Same bullet weight, same powder, different recomendataions

[js6seaj]

I've been putting some reloading data together from different powder manufacturers. I have noticed something that to me is strange. For the same bullet weight, same caliber, and same powder, sometimes there are different recommendations for the amount of powder. For example a 44 Special, 240 grain bullet, with Unique powder. One recommendation is for 6.5 grains, one for 7.6 grains, one for 6.3 grains. The only difference I and see is different makes, models, or tips. Speer, cast, Nosler. Hollow point, semi wad cutter, etc. So what gives? If it was a different weight, I could see it, or even different powder, but all that is the same.

 

[Fine Figure of a Man]

Bullet construction, alloy, hardness, bearing surface, all factors that affect pressure.

 

[js6seaj]

Bullet construction, alloy, hardness, bearing surface, all factors that affect pressure.

Makes sense, figured I was missing something. Thanks.

 

[Jonesy814]

Those bullets also likely have a different recommended minimum over all length. More bullet down in the case can result in higher pressure. A jacketed bullet will develop different pressure than an all lead bullet too

 

[WestKentucky]

Something else to look at is the way the data is presented. Some publishers just throw the data at you in the form of starting load, max load, and associated data for those recipes. These numbers change, but are usually somewhat similar. The waters get really muddy when you start seeing data marked as accurate load or some other way to distinguish a load inside that range as a recommendation because that depends entirely upon their test rig. It gets plum confusing when you see numbers veering off into Ruger Only load territory. Just read the data carefully and fry to figure out what it really means, but always work up to a load.

 

[otisrush]

Someone on this board once commented that the manuals document what was *actually tested*. So "Max Load", for example, isn't necessarily "Max Load That Generates Max/Safe Pressure"....but rather "Max Load Tested".

Once I heard that perspective it helped clarify why the numbers are often different.

 

[Dudedog]

Also different lots of powder can make a difference as well. Some powders are more consistent lot to lot than others, some may have more of a lot to lot swing.

 

[buck460XVR]

Those bullets also likely have a different recommended minimum over all length. More bullet down in the case can result in higher pressure. A jacketed bullet will develop different pressure than an all lead bullet too

^^^This, especially with revolver rounds that use a cannelure to determine OAL. Not all cannelures are the same and different bullets when seated to and crimped to the center of the cannelure, may create less or more case capacity, depending on how much bullet is inside the case. Many times load recipes for lead bullets may be for cowboy type loads or just to keep velocities down in attempt to lessen the amount of barrel leading.

 

[Toprudder]

Someone on this board once commented that the manuals document what was *actually tested*. So "Max Load", for example, isn't necessarily "Max Load That Generates Max/Safe Pressure"....but rather "Max Load Tested".

Once I heard that perspective it helped clarify why the numbers are often different.

That is the reason why I like to see load data with the pressures listed.

Speer does not list pressures, but will show different bullets (same weight) with vastly different charge weights. For instance, for 460 S&W they list two different 300gn bullets, their GDHP and UCSP.

300 UCSP, 300-MP powder, 28.0gn
300 GDHP, 300-MP powder, 38.0gn

Vastly different charges, and resulting velocities. The reason is that the GDHP is rated to take much higher pressure than the thinner jacket UCSP. The SAAMI listed pressure for 460 S&W is 65k psi, the same as the hottest magnum rifle cartridges.

 

[mdi]

Reloading manuals are not hard and fast formula. They are the published reports of the results they got using the listed components. The differences come from different manufacturing lots of the components, even bullets, different equipment and even though the equipment is certified, there can be differences. If two manuals had identical load data, I would question the source. If in doubt, use the lowest charge from the newest data...

 

[ArchAngelCD]

Not all data reports the max pressures. Some data will stop well below the maximum pressure limits because of bullet capabilities. If a bullet is known to fail @1200 fps the data will max out below the charge that will produce that velocity even though it's below the allowed pressures.

Different seating depth will also have a great effect on the max charge weight, especially in small cases like the 9mm.

 

[snakeye]

Also different lots of powder can make a difference as well. Some powders are more consistent lot to lot than others, some may have more of a lot to lot swing.

What are some of the specific powders that have a more lot to lot swing....

 

[Dudedog]

I saw a noticeable difference between some early lots of BE86 and a later one. I think the first couple jars I had were hotter than the later one say maybe 5%.
3rd and 4th of BE86 lots seemed to be in the middle of the first two. (these two lots were to close to tell apart)
WSF seems quite good lot to lot but I have maybe only used 10 different lots so still to small a sample.

I know the powder companies try to keep it really close for consumer canister powder but no idea how close.
I tend to think on the BE86 I used the first lots were on the faster side of what is allowed and the second lot was on the slower side so I had tolerance stacking.
Lots of powders I usedor have I have only used a couple lbs so way to small a sample to try to form any valid data most were really close.
To be truthful even with WSF where I have burned maybe 35 lbs I only have used about 6 different lots so the sample size is still to small.

Maybe Paul from Alliant could chime in and let us know what the allowable tolerance is lot to lot burn speed wise. 1%, 3%, 5%?

Hopefully Walkalong, BDS, ArchAngelCD, ArtofGolf........ (lots of the other guys) who used more lots can help out with your question.
We need some input here from the 250lb+ club guys