Can't get spec velocity...375HH...why??

[drdougrx]

I'd like some advise.  I shoot a 375HH and use 300gr nosler partition bullets.  I have a oehler chrono and load 72.5gr RL-15, CCILRM primers and Rem cases.  My rifle, a Rem 700 BDL SS has a 24" magnaported, crowned barrel.  My average velocity with this load is 2460FPS with an average Sd of 12 or less (meaning that of the shots fired, 95% attained a velocity of 2448fps - 2472fps).  As best I can figure the spec velocity for the cartridge is 2550fps, so I get 98% of spec.

I've seen some data in other threads that suggest this load would get 2600fps...I know it's probably academic...but...why is there so much disparity??

[Little Joe]

drdougrz
Go to Accurate Reloading Forums. Click on the reloading section then go to ChronoGraph Question by Big Country. I would post the link but it wont work when I post it on the thread. Just copy and past Accurate Reloading forums into your browser search engine.

Little Joe

[drdougrx]

 Thanks Joe...will do.

[Val]

I don't think there is such a thing as a spec velocity. The reloading manuals list a muzzle velocity which was attained with their test rifle. Their rifle could have a longer barrel, certainly different chamber and barrel dimensions due to tolerances, different batches of powder, etc. All this leads to variations in achieved muzzle velocities by indivdual firearms.

[drdougrx]

Thanks Val....spose I should say I get 1.5" groups at 100 from the bench.  I can get 2500+ consistantly when I use 74gr of powder which is kinda very over max.

[PaulS]

Different guns get different velocities. Even with the same pressure a gun can have a barrel that is just a little rougher or a ten-thousandths of an inch smaller in diameter and end up with a lower velocity with even more pressure than the book says it will get. The load in the book is to achieve a given pressure range and they always tell you to watch for excessive pressure. They do that because they know that your gun may be different enough to give dangerous pressures with a load that is under the listed maximum load. Most of the time that maximum load will be safe but change one component or have a barrel that is too rough or too tight and you can put your gun or yourself in danger without going beyond that load that says "maximum" in the book. It was tested in a "universal receiver" and not in your gun. It is the reloader's responsibility to use the information in the books safely - it is not the books author's job to protect you from yourself.