Working up a load to be used elsewhere a pipedream?

[rayfromtx]

I do a lot of competition benchrest shooting. We load between matches so we can adjust the load as the environmental conditions change to keep the rifle in tune. The load that works in the morning may be out of tune in the afternoon. It is a story worth telling if a competitor wins a competition after coming to the match preloaded. My understanding of this is that the variation in temperature and pressure affects the pressure curve within the barrel on ignition and will change the harmonics of the barrel. This affects the point on the harmonic wave in which the bullets are released.

Now let's talk about praire dog hunters. No other discipline requires a great deal more accuracy from a rifle than trying to hit a juvenile pd at 500 yards. Unfortunately we are virtually forced to load our ammo at home. I loaded my ammo for my recent trip based on some fine groups at 70 degrees, 95% relative humidity, and 1190 feet above see level. I then took those loads to CO. at 85 degrees, 30% relative humidity, and 4400 feet above sea level. As a competitor, I know that expecting that rifle to be in tune is nothing more than a prayer. Not only that but we don't take a target and a set of wind flags out to check if the rifle is in tune.

If we hit high or low, we blame it on misjudging the distance and if we miss right or left, we misjudged the wind. I'm wondering what the prairie dog experts think about this notion of trying to find a load in completely different conditions than those in which the load will be used.

Should this thread be in the hunting section. Feel free to move it there if that's where it should be.

[acloco]

".....the variation in temperature and pressure affects the pressure curve within the barrel on ignition and will change the harmonics of the barrel."

I don't think it affects the ignition source, as the bullet, brass, powder, & primer...are somewhat sealed, so the air and the pressure is a constant.

Personally, I DO believe that it is an air quality issue.

Watch the 9.90 class drag cars, they tune to the hundredth, because they know conditions.

[rayfromtx]

".....the variation in temperature and pressure affects the pressure curve within the barrel on ignition and will change the harmonics of the barrel."

I don't think it affects the ignition source, as the bullet, brass, powder, & primer...are somewhat sealed, so the air and the pressure is a constant.

Personally, I DO believe that it is an air quality issue.

Watch the 9.90 class drag cars, they tune to the hundredth, because they know conditions.

I think the temperature affects the speed of the powder burn in the cartridge and the density of the air in the barrel affects the pressure curve during ignition by "pushing back" against the accelerating projectile at a variable rate based on ambient conditions and, I believe, conditions within the barrel.

[jo191145]

As your well aware your load will be out of tune. How much out of tune you'd know better than me

I've read one of the reasons you BR shooters push the 6ppc so hard pressure wise is it stays more in tune at that range.
Still must be tweaked constantly but they agg better even if you tweak in the wrong direction.

FWIW
I just put together a high pressure load like that in my 204. Pretty much a last minute Hail Mary pass at an egg shoot load when the sane node no longer performed.
I did quite a bit of testing,tweaking and eventually even switched to WS2 coated pills to help control fouling and hopefully tighten the groups up a bit more.

Oddly enough after switching to WS2 I lost roughly 35 fps but testing proved the original powder charge was still the optimal choice.
I had a hunch that load would not change with the introduction of WS2 and so far I seem to be right. Make of that what you will

Of course, Hodgen Extreme or not I made darn sure my ammo saw no sunlight at the egg shoot

[Hotshot]

ray,

I think you are over thinking this. I have to admit I have always lived in the same area that I hunt pd's.
My objective in a varmint shooting load is to eliminate shots that won't hit the target if I do all other things right.
If the kill zone of my target is 2 inches, then a load that will shoot 1/2 in groups at 100 yards would have that 2 inch ability at 400 yards.
Therefore, when I develope a load that shoots consistant high .3's with some .2's now and then I don't have to worry if temp or humidity or barometric pressure changes my groups out in the dog town to .4's and .5's because they still do the job.

I don't know how much your loads might change from your conditions to the prairie dog towns you visit, but I doubt if those changes are huge as far as hitting the kill zone of a prairie dog.
If it continues to be a big worry to you, you could ship your guns and plenty of ammo to acloco and me and we will thoroughly test them for you.

[rayfromtx]

ray,

I think you are over thinking this. I have to admit I have always lived in the same area that I hunt pd's.
My objective in a varmint shooting load is to eliminate shots that won't hit the target if I do all other things right.
If the kill zone of my target is 2 inches, then a load that will shoot 1/2 in groups at 100 yards would have that 2 inch ability at 400 yards.
Therefore, when I develope a load that shoots consistant high .3's with some .2's now and then I don't have to worry if temp or humidity or barometric pressure changes my groups out in the dog town to .4's and .5's because they still do the job.

I don't know how much your loads might change from your conditions to the prairie dog towns you visit, but I doubt if those changes are huge as far as hitting the kill zone of a prairie dog.
If it continues to be a big worry to you, you could ship your guns and plenty of ammo to acloco and me and we will thoroughly test them for you.

Thanks hotshot-

Please email me your address so I can ship all this stuff to you right away. I am obviously over thinking this whole thing.

Seriously though, my rifle will shoot 1" at 100 with a bad load and .1 at 100 with a well tuned load. Out at 400 yards, that is a big difference. Naw, just send me the address and I'll have all this worrisome stuff on it's way to you post haste.

[acloco]

I think the temperature affects the speed of the powder burn in the cartridge and the density of the air in the barrel affects the pressure curve during ignition by "pushing back" against the accelerating projectile at a variable rate based on ambient conditions and, I believe, conditions within the barrel.

The bullet seals the end of the case and seals the chamber as soon as it engages the rifling and the powder starts to ignite, so, the combustion pressure from the powder being lit also seals the bullet.

Interesting....I still hold the air is the culprit, which is directly affected by temperature and humidity.

So....mother nature would be the factor on this one.

[heikki02003]

I'll share my thoughts.
I know very well about tuning a load to temp and humidity for benchrest shooting. N133 is the king of the Lapua PPC cartridge. It is a powder that is affected by TEMPERATURE. The hotter the powder is, the faster it burns. Benchrest shooters have been known to keep N133 powder and loaded rounds in coolers to maintain specific temps. I am a firefighter and know all to well the fire triangle. It is heat, fuel, and oxygen. Take any variable out of the triangle and combustion is not possible. Conversely, increase any of the components and combustion happens more readily. This is how temperature affects load tuning.
Now we have HUMIDITY. The more H2O in the air, the heavier it is, and therefor more energy is required to maintain the same velocity. Again coming from firefighting, the warmer the air by volume the greater the potential to hold more water by weight. That is why it is generally drier in the winter (lower Relative Humidity or RH) than it is in the summer (higher RH). So, the heavier the air in your barrel (and between muzzle and target) the more velocity needed, and therefor more powder. So to this sum up: The hotter it is - the less powder you need. The higher the humidity - the more powder you need. Here's the catch... The laws of physics, as stated above, suggest that as temperature increases, RH decreases. This is called the diurnal temperature variation, or diurnal effect. So as temp rises in the day (meaning less powder to maintain a given velocity), RH increases (meaning more powder to maintain a given velocity). This means that as the day progresses they SHOULD (and usually) cancel themselves out, but nature is nature and never always follows the rules (there are other environmental and geographical factors involved here, this is where benchresters talk about knowing the range, or local conditions).
All this being said... the differences here are slight. Take for example a benchrest match with ZERO wind. Benchresters refer to this as a trigger match, no wind reading skills are involved and it becomes a matter of shot execution AND A PROPERLY TUNED LOAD to both temp and humidity. Take two shooters who are equally skilled in the mechanics of shooting. Each shooter knows what load shoots best out of his gun at a said temp and humidity, knows the current shooting conditions, approximates a load for the given conditions, and they head for the line. The difference between these two shooters might be 0.100MOA. Lets just say the guy(or girl) that matches his load to the conditions shoots a 0.090" and wins, well the guy that messed up his load might shoot a 0.150" and take second.
This is the nature of benchrest. It is top of line firearms being shot by the countries top shooters, with many dollars being spent in load developments.
Now let’s talk gopher hunting and use myself as an example. I am buy no means my counties top shooter (by the way, our HV Canadian record is 0.052"). Nor do I shoot a top of line rifle (A $1300.00 BAT action and a $2000.00 March or Nightforce scope is too much for my pocket book), nor can I afford thousands of rounds of ammo just for load development, nor can I afford a dedicated fireform barrel or an entire quiver of 'spare' barrels. I shoot a factory Savage, and dread the day I shoot out the barrel. I shoot with a two dollar bipod off the roof of my truck, while some choose maybe the better route and go for a crapy rest and rickety old portable table the companies have coined 'shooting benches'. I still have a day job and don't shoot a gun for a living, so my mechanics are far from perfect. My eyesight is no S%&T, and I just can't go a morning without my coffee. I shoot a respectable 0.2" all day long... actually... no I don’t, it's more like, if I shoot all day long I might shoot a 0.2"; and post it online (for three shots not five). I enjoy shooting at gophers at 300yards and missing, then laughing about it or making fun of someone else for missing.
The bottom line... I simply don't have the gear, or the shooting ability, to notice a difference temp and humidity make. Quite honestly, me and my gun average 0.5", some groups are 0.3", while some might be 0.8" or bigger. I just can't with my ability and gear shoot good enough to notice the effects of temp and humidity once I have a load worked up. ESPECIALLY IN THE FIELD. There are just too many variables for me in the field that benchresters have the time, effort, and money to overcome in their sport. Variables such as wind, distance estimation, poor benches and support, poorly crafted receivers and badly cut button rifled barrels (I've looked down my Savage tube with a borescope!), poor brass (Lapua doesn't make .204 brass), bad bullets (I don't shoot custom top dollar Bruno's or Bart's) and the list goes on and on.
When I go out for gophers, I'm happy with about a 75% average with shots anywhere between 100 and 300yards. My rig is accurate enough to hit a tiny little gopher at 300yards, make a clean kill, and have me be happy about it.
Me, or the gophers for that matter, don't know exactly what a 10 degree temperature change, or a 30% humidity change does to my bullet (I have tried in vain to keep track of this in my log book). I still average about 1/2 MOA, not 0.052.

[rayfromtx]

Good points Heikki
There is a widely held misconception about humidity and air density. Humid air is actually less dense than dry air. There is a law that says that a given volume air at a fixed temperature and pressure will contain a set number of molecules. If one type of molecule is introduced in that volume of air, other molecules will be displaced. That means that when water vapor is introduced into that air, nitrogen is displaced. Hydrogen and oxygen are both lighter than nitrogen. As hydrogen and oxygen displace the nitrogen, the air becomes less dense. Humid air rises until it reaches a layer of air that is cool enough for it to combine into visible clouds. Water molecules are so small that if you lined them up end to end, it would take one billion of them to equal one foot.

In general there is more moisture in the air in the summer than in the winter. The relative humidity; however, is lower in the summer and higher in the winter. That is why more exterior drying occurs in the summer.

Indoors we control the temperature and therefore the relative humidity is lower in winter and higher in summer indoors.