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Post by edge on Jun 19, 2011 20:56:07 GMT -5
Most of the time when someone works up a duplex or makes a change they keep the total powder the same.
I ask why?
I am not saying that it is wrong, but you are changing two components at the same time.
My initial thoughts on duplex are we are using a powder that is a little or a lot too slow for the application and it needs a kick start.
IMO, a certain powder needs a kick start to get going properly, then if I need more powder why should I need more booster? Perhaps you do, but why?
If I got the pressure to say 30kpsi do I want higher pressure or do I want a longer burn?
It would seem that I should ( ideally ) use a pressure trace and a chrono to see what we should change. More pressure faster may dictate more booster, but more powder may do both too.
Someday I'll set up a chrono underground, but for now that will have to wait.
In general I have to go by muzzle flash to tell me if I am wasting powder and need more booster, but once I reach the "perceived" needed booster I just add or subtract the slower powder to look for the best accuracy.
I would be interested how other search out their loads and any chrony or PT evidence to back it up would be great.
edge.
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Post by sw on Jun 19, 2011 22:24:19 GMT -5
Edge,
I know the answer but my wife says it is time to go to bed so the answer will just have to wait. Hope this doesn't keep you up all night. Seriously I do know the answer.
Steve
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Post by wilmsmeyer on Jun 20, 2011 5:04:44 GMT -5
Edge,
I think one of the answers is bullet weight. In a load that has a very light bullet, more booster seemed to work for me a long time ago.
That's my theory...I'm sure SW will provide a much more clear picture then me.
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Post by edge on Jun 20, 2011 5:41:29 GMT -5
Edge, I think one of the answers is bullet weight. In a load that has a very light bullet, more booster seemed to work for me a long time ago. That's my theory...I'm sure SW will provide a much more clear picture then me. I agree that a light bullet needs more booster to get the powder up to a sustainable pressure, but once you are there and want to tweak the load why do need to adjust both powders? Clearly these powders are not equivalent otherwise you would never have needed the booster to begin with. Why 1 for 1, why not 1 for 2, or 2 for 1 , or why not just 1 more grain of the main powder? OR if you are shooting 10/60, a 6 to 1 ratio?? edge. |
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Post by sw on Jun 20, 2011 7:00:32 GMT -5
Edge,
I agree with the points made in your posts. I do not try to keep the total weight of my duplexes the same. RB would look up loads in load manuals for either 45 or 50 cal and find a load with the appx pressure he wanted and then tweaked the duplex until he got the velocity of the book load and then assumed he had the appx pressure of that load. He'd use various straight cased cartridges( 45 and 50 cal) and look up their pressures and powder weights. We can duplicate this method much easier by constructing our own cartridges in QL. So if he wanted a certain pressure for a certain wt bullet and believed 70g of powder was the weight needed to get a certain pressure, then he used 70 g and started with a low booster powder weight and slowly transition until he got the velocity he thought 70g should provide at his tgt pressure. This is why his duplex of 14/61(VV-110/H-322) which had 75g of powder and provided appx 2610'/sec was changed to 19/51 which has a total wt of 70 and yielded the same velocity. He decided that after looking up loads that 75g was a little "pressure starved" and 70 g total was "ideal" for the bullet wt/ velocity.
I do not keep the wt steady. I chrono the load and slowly increase my primer powder until I start seeing increased velocity increments per grain . I then go back to the last primer wt before the increased velocities occurred. Example: if each additional grain of primer yielded 20'/sec and then the next grain gave 35'/sec, the next 42'/sec, I'd go back to the last 20'/sec weight. Then I'd add grains to my primary powder and when, and if, I start seeing disproportionate gains per grain, I'd drop the booster a grain and continue adding to the primary powder until I had what I want. When the velocity starts dropping off with each added grain, I expect I may be blowing powder out the end of the barrel. A white sheet laid out on the ground in front of the muzzle can help tell when this point is reached. Maybe more later. Hope this helps on the history of RB's duplex method and what I do. My method likely isn't perfect but has some scientific basis, I think.
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Post by edge on Jun 20, 2011 7:26:07 GMT -5
sw, your way would seem to be more intuitively correct, IMO than the way most folks do it. Almost every person that I have read about their loads would be the same total weight and just a change to the ratio of that initial weight.
edge.
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Post by Richard on Jun 20, 2011 14:49:37 GMT -5
I have played with many duplex (and a few triplex) loads and do not always keep the total weight the same. As a matter of fact, tomorrow, I put together a load of 15 gr. 4759 under 60 gr. of H-335. Last week I only used 10 gr. with the same 60 main charge. The load was somewhat anemic so I thought I would spice it up with a little more booster ;D A second duplex with 10/70-- 4759/Varget will stay the same weight but I am adding five grains to the booster and removing five from the main charge??? I don't know? The load is a bit on the low side and I wanted to see where it would go with increasing the booster and lessening the main charge. Maybe it will not be what I want and will go back to the 70 main and keep the 15 booster? Gives me something to play with each week. I might just stumble on something I like................Like the 10/60--- 4759/H-322 load.
Heck if I just shot 60 gr. of N-120 with a 195 Barnes all year long, I would get bored out of my head ;D ;D
Richard
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Post by tar12 on Jun 20, 2011 18:38:18 GMT -5
The N120 and Barnes load is boringly accurate and did not take 3,000 shots and umpteen duplexes/triplexes to get there... ;D The thing with shooting saboted loads is you will never realize consistant centerfire accuracy with a sabot in the equation regardless of caliber or powder(s)..that horse has been ridden to death..surely you can see the folly in this Richard...duplex and triplex loads would take on a life of their with the full form die. That, IMO is the future of advancement in smokeless shooting.....
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Post by Richard on Jun 20, 2011 19:37:32 GMT -5
Sorry Tar...........I just had to throw that in ;D. You are probably right on the full form die and the wheels in my head are spinning it around. What made me think is that I am putting together a 6.5 ML for Jon. He has the full form die and sent me a couple of bullets. Its amazing how they just want to index and fit right in the bore. I did not push it down but can readily see the advantage. I doubt you would even need to use a wad. His barrel also has a chamber in it. No, I am not planning to shoot it, I'm leaving that up to Jon. When he gets it back he can tell you about it. I will take some pictures if he wants them posted. So, how about a truce?  I know you are a hunter and only interested in killing critters........I been there and done that for years and now am happy punching paper so let me play with my loads? Who knows, I might just stumble on one ;D And anyway, I have received numerous PM's from members on this board who appreciate the information since they are not able to get out to shoot as much as they would like! Richard |
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Post by jeremylong on Jun 20, 2011 22:09:50 GMT -5
Lol, I like all of it. Richard coming up with triplex, heck I am surprised he hasnt dumped 4 down yet. Its informative, but I can assure you that when I get out for deer season (my forte) it will be a minute of deer single powder in the 45. Well that is unless I find a duplex that gets me a BIG improvement. Maybe a full form die sabotless, but who knows. Soo, count me in, I like reading the weekly reports, even if I know I probably wont try it....
Gotta keep trying, you just never know what you may stumble on....
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Post by Jon on Jun 21, 2011 3:29:00 GMT -5
Richard. I have no problem with pictures being posted I just hope no one laughes to hard because it will probably be quite odd looking to most people. The barrel is slightly tighter at the muzzle. I may have to make a small shorter starter for now. As you noted the barrel is quite long. It's not hard to make it shorter.
Jon
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Post by rossman40 on Jun 21, 2011 9:55:48 GMT -5
With a duplex or even a triplex what you are doing is changing the burn rate or pressure curve of the powder or charge. Instead of making a whole new powder your doing it by mixing powders already on the market. So far we have been dealing with fairly simple combos but as you search for higher performance you may get closer to the line. You should be able to tailor it to a specific bullet weight and barrel length but if you fine tune it more other factors creep in. Factors such as bore resisitance, charge temp and even type of bullet construction. Then there is also the dealing with pressures as the charge "train" progresses thru the burn. If powder "A" does not bring the chamber pressure to a certain point then powder "B"s burn rate may not be to expectations. If say powder "A"s pressure is increased due to barrel fouling will the burn rate of powder "B" increase?. When dealing with single base powders with fairly close burn rates IMO is fairly safer then say using double base powders.
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Post by GMB54-120 on Jun 21, 2011 21:20:31 GMT -5
A comparison between using 2 singles, 2 double based and a single/double based duplex would be very interesting in a pressure test barrel. Ive wondered how that part fits into the "duplexing equation".
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