Casing Weight Question

Anthony C. · March 13, 2009, 05:28 PM

Alright, here's the situation:
The cartridge I shoot is .308Win. Since I'm using a new type of rifle powder, I needed to find my accuracy load. I tested between the minimum and maximum safe powder weights, and found my accuracy load, which ended up yielding between .16moa and .26moa at 200yds. Those results occured when I was using 153.0gn Hornady Match casings. When I bumped down to casings weighing between 152.0gns and 152.7gns, I found my groups opening up to .5moa to .65moa. The only thing I changed was the case weight. I continued to use the same weight primers (5.2gns), 2.004" long brass, same weight bullets (168.1gns), and the same length bullets (1.111" long).
I probably go through more steps during hand-loading than lots of folks, but usually it's rewarded with more accuracy.

Here's my question:
Do the lighter weight casings (all Hornady Match) have more internal volume? I assume this is the case because the outer dimensions of all the casings are identical...therefore it would stand to reason that the lighter the casing, the more internal volume the casing would have.
If that's the situation, my group sizes opening up would make sense, as I expect a velocity change due to loading the same amount of powder into casings having more internal volume than that of my accuracy load recipe casings. What do you guys think? Are you seeing an increase or decrease in velocity when changing your casing weights?

March 13, 2009, 05:28 PM	#1
Anthony C. Member Join Date: August 5, 2008 Location: Tennessee Posts: 28	Casing Weight Question Alright, here's the situation: The cartridge I shoot is .308Win. Since I'm using a new type of rifle powder, I needed to find my accuracy load. I tested between the minimum and maximum safe powder weights, and found my accuracy load, which ended up yielding between .16moa and .26moa at 200yds. Those results occured when I was using 153.0gn Hornady Match casings. When I bumped down to casings weighing between 152.0gns and 152.7gns, I found my groups opening up to .5moa to .65moa. The only thing I changed was the case weight. I continued to use the same weight primers (5.2gns), 2.004" long brass, same weight bullets (168.1gns), and the same length bullets (1.111" long). I probably go through more steps during hand-loading than lots of folks, but usually it's rewarded with more accuracy. Here's my question: Do the lighter weight casings (all Hornady Match) have more internal volume? I assume this is the case because the outer dimensions of all the casings are identical...therefore it would stand to reason that the lighter the casing, the more internal volume the casing would have. If that's the situation, my group sizes opening up would make sense, as I expect a velocity change due to loading the same amount of powder into casings having more internal volume than that of my accuracy load recipe casings. What do you guys think? Are you seeing an increase or decrease in velocity when changing your casing weights?