Reloading – Part 3
Last month I covered the process of reloading the casing. So at this point we have several rounds complete and we have zeroed the rifle at 100m. The next and final task is to find out the speed of the bullet through the rifle.
With factory ammunition, there is often a ballistics chart either printed on the box or inside. The chart gives the speed (velocity) of the bullet and the energy (force). The information will often also give the trajectory. Trajectory is the path of the bullet in flight at various distances. This is measured at the factory under controlled conditions. During the flight of the bullet, both the velocity and energy decrease depending on the distance the bullet has travelled.
Both the speed and the energy of the bullet are important. They are usually measured on exit of the muzzle and for shooting deer in the UK there is a legal minimum velocity and energy that the bullet must produce.
In England and Wales it is 1,700ft/ lb of energy and 2,450ft/ sec velocity. In Scotland the energy is higher at 1,750ft/lb, but the velocity is the same. I won’t go into the whys and wherefores here, but in Scotland the legal minimum bullet weight for deer other than roe is 100 grain. The minimum bullet weight in England and Wales is 50 grain for shooting muntjac and Chinese water deer. I always stick to 100 grain for roe and use heavier rounds for the larger species.
Humane despatch is what we are all looking to achieve and the energy of your chosen round needs to be adequate enough to enable that.
To measure the speed of your bullet exiting your rifle it is necessary to get hold of a chronograph. Many rifle clubs have them, if you do not have your own or you may know someone that is willing to help.
Set the chronograph up as the instructions state and fire three rounds through the guides marking the speed of each round after each shot. It is very likely they will be different, hopefully you have taken care to load accurately and the speeds will not differ by much. Add the total speeds together and divide by the number of rounds you have fired to get the average speed of the bullet exiting your chosen rifle. A word of warning here, ensure that your line of fire will pass in between the guides and not destroy the whole kit!
Once that is done then go to the Internet and check the bullet manufacturer’s ballistic information for the bullet you are using. This will give you a ballistic coefficient of the bullet at the speed it is travelling. From there the trajectory of your bullet can be worked out for the variable ranges you are firing at.
My results were:
Bullet speed: 2,740 ft/sec or 836 mps. Ballistic coefficient = .501
Using the Swarovski Optik ballistic app this gives the following data for the Swarovski Z6i
Zeroed at 100m:
150m the drop is 3.47cm = 2 clicks high. 200m the drop is 11.35 cm = a further 4 clicks high.
250m the drop is 23.99 cm = a further 4 clicks high.
300m the drop is 41.79 cm = a further 4 clicks high.
This was all achieved using the maximum load for the Hodgdon H414 powder, which produced a perfectly acceptable grouping on the target.
If I want the group to be even tighter then further experimentation will be necessary with either the seating depth of the bullet, the quantity or type of powder loaded or both.
Hornady Lock N Load equipment was used throughout this series.