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Thread: Ammunition Performance

  1. #1
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    Question Ammunition Performance

    Has anyone done a performance comparison on ammunition loaded with a crimped bullet a non crimped bullet. The bullet either having a crimping cannelure or no crimping cannelure.
    All other parameters being the same.
    Would be interested in their findings.

    Al
    AlBur
    Always Remember "Utopia Does NOT Exist"

  2. #2
    Randy Bohannon's Avatar
    Randy Bohannon is offline “Junes1 is a whining bellend”
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    In the 308 and 30-06 with a Lee factory crimp die ( No cannelure needed in theory ) I found that a light crimp, or barely any pressure on the downstroke of my Rockchucker, reduced ES and tightened up groups on 125 grain bullet loads but didn't make much difference on the heavier bullets ( 150 and 165).

    My theory is that the 125 grain bullets with their short shank benefited from a an increase in neck tension allowing the the ball powder( BL-C(2) ) to ignite more evenly before the bullet leaves the case mouth. I was using magnum primers in these loads and I think the crimp helped prevent them blowing the bullet out of the case before the powder had ignited fully. Too heavy a crimp reduced accuracy though the improvement in ES of the velocity remained the same, the theory here being that the bullets were being deformed excessively by the die and perhaps losing concentricity in the process.

    Thinking about it a bit more I then tried a light crimp on some long-seated 155gr Sierra Matchking loads which because of the boat-tail also end up with not much shank in the case neck and found similar results though less pronounced results. Achieving consistency in the crimp with the lee dies was difficult and this was reflected in the ES measured. I would get five rounds within 10 fps ( or the limit of accuracy of the chronograph) and then a round out by 50 fps or more in circumstances where the uncrimped rounds had an ES of consistent 30 fps over something like 50 rounds. The powder used for these loads was RL15

    The heavier bullets had long parallel shanks and crimping groves didn't seem to respond measurably to crimping, there were some slightly improvements to ES and grouping but I didn't fire enough rounds to come up with any meaningful statistics.

    In the 06 with it's long neck and firing almost exclusively long hunting bullets of 180 grains and up almost no difference was seen at hunting distances, excpet that too heavy a crimp again ruined accuracy. Part of this is that I have a few stable loads with RL17 that produce single figure to low twenties ES variations anyway.

    In that rifle I lightly crimp bullets if there is a groove, mainly out of superstition of having the bullets pushed into the case by the battering of repeated recoil in the magazine. The only time I have had bullet setback was with cheap eastern European factory ammo ( MFS if anyone has heard of it ) after empyting a magazine of all but the last round twice on a drive. The bottom bullet was noticeable shorter but fired just fine and went more or less where the rest had gone when I noticed and chambered it.

    In short, it depends very much on the specifics of the load. If you have a load you are trying to tune for lower ES via consistent neck tension, it can be worth a try.
    "An infinite number of monkeys banging away at type writers for an infinite period of time will eventually reproduce Hamlet" Thanks to discussion forums we now know this to be untrue.

  3. #3
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    Randy's above is a good piece of work resulting from proper detached study.

    I would add that IMO consistent taper crimping requires highly consistent trim lengths on cases, as a few thou longer or shorter will materially influence the effect on retention. In my target shooting days, I didn't think the advantage worth the additional effort - it may have paid off if I'd done more at 1000 yards or over.

    Regards,
    MikB
    ...history... is, indeed, little more than the register of the crimes, follies, and misfortunes of mankind. (Edward Gibbon: Decline and Fall of the Roman Empire)

  4. #4
    Randy Bohannon's Avatar
    Randy Bohannon is offline “Junes1 is a whining bellend”
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    Quote Originally Posted by MikB View Post
    Randy's above is a good piece of work resulting from proper detached study.

    I would add that IMO consistent taper crimping requires highly consistent trim lengths on cases, as a few thou longer or shorter will materially influence the effect on retention. In my target shooting days, I didn't think the advantage worth the additional effort - it may have paid off if I'd done more at 1000 yards or over.

    Regards,
    MikB

    In my experiments I found that uniformity in trim length was an important factor in chasing down not just extreme spreads in velocity but also the Standard deviation of the velocities of those shots to the mean. I should qualify this by saying that this experiment was only performed with one load in one rifle but enough shots were fired to get significant data.

    This makes sense as the neck is the bit doing the gripping of the bullet in the first place but it did surprise me how much difference a few thou in neck length ( all being below the SAAMI maximum case length of course) made to consistency. I make this point as many shooters tend to trim cases back to some max- x thou length after fire-forming and then shoot those same cases until one or more goes over length ( perhaps 3-5 reloading) before trimming again. My experiments that the most consistent approach, bearing in mind small differences in individual cases will cause them to expand at slightly different rates, is to trim after each firing for the most accurate ammo ( This is not a hunter's dilemma) whether the individual case appears to need or not. Batch consistency is the key after all.

    Looking around it may be seen that the most accurate shooters of the most accurate rifles in the most accurate chamberings do not crimp but rather rely on careful prep of the best, most consistent cases and vary neck tension by controlling the degree of neck sizing they perform.

    This is a world of bushing and even custom dies and so is beyond the scope of most casual shooters, myself included.

    I find the Lee neck die to produce excellent, concentric ammo. I was on the firing line at Shorts one day with a friend who has lots of very nice rifles and reloading kit. He was lecturing someone or other on the importance of concentricity to accurate ammo and thereby extolling the virtues of his Wilson die and Harrel press system. He picked up some of his amazingly shiney 6.5x55 rounds, loaded with Berger match bullets so far out there couldn't have been much shank in the neck, and put them on his concentricity gauge ( he's the sort of guy who would bring one to the range...) and measured about 2thou run-out at the the ogive. He then grabbed a round at random from my MTM box ( 30.06 Barnes 168gr TSX hunting ammo ) to be used as the inferior example. Unfortunately for him the run-out on this Lee collet neck sized round was barely registered by the dial indicator on the gauge...

    He picked up another round and got the same result, flustered now he started to measure every round until he found one that had more run out than his 6.5x55 round.

    Now the cases for all my ammo are prepped to the same standard ( It gives me something to do when I'm at a loose end in my flat in the middle of London) and the barnes bullets are usually more dimensionally accurate than drawn bullets but the concentricity was a function of the Lee die. I'm not claiming my Tikka sporter 30.06 outshot his custom barrelled Keppler 300mt target rifle because of this, rather that in terms of ammunition and nothing else, my Lee kit was producing better ammo than his expensive Wilson stuff. He called me a few days later to tell me he'd bought a Lee collet die after reading about some bloke setting a world record using one.

    The reason for the long winded story is that if consistency of ignition can be found by means other than a crimp, you can leave the bullet/neck junction alone and potentially not mess up with the excellent results the collet dies give.
    "An infinite number of monkeys banging away at type writers for an infinite period of time will eventually reproduce Hamlet" Thanks to discussion forums we now know this to be untrue.

  5. #5
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    To crimp or not to crimp...that is the question

    I full length size, then use a Lyman M neck sizing die for 30/30 and 7.5 Swiss, loading cast. I have found that if I get the M die set "just right" I do not need to crimp at all. depends on the bullet of course. The Loverin type bullets do not normally have an actual crimp groove. The 44/40 bullet, has a crimp groove and def needs a crimp...I prefer the factory crimp. Consistent trim length, already mentioned is also a very relevant factor. The various (USA) reloading manuals I have, recommend no crimp at all. It is interesting to see that the crimp/case length can produce velocity variations and I am not sure if any detailed analysis has been carried out on this, particularly with cast bullets. We all take pains to get consistency with bullet weight/powder weight but possibly neglect a very important factor in obtaining consistent shots. A USA examination of the Swiss GP11 military round found almost clinical consistency in every aspect of the cartridge and the GP11 cartridge is noted for its extreme accuracy. Unusually for a miiltary round the GP11 has a heavy crimp groove in the FMJ bullet, + a wax coating! Must be something in this.

    Mike95

  6. #6
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    Quote Originally Posted by Randy Bohannon View Post

    ....I'm not claiming my Tikka sporter 30.06 outshot his custom barrelled Keppler 300mt target rifle because of this, rather that in terms of ammunition and nothing else, my Lee kit was producing better ammo than his expensive Wilson stuff. He called me a few days later to tell me he'd bought a Lee collet die after reading about some bloke setting a world record using one.

    The reason for the long winded story is that if consistency of ignition can be found by means other than a crimp, you can leave the bullet/neck junction alone and potentially not mess up with the excellent results the collet dies give.
    No disagreement here. If properly set up, almost any decent die/press combination has a potential for consistency equal to almost any other. If the user throws away advantage by (as in your example) insufficient bearing surface seating in the caseneck, no precision or expense of tooling will regain it.

    If you buy a gold-and-diamond chess set, that won't make you a Grand Master.

    Regards,
    MikB
    ...history... is, indeed, little more than the register of the crimes, follies, and misfortunes of mankind. (Edward Gibbon: Decline and Fall of the Roman Empire)

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