Thread: Case capacity effects on velocity

Well done

Originally Posted by DAF

Well done

I'm stoked. Perfect waterline the whole weekend. Got hammered by the wind at 1K on Sat, but very happy with the way the ammo is going...

Gonna have to come listen to your case prep steps, hehe.

Originally Posted by ebf

Ha ! The OCD reloading paid off...

Shot my first 60.nn on a 800yd target this weekend up in Gisborne. So that's 10 consecutive shots into a 255mm circle

Is it the reloading or the shooting tho?

Wind rarely blows horizontally in this part of the world.

Reloading VC, widest part of a circle is on the mid-line, so if you can keep all your rouns at the same vertical level (small ES) you have the best chance of placing them all inside the circle if your wind calls are good. On the mid-line, you can afford to make a 0.5 MOA wind error, if you shoot 0.5 high and make the same wind error, you are outside the center bull...

Originally Posted by ebf

I've been weighing my target cases.

The Lapua cases are noticeably lighter than the ADI and PSD cases I used before.

So this got me thinking, if you use the same amount of powder and the same weight projectile, what effect would a lighter case (assume it has more internal capacity ?) have on velocity ?

Asked another way, if you batch your cases and projectiles by weight, would you use the heavier projectiles with the lighter or heavier cases, and why ?

I have been batch shooting S&B 303brit brass, 1943 mil brass and Winchester brass at Trentham all with the same load 38gr ADi2208, I have not noticed a difference.

Now out at 1000yds Im told that 1gr can make a 1inch difference in height. So yes batch cases. So a non-mil case might shoot a little lower as its capacity is higher but you may only see that at 800yds+ 45gr of ADI 2208 in a Lapua case and fed 210M primer is just supersonic at 1000yds, it maybe that a heavier ADI case will bump that velocity up 50fps so you can use a wee bit less powder, or get a wee bit more velocity. The lapua brass is suberb quality IMHO so its what to use for best consistancy I think.

PS I have weighed my projectiles and the match ones (15gr Nossler/HBC) dont vary much, ie < 0.1gr. If I am feeling keen I batch the 303brit FMJs but they only differ by <0.2gr.

Well done good Sir (EBF) on your 60.nn

My shooter had a good weekend too, his first 60 (no X ring) at 500 yards. He can't blame equipment or reloader anymore.

Originally Posted by ebf

Hehe Dave, no TV, so lots of time to read and think about these types of things.

The physics of it fascinates me... Would you get higher or lower pressure (and resultant velocity) for a given power weight and projectile weight if the combustion chamber is larger or smaller ?

Higher pressure is supposed to happen in military cases as the walls are thicker so you have to back off the load.

Wait til you get hooked on the tribology....a great sleeping aid.

@Cyclops, they did not have X targets loaded either for Gizzy champs

how is the 308 build coming along ?