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Ladder Test Question ???

 
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  #8  
Old 01-27-2006, 04:35 PM
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Re: Ladder Test Question ???

what about barrel heat? how long to take 15 shots?
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  #9  
Old 01-27-2006, 04:48 PM
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Re: Ladder Test Question ???

I'm not trying to start an argument or anything, but it seems to me your OCW method is not different than the load 'em up and see if they shoot method. That's what I have always done in the past. Load three of each charge weight and see which one shoots better. I'm sure you've mentioned it before but what makes the OCW system different (I'm a little slow sometimes)?


ADDED AFTER I DID A LITTLE RESEARCH:

I understand now. Seems to be the old load 'em and shoot 'em method coupled w/a bit of attention to bbl harmonics. I'm sure it will work just as well as a ladder test. Seems to me you could get from point A to point B w/alot less loading and firing w/the ladder test though.
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  #10  
Old 01-27-2006, 04:49 PM
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Re: Ladder Test Question ???

That would depend on the cartridge, and the outside temperature, and config of the barrel. Around 2 minutes between shots is what I normally take with 22-250, .243 win, .308, 30-06, etc. With a heavy barrel you could cut a little bit of time off that, but as you get deeper into the round robin firing sequence, you may want to allow a little extra time between shots just to be sure.

Dan
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  #11  
Old 01-27-2006, 04:54 PM
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Re: Ladder Test Question ???

Bill,

The philosophy is treated in depth at my website. Those shots aren't fired three at a time at the same target. They are fired one at a time, in succession, across all five or six targets. Then you repeat the process twice more, leaving three shots of the same charge weight on each bullseye.

Then you don't pick the tightest group--you pick the group which seems to be at the center of a common POI. That gives you a very stable load, and makes a much better platform to begin tuning for long range (reducing ES) from.

This test basically does what the ladder test seeks to do--only it does it with much more valid results.

Dan
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  #12  
Old 01-28-2006, 05:31 AM
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Re: Ladder Test Question ???

I WILL TRY BOTH WAYS

THANKS FOR THE INFO
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  #13  
Old 01-28-2006, 02:06 PM
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Re: Ladder Test Question ???

[ QUOTE ]
what about barrel heat? how long to take 15 shots?

[/ QUOTE ]

It depends on how well the barrel has been stress relieved. Many factory barrels bend as they heat up 'cause they're not uniformly stress relieved. And how they're fit to the receiver can cause problems, too. Proper stress relieved barrels correctly fitted to receivers bedded decently typically don't start flinging wide shots as they heat up. Read on......

A friend took his .308 Win. rifle and shot 40 consecutive shots about 20 to 30 seconds apart at a 600 yard target. Starting with a cold barrel, all 40 shots went inside 2 inches; under one-third MOA. His barrel was pretty darned hot after 40 shots, but it obviously didn't bend or warp any at all.

I've shot several 15-shot .30-.338 Mag. test groups at 1000 yards with a shot about every 30 seconds. The largest group was about 7 inches. Again, those barrels didn't warp or bend and they were pretty hot indeed.
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  #14  
Old 01-28-2006, 02:30 PM
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Re: Ladder Test Question ???

Green 788, I went to the link you posted and read it as well as Chris Long's article. Very interesting. Very noticable was all the theory, formulas, numbers, et al. Like virtually all that's in pring about barrel harmonics, there's no mention of any actual tests made to measure barrel movement when fired.

The only person I know of who has recently measured barrel whip or vibration during firing is a resident mechanical engineer at the US Olympic Training Center. His measurements were made with accelerometers close to the muzzle (not attached 'cause that would change the barrel's resonant frequency) that measured the muzzle movement from when the trigger released the sear to bullet exit. Here's some stuff he learned.

Rifle barrels have a fundamental frequency that's low; typically 40 to 80 Hz. The high frequency one hears when they tap a barrel is a harmonic (around the 20th to 30th) of the fundamental.

When fired, there is only one whip of the barrel that causes bullets to exit at different points. That whip is about one cycle of the barrels's fundamental frequency. It's much like taking a garden hose that's laid out straight, then grabbing one end end to whip it and you see the single wave go down the hose.

The high frequencys noted at the muzzle were insignificant in changing the direction bullets go.

A given barrel alone will have its own resonant frequency. Fit it to a receiver and the barreled action's resonant frequency will be different than the barrel alone. Mount a scope on that barreled action and things will change again. Then bolt that scoped barreled action in a stock and changes will happen again.

Many years ago (1930's?), one of the US military arsenals did some tests using spark photographs of the muzzles of two bolt action rifles; a Springfield M1903A3 and a British SMLE. The objective was to find out why the SMLE shot smaller groups at long range than short range while the reverse was true with the M1903A3. 'Twas discovered that the M1903A3 .30-06 ammo had a lower muzzle velocity spread and its bullets were leaving the barrel at about the same place in the barrel's vertical whip. Short range accuracy with the M1903A3 was pretty good but at long range it fell off quite a bit. The SMLE was a different story, however. The greater muzzle velocity spread of the .303 ammo didn't cause larger groups at longer ranges. Instead, the faster .303 bullets were leaving the barrel when its whip made the muzzle point at a lesser elevation angle and the slower bullets left when the barrel whip put the muzzle axis at a greater elevation angle. Slower bullets were launched at a greater angle than faster ones; their trajectories came together for best accuracy at 800 - 900 yards. No wonder the SMLE was a favorite for long range work.
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