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O.A.L., seating depth, powder charge... 3 dark territories for me.

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  • O.A.L., seating depth, powder charge... 3 dark territories for me.

    Hello everyone,

    Im new to handloading, starting to get a feel for it, but there are few variables that do not make me comfortable yet, as I do not want to damage my rifle or myself... So here are some questions:

    I made about 100 rounds of .308's, followed recommended recipe from powder manufacturer. I understand that i did not get same results, but I would like to tinker with the recipe a bit
    • Speer 150 gr bullets, #2022
    • Hodgdon Benchmark powder, 40 gr
    • re-used cases
    For now I am satisfied with accuracy, chronograph readings were below the powder datasheet, but in previous post I have been told that its ok.
    I have measures the COAL of my rifle using 2 home-made methods, and its longer than 2.9". All datasheets that I have seen so far have pointed out to seat the bullet no more than 2.8". I understand the reason behind that. I have watched some youtube videos, and the need to seat the bullet 0.010" from COAL lenght, but apparently I cannot do that with my rifle
    I understand that adding more powder may increase my velocity but also increase the pressure. (I will stick to low end, 40 gr)
    I would like to take 5 or so of my reloads and seat them 0.005" lower (2.795") , take another 5 or so and seat them lower than that (2.790"). How would this change my trajectory? How low can I go before its considered dangerous?
    It will also increase my pressure, how would I know that there is too much pressure (except for my rifle exploding)? Is there a way to calculate the pressure without measuring ? Is there any way of knowing that the pressure is too great?

  • #2
    My opinion is that you should stick to the recommended OAL and increase your powder charge slightly, taking a 'ladder' approach. You shouldn't try to increase your pressure and fps by shortening the OAL. As always, stay below the max charge shown in the book. Are you having an issue with the OAL recommendation not fitting your magazine?

    How are you measuring the OAL? If you don't have a good set of calipers, you really should spend $20-$40 and get one. Some are more expensive but you can get an accurate one for pretty cheap. You shouldn't be using 'homemade' methods to measure the length of the finished cartridge, or the cartridge case for that matter.
    "Beware the fury of a patient man." - John Dryden

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    • #3
      Originally posted by talltexan View Post
      My opinion is that you should stick to the recommended OAL and increase your powder charge slightly, taking a 'ladder' approach. You shouldn't try to increase your pressure and fps by shortening the OAL. As always, stay below the max charge shown in the book. Are you having an issue with the OAL recommendation not fitting your magazine?

      How are you measuring the OAL? If you don't have a good set of calipers, you really should spend $20-$40 and get one. Some are more expensive but you can get an accurate one for pretty cheap. You shouldn't be using 'homemade' methods to measure the length of the finished cartridge, or the cartridge case for that matter.
      One method that I used to measure my OAL is from here using method #1. Another method that I used is cutting a case with dremmel into 4 pieces (up to a neck), where bullet has some tention, but very little. I do have calipers, otherwise I would not be able to distinguish 2.795" from 2.8" Both readings were over 2.9", so no point of measuring precisely, as I would not be able to seat a bullet at 2.9" anyway. 2.8" OAL does fit my rifle, but I would like to experiment with shortening it to see what results I get, that's why Im asking if its safe, and what signs to look for when the pressure is approaching dangerous levels

      Powder measurements were taken from Hodgdon website. I'm using 40 gr, and I expected velocity was around 2,550-2,600, but chronograph showed 2100's.
      Click image for larger version

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      • #4
        First lets clear a few things up...
        1. The COAL you are obtaining by using the method in your link is cartridge overall length for that chamber. Said another way, it is attempting to get you to measure the maximum cartridge OAL that the rifle will accept with a given bullet before the bullet gets embedded into the lands (beginning of the rifling). When we are doing this we are actually working to the bullet OGIVE, or the curve of the bullet that is the same diameter as the inner diameter of the rifling, which is smaller than the actual bullet diameter where it sits in the case neck. For you particular situation, you do not need to worry about this.
        2. COAL in the book (sometimes discussed as simply OAL) is nearly always close to or at max SAAMI overall length of a given cartridge from the base of the case to the tip of a bullet. Heavier bullets, lighter bullets, spitzers, VLD's, all have different dimensions so SAAMI is a max 'recommended' length.
        3. Pressure decreases as COAL increases UNTIL the bullet is seated at or into the lands. If you hit the lands pressure increases, and increases rapidly the deeper into the lands it goes. Pressure increases as the bullet is seated deeper into the case (shorter COAL).
        4. If you are seating 2.800 you are 0.010 under SAAMI max of 2.810 and 0.310 over SAAMI minimum. Again, the swing is because of different bullets in a SAAMI spec chamber. Your factory rifle uses a SAAMI spec chamber. See page 110 for the 308 Win specs: https://saami.org/wp-content/uploads...sting-Copy.pdf
        For your question, sure, go ahead and start moving the bullet down or out. 0.005 is pretty small for testing purposes. You can make that +/- 0.010 if you are feeling overly cautious, or take bigger swings up to 0.040. You powder charge is about right for this type of testing (don't fiddle with those jumps with a large charge). If you shoot 10 shot groups with each adjustment you should see 1 group outperform the others. Take that group and verify/fine tune it with +/- 0.010 groups. From there, adjust your powder up with the best grouping.

        CAUTION: This post discusses loads or load data that may or may not be appropriate for your gun or for the cartridge(s) and components mentioned. Due to typos, variations in guns and components, and the abilities and judgement of users of this data, neither the writer, Handloadersbench.com, nor the staff of Handloadersbench.com assume any liability for damage or injury resulting from using this information. DO NOT ATTEMPT TO DUPLICATE THE DESCRIBED LOADS without first working them up from a published safe starting level charge while watching for pressure signs. If you don't know how to do that please don't try, for your own safety and the safety of others.

        EDIT: replaced 0.310 under SAAMI minimum with '0.310 over SAAMI minimum'
        Last edited by golong; 4 weeks ago.
        Friends don't let friends shoot factory ammo.

        Continuous effort - not strength or intelligence - is the key to unlocking our potential.
        -Winston Churchill

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        • #5
          I doubt you will see much change at all by seating the bullet deeper. You are not close to max load. You may or may not see a change in accuracy either.

          COAL or OAL is simply the length of the loaded cartridge from base to bullet tip. Your max COAL may simply be the max length that will cycle thru the magazine and chamber.

          It sounds like you need to study what CBTO means. Cartridge Base To Ogive. The Ogive is the part of the bullet that first contacts the rifling aka lands. Generally, bullets perform well when the Ogive is 0.010"-0.030" from touching the rifling when chambered. Weatherby got rich by increasing the velocity of their ammo by bullet "jump" of around 0.100". Some copper bullets have their best accuracy at 0.080". Some hand loaders develop their loads by starting low with the bullet touching the lands, finding the max load, then increasing the jump to the lands a little at a time in an effort to maximize accuracy. They may even be able to increase the powder charge a bit. That plus the jump can add considerably to velocity.

          Chasing the lands can drive you crazy, and is usually done by experienced loaders. For now I suggest you stick to book COAL and tweak your powder charge to find that sweet spot or max load. Paul B has a good explanation of how to find you CBTO if you don't have commercial tool for that purpose. Maybe he'll post it and I'll make a Sticky out of it.
          It's not that Democrats are so damned ignorant. Their problem is that everything they know is wrong.

          Wimachtendienk, Wingolauchsik, Witahemui

          He who knows not and knows not that he knows not, is a fool.
          He who knows not and knows he knows not, is wise.

          Comment


          • #6
            Shortening OAL increases Pressure because it makes the case volume smaller.

            .005" shortening a bottleneck rifle cartridge will not reduce volume any notable amount, thus will not increase Pressure any useful amount.
            Add half grain powder and a full grain to another set.

            I have never loaded a .308 longer than 2.810, because my magazines will not permit it.

            Google "reading cartridge pressure signs", several good articles exist, and it is NOT VERY EASY OR RELIABLE.
            Primers getting loose, impressions on the case base of openings in the bolt face, primer extrusion and cratering. "Flat" primers are the first, and lousiest thing people look for.

            Comment


            • #7
              Accuracy will improve by seating them deeper. The 150 Speer is a short rock that wants to jump the Grand Canyon. An OAL of 2.750 is where that thing will most likely be happy.
              Friends don't let friends shoot factory ammo.

              Continuous effort - not strength or intelligence - is the key to unlocking our potential.
              -Winston Churchill

              Comment


              • #8
                let's simplify things a little.

                changing the oal just changes when the bullet comes out of the barrel.
                it can help tighten up groups by moving the point of when the bullet leaves the barrel in relationship to there the whipping around barrel is pointing at the time. [barrel harmonics]

                the 'factory's' use it because it is simple to measure, open the calipers and close them on the completed round,,, there ya go.
                what they are really giving you is a case volume measured from the base of the bullet down to the primer in a simplified form, easy to communicate and understand.

                powder amounts.
                you increase velocity by adding more powder.
                it does so by increasing the amount of gas produced,, to push on the bullet a little longer.
                simple as that..... kind of.
                it also increases pressure because it increases gas volume.
                the trick is to stay at or under maximum pressure for as long as possible to produce the highest velocity, in other words use the most of the slowest powder.
                pressure when measured ranges from a quick spike and a quick drop /\ off to a maximum average pressure say 50-K psi. [this would be a fast powder]
                the slower powder rises to the same 50-K it just stays there longer /===\.

                hopefully that helps some.


                Comment


                • #9
                  Originally posted by Domo View Post
                  Powder measurements were taken from Hodgdon website. I'm using 40 gr, and I expected velocity was around 2,550-2,600, but chronograph showed 2100's.
                  How long is your barrel,,,,,,,,,,,,,,,,, and how long is/was the barrel Hodgdon used?
                  Also was your chronograph set the same distance from the muzzle as Hodgdon's was?

                  These differences MATTER when you want the numbers to be "the same".

                  Comment


                  • #10
                    What golong, damannoyed and oleyeller said.
                    "The United States Marine Corps is a drug and I am a recovering addict."

                    "American by birthright… U.S. MARINE by the Grace of GOD!"

                    "And on the 8th day God created Marines and like fish, we came from the sea!"

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                    • #11
                      "Chasing the lands can drive you crazy, and is usually done by experienced loaders. For now I suggest you stick to book COAL and tweak your powder charge to find that sweet spot or max load. Paul B has a good explanation of how to find you CBTO if you don't have commercial tool for that purpose. Maybe he'll post it and I'll make a Sticky out of it."

                      T'wern't me. I did the one for setting up a sizing die but never have done one on CBTO. OOPS!
                      Paul B.

                      Comment


                      • #12
                        Originally posted by Paul B View Post
                        "Chasing the lands can drive you crazy, and is usually done by experienced loaders. For now I suggest you stick to book COAL and tweak your powder charge to find that sweet spot or max load. Paul B has a good explanation of how to find you CBTO if you don't have commercial tool for that purpose. Maybe he'll post it and I'll make a Sticky out of it."

                        T'wern't me. I did the one for setting up a sizing die but never have done one on CBTO. OOPS!
                        Paul B.
                        Not the explanation you were referring to, but I posted a link to a video in one of the OP's other threads that shows how to do it with a stripped bolt and seated bullet.

                        The closest cure-all for not chasing the lands is Hybrids. Start them at 0.015 and let that grow with the erosion. Still won't help obtain the best accuracy with most top load or BDM since they are still too long from the onset. The Speer's will shoot pretty nice groups with a big jump. I buy a bunch of .308 and .264 Speer FB for expanding brass. Most of my loads were jammed intentionally, but I did play with backing them off to see how they did. Nothing to complain about for around $0.19 per bullet.
                        Friends don't let friends shoot factory ammo.

                        Continuous effort - not strength or intelligence - is the key to unlocking our potential.
                        -Winston Churchill

                        Comment


                        • #13

                          golong , Thank you for valuable information. I will not go over the max powder charge, I will just seat bullet deeper to see how it affects. It will be in small steps, and I will not do anything dangerous (i like my rifle too much to damage it). If i start seeing dangerous changes (recoil, primers damaged), i will not use any deeper seated ammo.

                          olyeller you are correct, in future i will read-up on CBTO. Sounds like it would be too deep information for me to handle at this time.

                          Damannoyed I do not want to shorten the neck of the cartridge, I wanted to seat the bullet deeper. I did google the subject, and I did see some signs on my co-worker's reloads. I did notify him about that. According to Hodgdon website, they were using 24" barrel, I have 22"; twist was 1:12", I have 1:10" chronograph must have been close (not 2 ft away), but few inches from barrel. Would that be enough to reduce velocity by 20%? (2500's in test condition vs 2100's in my test).

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                          • #14
                            Domo, Damannoyed is not telling you to shorten the neck, he is talking about decreasing the effective volume of the case by seating the bullet deeper. Reread his post and you will see what he means.
                            FWIW, he is exactly right.

                            Signs on your co-worker's reloads are meaningless to your reloads. Each chamber is different, as is each barrel, ad infinita. It is good you told him about it so he can address it if need be.
                            It's not that Democrats are so damned ignorant. Their problem is that everything they know is wrong.

                            Wimachtendienk, Wingolauchsik, Witahemui

                            He who knows not and knows not that he knows not, is a fool.
                            He who knows not and knows he knows not, is wise.

                            Comment


                            • #15
                              A chronograph that close will usually have errors induced by muzzle blast..

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