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Thread: Cheating the scale

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    Default Cheating the scale

    New reloader loading 357 mag, but finding inconsistency in velocity when chronographing (100+fps swing w/in 6 shot string). If it is a powder inaccuracy, how can I weasel by with a regular RCBS scale? 3 loads tried today, all with similar inconsistency: 12, 14, and 15.6 grains of Hercules 2400 - 150G Nosler JSP, .

  2. #2

    Default .357 loads

    It may not be the powder. I use an old 505 RCBS scale and it works just fine. If the cases are not consistent in length, the crimp may not be consistent either resulting in varying bullet pull. What primers are you using? With 2400, they don't have to be magnum primers. That is a lot of velocity variance. Do you weigh every load?

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    I did weigh every load. I eyeballed the scale's zero as best as possible, but I wondered if that wasn't enough. The powder is also old, it's Hercules 2400, which I hear now is sold as Alliant. I don't know how old that makes it, but it's in a tin and cardboard tube-container. The seating depth varied between 1.85 to 1.7. Would untrimmed cases (all of proper length, but I didn't trim) cause a velocity difference that great?
    How much of a velocity difference do experienced reloaders find when eyeballing a traditional scale versus digital scale powder weights?
    Also for velocity, I've reamed primer pockets and flash holes, including an inside taper on the flash hole exit, on once used brass ready for sizing. The primer pockets are now clean, but somewhat ribbed from reamer jitter. How is that avoided?

    You haven't seen a JKR come across the rack in the last month, have you?

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    Don't mess with flash holes, that maybe your problem. However I tend to believe the problem is with case length and different crimps due to case length.

    Forget the powder, you are dealing with a double base powder and the stuff does not deteriorate like single base rifle powders do.

    No matter what scale you use that will not cure your problems.

    I have not crimped a pistol bullet in the seating die in over 30 years. I use a separate die to crimp with after seating. This saves a lot of problems.

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    I have only reamed flash holes and primer pockets in current brass, not in the just fired 357s. I did not intentionally crimp these loads, unless the RCBS seating die has some sort of crimping bend (I don't think so, but still learning). I tried to pound out a few loads during set-up of the seating die with a bullet puller, but I was in danger of breaking the puller before I saw the bullets give any-indicating a pretty snug fit anyway.

    Would using an inside-case lube help for future loads, if an unavoidable crimp is to blame? The dies are used, but belonged to a gunsmith prior so I assume were not abused.

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    Lets get down to basic. There are to types of crimps. Taper crimp and roll crimp. If you were shooting an auto loader you would have a seating die with a taper crimp. You are using a revolver ctg., therefor your seating die has a roll crimp provision.

    It is difficult to adjust a seating die to seat to the length you want and to get the roll crimp in the right place, when you have brass the length is not the same. Can you see this?

    Are you using jacketed bullets? This is another factor. Where you crimp the case into the bullet is another factor. If jackets then you need to crimp in the cannalure.

    If you are using cast then you need to crimp in the crimping groove.

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    Thanks,

    I understand those basics, but you do make me wonder if the seating die I used provided a taper or a roll crimp. The die, nor did the box, indicate either, but I believe there was an 83 on the die-does that number represent a taper or a roll crimp, or is it for some other purpose?
    The bullets were all seated to land the cartridge rim in the cannalure. Ah-you say that, because the 357M is a revolver cartridge, the die most likely provided its own roll crimp, without need of a crimping die. this means that, for the next set, I'll trim the brass after resizing.
    After plugging numbers into excel, the most consistent load today was 14g of 2400. Even then, my standard deviation was over 22, with a full range from 1230fps to 1319fps (diff of 89fps between 12 fired rounds).

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    To check your bullet seat for a crimp function, back out the bullet seat from the die and loosen the die in the press. Put a sized and trimmed brass in the press, push it up all the way, then move the die body down into the press until you feel the crimp touch the brass. You then advance it just enough to give you the crimp roll that you want and lock it in. Now adjust the bullet seat back in until you have the proper bullet seating depth based on finished OAL. It usually takes a bit of trial and error to get both the crimp and bullet seat just right when they are contained in the same die.
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    The only thing you have to do with the primer pockets is get the black residue out.

    And you're talking about tiny potential variations in scale reading. It's a good scale, and you're simply not likely to get enough variation to cause anything close to the variation you are seeing. Heck, with 2400 I use the scale only to set my powder measure, then dump directly from the measure into all my cases. And I don't see anything even close to your variation! Cross the scale off your list as a potential varaible causing the problem.

    But that is a HUGE range in seating depths, assuming we're talking about the same bullet in your different loads. Seating dies are designed to give you the same OAL, so if seating depth is varying, the only thing that can be going on is variation in case length. Not only will that cause the case rim to be pushed further or less into the crimp function on the die (doesn't matter which type we're talking about at this point). As a result you are going to get all kinds of whacko changes in crimp tension.

    Then there's the problem of where the case rim is resting on the bullet when you crimp. Could be in the middle of the canelure, could miss it completely. With your seating depth range of .185 to .17, that's a .015 difference, and lots can happen in your canelure alignment with that much slop in case length.

    Time to get on with the case trimming, or at least to sort cases and readjust the seating die to match each batch. Once you cases are all the same length, then you can futz around with roll versus taper crimps, but it isn't going to make a whit of difference which you choose if your case length is varying by .015.

    And quit worrying about the scale. You've got more important things to take care of. If you're building a case to buy an electronic scale, go buy the thing and be at peace, but buy a case trimmer at the same time so you can solve your problem and get back to shooting! ;-)

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    I would much rather NOT spend any more on reloading than I have, so keeping the scale is fine with me. If a .015 spread between OAL is unacceptable, then I will trim the cases. Next question. The cases are expanded and ready for bullet and powder. Will I need to resize them before trimming?

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    One thing that will save a lot of headaches is to develop a system for loading.

    When I dump my brass, I start the cleaning process, I first clean with a chemical cleaner, then full length size, check for length, trim if needed. I now go to vibratory ceramic chemical clean.

    Now my brass is ready for loading. Because I use a automated loading machine. The rest of the process is a little different for me than it is for you.

    Bell case mouths and primer seating is your next step.

    Dump powder charges.

    Seat bullets and crimp.

    By the way a taper crimp is only required for cases that head-space on the mouth for autos. cases such as .380, 9mm, .45acp etc.

    I do not like to crimp in the seating die. I use a separate crimp die, because you can keep the bullet in better alignment this way.

    By the way I also dry polish after I'm all done to remove any lube and to hide the bulge at the base of the bullet in the case. This is the same the factories do.

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    I can tell you with 99% certainty that your RCBS scale is not the fault here. Going to an electric scale will only compound the problem.
    I gave up looking at my chrongraph a long time ago. If the revolver groups the load well it is time to move onto something else to worry about.
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    Sometimes chronographs are a bad thing, ie variations in velocity aren't always a huge detriment. The primary reason I use a chrony is to get a feel for how close I am to a max load, but I never let chrony readings steer me away from what really matters, ie group sizes.

    First off I'd highly recomend getting a good powder thrower, they are a huge time saver over individually weighing charges, and there is evidence that they produce smaller groups.

    As to what straightwall magnum handgun cartridges seem to like to get good consistant powder burns, a nice tight grip on the bullet which is provided by case sizing and crimp. There was an article in handloader where they tested increased bullet crimp and found velocity spread tightened up.

    I've found the slower powders 2400, lil-gun and H-110 seem to burn most consistantly at the higher charges. Also 2400 seems to work best with std, not magnum primers. The 357 mag burns a relatively small charge of powder, and doesn't need a blowtorch to set it off.

    With all that said, go back and concentrate on group sizes. Whatever charge weight provides the tightest group is the one to use, even if velocity spread is higher than you'd care for.

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    Quote Originally Posted by estern View Post
    New reloader loading 357 mag, but finding inconsistency in velocity when chronographing (100+fps swing w/in 6 shot string). If it is a powder inaccuracy, how can I weasel by with a regular RCBS scale? 3 loads tried today, all with similar inconsistency: 12, 14, and 15.6 grains of Hercules 2400 - 150G Nosler JSP, .
    estern:
    Here be the way I see it. Your concern is inconsistent velocities.

    Uniforming primer pockets is a good idea. It will help keep the primer below the surface of the case head, and should result in more uniform seating of the primers, which works towards more uniform ignition.

    Your seating die will only crimp if it is adjusted to do so. Itís not automatic, although you could have it adjusted it to crimp accidentally. If your rounds are Roll crimped, you could easily tell just by looking. I shouldnít think youíd have a taper crimp in a seating die.

    As has been pointed out, you can seat as a separate operation, if you canít fathom how to adjust for crimp and seating at the same time.

    I suppose, that a lot of your variation in OAL could be due to variations in the bullet tips. I doubt if OAL is much affected by case length.

    As for variation in velocity, I suspect youíll get more variation when you donít have a crimp, than when you do, so perhaps you need to crimp.

    If I were you, I'd adjust for crimp, and see if you have better consistency in your chronographing.

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    I love chronographs. I don't worry about getting the powder scale exactly on zero either.

    You are shooting a revolver with six different chambers. I would not consider 100fps a large deviation for a revolver.

    If the load is in the velocity range you are looking for and groups well I would call it a good load.


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    Advice is appreciated. I measured the brass for uniformity and found that, although all were under the case length max, the variation was great and the mouths were not even square. Trimmed 60rnds last night to 1.27, or a hundredth less than the published trim length. I tossed anything that was still short, or not trimming clean all the way around.

    As long as I can still crimp in the cannelure, which is .04 wide, I should be fine, no?

    One last thing about RCBS 357 dies. Do they crimp the bullet with the inside of the die body? If so, the adjustable setscrew is for bullet seating depth only, and if I wanted to increase or decrease the crimp I would have to move the die closer or further from the top of my shell holder when in the 'up' position (i.e., push the cartridge itself in less or more). If that is incorrect, please correct.

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    Quote Originally Posted by estern View Post
    One last thing about RCBS 357 dies. Do they crimp the bullet with the inside of the die body? If so, the adjustable setscrew is for bullet seating depth only, and if I wanted to increase or decrease the crimp I would have to move the die closer or further from the top of my shell holder when in the 'up' position (i.e., push the cartridge itself in less or more). If that is incorrect, please correct.
    This is correct.
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    Quote Originally Posted by estern View Post
    Advice is appreciated. I measured the brass for uniformity and found that, although all were under the case length max, the variation was great and the mouths were not even square. Trimmed 60rnds last night to 1.27, or a hundredth less than the published trim length. I tossed anything that was still short, or not trimming clean all the way around.

    As long as I can still crimp in the cannelure, which is .04 wide, I should be fine, no?

    One last thing about RCBS 357 dies. Do they crimp the bullet with the inside of the die body? If so, the adjustable setscrew is for bullet seating depth only, and if I wanted to increase or decrease the crimp I would have to move the die closer or further from the top of my shell holder when in the 'up' position (i.e., push the cartridge itself in less or more). If that is incorrect, please correct.
    Yup.

    Adjust die body to just barely touch an empty case when the RAM is all the way up. Then adjust the seater to get the bullet just into the cannulure groove, then re-adjust the body down for the crimp.

    Don't over-do it.

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