Book powder charge difference

[C-130 Dude]

I know there are more than a couple of reloading books out there that have the same load, but different charge weights for the same load using the same bullet and powder type.

However, when I see a difference of 2+ grain difference in the same load I begin to wonder just what the heck.. These are for standard 308win guns, not service rifles.

E.G., 308win, IMR4064

Sierra #6- 168 SMK, 44.3 max
VS
Hodgon #2021- 168 SMK, 45.9C max

AND

Sierra #6- 175 SMK, 42.3 max
VS
Hodgon #2021- 175 SMK, 45.6C max

Am I missing something?

 

[birddog 68]

Am I missing something?

No you're not. I'm fairly new to reloading (10 years) and I noticed if I look at 3 sources I will get at least 2 different.
I just use it for a ballpark figure since all rifles are different.
I start low to midrange and work up slowly until my rifle tells me that I am at max and then back it off at least one grain.
I noticed Nosler and Speer are usually on the hot side compared to hodgdon.

 

[cohunt]

Each test gun is slightly different(as is your rifle), and they usually use different primers and brass too. Also- the date the load data was printed (older data was usually a little less muddied by lawyers)--- don't forget that different lots of powder will often times have slightly different burn rates. Reload books are guidelines, not hard set rules----- that's why ALL the reload data books say "start low and work your way up"

 

[Wedgy]

These two different speeds are the same load in RP brass and Nosler respectively. The Nosler is thicker and has less volume than the RP. I usually try to check three sources and get a consensus of the data, but as you see there are a lot of variables including the difference in powder lots, bullets, primers, etc.
The Berger book is very conservative compared to other sources but there's nothing wrong with that.
88.0 = 3,070 3,209
88.5 = 3,109 3,218
89.0 = 3,114 3,223
89.5 = 3,121 3,212

 

[CanisLupus]

However, when I see a difference of 2+ grain difference in the same load I begin to wonder just what the heck.

They're not necessarily the same load. Only a couple variables that are obvious to the reader of the manual are being considered … could be different chambers … could be different barrel lengths … could be different cases (i.e. overall geometry/capacity) … could be different primers … could be different ammo loading procedures … could be different testing conditions …

 

[C-130 Dude]

They're not necessarily the same load. Only a couple variables that are obvious to the reader of the manual are being considered … could be different chambers … could be different barrel lengths … could be different cases (i.e. overall geometry/capacity) … could be different primers … could be different ammo loading procedures … could be different testing conditions …

Woulda, coulda, shoulda. You miss the point. The reader has no choice but to consider the book data. If you aquire and read the book data, you just bought into the data. However, anyone that does not start workup below max loads (to start with) takes their lives into their own hands. This is accepted by all reloaders, regardless of what caliber selected. In the case of the 175 SMK load I mentioned, there is a 3.4 grain difference between 2 book makers. I've never seen that much disparity. Granted, the Hodgon data is a compressed load. But I was able to charge 45.3 without compressing the powder. (2.810 oal) This was in a '15 LC case, which we all know tends to be smaller than most. I'm just very dismayed at the differences at published book data. If you happen to have the manuals I used, take a look at the test guns and components used. Not a big difference here.

 

[cohunt]

The "reloading manuals" all used to actually have pages up front on how to "properly reload metallic cartridges" , they were more like books than just data pages--- but that's when people used to read books---- I havent bought a manual in years but I'd put $ that they still all have disclaimers to start low and work up, and that reloading can be a dangerous activity.

The main differences are going to be the test barrel, chamber, and powder lot-- but cases can play a fairly large part in it too.

I tend to try to use multiple sources but especially refer to the data the powder and bullet manufacturer posts.

Do the different manuals list pressures? I have noticed that certain manuals will show a max charge- but if you look at the pressure for that charge it can be considerably lower than max saami pressures

 

[C-130 Dude]

The "reloading manuals" all used to actually have pages up front on how to "properly reload metallic cartridges" , they were more like books than just data pages--- but that's when people used to read books---- I havent bought a manual in years but I'd put $ that they still all have disclaimers to start low and work up, and that reloading can be a dangerous activity.

The main differences are going to be the test barrel, chamber, and powder lot-- but cases can play a fairly large part in it too.

I tend to try to use multiple sources but especially refer to the data the powder and bullet manufacturer posts.

Do the different manuals list pressures? I have noticed that certain manuals will show a max charge- but if you look at the pressure for that charge it can be considerably lower than max saami pressures

I was only referencing max on one load, the 175 SMK. The 168 SMK was there as an additional example. I refered to both the bullet maker AND the powder maker. There is a big difference. BTW, every book lists min and max powder charges, as they tested them. I did use multiple sources. I've been reloading for 52 years now and I find this disturbing to find this big disparity. I was hoping someone out there could shed some light on why.

 

[cohunt]

I was only referencing max on one load, the 175 SMK. The 168 SMK was there as an additional example. I refered to both the bullet maker AND the powder maker. There is a big difference. BTW, every book lists min and max powder charges, as they tested them. I did use multiple sources. I've been reloading for 52 years now and I find this disturbing to find this big disparity. I was hoping someone out there could shed some light on why.

Did they list pressure?

 

[Salmonhead]

It gets really exciting when one source min is above another source max. More fun when a source lists a projectile of lesser weight with lower max charge than a heavier projectile of the same make and same powder. Another common thing is a group of data will be tested to much lower top pressure. Example is testing out one bullet to 58k psi and other bullets for the same cartridge to 62k psi.
Books are not absolute. Too many variables. Compile as much data from as many sources as possible and make an educated guess where to start with that rifle and work up slowly.
A good way to adjust powder is to start low and increase powder until book velocity is met. If the pressure is listed in the recipie, you will be there when the velocity is achieved. John Barsness talks about that method in his books.

 

[MagnumManiac]

The simple answer is that cartridges and firearms are NOT constant, which is why data between tests are different…
Have you had a rifle/cartridge that was faster or slower than the book velocity with IDENTICAL COMPONENTS?!
Reloading manuals are guides, pressure is not constant, even in a test barrel, they use a "fudge factor" set out by SAAMI, whatever the reference ammo says rarely, if ever, matches another test barrel, or test barrel operator. Every Reloader should know this PRIOR to ever charging a case with powder…just like charges given on the interwebs that worked in Joe Blows rifle, this does not mean it will be safe in your rifle.
Luckily, I can test pressure and often max loads that differ between manuals are safe, even when there is a 5%-10% difference.
An example is 338WM load with 225g bullet and max charge of RL19 in Speer #13 is 78g, no other manual, including Alliant's own data, comes anywhere near this charge weight, 75g appears max in just about all manuals.
When I tested it, it was still below max pressure by 3,000psi and the 75g load was below 58,000psi.

Cheers.

 

[C-130 Dude]

The simple answer is that cartridges and firearms are NOT constant, which is why data between tests are different…
Have you had a rifle/cartridge that was faster or slower than the book velocity with IDENTICAL COMPONENTS?!
Reloading manuals are guides, pressure is not constant, even in a test barrel, they use a "fudge factor" set out by SAAMI, whatever the reference ammo says rarely, if ever, matches another test barrel, or test barrel operator. Every Reloader should know this PRIOR to ever charging a case with powder…just like charges given on the interwebs that worked in Joe Blows rifle, this does not mean it will be safe in your rifle.
Luckily, I can test pressure and often max loads that differ between manuals are safe, even when there is a 5%-10% difference.
An example is 338WM load with 225g bullet and max charge of RL19 in Speer #13 is 78g, no other manual, including Alliant's own data, comes anywhere near this charge weight, 75g appears max in just about all manuals.
When I tested it, it was still below max pressure by 3,000psi and the 75g load was below 58,000psi.

Cheers.

I shot identical loads in my AR308 and my bolt 308. Both 20in barrels. The loads were both in the middle of book charge. 42.0/168SMK. The velocities were 68 fps different. Not close to over maximum pressure.

 

[MagnumManiac]

I shot identical loads in my AR308 and my bolt 308. Both 20in barrels. The loads were both in the middle of book charge. 42.0/168SMK. The velocities were 68 fps different. Not close to over maximum pressure.

Quite possible the difference was due to action type, but unless you have pressure testing equipment, that is just an assumption by me.

Cheers.

 

[PBramble]

there's generally one major factor in the listed numbers in the book. Lawyers. some companies are more conservative due to today's litigious society. I had a book that showed 42 gr max for .308. We safely found and accurate load with good velocity at 44. the reference books are just that, good information to start with.