Sunday, August 21, 2005

Velocity Measurement

Recently, a reader from the Carnival of Cordite asked what velocities we can expect from factory ammunition. For years we have expected that the velocities from factory ammunition will vary somewhat from the velocity we actually measure, for a variety of good reasons. Barrels vary. The factory usually takes their readings from specially designed pressure barrels. Temperatures vary widely during the shooting year, and temperature affects pressure. Pressure affects velocity. We don't often find the same velocity in the field that we find in the ballistics tables, although the companies have been trying lately to get closer to the velocity that the shooter will see in the field.

Still, the question was a good question, so I loaded a couple of rifles into my pickup truck and went out to find the answers. I went over to Wal-Mart on my way to the woods and picked up some ammo. I tried to get a slow round and a fast round, so I purchased the Remington Express 100 grain Pointed Soft Point Core-Lokt in .243 Winchester and the Remington Express 170 grain Soft Point Core-Lokt in .30-30 Winchester. These two types represent standard ammo that can be found virtually anywhere in the United States. The Remington ballistic tables are here.

The rifles were also standard rifles that anyone might find on the hunting grounds. The .30-30 was the same Winchester 94 that I wrote about earlier. It has a 20 inch standard barrel and peep sights. The .243 is a Model 10FXP from Savage Arms. This rifle is brand new, having recently been purchased at Wal-Mart. It is last years model and came with a scope. It has the synthetic stock and looks a lot like this rifle.

I went to my Dad's place in the woods and set up the chronograph. I enlisted my brother as a range assistant and we began shooting. The results were suprising.

In the above picture, David is squeezing the trigger on the Savage. This was one of the first six rounds fired through this rifle, and I expect that velocities will increase as the barrel becomes broken in. Note that he is using a position we call pickup prone and is making good use of the Kelly-Tappin machine rest that stays behind the seat of my truck at all times.

In this photograph, we see David from another angle. Here we can see the chrongraph on a tripod and a target downrange at the base of a pine tree. Dad wants to kill this pine tree, evidently, as he always puts the target holder at the base of that tree. For the record, we were shooting in partly cloudy conditions with little or no wind. The ambient temperature as measured by a circa 1964 Coca-Cola thermometer was 96 degrees in the shade. The relative humidity approached 100 percent. It was a standard Louisiana summer afternoon.

The results? I was surprised. The Remington ballistic tables list the .243 Win, 100 gr PSPCL as having a muzzle velocity of 2960 fps. My measurements with my rifle and my Chrony showed an average velocity of 2997 fps.

We switched to the Winchester 94 and the .30-30 ammo. The Remington ballistic tables show this ammunition ( Rem Express .30-30 Win, 170 SPCL) as having a muzzle velocity of 2200 fps. My rifle and my Chrony showed an average velocity of 2159 fps.

So, it looks like my measurements are real close to the Remington factory tables. They are to be commended for putting together such a table. I am considerably surprised at how close the velocities were.

I don't see my brother but once a year, or so. He lives in Vermont and when he comes down to visit Momma, we only get to spend a couple of hours together, so it was good to spend some time shooting with him.

Now, I have to get some powder and bullets and start working up reloads for the Savage. I expect that this box of factory ammo is all I am ever going to put through it.

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