Out of 30 rounds I shoot at a time, I typically see velocity variations anywhere from about 45 fps to 85 fps, every now and then, even higher.
All this is based on the 223/556; other calibers may be different.
And, just to be clear, very often with only 5 or so shots fired, I do see low ES's. But by the time I get 30 shots in, the ES has increased dramatically - just about every time. This shows that small sample sizes do not truthfully indicate reality.
So, I began to wonder, with +/-0.1 charges (double weighed), quality components, i.e. 77 gr SMK bullets, Lapua cases, Federal 205m primers and Varget powder, where does this 60ish ES come from?
I thought, could this be as simple as tolerance stacking? Well, yes it could! In case you don't know what tolerance stacking means, it means that the variation of all the individual components add up in the same direction. Normally, at least we would hope, the individual variations would "average" out, but when they all add up in the same direction, the result impact can be larger than we expected.
OK, so I'm doing this with QuickLoad. It's not perfect, but I really don't know of any real-world way to isolate one effect from all the others, so QuickLoad it is.
You can see the components I varied, one at a time, and this doesn't include all the influences but it will give us a pretty good idea how each component isolated affects velocity.
The reason there are two tables is one is for tolerance stacking in one direction, and the second table is for tolerance stacking in the opposite direction. As I suspected that effects in the positive direction are a little different than they are in the negative direction.
So once we have the effects of both, and we've added them up, the possible ES is the sum of the positive and negative effects. That is, one shot could have all positive tolerances and another shot all negative tolerances. The difference between them would give us the ES.
Here's the tables.
![Image]()
The ES for the combined effects is given at the bottom right of the bottom table.
These are pretty reasonable variations. And, as we can see from the ES the combination of all the small effects can generate a pretty large number.
So, based on the limited variables I've used here, it is not unreasonable to get large ES's. I watched an Eric Cortina video where he was breaking in a new barrel and was measuring velocities to see if the barrel would speed up as more shots are fired. This was a precision rifle/barrel in a F Class set up. He shot groups of 10 at a time until he had shot 200 rounds. He showed the ES as he went and even with this precision set up he got a lot of ES's of 50 fps.
![Image]()
Here's a chart that really shows how much each component variation affects velocity. The diamonds are the sum of the positive and negative stacking.
Not much doubt where most of the effort should go is there? Case capacity is the biggy, followed by charge weight. You can pretty much forget about bullet weight and neck tension. Of course it could be those things actually vary more than the values I used.
All this is based on the 223/556; other calibers may be different.
And, just to be clear, very often with only 5 or so shots fired, I do see low ES's. But by the time I get 30 shots in, the ES has increased dramatically - just about every time. This shows that small sample sizes do not truthfully indicate reality.
So, I began to wonder, with +/-0.1 charges (double weighed), quality components, i.e. 77 gr SMK bullets, Lapua cases, Federal 205m primers and Varget powder, where does this 60ish ES come from?
I thought, could this be as simple as tolerance stacking? Well, yes it could! In case you don't know what tolerance stacking means, it means that the variation of all the individual components add up in the same direction. Normally, at least we would hope, the individual variations would "average" out, but when they all add up in the same direction, the result impact can be larger than we expected.
OK, so I'm doing this with QuickLoad. It's not perfect, but I really don't know of any real-world way to isolate one effect from all the others, so QuickLoad it is.
You can see the components I varied, one at a time, and this doesn't include all the influences but it will give us a pretty good idea how each component isolated affects velocity.
The reason there are two tables is one is for tolerance stacking in one direction, and the second table is for tolerance stacking in the opposite direction. As I suspected that effects in the positive direction are a little different than they are in the negative direction.
So once we have the effects of both, and we've added them up, the possible ES is the sum of the positive and negative effects. That is, one shot could have all positive tolerances and another shot all negative tolerances. The difference between them would give us the ES.
Here's the tables.
The ES for the combined effects is given at the bottom right of the bottom table.
These are pretty reasonable variations. And, as we can see from the ES the combination of all the small effects can generate a pretty large number.
So, based on the limited variables I've used here, it is not unreasonable to get large ES's. I watched an Eric Cortina video where he was breaking in a new barrel and was measuring velocities to see if the barrel would speed up as more shots are fired. This was a precision rifle/barrel in a F Class set up. He shot groups of 10 at a time until he had shot 200 rounds. He showed the ES as he went and even with this precision set up he got a lot of ES's of 50 fps.
Here's a chart that really shows how much each component variation affects velocity. The diamonds are the sum of the positive and negative stacking.
Not much doubt where most of the effort should go is there? Case capacity is the biggy, followed by charge weight. You can pretty much forget about bullet weight and neck tension. Of course it could be those things actually vary more than the values I used.
