Basic (Newbie) Questions about Primers and Mirage

[privateer]

Just to be sure I understand the whys...

1. Primers - All things being equal (powder load, bullets, OAL, etc.) how does Primer brand make a difference between rifles. i.e. if one primer is better than another (CCI BR vs. Federal Match), becuase it is more consistent, then wouldn't it be better in every rifle? What am I missing? Is it a rate of ignition which correlates to a particular pressure profile? If so, can you just pick a primer and then pick a powder or tune a powder to the primer?

2. Mirage - I understand that mirage moves the apparent actual image. What I want to know is how much does it actually move. I have heard people at the range blame missed shots on the mirage. On a bad mirage day, say at 200 yards, how far can it really move the apparent target (1" or more)?

Thx.

 

[Fred Bohl]

privateer,

I have been testing mirage effects using digital imaging through both spotting scopes and rifle scopes with the intent of possibly using image analysis and correcting software (active compensation - like the big astronomic observatories use). My testing has been done here in northeast Wisconsin so your results will probably differ. The maximum observed displacements of observed image from true position have been:

7.2 inch at 600 yards

4.0 inch at 300 yards

2.4 inch at 200 yards

1.1 inch at 100 yards

Note that these all were obtain on different days under slightly different conditions for each range.

 

[privateer]

Thank you Fred. Are the effects temperature dependent? i.e. I am just beginning to learn about mirage, do you learn to read mirage visually only, or do you have to factor in what you see along with the ambient temperature (for reference I live in Florida so it can be 90 to 100 degrees.)

 

[glo]

There are two things I know about primers. One is that each manufacture uses a slightly different mix. This meaning the mix burns hotter or with a greater energy. Two is that all you need is enough of a mix to efficiently ignite your powder. Large rifle primers are good enough to igniting anything from 40 to 70 grains of powder. For powder charges less then 40 grains the small rifle primer was invented. For powder charges greater than 70 grains and some spherical powders the magnum primer was invented. I have forgotten the difference between a standard and match primer.

Know that we have hundreds of different cartridges from the 17 caliber thru to the 50 BMG. There are a lot of different types of primers made today to work with these many different cartridges.

For many years, all I have ever used was Winchester LR. That’s because I could get 100 or 1000 from my local gun store when I needed them. The best thing you can do is ask what other people are using for a specific cartridge, see if those primers are available on a regular basis from local store. Then work up some loads that give you your best group or lowest standard deviation. I don’t think there is a magic “primer”.

As I remember from a test that as done in the late 70’s (Shooting Times) using large rifle primers. The Federal 210 was the hottest, the Remington 9 ½ had the most energy and the Winchester LR was on average both the hottest with the most energy. All the rest of the primers (17 or so) followed in behind with no rhyme or reason as to heat or energy, this being an unscientific test comparison as well.

 

[BoydAllen]

The thing that you need to understand about component testing is that generally it ignores the idea that, for a given rifle powder and bullet, tune is velocity dependent. If you have a load tuned up so that it shoots well, and switch a component that changes the load's pressure and therefore velocity you will be out of tune unless the increase or decrease takes you all the way to the next accuracy "node". Every so called primer accuracy test that I have read or heard of is therefore mostly useless, unless the primers being compared produce the same velocity, which is unlikely.

If you want to study mirage set your rifle up as early as you can manage, on a sold rest. Aim at the center of a target so that you can look through the scope without touching the rifle. As the day goes on observe the motion, and position of the target relative to the scope reticle. make sure that you use a high magnification parallax adjustable scope. let us know what you observe. don't touch the rifle until you are finished.

Added later: Mirage is caused by the earth heating air that then rises through the relatively colder air above it. Because it is less dense (the warmer air) it has a different refractive index. As bubbles of warmer air rise, the image of what is viewed through them is modified causing the apparent position of a target to appear to jump around, when it is viewed with a high magnification scope. Having a fixed point of reference, the scope's reticle, makes this more apparent. Even though the motion and apparent target location displacement are not visible at lower magnifications, they are still present, and the latter can cause significant group enlargement. As wind increases the bubbles of warmer air rise at an increasing angle from vertical till at some wind speed they are swept away before they can interfere with one''s view of the target. Up to that point, with a high magnification scope, the patterns in which they rise may be used as an indication of what the wind is near the target. The expression is "reading mirage". When a the wind stops altogether for a moment, the bubbles of hot air rise straight up resembling boiling water, and the target image will be displaced a considerable amount upwards. Shots fired at the same aiming point will go out of the group in an upward direction. If a shooter is unaware of this phenomenon and cannot see the mirage because he is using a lower magnification scope he may incorrectly attribute the shots displacement to some other factor,which he then will try to fix. As a general rule, the apparent position of a target is displaced in the direction that the mirage is "running" (that the bubbles of hotter air are being blown by the wind). Because it is caused by a difference in air density high temperatures are not required. I have read that you can get mirage off of snow. The sun's heating of the earth is the major factor, so mirage tends to increase as the sun heats the earth between the shooter and the target. Generally there is little mirage first thing in the morning. Time to go to work.