WHAT IS AN OPTIMAL CHARGE WEIGHT

LOAD?

With any given bullet and powder combination, there

will be a specific amount of that powder which will

cause the bullet to exit the muzzle at the "friendliest"

portion of the vibration cycle. This does not necessarily

correspond with the tightest velocity figures, however.

Many load recipes have over the years become the "go

to" recipes for trying out a new rifle. If your rifle fails to

shoot one of these "tried and true" recipes well, you may

well have a rifle integrity problem.

Consider the Federal Gold Medal Match .308 win ammo.

How can one recipe shoot so well in so many rifles?

That's what we're after in the OCW load--a load recipe so

stable and predictable that it does indeed rise above,

and to some extent disprove the "all rifles are different" adage of lore...

Think about it this way. Some kids like mashed potatos, some don't. Some kids will eat thier peas, some won't. Some kids like bananas, some hate 'em. But show me a kid that doesn't like chocolate ice cream and I'll show you one bizarre little character! :) An OCW load is like chocolate ice cream to your rifle. If your rifle doesn't like the recipe, there is likely something weird about your rifle.

If you perform the OCW load development properly,

you are not (in the initial stages) seeking the optimal

load for the test rifle. Heresy? Not really. There are

many known "universal recipes" that work well in most

rifles chambered for them. Ken Waters has made a pretty

penny with his book "Pet Loads" on this concept. Many

of the Waters loads have worked beautifully in my rifles,

and acquaintances have had the same experience.

Federal's Gold Medal Match .308 loads do well in

practically any .308 not needing a gunsmith's attention.

How can this be? If you subscribe to the philosophy that

"all rifles are different," and therefore need individual

loads tailored to accommodate their idiosyncrasies, how

do you explain the near universal MOA performance of

loads such as the Federal GMM? Universally good

recipes do exist. Upon realizing this, my questions have

been "How do such recipes work?" and "How can I

develop such a load?"

Recent conversations with very learned mechanical

engineers are affording me some better understanding of

just why an OCW load works so well in the majority of

rifles chambered for the cartridge at hand.

Here are some of the major points coming to light:

Uniformity of velocity (meaning low extreme spreads of

velocity) are definitely not an indicator of the OCW

zone. We are actually finding that in many cases the

OCW zone does not have the tightest numbers--at least

initially. Fine tuning of the recipe with seating depth

variations and primer changes will improve the velocity

consistency, but simply shooting a succession of

graduated charges over the chronograph and looking for

a tight velocity spread will not lead you to the OCW.

As the reader comes to understand more about the main

shock wave (link Chris Long's pages elsewhere in this

webpage) it will become easier to understand how

bullets with larger extreme spreads in velocity can still

group tight (at closer ranges), while bullets with

seemingly tiny extreme spreads may group poorly. You

can tighten the extreme spread to improve long range

accuracy AFTER you identify the OCW.

Engineer Chris Long's model of barrel

behavior suggests (simply put, and in part)

that the initial shock wave, generated by the powder

charge's ignition, travels at the speed of sound in

steel (about 18.000 fps) from the chamber to the muzzle, then back, in a repeated pattern. When this wave is present at the muzzle, there is

naturally much turbulence and obturation of the

"roundness" of the bore at the muzzle. However, when

this main shock wave has reverberated back to the

chamber end, the muzzle is relatively stable. This

window of opportunity, according to Chris, is the best

time for the bullet to exit the muzzle. The barrel is

basically straight, and relatively calm.

(Read later about the "scatter node" which is the point

at which the bullets are being released from the bore

when the shock wave is at the muzzle. I call this area

the "scatter node" because it will produce a scattered group,

throwing flyers at random. This is the most

inopportune point of all for bullet release, the scatter node area

can be easily seen during an OCW test, and generally 1 to 2

powder graduations above the scatter node charge will have

you right in the OCW zone. The existence of the scatter node

is the main reason the conventional ladder (Audette) test often fails

to yield useful results--see OCW vs. Ladder on this site).

The OCW load would then have the optimal amount of

powder to push the bullet at just the right speed to be

exiting the muzzle when this shock wave is at the other

end (the chamber end) of the barrel.

This shock wave travels at the same speed regardless of

barrel length or girth (about 18,000 fps).

We note that OCW loads seem to perform very well

regardless of barrel length. (We're not considering non-

typical barrel lengths here). This makes sense because

the relationship between barrel time (the length of time it

takes the bullet to exit the muzzle) and the oscillating

shock wave is close to the same; in other words, in a short

barrel the shock wave reaches the muzzle and returns to

the chamber faster, but alas, the bullet reaches and exits

the muzzle faster also.

The harmonics which ride the main vibration node are

only of minor importance to accuracy in most cases. It

would appear that the effects of the subtle harmonic

vibrations can be largely negated with seating depth

adjustments, but a true OCW load will normally be

MOA or better in a good rifle without seating depth

tuning.