Case capacity in a 375 H&H

COREY

COREY

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Hello All,

I am loading the 375 H&H Mag for my Ruger #1H and I have a couple questions to ask. The overall length of the round is supposed to be 3.600", but I have pushed the bullet forward to get closer to the rifling; the new OAL is 3.680".'

One of my questions is with regards to minimum charge. I know that the minimum charge is marked to make sure that you do not end up with pressure spikes from unpredictable powder burn. If I increase the case capacity in this way, should I be worried about the minimum charge?

My other question is with regards to the other end of the spectrum. With the extra amount of space, could I incerease the charge slightly without causing excessive pressure?

Thanks,

Corey
 
The Speer book is showing that the min. load is 4 grains below the maximum load with IMR 4064 for the bullet I am using. What I am trying to figure out is if the numbers in the manual are still acurate. Can I ring a bit more fps out of it now, and should I be worried about the min charge?
 
well, you can calculate the additional volume you gained. 1/2*3.14159*.375*.375*(3.68-3.60)=.0177in3 (x25.4^3) or 290mm^3

So now all you have to do is find out how many grains fit into .0177 cubic inches (290 cubic mm's).


Keep in mind though that as the increased volume will lower pressures, the shorter leade/freebore will increase pressures.
 
Okay...here's what I think...

With a 300 grain Sierra bullet and an OAL of 3.600", minimum load would be 61.3 grains of IMR-4064 and maximum would be 67.9 grains.

With the same bullet and an OAL of 3.680", minimum load would be 62.5 grains of IMR-4064 and maximum would be 69.2.

I generally suggest:
IMR-4064 From 52.3 grains to 68.7 grains
Remington 9-1/2M Primer
 
I'd back off the max a few grains and load some up, slowly going up in half grain increments. If you have a chrony or know somebody who does, use it and keep an eye on velocity, which is a good way to guesstimate pressure. IF you see some speed #'s that are above what the manual says, you better back off a bit. :)
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Corey -

Start at the recommended minimum load from the manual - seating the bullet into the lands will not get you into trouble if you proceed from this point. The .375 H&H is a large case, so you can increase in incriments of 1.0 gr. If you can shoot over a chronograph, this is the safest way to develop your loads, because when you reach the maximum velocity listed in the manual with any given powder and bullet you know you are also at the maximum pressure. In this way you do not have to rely on sticky bolt handles, flattened or leaking primers, or case head expansion to tell you when you are entering dangerous territory. When you reach the maximum velocity published in the manual - that is your maximum load - do not go further even if you are well below the published maximum load! The fact that you are seating into the lands means you might achieve maximum pressure with a lighter powder load. Once you have determined what the maximum load is in your rifle, often dropping a grain below maximum will improve accuracy and case life - often with a very minor loss of velocity.
 
Somewhere between min and max you'll find the sweet spot for accuracy in your rifle, that can be a factor for those longer shots so you may not need to stress over getting that last few FPS.
 
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