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Importance of Crimp Depth

Discussion in 'Shooting Related Threads' started by Border Bandit, Feb 10, 2012.

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  1. Border Bandit

    Border Bandit Well-Known Member

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    I'd appreciate it if our reloading friends would share their thoughts, and help me understand the importance of CRIMP depth and it's effect upon shell performance. (pressure velocity etc.)

    mike
     
  2. TinMan88

    TinMan88 TS Member

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    Depth of crimp would drive pressure certainly but it could also contribute to uniform ignition. (slow powder or low pressure recipe) Rolling the leading edge of the wad with a deep crimp could be bad news.TM
     
  3. icelander36

    icelander36 Member

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    Google Articles by Tom Armburst. He has articles about the effect of crimps. Shallow looses pressure and too deep raises pressure VERY high. He has a lot of good information on primer comparison also. Lyle
     
  4. wayneo

    wayneo Active Member

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    Mike, the link I'm sending is a great article about primer substitution. Scroll down about half way, Tom has a chart on how crimp depth effects pressures and velocities. The whole article is a must read for shot-shell reloaders.

    Wayne

    Icelander....must have been thinking about this article at the same time
     
  5. icelander36

    icelander36 Member

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    We sure were. I was looking in my saved papers to get that link for him just now. He has a lot of articles about reloading that have kept me out of trouble loading for game shoots. The crimp depth was a real eye opener. Lyle
     
  6. Stl Flyn

    Stl Flyn Well-Known Member

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    Crimp it to the same level as when it was factory.
     
  7. mike campbell

    mike campbell Active Member

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    That data suggests I can probably save some money without sacrificing performance if I take out 1/2 grain of powder and increase my crimp depths to 0.090".
     
  8. Unknown1

    Unknown1 Well-Known Member

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    Crimp depth governs peak chamber pressure.

    The standard for hand reloads is .055". Powder companies generate the published data for their consumer powders and OTC primers and wads using that measurement.

    Manufacturers may use a different crimp depth for factory shells. They tell the powder companies what load they want to push at what speed, what primer specs they'll use and how much capacity the powder has to fill and the powder makers deliver a blend that meets those requirements. Since you don't use the powder they use, don't use the crimp depth either. They are usually shallower than .055" and you WILL lose velocity and pellet energy. I've tested it with both 1 oz and 1 1/8 oz loads in STS hulls with Claydot powder.

    Keller
     
  9. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Too deep also wears out your hulls faster. Too shallow and you'll get an imcomplete pressure burn leaving powder residue. Hard to cheat experience the factories and knowledge some people that know how to reload have.

    Hap
     
  10. icelander36

    icelander36 Member

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    Mike,

    I tried doing that and just blew big holes in my patterns. I finaly stuck with .055 depth and varyied my powder drop within Alliants guidelines to get the best pattern coverage. The pattern board is shooters best friend to let you know what load your gun likes. My guns all have a preferance as to what I load and in what shell, which powder, what wad and even which primer I use. One gun will shoot very good patterns with shell X but not good in shell Y and another gun will not do good with either one of those but another shell and load. The size of the bore and the amount of choke also makes a very big differance when I trade from gun to gun and shell to shell. I can open up or tighten down my size and density of patterns just by changeing shells or componants with out changing chokes. Sounds like hocus pocus but for me it works. Lyle
     
  11. Unknown1

    Unknown1 Well-Known Member

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    <blockquote><I>"That data suggests I can probably save some money without sacrificing performance if I take out 1/2 grain of powder and increase my crimp depths to 0.090"."</i></blockquote>Working out a ballistic combination by-guess and by-golly is a REALLY bad idea!

    Keller
     
  12. dhip

    dhip Active Member

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    Shoot,as long as the shot don't roll out when put into gun I'm happy,,,LOL

    Doug H.
     
  13. BDodd

    BDodd TS Member

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    General rule of thumb is the depth should be the same as the thickness of a dime. More makes more pressure and less makes less pressure. .......breakemall
     
  14. Bird30

    Bird30 TS Member

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    What I have always be told was the thickness of a dime or .050 unless you use a roll crimp, which shooters don't use anymore except with slugs.

    Dave
     
  15. Border Bandit

    Border Bandit Well-Known Member

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    Thanks guys. Tom Armburst's data is an eye opener. I'll share the data that brought me to ask this question.

    Shell #1 Crimp depth 0.048 Pressure: 8470 Velocity: 1201

    Shell #2 Crimp depth 0.042 Pressure: 8720 Velocity: 1214

    Shell #3 Crimp depth 0.046 Pressure: 9400 Velocity: 1232

    Shell #4 Crimp depth 0.034 Pressure: 8890 Velocity: 1216

    Shell #5 Crimp depth 0.044 Pressure: 10050 Velocity: 1261

    Shell #6 Crimp depth 0.037 Pressure: 9030 Velocity: 1228

    Shell #7 Crimp depth 0.032 Pressure: 7680 Velocity: 1197

    These shells were loaded on a fairly new, well cared for P/W 800+ with motor drive. Once fired, cleaned and inspected Rem Nitro Gold, selected by loaded weight, mid-run from a single run of 250. Rem STS primers, 19.2gr Am. Select, & Spolar Gold Windjammers. Needless to say, the variances are astonishing.
     
  16. BD457

    BD457 Member

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    WOW! Am I glad I read this post. I just loaded up a bunch of 1 1/8 with 19 grains GD in STS hulls, Win 209, and WT12's. I took 'em out last night and they "felt" pretty hot. I was a bit concerned when I loaded 'em that the crimp was deep but didn't worry about it too much. NOW...... I'm worried and might even unload 'em. They measure about .090" using a depth caliper from the top edge down to to the top of the petals. I looked at the primers after shooting the rounds and all looked pretty good.

    I was also a little concerned when I loaded them that the shot was able to rattle around in the crimped shell, but it's a published load.
     
  17. balance365

    balance365 TS Member

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    Looking at the data, say what you want about variance, but I am not seeing a correlation between crimp and pressure. The .044 depth spike some high pressure, but the .048 depth is down to almost the same pressure as the .032 depth. You have some other variables going on there that you need to understand before you can start talking about crimp depth effect.
     
  18. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    I agree with balance365, check your powder drops? Other than wearing out the hull pre-maturely, I don't think it matters a whole lot either?

    Hap
     
  19. Border Bandit

    Border Bandit Well-Known Member

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    Hap, you and balance, sent me searching for more reasons. The factory "O" ring under the powder bushing in my 800+ WAS a flat/squared off one that had a "hump" where it was catching on the powder bushing as it passed. Perhaps, tripping over that was causing erratic drops, although I could never see any variances when I checked, mid run and at start & end, usually a flat at a time.
     
  20. Stl Flyn

    Stl Flyn Well-Known Member

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    There are so many variances in loading, that worring about the crimps really just adds more doubt, in which would affect your shooting. I know it is winter and all. We need things to talk about. All reloaded shells vary in some form or another, especially in velocity. If you are loading shells that have data with pressures up to 10800 psi. change your load. Anything under that just shoot! You will never get a consistent crimp depth anyway, especially talking 100ths of an inch. Now you are measuring crimp depth. Yikes! If it makes you shoot better than by all means do it. It is all psychological. Jon
     
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