Compressed Loads and Velocity
 

I have a question about a load in Nosler's Reloading Guide. For those of you who may have the 5th addition, there is a load on page 388 for 8mm Mauser sing a 200 grain partition. 52 grains of IMR4350 produces a velocity of 2698 fps. The load is marked as compressed (101%) and the most accurate tested for that powder.

I turned back to page 387 to look at the 180 grain loads and the fastest load listed is only 2669 fps (Varget) with a BT. In fact, they have the same IMR4350 load listed (52 grains) at a velocity of only 2545 fps for a 180 grain BT.

How is it possible that the fastest 200 grain load is faster than the fastest 180 grain load? And why is the same 52 grains of IMR4350 pushing the 200 grain bullet faster than the 180 grain bullet?

RE: Compressed Loads and Velocity
 

The heavier bullet has to be seated further into the case to meet the overall length requirement. This decreases the volume of the combustion area, which raises the pressure and increases the velocity.

RE: Compressed Loads and Velocity
 

Thanks Jason. But that would mean the 180 grain max loads are listed well below max pressure then. Not sure why they would post the data that way.

RE: Compressed Loads and Velocity
 

Jason certainly has something there, and it goes along with the following idea, which is based on both powder burning rate and cartridge case volume:

I suspect the reason for this is that the 52-grain load is more efficientwiththe 200-grain bullet (gets the most out of the amount of powder) than with the 180-grain. I'll bet that you could use MORE than 52 grains of IMR 4350 with the 180-grain bullet, and get even higher velocities, IF you could get more IMR 4350 into the case and still be able to seat a bullet! But since the case doesn't have enough room to try this with IMR 4350-sized powder grains, you will never know!

However, if you tried this test with WW 760, H414, or even Norma N204 powder, all three of which are dense enough to allow you to put a heavier weightthan 52 grains into the 8X57JS case, you could give it a try. Of course, you'd have to start with like 50 grains of any of these, and work up no faster than 0.5 grain at a time, load up five, and chronograph them as you worked up, making sure you got no loosening primer pockets while doing it. You might be surprised at how fast a 180-grain bullet can be SAFELY driven from a strong 8X57mm, IF the right powder is found.

(No, I don't really know. I have only worked with the 8X60RS, which will let me put in more powder w/o compressing the load. With one load, I was able to get 2620 FPS with 200-grain Nosler Partitions.))

RE: Compressed Loads and Velocity
 

Nosler lists the 180 grain IMR 4350 load at 99% load density, so the load is not compressed for that bullet and you would think maybe they could have added another .5 grains or so, but they chose not to for some reason.

RE: Compressed Loads and Velocity
 

Well, Sling, just how much IMR 4350 can you get into your 8X57mm cases? IF you can get significantly more in, you could try working up higher than 52 grains and see what the results might be. One-half grain at a time, or course, to be safe. All rifles are individuals, and although 52 grains with the 180-grain bullet might well be max. in Nosler's test rifle, yours might max out ata higher (OR LOWER) powder charge level.

RE: Compressed Loads and Velocity
 

I have a newer rifle (Rem 700 Classic),and the compressed loads are finewith the 200 grain bullet.

I normally do not exceed max loads, but in this case, I think I am going to try to slowly work uppast that 180 grain max load.