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Thread: Duplex loads and slugs...

  1. #1
    Boolit Master Cap'n Morgan's Avatar
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    Duplex loads and slugs...

    I never had any real succes with the slower powders like Herco and Blue Dot in my slug loads. The velocity was always erratic and so was the groups. The faster powders like Unique and Red Dot gave much more constant, albeit slower velocity and grouped much better.

    Spurred by BT's Fury slug test, I loaded up a couple of primed 3" shells with my 570 grains Brenneke clone on top of 40 grains Steel, a x12x seal, a 1/2" felt wad and finished with a roll crimp.
    Fired over the chrono they gave an average velocity of 1420 fps with about 30 fps variation. This looked promising!

    I then tried a slightly reduced load (38 grains Steel) in once-fired 2-3/4" shells. I didn't use a chrono but decided to try for a group right away. The first two shots felt alright, but the third had a telltale double report, indicating a hangfire/blooper. I decided to stop right there as I already have one shotgun barrel with a sack near the muzzle due to a blooper.

    Thinking that maybe a bad crimp, combined with the thin skivred edge of the shells was responsible for the erratic velocity, I tried the same load in a shortened (2-1/2")shell with only the x12x seal under the slug and a nice, solid crimp. The first shot read 1200 fps the next 1350. Obviously something was not right here...

    I began suspecting that the primers (CCI 209) was not up to the job. The 3" shells had worked flawlessly but they were from a batch of primed new shells someone once gave me and I have no Idea of the primer used, and since I haven't been able to find any 209 magnum primers over here, I decided to try a duplex load instead.

    Now, duplex loads are something most'internet experts' warn against, but I had used them with good results in 577/450 Martini Henry loads back when I was young, immortal and didn't know any better So, throwing caution to the wind, I tried the same setup as before, but this time with only 25 grains of Steel over 5 grains of Red Dot for a combined powder weight of 30 grains. Lo and behold, this time the average velocity was 1290 fps with a spread of only 24 fps for 4 rounds!

    It seems as if I have been wasting a lot of unburnt powder in the quest for speed. Next step will be to load a batch and see how well they shoot. All my best groups have been made with fast burning powder and have all been subsonic when leaving the muzzle. It shall be interesting to see if the slug still will produce decent groups with the speed in the 1300-1400 fps range. I'll probably end up with a sore shoulder, but science often demands sacrifices
    Cap'n Morgan

  2. #2
    Boolit Grand Master

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    What would be interesting here is someone like megasupermagnum with pressure testing equipment would run some pressure tests on that load.

    Shotshell reloading being what it is, and having blown one gun up, I am reluctant to stray far from published data or at least "known safe" data. As you are probably aware, just a change of primer can affect load pressure by up to 3000 PSI which is a rather high percentage on a load of around 10,000 PSI. Also, short hulls without cushion leg wads seem to run higher pressure for same charge as a longer hull with a cushion leg wad. From my "research" of browsing load data from different sources this seems to be most noticeable with faster powders and likely due to reduced volume at ignition ~ that is no give to the wad column.

    Slower powders seem to be more forgiving that way. Steel is on the slow end of the burn rate and has been reported to like high payload weights and dense charges. turbo1889 posted quite a bit about Steel and made similar comments to yous in that you don't want to download with it. If your duplex charge solves that it should also be applicable to Blue Dot and other slow powders. Of course duplex loading is a very controversial subject except for small smokeless charges under BP in cartridge guns which seems to be an acceptable practice.

    It would be interesting to find out if a light charge of fast powder like Red Dot under a slow powder would be safe and acceptable practice. Many have commented about erratic performance of Blue Dot at low temperature so similar situation of poor ignition and/or incomplete burn. I've had erratic performance of Blue Dot under 1 oz. slugs with powder charges somewhat lighter than the recipe called for. BD likes a heavy payload and dense loading.

    I am guessing you didn't experience any pressure signs such as sticky extraction? It doesn't seem to take a lot to change pressure considerably with shotshell reloading.

    I'll be watching for further developments here.

    Longbow

  3. #3
    Boolit Man
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    Interesting! Please keep us informed .

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    Boolit Master Cap'n Morgan's Avatar
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    And so it begins...

    Did a small test yesterday to see how the duplex loads would shoot. I made the mistake of not bringing the chrono with me so I couldn't verify the velocity against the target hits.
    The distance was a tad over fifty yards, and the five shot group was slightly under five inches vertically but only two inches horizontally as you can see in the first pic.




    I have never noticed that much stringing in my slug groups before, but all five shots felt good when the trigger broke, and the target doesn't lie..

    Today I tried five more slugs. The components were the same, only this time the propotions were 7/20 Red Dot/Steel instead of 5/25, and this time I brought the chrono with me!
    The group was pretty much like the previous, only more stringed vertically. The horizontal spread was less than two inches.

    When comparing the target with the velocity of each slug, an interesting thing shows up:

    Shot 1: 1258 fps
    Shot 2: 1243 fps
    Shot 3: 1246 fps
    Shot 4: 1263 fps
    Shot 5: 1221 fps
    (Average velocity 1246 fps)

    The two fastest shots (1+4) both struck below center.
    The two "average" shots (2+3) struck center
    The "slow" shot (5) stuck above center.

    Of course, this is by no means solid proof, but it seems as muzzle-lift is stringing the groups considerable, even if the max difference in velocity is only 42 fps!
    In the first group I held the forend in a firm grip, while the second group was shot with only a light grip on the forend. The gun is an o/u with a 30" barrel. Perhaps a 20"
    barrel would do better as the slug would have left the barrel little earlier = less muzzle jump.

    I will do another test, perhaps with Blue Dot instead of steel (and a bear grip on that forend!) to see if it changes anything. Ten shots within two inches horizontally is not a fluke. The Brenneke clone clearly has potential at higher speeds.


    BTW: Those three tiny holes in center of the second pic are from my Sako 6mm PPC at 300 meters. No problems with that one

    Cap'n Morgan

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    Boolit Master
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    This is great timing, as after seeing what Bloodtrail did, I think I'll break out the STEEL powder. I have not used that powder in a few years, and I have never loaded anything except steel shot with it. I have not noticed any problems with Bluedot though, it is likely the most forgiving magnum powder in existence. I will do some testing, although with the full bore round ball, which lucky weighs around 580 grains. My normal loads use a Federal 209A primer, which I use in nearly everything. Charges with bluedot are usually 30-38 grains, and I have not noticed any problems at those levels. I do have the CCI 209, so I'll give that a try. If you can get your hands on Win 209, CCI 209M, or Fed 209a, I would use those.

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    Boolit Master

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    Turbo1889 discovered that an equal charge of Steel for a recipe instead of Blue Dot would give greater velocity with less pressure. (his graph is somewhere in the old posts). I used that idea sucessfully in a number of loads.
    "My main ambition in life is to be on the devil's most wanted list."
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    Boolit Master
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    Quote Originally Posted by Hogtamer View Post
    Turbo1889 discovered that an equal charge of Steel for a recipe instead of Blue Dot would give greater velocity with less pressure. (his graph is somewhere in the old posts). I used that idea sucessfully in a number of loads.
    Hal, do you mean equal volume, or equal weight?
    "We take a thousand moments for granted thinking there will be a thousand more to come. Each day, each breath, each beat of your heart is a gift. Live with love & joy, tomorrow is not promised to anyone......"

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    Equal weight. Steel is bulkier than blue dot and takes up slightly more room in the hull. Actually I didn't finish the thought. Since lower pressure is available using Steel you can use more Steel and really ramp up velocity. I know this from pressure testing through Tom Armbrust.
    "My main ambition in life is to be on the devil's most wanted list."
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  9. #9
    Boolit Master
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    Quote Originally Posted by Hogtamer View Post
    Equal weight. Steel is bulkier than blue dot and takes up slightly more room in the hull. Actually I didn't finish the thought. Since lower pressure is available using Steel you can use more Steel and really ramp up velocity. I know this from pressure testing through Tom Armbrust.
    For the really heavy slugs this may not be a good thing. 1100 fps with a 1 3/4 ounce slug is bad, 1200 fps is brutal. If you could get 1300 fps with STEEL, you would be hurting bad.

    I'll pressure test some to see how they like different primers. I also have 100 Federal 300 grain trophy copper sabot slugs I can load. That might be fun to try with STEEL. I know I can get 1900 fps with bluedot with those. I wonder if STEEL couldn't break 2100-2200 fps.

  10. #10
    Boolit Master bikerbeans's Avatar
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    My experience with duplex loads in shotshell is limited to loading starting shells for a couple of my friends antique English tractors. I found it necessary to put a barrier (tissue paper) between the priming charge and the main charge. If you don't separate the charges they will mix together.

    My friend gave me one of the original paper starting shells (Eley, IIRC) to open up and I found the priming charge had been compressed into a disk to prevent migration.

    BB

  11. #11
    Boolit Grand Master

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    BB out of curiosity was that priming charge black powder?

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    Quote Originally Posted by megasupermagnum View Post
    For the really heavy slugs this may not be a good thing. 1100 fps with a 1 3/4 ounce slug is bad, 1200 fps is brutal. If you could get 1300 fps with STEEL, you would be hurting bad.

    I'll pressure test some to see how they like different primers. I also have 100 Federal 300 grain trophy copper sabot slugs I can load. That might be fun to try with STEEL. I know I can get 1900 fps with bluedot with those. I wonder if STEEL couldn't break 2100-2200 fps.
    I can't wait to see these findings.

  13. #13
    Boolit Master bikerbeans's Avatar
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    Quote Originally Posted by longbow View Post
    BB out of curiosity was that priming charge black powder?
    Kent,

    Both the priming and main charge were smokeless. This finding based upon a torch test. It makes sense to me because I don't think the combustion products from holy black would be good for the internals of the engine.

    BB

  14. #14
    Boolit Grand Master

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    Okay. Thanks BB. Like I said, just curious.

    BP is used to light off a few other things because it ignites easily and burns consistently. I wouldn't expect the small amount of BP that might be used for the priming charge to be enough to harm an engine if it were used especially since the fuel burning would follow. Whether Diesel or gasoline the combustion process should clean out any BP residue. Not disputing what you are saying at all, just my thought process. For starting an engine I'd guess you'd want a slow powder with long burn and lots of expanding gas so it might be hard to light. A priming/booster charge makes sense.

    So a quick internet search turned up about an equal number of comments about some starter cartridges being BP and some slow cordite. If slow cordite a fast burning priming charge makes sense. Also apparently some shotgun shell starter systems did not act directly on an engine piston but on an external piston which operated a mechanism to turn over the engine. The only engines I have heard of using shotgun shells are tractor and airplane engines but I'm sure there are others. The learning never stops!

    Back to the subject at hand... Cap'n Morgan has opened up a can of worms here! Bullseye, Red Dot or similar burn rate powders used at 3 to maybe 5 gr. igniter charges may have their place in some higher velocity/slow powder charges under slugs (thinking 12 ga. here). Could be useful under heavy slugs at moderate to high velocity with really slow powder. Ed Hubel said his loads using large charges of relatively slow powders to obtain long acceleration and high velocity didn't recoil badly.

    Hard to develop without pressure testing equipment though. It seems to me Lyman had an article about shotgun powder charges, ignition, etc. and demonstrated that by changing things slightly velocity did not change significantly but pressure went way up. The point was that a chronograph doesn't tell the whole tale.Tom Armbrust also warns that just a primer change can affect pressure by 3000 PSI.

    I'll wait for msm to do some pressure testing before venturing into this I think.

    Longbow

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    Capt: I have to ask,,, are you a native of Denmark, or are you an American Transplant? You sure talk like us. Maybe you did some time in the US?

    Please explain your heritage and affiliation with the english language. I need to know this for future reference.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

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    Boolit Master Cap'n Morgan's Avatar
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    Quote Originally Posted by W.R.Buchanan View Post
    Capt: I have to ask,,, are you a native of Denmark, or are you an American Transplant? You sure talk like us. Maybe you did some time in the US?

    Please explain your heritage and affiliation with the english language. I need to know this for future reference.

    Randy

    Randy

    I'm as Danish as they come, and have, sorry to say, never visited your great country. I have ,however, read an awful lot of gun rags and books ever since the eighties and have slowly picked up the gun jargon over the years. Besides, almost all my reading these days is done in English. Only six million people speak and write my native language (and most of them badly). I like reading biographies and war history and it's great to have so much more literature to choose from when mastering the English language, be it books or stuff on the internet - like, for instance, the great Cast Boolits forum!

    I also run my PC with English (US) settings; when you're trying to fix some technical problem, googling a Windows error message in English will always provide a large number of answers.

    The only real problem I have is that my brain is hard-wired for the metric system, and since I always follow the adage "When in Rome..." it means that I must convert all measurements to imperial as not to confuse my fellow Booliteers

    Hope this answers your questions, Randy.
    Cap'n Morgan

  17. #17
    Boolit Grand Master

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    Hahahaha! "...my brain is hard-wired for the metric system..." Mine too!

    I was brought up mostly using the British Imperial system and converted to metric in high school and technical school later in life. I am a mechanical designer and pretty much all the designing and drafting (now 3D modeling) is done in metric so for the most part I think in metric... except it took me a long time to get used to temperatures in Celsius and my micrometers are in imperial so I think in imperial for small dimensions (thousandths). A weird mix!

    If I am designing press fits or shaft clearance fits I do it in Imperial then convert to metric. All other dimensions are in millimeters, masses in kilograms, forces in Newtons.

    I'd say many if not most Europeans are fairly fluent in English and certainly moreso than most North Americans and UK citizens are in European languages. French and Spanish may be a bit of an exception. It makes me feel a bit stupid in that I only know English. I don't even know French Canadian French... which is somewhat different than Parisian French which we had to take in high school believe it or not.

    My family went to Iceland for vacation 1 1/2 years ago and while street and building signs were in Icelandic (of course), virtually every Icelander we talked to spoke English quite well if not fluently.

    Not sure if being bilingual has anything to do with "duplex" or not just to try to stay on topic. Okay poor attempt... I'll shut up now!

    Longbow

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    Yeah it does, but now after seeing your slingshot I have to ask,, Do you own a machine shop? Cuz from all your postings it kind of looks like you do, or at least run one with fringe benefits.

    AS far as that metric thing half the stuff I make for our NAVY, and I think you guys have some too, all is designed by Germans and Junior Engineers from Raytheon who think metric is cool. I have to either multiply or divide by .03937 for most everything.

    I love it when these turds convert using .03739! makes for some interesting conversations.

    Longbow sorry you have been infected by this disease too. I thought since you were closer to us it might not have crept into your life. But NO!

    It kind of funny cuz about 3/4 of the Cummins Engine in my Jeep is metric and built in Germany. And yet it is a completely American Company. You'd think I would have converted by now instead of just "Living with it?"

    Hope everyone is well.

    Hopefully our Senses of Humor are not Metric or Imperial. I'd hate to have to convert to that.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
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    Boolit Master Cap'n Morgan's Avatar
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    Well, I certainly have "fringe benefits" at work. I'm a Tool & Die maker by trade. These days I mostly design stuff in 3D like Longbow (parts and injection molds) but I still run a couple of CNC machines (mill and EDM sinker) in between the design jobs. Also, I fill out the position as "The old, know it all, geezer you ask when in doubt" (and I sometimes play the role of psychiatrist when the boss needs to vent his spleen) In return I get to use all our machinery as I like after work and on weekends.
    Cap'n Morgan

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    My shop is in my back yard so I don't have far to go to work. I'm a one man operation with lots of buddies who run bigger shops.

    I farm out most of it nowadays. I usually make prototypes and then farm the production out. Example: my Hand Reloading Press. I farm all the parts out, and I only assemble them.

    Always looking to develop new products I can sell on the Website, and Slingshots are looking pretty good right now.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

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BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
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