OzFclass

williada wrote:

1. Scientific scales to measure the weights of the components.
2. The bullets were batched by base to ogive length, body length, boat tail length and angle and the jackets and core were subject to internal concentricity measurements on a Juenke machine as well as jacket hardness measurements which can vary the friction and gas seal. Cases were volume sorted
3. The use of an infrared temperature gauge measured when the barrel was at operating temperature and use in conjunction with a Pressure Trace attached to the computer we mapped the pressure profile of each shot, compared it with a group of traces and also look at appropriate barrel lengths for the powder being used. This system quickly picks up the primer variable and suitable barrel lengths. Each shot was released at the same time interval.
4. We used two chronographs and a density altitude meter.
5. Identified the barrel compensation profile to get a closer match with simulated computer results as well so the SD’s were meaningful.
6. Repeated the tests time and time again.

williada wrote:Tim the answer is, “Yes”. The experimental setups a few of us have used set tight parameters to analyse one variable at a time to test a hypothesis statistically. This requires groups of paired barrels of different dimensions, a control group of match ammunition and in my case a machine rest to take out the human factor in the recoil which can alter velocity as much as 25 fps.

The sort of equipment used to verify the quality of the ammunition included:

1. Scientific scales to measure the weights of the components.
2. The bullets were batched by base to ogive length, body length, boat tail length and angle and the jackets and core were subject to internal concentricity measurements on a Juenke machine as well as jacket hardness measurements which can vary the friction and gas seal. Cases were volume sorted
3. The use of an infrared temperature gauge measured when the barrel was at operating temperature and use in conjunction with a Pressure Trace attached to the computer we mapped the pressure profile of each shot, compared it with a group of traces and also look at appropriate barrel lengths for the powder being used. This system quickly picks up the primer variable and suitable barrel lengths. Each shot was released at the same time interval.
4. We used two chronographs and a density altitude meter.
5. Identified the barrel compensation profile to get a closer match with simulated computer results as well so the SD’s were meaningful.
6. Repeated the tests time and time again.

Just as an observation, the target is usually big enough to accommodate the typical variances shooters have with their reloading if they can read conditions so people should not think they need all the above mentioned equipment. But what the experiments do allow us to do is explain why a shot went there.

The competition is so hot today, the lessons need to be imparted to create a level playing field and while we have a good waterline, it’s that odd shot or outlier that can do you. That needs to be eliminated where possible such as those corner shots I have talked about and one I see on your target assuming it was not a sighter.

One final point about mid distance testing, an elevation spread is not bad if the rifle is positively compensating and still holds the scoring ring and is least wind sensitive. It will be better out further. Many people think that a tight spread at mid range is great, but the heavy barrels we use have a tendency for the mid distance to be a point of compensation. Remember, past a point of compensation the vertical falls away in the form of negative compensation and poor primers will find you out with further distance. You simple have to identify the barrel profile and load accordingly to get the best from it and don’t use it at an unsuitable distance.

Further improvements on group can be made with low SD’s IF reflected vibrations are not interfering with muzzle shape and the barrel is of the right harmonic length to match the powder and primer. Of course the throat angle will have a bearing on ignition and velocity as does seating depth.

Norm wrote:Hey Plumbs,

I have some sheep elasticator rings in the shed. If I put them on will I score more?

Norm wrote:I have some sheep elasticator rings in the shed.

johnk wrote:

Norm wrote:I have some sheep elasticator rings in the shed.

On another subject, I use one of these under the bowl when I wet moly projectiles to stop splash running down the centre stem of the vibrator.

DenisA wrote:

johnk wrote:

Norm wrote:I have some sheep elasticator rings in the shed.

On another subject, I use one of these under the bowl when I wet moly projectiles to stop splash running down the centre stem of the vibrator.

I'd be careful, you might end up shortening your vibrator.

williada wrote:Tim, thanks for posting your target. There is a lot of information behind what I said. Sorry for that. Some people have read earlier posts and have an understanding of barrel profiles in terms of their compensation profile, positive , neutral or negative. But sometimes a shot or two are not pilot error but caused by how your rifle system and loads perform. Over long matches these points add up and can cut people out of a place in competition. Its just about tidying up those little things and that starts by knowing what your barrel is doing to properly identify the causes of the odd shot in order to work on a solution. This is a great learning exercise. I suppose what we see sometimes is in the eye of the beholder and the patterns don't stick out unless they are revealed by formal testing over a long time. It can be like looking at the stars in the night and identifying the "Southern Cross" or the "Saucepan". But hey, the ancients navigated by them.

Here's what I see in your group without relating it to a compensation profile and how it might form at different distances.