Questions on max loads.

[Mr. Mike]

Just getting back into reloading. I do start low and work up to loads and not all that interested in getting the hottest loads or the fastest velocities. I have gathered 8 different reloading information forms. I will only use the 5 that show the specific powder and bullet weights. This will all be for .308 Win., IMR 4064 powder, and 150 gr. sp bullet. This is what I found to be the listed max loads/fps for the above information:
1. max load 44.9 gr/ 2700 fps
2. max load 44.9 gr/2800 fps
3. max load 48.2 gr/2900 fps
4. max load 48.0 gr/2920 fps
5. max load 47.7 gr/2902 fps
OK, I know that different barrels and lengths will change things a bit but given the same powder and the same projectile one would think the difference between max loads would not be as far apart as 3.3 grs? I am sure that once I start to work up a load and examine each increase for signs of pressure I will arrive at my own max load but just trying to understand these differences from the so called manuals. Anyone have any ideas why this is?

[jwrowland77]

Each one has their own testing barrels and lawyers.

Situation like this, I go with Powder Manufacture as long as they have data listed for the bullet I'm doing.


That's what I did when I did my workup of IMR 4064 using a 175gr SMK.

[Bart B.]

Each barrel's bore and groove diameters could vary enough to cause a 3 grain spread in powder for the same visual pressure signs. There's easily a .002" spread in a .308 Win. barrel's groove diameter and .003" spread in bullet diameters. A big diameter bullet shot in a small groove diameter barrel will have very high pressures for even some suggested starting loads.

And 3 different people will have 3 different interpretations of given pressure signs for a given load.

All of which means most load estimates for data are measured with a rubber ruler and how much it's stretched to meet the loader's objectives.

Best sources, in my opinion, are those from powder companies listing pressure data derived from proper measuring systems and bullet companies testing their products.

[SpringOWeiler]

I always recommend choosing the suggested accuracy load given by the manufacturer.

[Slamfire]

Reloading manuals are a guide. Your rifle will be different. Since the slope of the pressure curve is exponential, tiny changes in anything mean huge changes in pressure.

I do recommend load testing over a chronograph, since there is “no free lunch”. If velocities over the chronograph exceed book values, you can bet that pressures are exceeding maximum, even if the classic symptoms of sticky bolt lift or blown primers are not evident. I am of the opinion that if I see classic over pressure symptoms, I exceeded a maximum load a long time before.

[NWPilgrim]

Powder lots can vary 5-10% as well. All the variables added together can stack differently.

I would start below 44 gr for sure. And consider the 44/49 gr range as a "watch carefully" zone.

[pathdoc]

What they've all said.

The big issue is how they do the testing. Variables such as the type of brass, the primer used, the firearm used (pressure barrel versus sporting or milsurp) and its barrel length, how many rounds that barrel has fired, etc. can all gang up to change things. Not all shoots can always be done at standard temperature and pressure on a climate-controlled range, which means that those variables have to be corrected, either by firing against reference ammo which IS shot at STP or by correcting it mathematically against prevailing conditions (whose measurement might have errors). Gain or loss of velocity per inch of barrel length is dependent on the actual velocity, and MAY be dependent upon the nature of the powder. The composition of the bullet can radically change the way it behaves in the barrel, even for the same bullet weight, primer, and powder charge. 150gn sp (assuming you mean spitzer or softpoint or both) can cover a lot of territory.

[steve4102]

Use this!

http://www.hodgdonreloading.com/

[Clark]

With a 22" 308 surplus 4895 [read H322] 150 gr Sierra I got 3050 fps and groups ok, but 3100 fps and all loose primer pockets.

By the time I backed off a safety margin I would be down to 2900 fps or less.

[Mr. Mike]

I surely do wish to thank all those who offered their views on my question. I guess that I will continue to do what I did all those years ago....start low and work my way up to the loads that give me the best consistent accuracy with out any signs of excessive pressure.
Again, thanks.
Mike

[Hunter Customs]

I surely do wish to thank all those who offered their views on my question. I guess that I will continue to do what I did all those years ago....start low and work my way up to the loads that give me the best consistent accuracy with out any signs of excessive pressure.
Again, thanks.
Mike

That's my thoughts and the way I do it Mike, I'll always sacrifice velocity for better accuracy.

Best Regards
Bob Hunter
www.huntercustoms.com