testing ammunition
It would be nice and easy if all groups test at this size!

Troubleshooting tips when you’re testing ammunition

When we set out to test ammunition, whether it is factory or handloads, exactly what are we attempting to achieve? 

We are aiming for (bad pun) a balance between velocity and group size. 

Before you start, check that the telescopic sight and bedding screws are nipped up tight. Guess who got caught by that one?

Whether you fire a five-shot or three-shot group is up to you. It can be done with a minimum of equipment but you do need a chronograph. It is normal to shoot groups at 100 yards or 100 metres. 

When testing loads, if all goes well you will shoot acceptable groups at an acceptable velocity. But what do you do if the results are less than satisfactory?

If you are using factory ammunition, the options available are limited. You could change the weight of the projectile in the same ammunition, if it is available. Or, similarly, change brands and retain the same projectile weight. 

Unfortunately, there is not a lot of room to move. The projectile weight may be influenced by exactly which animal you intend to shoot.

Handloads are a horse of a different colour! 

Initially, check several manuals for a powder somewhere in the middle of those listed. Yes, I know that with shortages, what you want may not be available. 

Reloading ammunition
The correct powder goes a long way to making a load accurate

If the velocity is below a reasonable figure for the caliber, the first step should be to use the next fastest powder. 

Some shooters chase velocity at the expense of accuracy, but I suggest it should be the other way around. 

If the group accuracy is a problem, the first item to look at is the powder, then whether the projectile has a boat-tail, and then seating depth. 

In the first instance, it is probably a good idea to start with a powder around the middle of those listed. In addition, for ball powder and loads over about 50gn, a magnum primer is probably a good idea, if they are available. 

If the shots are vertical, the convention is that more powder is needed; if horizontal, most claim wind or a sighting error, but I am not convinced. I would try ½gn of powder more and see what that produces. 

If the velocity is not up to your expectations a faster powder or lesser projectile weight is called for. 

If the size of the group is outside your parameters you simply have to use another powder. 

Convention suggests that heavier projectiles require a slower powder but that statement is not carved in granite.

Sometimes very small changes will have a marked effect on group size. Changing primers is a typical example. 

With some cartridges, I have found that sometimes a powder slower than normal will reduce the velocity a bit but the load is much more accurate. They’s worth of considerating. 

Another issue that is seldom talked about is the speed of the actual shooting. This can have a marked effect on group size.  

I normally shoot three-shot groups at a comfortable pace but it does not work with all cartridge/rifle combinations. 

.257 Weatherby Magnum
.257 Weatherby Magnum has a slim barrel that heats up quickly, disrupting accuracy

I have a .257 Weatherby Magnum rifle that has a slim barrel. With 70-plus grains of powder propelling the selected projectile, three-shot groups at a comfortable pace are in excess of three inches (76mm) in size. The barrel, of course, heats up rapidly. 

If I allow 10 minutes between shots the group size shrinks to less than one inch. 

The other issue seldom talked about is the effect of barrel fouling on group size. 

Starting with a clean barrel, barrel fouling becomes an issue somewhere along the line and thus it requires cleaning of combustion residue and, more importantly, copper to allow the barrel to shoot a correct group size.

Take your time and shoot carefully. The results will be worth it.




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Ron James