"Loads close to the max pressure are more accurate"

[MachIVshooter]

I always figured that a gun is made for a cartridge at a given pressure, which is usually a certain range under the the maximum rated. Thus, a load around that pressure--which will be near maximum even if just at a technicality (90% is 'near maximum' after all)--will usually be more accurate.

Pretty much this. Though every gun is different, most tend to perform better with the bullet and operating pressure/velocity they were designed around.

Simply put, it is a "window of efficiency", something that is not unique to firearms. Machines work best when operated within their design parameters, and performance often degrades when they're run below or pushed beyond those parameters. Think of under or over loading cartridges in the same way you would lugging or overrevving an engine.

 

[willypete]

Engines=/=firearms. Yes, they're both machines with moving parts that handle varying pressures, but so is a dishwasher. You gonna tell me that a Kenmore is the same as a Winchester?

The "load to near max pressure" statement is a farce. There are accurate loads achievable at much lower than max pressure (ever loaded a smokeless cartridge with blackpowder?) for many different cartridges. The existence of actions capable of handling pressures higher than those the cartridge was originally designed for is a perfect example of the irrationality of the idea of loading around max pressure. Weatherby actions, Ruger #1, Ruger revolvers, modern actions containing older cartridges (think .257 Roberts in an action that is also available in .270 winchester, it's a difference of roughly 7,000 psi!) all provide examples of such actions. And yet, there are also examples of accurate loads available across all sorts of pressure ranges!

Some powders do have pressures at which they like to operate, but that's not what my original post was about. For a given powder that has a pressure spec it likes to hang around (H110, IMR7828), I'm sure I can think of one or more that will operate at a wide range of pressures (BP substitutes, BP, W231, H335).

 

[MCMXI]

The "load to near max pressure" statement is a farce.

Why do you think that the Savage F-T/R rifle has a 30" barrel? Why do PALMA shooters and many F-Class or Benchrest shooters use 30" or longer barrels? The answer is VELOCITY which requires PRESSURE. I've never met a PALMA or F-Class shooter, or Service Rifle shooter for that matter, who downloads to achieve better accuracy.

 

[Clark]

Deus Machina

I always figured that a gun is made for a cartridge at a given pressure, which is usually a certain range under the the maximum rated. Thus, a load around that pressure--which will be near maximum even if just at a technicality (90% is 'near maximum' after all)--will usually be more accurate.

I am 61 now, but my father was designing guns 60 hours a week when I was 5 years old. He took me with him on Saturday. He was chief engineer with a big office, but we would go out in the dirty shop and deal with guys in greasy overalls.

I figured that all that red stuff on the ground was blood, from shooting people with the guns.

Now that I am older, I suspect it was hydraulic fluid.

He also showed me how to calculate stress in a gun as a function of chamber pressure.

But when I try to blow up guns, they never blow up at the calculated pressure. Guns are much harder to blow up than the math suggests.

I am beginning to suspect that the stress strain curve for metals is measured in static conditions, and the millisecond or two that firing a gun stresses the metal is a dynamic condition for which I have no formal data.
I do have some seat of the pants feel for it. It is ~~20 % ~~ 40% more than I calculate.

 

[USSR]

Accuracy begins and ends with consistent velocity. Period.

Shoot the powder / bullet that gives you the most consistent exit velocity and you'll find you most consistent grouping, every time.

Nope. I used to believe that when I was young and inexperienced. But then, extensive load development work with a chronograph opened up my eyes. I was shocked when I saw that the loads with the lowest ES and SD numbers were not the most accurate loads. Now I simply use the chronograph to establish what the average velocity is for a particular load that is accurate out of my rifle.

Don

 

[willypete]

Why do you think that the Savage F-T/R rifle has a 30" barrel? Why do PALMA shooters and many F-Class or Benchrest shooters use 30" or longer barrels? The answer is VELOCITY which requires PRESSURE. I've never met a PALMA or F-Class shooter, or Service Rifle shooter for that matter, who downloads to achieve better accuracy.

You don't seem to understand my premise. The most accurate loads in a given chambering are not necessarily those loads which run at or around max pressure. Heavy, long barrels in competitions requiring open sights and off-hand or free standing shooting positions are typically chosen because they help the shooter attain a longer sight radius (which contributes to accuracy) and mitigates outside influences which could cause the shooter to come off target (also contributing to accuracy). The longer barrel also boosts velocity, which is very helpful given the ranges at which some of those matches are conducted. Heavier guns tend to be easier to shoot accurately when a human is involved in the equation. They also mitigate recoil when shooting from a bench. My original post had nothing to do with barrel length; it is about the idea that loads around the maximum pressure for each cartridge are arbitrarily more accurate than loads not around the maximum pressure for each cartridge.

Regarding match shooting, I have some loads for .30-06 that I shoot in service rifle that I download by approximately 35% (pressure by manufacturer data; the actual charge is about 12% below max weight) because they are more accurate than loads running at max pressure. Load development varies with gun/cartridge/component variations, but the max pressure is a safety guideline, not an accuracy guideline.

The fact that there are some very accurate loads which are nowhere near maximum pressure for a given cartridge runs contrary to the falsehood that cartridges must be loaded to their maximum pressure to achieve a semblance of accuracy.

Nope. I used to believe that when I was young and inexperienced. But then, extensive load development work with a chronograph opened up my eyes. I was shocked when I saw that the loads with the lowest ES and SD numbers were not the most accurate loads. Now I simply use the chronograph to establish what the average velocity is for a particular load that is accurate out of my rifle.

Don

I was very surprised when I learned this as well. While the internal ballistics may be very uniform, the external ballistics depend on other additional factors. Isn't shooting stuff fun?

 

[MCMXI]

Nope. I used to believe that when I was young and inexperienced. But then, extensive load development work with a chronograph opened up my eyes. I was shocked when I saw that the loads with the lowest ES and SD numbers were not the most accurate loads.

Given the variables in components, particularly bullets, it's possible to shoot a smaller group with higher EVs and SDs but there's no question that given a large enough sample under controlled conditions, there's a correlation between EV and accuracy/precision.

 

[MachIVshooter]

Engines=/=firearms. Yes, they're both machines with moving parts that handle varying pressures, but so is a dishwasher. You gonna tell me that a Kenmore is the same as a Winchester?

Of course firearms aren't internal combustion engines. But analogies aren't about using the same nouns, are they?

The use of dissimilar things to draw parallells and make points is not inherently flawed. You just have to make the right comparisons and word it correctly.

There are accurate loads achievable at much lower than max pressure (ever loaded a smokeless cartridge with blackpowder?) for many different cartridges.

Of course there are, if the twist rate and velocity are still appropriate for the bullet.

I have found that best accuracy is acheived pretty close to factory loads in most rifles. Light-for caliber bullets at screaming velocities often have erratic performance, and heavy-for caliber bullets spinning too slowly don't shoot well. Try firing a 110 gr. spitzer out of a 300 RUM at max velocity or a 250 gr bullet from a .30-30 and tell me it doesn't matter what velocity you load to. Taken to less extreme examples, I find best accuracy in my .25-06 with 100-120 gr. bullets loaded pretty near the top.

 

[joed]

In 35 years of loading cartridges I've found that the best accuracy generally does show up near max loads. I've only seen this with rifle cartridges and I'm sure there are exceptions.

I had one cartridge give great accuracy just above the minimum load once. But as I kept increasing the charge I saw accuracy fall apart and get better again. That cartridge and gun ended up very near max with great accuracy.

 

[ranger335v]

"Shoot the powder / bullet that gives you the most consistent exit velocity and you'll find you most consistent grouping, every time. "

Nope, that's badly incorrect.

 

[627PCFan]

Unfortunately I had a barrel that would not shoot anything accurately unless it was loaded over max and then some. That barrel aside I find slower does it

 

[Clark]

The reason benchrest guys are pushing the brass to the limit, is overcome wind.

The extra recoil from hot loads is not doing them any good.

The 30BR guys have the most immunity to wind, and they are having to touch the butt of the rifle with their shoulder, because there is so much more recoil.

 

[murf]

i'm not buying it either.

murf