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Thread: Case headstamp and seating depth

  1. #11
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    While Hawkmoon's description of my reloading methods makes me sound like a bench rest shooter, I'm not really that anal. In reality. . .

    My brass gets sorted by headstamp only because an undersized resizing die is used on thin-walled brass. This done to maximize the grip of those cases on the bullet and minimize the amount of bullet setback suffered when those rounds are chambered. Got a lot of thin-walled brass. Some folks can be real persnickity about their COAL's just after reloading, but the only COAL that really makes much difference is the one when the round is chambered and the hammer is falling.

    And if you think COAL (and seating depth for the same bullet) stay the same between the time a round comes off your press and the time it's fired, re-measure the COAL of a top round in a full magazine after it's slingshotted into the chamber (but not fired). You may be surprised.

    Only bullets weighed are those I cast because I'm a really bad caster. The SAAMI spec for 45 Auto bullet weight is 1.5% and even my nice looking ones can exceed that by a fair amount.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Last edited by niemi24s; 7th April 2022 at 06:27.


  2. #12
    Join Date
    22nd December 2019
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    Consistent bullet seating depth used to drive me nuts, when I attempted to maintain an exact dimension. I did realize after awhile it probably doesn't make much difference for my type of shooting. The other dimension I would toil over was case length. Having read that the 45acp headspaces off of the case mouth I began to sort by case length to optimize my load. Talk about a cat chasing its tail. I got over that one too.

  3. #13
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    As an NRA Bullseye shooter, probably the most important feature of ammunition is its ability to feed reliably. Nothing worse than an FTRB in a Rapid Fire string (5 shots in 10 seconds). And after only 60 years of that silly game I'm convinced 99% of the reason for low scores is the shooter - not the ammunition being shot or the gun it's being shot in.

    Extra time spent agonizing over nitnoy stuff while reloading is better spent at the range making noise.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Likes (2) :
    BrettID (8th April 2022), Murray (7th April 2022)


  4. #14
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    It took a while, but I finally got around to measuring a few boxes. Since it was a bit of a slog, I'll share my results so others may benefit. When it came to the stats, I got lazy and used calculator.net. The links below give you the full details including each individual measurement. For example 2640 = 1.2640" COAL. I used my Neiko digital caliper (cheapo online, but seems okay to me). It looks like it reads out to +-0.0005", which is probably more accurate than me. I would guess the HP rounds are harder to get a good measurement on given how uneven the tops are, and I only had 6 left of one brand. The two things that surprised me most are that the cheap brand A was surprisingly consistent, while my own reloads, despite taking the advice here and letting go of my measure/fiddle seating depth habit, were very consistent. Granted, for every round I loaded, the manufacturer probably popped out 10,000.


    In summary, I should lighten up:


    Brand A FMJ (50 rds) - Avg COAL = 1.2585", SD(Standard Deviation) = 0.0038", Range 1.2505" - 1.2645"
    Brand R FMJ (50 rds) - Avg COAL = 1.2616", SD = 0.0045", Range = 1.2485" - 1.2685"
    GDHP (only 6 rds) - Avg COAL = 1.2073", 1.2065"-1.2080" (not much data for stats)
    GS HP (20 rds) - Avg COAL = 1.2078", SD = 0.0053", Range = 1.1985" - 1.2170"
    My reloads "Murcor" (50 rds) - Avg COAL = 1.2120", SD = 0.0014", Range = 1.2090" - 1.2155"


    Refresher on Standard Deviation: for the first example above, Avg COAL 1.2585" with SD 0.0038" means about 2/3 of the rounds are +-0.0038" of the average, or 1.2547"-1.2623". The wonks will point out that I haven't established how "normal" my distributions are, but I can't even say I play a mathemetician on TV.




    Brand A FMJ:
    https://www.calculator.net/statistic...22#inputfields


    Brand R FMJ:
    https://www.calculator.net/statistic...15#inputfields


    GDHP:
    https://www.calculator.net/statistic...19#inputfields


    GS HP:
    https://www.calculator.net/statistic...21#inputfields


    Murcor FMJ:
    https://www.calculator.net/statistic...21#inputfields

  5. #15
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    OK, so far you've gathered a lot of COAL data on ammunition as it's sitting the box. But that's only half the story because you don't shoot it while it's in the box. You shoot it after it's chambered in your gun.

    The other half of the story is how much the COAL of a round is reduced during the chambering process. Try this with any CCI ammunition if you have any:

    • Measure the COAL of a round,
    • Load that round as the top round in your highest capacity magazine,
    • Slingshot that round into the chamber,
    • Eject that round and
    • Re-measure its COAL.

    The difference between the two (before & after) COALs of that round is ___________
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  6. #16
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    Quote Originally Posted by niemi24s View Post
    OK, so far you've gathered a lot of COAL data on ammunition as it's sitting the box. But that's only half the story because you don't shoot it while it's in the box. You shoot it after it's chambered in your gun.

    The other half of the story is how much the COAL of a round is reduced during the chambering process.
    Immaterial in this case. Re-read the opening post. Murray asked if his loading technique was faulty because of the variance in COAL of his reloads. I suggested comparing the consistency of his reloads against the consistency of factory ammunition. Basically, his standard deviation is less than half that of factory ammunition, so I'd say there's nothing wrong with his technique.
    Hawkmoon
    On a good day, can hit the broad side of a barn ... from the inside

  7. #17
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    I'll still give it some consideration to take a few measurements. It's a chrono day anyway, which was super fun the first time I did it before quickly turning into a chore. I've been curious about that change after seeing niemi24s mention it in other comments. My mileage may vary by level of enthusiasm once I get there.

  8. #18
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    I managed to get in some quality chrono and caliper time yesterday. Eyeballing the results I probably have some minor errors like managing to get the cartridges out of order or sloppy measuring unless some managed to grow 0.001-0.002 in transit. I suppose that's why we use stats to filter out some of that noise, and if I were to take an honest stab at accounting for factors beyond my skill level, maybe the lower air temperature shrank the metal in the calipers slightly to give me slightly higher readings. Here's a summary of what I did for our mutual entertainment. To keep things somewhat on topic, I did this on my reloads. It's not exactly what you see above to keep me sane and in the good graces of my range neighbors.

    The gun: RIA 5" GI as seen on this forum
    The magazine: Factory (MetalForm?) 8 round, recently cleaned but probably a little aged by now
    The sample: rounds 1-24 of "Murcor FMJ" (3 full mags)
    The method: load 8 rounds in reverse order, slingshot round #1, eject/slingshot the next round, measure, repeat.
    bonus on mag #3: I went for a second chambering on this mag to see what would happen

    consideration: round #1 consistently failed to slingshot into battery, requiring a second attempt every time. On the last mag, I managed to get the round so short it would probably have been unwise to fire it even if it successfully chambered to fire on its 3rd trip through (2.1430"). Its nose was pretty badly deformed at that point as well.

    Here's a glamour shot of the setup showing that round next to an unchambered one:

    chambering_experiment_glamour_shot.jpg

    a closeup with the mag underneath to level them out

    chambering_experiment_closeup_side.jpg

    and a top view showing the battering in the reflection and how overseated the bullet is
    chambering_experiment_closeup_top.jpg

    All that being said, I did find some measurable shortening. Assuming correct ordering this is the original set of measurements:

    Statistics Calculator
    Avg: 1.2584", SD: +-0.0038"

    After chambering once:
    Statistics Calculator
    Avg: 1.2128", SD: +-0.0026"

    Oddly enough, after chambering is closer to the whole box number. I suspect something went wrong here, and I should have done the whole exercise at the range.

    Mag #3 after 1st chambering:
    Statistics Calculator
    Avg: 1.2110", SD: n/a in my opinion, not many rounds

    Mag #3 after a 2nd chambering:
    Statistics Calculator
    Avg: 1.2066", SD: n/a in my opinion, not many rounds

    These two are nice because I know they're comparable and in the same order despite the small population and some of them inexplicably growing between measurements.

    In conclusion, my measuring skills need some practice, but hopefully everyone gets a chuckle out it and can see from mag #3, round #1 that repeatedly chambering a round is so bad you can plainly see it. I'll leave out the chrono results since this is getting too long, but let me know if you'd like to see them in a future post here.

  9. #19
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    Subtraction of your first two averages seems to indicate the bullet setback suffered by these 24 rounds was in the neighborhood of 0.045" to 0.046". And wading through your sea of statistics leads me to believe the setback of individual rounds ranged from 0.0205" to 0.0515". If any of that is correct, I would call this amount of bullet setback excessive and recommend you examine your reloading procedures to find a cure for the poor grip your cases have on their bullets. These large amounts of setback do much to explain why those top rounds in your full magazines would not slingshot successfully into the chamber.

    Search this forum for the phrases bullet setback and case grip on the bullet​ for more information.
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]
    Last edited by niemi24s; 26th April 2022 at 21:00.


  10. #20
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    Thank you, I'll do that. I may be over-flaring the cases and pretty sure I'm not crimping at all, though I was hoping to get away without that part.

    To complete the exercise, I see the extra seating ended up affecting velocity a little while remaining in a safe looking range to me:

    Mag 1 + 2 (twice chambered) 15 out of 16 chrono'd, avg ~763 fps
    Mag 3 (thrice chambered): 7 out of 8 chrono'd (less the badly damaged round) avg ~761 fps, skewed by 721 fps on the first round. Ignoring that, I only get 766 fps
    remainder of box (once chambered): 20 out of 26 chrono'd, avg ~750 fps, slightly skewed by the last two rounds way down at ~700 fps

    I suppose if these magnitudes seem a little low, I might not have a good seal and be sending too much hot gas right around the bullet. Impressive looking at night, I'm sure, but not my intention.

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