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Relaoding - theory

Discussion in 'Shooting Related Threads' started by Wolfman, Sep 6, 2010.

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  1. Wolfman

    Wolfman Member

    Jan 29, 1998
    Ok - so we know that the deeper the crimp, the higher the pressure generated by the charge (all other factors held constant). Now the questions is:

    Does this improve powder burn and more complete combustion resulting in a cleaner barrel?
    Does it increase/reduce/no change in recoil?
    Does this change the speed of the shot column or possible the pattern tightness?

    Does it make any difference other than the pressure?

    Inquiring minds would like to know.
  2. goatskin

    goatskin TS Member

    Jun 24, 2009
    Doggai is right.

    Playing with increasing pressures WILL have consequences, many/most of them unintended.

    With a whole series of 'depending', 'possibly', 'if then', ... the MOST predictable result you <i>MAY</i>have (cleaner burn) is somewhat trivial.

  3. Quack Shot

    Quack Shot Active Member

    Mar 14, 2006
    My answer is basically to crimp your shells to established standards and don't play with it. I seriously doubt there would be any benefit to patterns or cleanliness by increasing the crimp depth. The only thing you may get is a little increase in velocity and more pressure than you intended to create. As long as you have enough of a crimp to make the load "work", any additional crimp depth might be a hazard.

    There was some information put forth by Tom Armbrust at one time regarding crimp depth. I also believe I had read something from Neil Winston in the past. If there was anything in the way of a distinct advantage in adjusting crimp depth, I believe I would have been doing so already. I did an informal test regardinng crimp depth and velocity/consistency myself, which was inconclusive. I would have had to fire a ton of shells in several guns/barrels to even get the basics. Not having pressure testing equipment would also limit the value of the testing I did. I saw a very slight increase in velocity relative to an increase in crimp depth, but it was not consistent enough, nor did I use a very wide range of crimp depths. There was a very slight difference in SDs between the groups of crimp depths, but it was not enough of a sample to be valid.

    I will be quite happy in crimping my shells to look as good as factory and at an established depth. I use a depth of .040" - .050" as a target. In reality, they may vary a bit more than that, but the average would be somewhere in that range. Some data sources have stated as much as .060" and as deep as .090". If my average is .045", I doubt I'm losing anything or missing out on a cleaner burn, better patterns, better consistency, etc. I also don't worry about increasing pressures, since the loads I use start out at a low enough pressure to allow some headroom for these kinds of variables.
  4. grntitan

    grntitan Well-Known Member

    Mar 25, 2009
    IL(The gun friendly Southern Part)
    I've noticed if you get too carried away with deeper crimps especially on todays thinner walled hulls that you end up crushing the shell before obtaining a crimp of much deeper than normal dept. The old cardboard wads that would require proper seating pressure would've been much easier to experiment on crimp dept. With the more modern wads i think your somewhat limited on what dept you can obtain period. IMHO---Matt
  5. dverna

    dverna Active Member

    Jan 29, 1998
    I doubt there is any practical affect on load performance.

    I shot a 99 with my "reject" shells. Domed crimps, dished crimps, split crimps, crimps with folds, buckled crimps, buckled hulls.

    I had to force some into the chamber.

    Don Verna
  6. School Teacher

    School Teacher Well-Known Member

    Jan 29, 1998
    Louisville, KY
    If you are reloading for "games" with slower burning powders like Alliant Herco or Blue Dot and pushing 1 1/4 plus oz. of shot, my understanding is that you need a firm crimp to ensure a complete burn. That said, pushed out crimps would not be the best crimps.

    I don't mind crimps that are consistently slightly dished in with a light ot standard load but I would not care to experiment with deep crimps on near maximum loads.

    Find a load that works for you and stay with it. Experimenting only plays with your mind when you call for the bird.

    Ed Ward
  7. JACK

    JACK Well-Known Member Supporting Vendor

    Apr 28, 2006
    NW Wisconsin
    These "too deep"?


    This is the "factory setting" from MEC. Did not adjust a thing.
  8. phirel

    phirel TS Member

    Jan 29, 1998
    Wolfman did ask some interesting theoretical questions. Pressure does increase the burning rate of powder, and conversely, the burning rate does increase pressure. This has been clearly demonstrated by most, probably all of us when we have a slightly cocked wad. The very low pressure resulting from this results in a lot of powder debris in the barrel.

    The specific question posed, would increasing the pressure by increasing the crimp depth result in a more complete burning of the powder requires an answer with consideration to several aspects. To me, the pressure curves infer that with a powder well matched to a specific load, slightly increasing the pressure with a tighter crimp, would raise the pressure but not result in a more complete powder burn. The powder would simply burn faster.

    However, in a reload using components not well matched to the load (slow powder in a light load, tapered wad in a straight walled hull, etc.) the slight pressure increase from a tight crimp could increase the total amount of powder burned. These poorly matched reloads may not achieve the pressure threshold required for maximum combustion of the powder. The additional resistance produced by a tight crimp could move the pressure toward this threshold.

    In a practical sense, striving to make a load with poorly matched components better by increasing the crimp depth is foolish. The solution is to use loads with components that are designed for the load. It is important to realize that reloading manuals list safe loads. These safe loads may, or may not be the best loads.

    Wolfman did make a fundamental error in another part of his question. He assumed that complete combustion of the powder would result in a cleaner barrel. Some powders completely burn and leave a residue in the barrel. This residue is not unburned powder, it is what is left after the powder burns. Powder is made in part from ground up wood. When wood burns, it leaves ashes. A powder that burns and leaves very small, difficult to see, particles of residue in the barrel are thought to be clean burning powders. Powders that leave easily seen particles of residue and considered dirty powders. However, the total residue left in the barrel from these two types of powders may be the same. We assume that if we cant see it, it is not there. Of course, we are not surprised when we push a white rag down a clean looking barrel, it comes out black.

    Pat Ireland
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