Powder charge/accuracy question...

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As you all know, different reloading manuals have different max loads for the same powders. Has anyone here experienced a situation where you found an optimum load for a certain powder that may have been slightly under the max load listed in one manual, and then noticed in another manual that you can load the same cartidge quite a bit higher and ended up finding better accuracy with a higher charge of powder???

For example: I found an optimum load for my .243 of 42 grains of RL 22, and my groups opened up when I went up to 42.5 grains (max load listed in the Nosler book). I've seen in some other reloading manuals where I can load this cartridge up to 44.6 grains. Has anyone experienced a load where you've obtained optimum accuracy at a certain load, with the groups opening up with higher charges, and then found a an even higher charge that shoots even better? I'm not sure this is making sense, but hopefully someone can make sense out of it...[^]

Another example: I found that with IMR 4350, a charge of 40.5 grains shot well but at 41.0 grains the groups opened up...then at 41.5 grains they seemed to get tigher again. Is this a fluke, or can there be several loads with a certain powder that shoot extremely well at various intervals on the loading scale???

Thanks for the input?

Eric
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Warbirds

If I am going to be pushing the envelope or thinking about it I always email the powder company first, and cite both references. They will reply right away.

quote:Is this a fluke, or can there be several loads with a certain powder that shoot extremely well at various intervals on the loading scale???

No fluke in my opinion, the group is not the only thing to consider sometimes you're groups will be similar or practically right on top of eachother but you're trading recoil and knockdown power (FPS). Want less recoil obviously back off the load as long as it's still shooting nice groups, want a few more FPS to try and get everything you can out of that bullet then you may have to live with the increased recoil.

As always study the cases for all the usual signs of an overly hot load.

R/

Dave

People everywhere confuse what they read in newspapers with news.

-- A. J. Liebling

surekill

Alot of the diff data is where the manual comes from LIKE the sea level of diff places has a factory in loads.

---

1 shot is all ya get so make it a " SUREKILL " (T/C Encore-/-Contender/ MATHEWS SWITCHBACK Shooter)

JustC

There are more than 1 charge that will operate under the harmonic frequency that the barrel likes best. I almost always find a low end and a high end harmonic. However, judging by the MV, you may wish to use the lower end harmonic to save brass life and throat life.

why chase the game when the bullet can get em from here?....
Got Balistics?

nononsense

Eric,

Barrels vibrate when a bullet is fired. There are areas within the vibrations that are referred to as nodes. These nodes are indicated by changes in group size or shape. Usually your loads improve as you increase the charge weight, then get slightly worse, then improve again. You are seeing the node of the vibration that is optimized by the velocity.

Here is another way of explanation:

Every barrel develops harmonic vibrations when a cartridge is fired, similar to a string being shaken. A gun barrel's vibration can be described as a 3 dimensional sine wave, or corkscrew movement and is caused when the bullet is accelerated into a rapid spin by the rifling.

(I forgot to add this...)


It is impossible to entirely eliminate barrel movement. Even a thick barrel's muzzle will move with every shot and any velocity variation will alter where the muzzle is located as the bullet departs. This random movement of the muzzle gives rise to increased group size. Most experienced gun builders agree it is best to allow a barrel to flex. The idea is if the barrel's movement can't be eliminated the next best thing is that it flex consistently. That's why good shooting guns usually have their actions and only the first inch or so of the rear of the barrel bedded tightly into the stock to hold the receiver firmly, with the remainder of the barrel free floated. In addition short, thick barrels have wide(r) nodes so velocity isn't as critical to achieving a sweet spot.
Because the velocity of the bullet passing through the barrel affects the way it flexes accurate loads should deliver as consistent a velocity from shot to shot as is possible. You can control this to a degree but it is impossible to entirely eliminate shot to shot velocity deviation. At around a variation of 10 to 12 f/s it may become almost impossible to reduce the effect any further.
It has long been understood that barrels perform best within certain velocity ranges. These velocity ranges are commonly referred to as a "harmonic nodes" or "sweet spots". The reason for this is that the tensile strength (or the ability to resist further bending) of the metal alloy increases as it moves further away from it's static state. The barrel gets stiffer when it is forced to the extremity of its movement. At the point of maximum movement, slight velocity variations change the muzzle location less; resulting in lower shot dispersion and thus a smaller group size. What most shooters don't understand is the harmonic vibration is related to the mass of the bullet. Therefore, once the harmonic node(s) for a given weight bullet is identified, a lot can be learned, if you know the velocity.
In the days of yore (BC -- before chronographs), it was necessary to blindly hunt for loads that worked. Once a good load was found, changing any component could render the whole process useless (since changing components varies pressure and velocity) and one pretty much had to start from scratch if anything changed. A chronograph provides direct insight into what your loads are doing, and what you need to do to make them work better. You will be able to immediately determine if a changed component produces velocity outside of the range the barrel likes. In most cases simply adjusting the powder charge will correct the problem.

FrancF

Not to get away from the subject Have you seen thoes barrel resinators<sp> that slip on the barrel to change the harmonic vibrations?

Gimmick?


NRA Life Endowment Member

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quote:Originally posted by FrancF
Not to get away from the subject Have you seen thoes barrel resinators<sp> that slip on the barrel to change the harmonic vibrations?

Gimmick?


NRA Life Endowment Member




not according to my gunsmith. He has seen VERY positive results with the Limbsaver harmonic stabilizers.

Eric
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JustC

a poor man's BOSS.[;)] I dislike the BOSS for it's ignorant loud muzzle blast (louder than my VAIS or KDF breaks) and it's ability to become loose and change the setting. Those limbsaver deals probably work well, but man if you think the BOSS is ugly[xx(]

I would prefer to find a handload that likes my barrel and be done with it.[8]

why chase the game when the bullet can get em from here?....
Got Balistics?

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quote:Originally posted by JustC
a poor man's BOSS.[;)] I dislike the BOSS for it's ignorant loud muzzle blast (louder than my VAIS or KDF breaks) and it's ability to become loose and change the setting. Those limbsaver deals probably work well, but man if you think the BOSS is ugly[xx(]

I would prefer to find a handload that likes my barrel and be done with it.[8]

why chase the game when the bullet can get em from here?....
Got Balistics?


Ugly they are.[;)] John said one of his customers cut his groups by 2/3 with the limbsaver one. He said it tooks some moving it back and forth to find the sweet spot, but they really do work...

Eric
allamericanarmsco@frontiernet.net

All American Arms Company

www.galleryofguns.com
VIP Code: AAAC

Veteran Owned and Operated

Pinhead

I don't have a strain gauge to prove it but I have noticed different maximum loads from the same weight of bullets from differenct manufacturers. Usually this is caused by the amount of bearing surface that the bullets have according to bullet type(boattail, round nose, spitzer, etc.). In the old days I measured this very carefully on sample bullets before loading and chrongraphing the different bullets. I have since given up chasing things like that and mostly rely on the factory manuals for starting points and then proceed from there, watching very carefully for pressusre signs such as flattened primers, measuring case head expansion and velocity variations. There are a lot of variables that make up velocity and pressure changes but bearing surface of the bullet is one of them. Rate of twist and number of lands and grooves also unfluence these variables. My experience anyway.

JustC

so does the hardness of the jacket material. Sierra has a harder jacket than a lot of other bullets, so this often leads to lower charges for max.

why chase the game when the bullet can get em from here?....
Got Balistics?