases for iron sight plinking.
                              2. During the Boer War the Boers ordered 7X57 ammo. The German ammo supplier had no cases so cases for the 53mm long 7.65 Mauser were used apparently with no problem.

                              When I was making cases for the 7.65 Mauser from .30-06 I had several bright ideas.
                              A. The 7.65 Mauser has a short neck so I decided to make the necks as long as possible and still fit the chamber. I FL sized .30-06 cases and left the necks way too long. The Mauser chamber has a square edge at the end. I flared the cases to have a slight trumpet shape so they had to stop at the end of the chamber. These cases were trimmed slightly checked for fit. I continued flaring and trimming until they stopped on the chamber mouth but allowed the bolt to close. Once the chamber length was found I measured the test case and found it was .040 longer than the trim length used for new factory ammo.
                              B. These cases were then carefully fired with moderate loads resulting in backed out prImers. It turned out that the cases shortened about .007 when the body was expanded by fire forming. Next I made up ammo that head spaced on the case mouth, head spaced on the shoulder and I had the bullets jammed into the lands. These cases also got shorter when fire formed.
                              C. It appears that using this method to blow a shoulder forward is not such a good idea. Making a rimless .444 Marlin does not seem to either.

                              Moving on to a more useful matching of chamber and case.
                              When shooting long heavy cast bullets in a .40-65 or .45-70 you can get lead foil rings scraped of off the bullets. When there is a gap at the case mouth the soft bullets can expand into the gap due to acceleration.
                              To avoid finding foil rings stuck to your case mouths you can use cases that a long enough to fill the gap.
                              That is easy with the .40-65. When .45-70 brass is formed to .40-65. It grows about .030 longer so it is easy to trim to 2.125 to fit my chamber.

                              For the .45-70 some shooters "stretch" their cases with an expanding tool. Others buy .45-90 brass and trim it to fit.

                              What I learned
                              1. In some rifles brass can be allowed to stretch from a lot of reloading without danger. I do this to skip a lot of trimming. I do trim when cases get uneven or vary from each other. However you have to know your chamber length exactly.
                              2.Bottle neck cases shorten quite a bit when the body is blown out by fire forming. When the case is FL sized you do not get all of that length back.
                              3. Head spacing a long rifle case on the mouth is not such a good idea.
                              4.Some short neck rounds might benefit from letting the case lengthen by not trimming.
                              5. You can get rid of the lead foil trash on the case mouth when shooting BPCR rifles.

                              Most important was the technique for measuring the chamber length. By repeatedly flaring and trimming over length cases I could find the exact chamber length.

                              In addition when flaring annealed brass it is possible to flare it .030 larger than the chamber neck. You can then carefully shove the case in. The oversize flared case mouth is squashed to fit the neck diameter exactly. You can then carefully extract that case and measure the end of the little trumpet. That diameter is the exact diameter of your chamber neck. If you doubt the method no big deal. It costs nothing at all and you can easily repeat the process until you have confidence in your measurement.
                              Last edited by ireload2; 12-07-2018, 05:08.