For many years before i was a reloader, i would buy factory ammo, all brands, and save the brass because “someday i was going to reload.” Well i did and I’ve been reloading now for about 5 or 6 years. I shoot a 270 Win. I recently decided to use a bag of Hornady brass that i had collected and develop a load for elk. I’m a bit of a data nut, thus I measure muzzle velocities etc. Doing 3-shot groups at the range, i noticed i had 2 different types of brass, some with Hornady stamped, others with Frontier stamped. Some of my groups were all Hornady, some all Frontier, some mixed. A quick google search told the story of where the Frontier brass came from, not important for now. The all-Hornady groups and all-frontier groups had pretty low Extreme Spread of 35-40fps. Something much more unexpected was that the Frontier cases produced significantly higher muzzle velocities than the Hornady cases, by 100 fps or more with the same powder charge, primer, bullet, everything. And the 3-shot groups with the mixed brass were a disaster, 140fps ES. Tonite i decided to weigh the Hornady’s vs the Frontiers to see which ones are heavier, which contains more brass. Turns out the Frontiers are heavier, 11-ish grams vs 12-ish grams. So why such a difference in muzzle velocity ??? All were full length sized at the same time. 3000 vs 3100+ fps difference. I’m sure there’s a logical answer and i can guess, but i want to hear what the HT wisdom has to say. Cheers… Pete
Case volume physics
- Thread starter Blaser270
- Start date
millerkiller77
Well-known member
35-40fps es isn't considered low , and 3 shot groups are going to have you chasing your tail all day when trying to nail down consistent data.
- is all the brass out of that same rifle?
-case weight is mostly irrelevant, internal case capacity is critical
-reloading process? Are you annealing, shoulder bump, trimming exactly the same?
- is all the brass out of that same rifle?
-case weight is mostly irrelevant, internal case capacity is critical
-reloading process? Are you annealing, shoulder bump, trimming exactly the same?
D_Walt
Well-known member
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- Apr 15, 2020
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- 725
A full case = higher pressure and higher velocity. More brass in the case means less room for powder, thus a higher load density (a more “full” load of powder). If you don’t have any pressure signs you can up the powder in the Hornady Brass and get a higher velocity - but the same load may pressure out in the heavier brass.
Farmerj
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Guess I’d measure the water volume on both…
@millerkiller77 , same rifle, same full length sizing with slight shoulder bump on the cases all in one sizing session, cases were once fired factory ammo, not annealed, all trimmed exactly the same. 35-40 fps ES is way better than factory ammo so I’m happy there. I’m not good enough to shoot 500 yds.
@D_Walt , that’s where my head was guessing.
@D_Walt , that’s where my head was guessing.
std7mag
Well-known member
Interior volume is the true measurement for your cases.
35-40fps for ES is about what I'd expect for factory ammo.
Handloads, low teens to single digit.
And do that over 10 or 20 rounds to give you a more realistic measure.
Oh, and don't mix rifle brass!
Pick one and use it!
35-40fps for ES is about what I'd expect for factory ammo.
Handloads, low teens to single digit.
And do that over 10 or 20 rounds to give you a more realistic measure.
Oh, and don't mix rifle brass!
Pick one and use it!
You made some good observations.
If they have the same external dimensions (which they do, since they were shot in the same rifle and reloaded with the same dies), they’re made of the same material (brass), but one weighs more than the other (by 12 grains [at least I assume you mean grains because 12 grams = 185 grains]), then logic would have it that the heavier cases have thicker walls, therefore they have less case capacity. Same powder charge in a case with less capacity will result in higher pressure and higher velocity.
You see the same thing when people switch to thicker brass like ADG. They have to work up a new load, starting lower, to avoid shooting higher pressures than they intended.
If they have the same external dimensions (which they do, since they were shot in the same rifle and reloaded with the same dies), they’re made of the same material (brass), but one weighs more than the other (by 12 grains [at least I assume you mean grains because 12 grams = 185 grains]), then logic would have it that the heavier cases have thicker walls, therefore they have less case capacity. Same powder charge in a case with less capacity will result in higher pressure and higher velocity.
You see the same thing when people switch to thicker brass like ADG. They have to work up a new load, starting lower, to avoid shooting higher pressures than they intended.
