03-29-2012, 02:25 AM #1Valued Member
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- Mar 2012
- Rural South Carolina
Primer Reliability Considerations
Pistol primers should never be used in rifle cases though as many have discovered they are the same size.
Also as is known the cups are thinner on pistol primers and thus needed because handguns do not tend to have a large amount of available striker energy as the springs they utilize in small spaces just don’t have the energy and if they did the handgun would be very hard to operate. Also if you measure the height of a pistol and a rifle primer you will find they are different with the handgun primers not being as tall thus if you try to put a rifle primer in a 45 ACP case you will have a high primer condition. Conversely putting a large pistol in a 30.06 case will give you a deep seated primer and unless you are shooting cast bullets with low pressure loads you are asking for a face full of hot gas. Don’t even think about it.
Primer reliability on US ammunition is extremely good. The industry standard allows for one misfire in a million which is actually a very high rate and actually closer to one in three million. This is the same requirement for military ammo.
That being said if you have ammo that has been properly made, stored and cared for and you get a misfire 99.999% of the time the failure to fire is weapon related. Primers need two things for reliable ignition in the firearm, they need energy and velocity. Remove one or the other and you will experience misfires.
How are primers tested in the ammo plants? A fixture is made wherein a primer is inserted by hand into a cup and placed in a fixture with a floating striker (firing pin) touching the primer. The fixture releases a steel ball which drops from a given height and impacting the striker which is in direct contact with the primer. The ball arrives at the same velocity if released from the same height in a very repeatable fashion. Two things are derived from such testing. The ALL NO FIRE height which is the highest height the ball can be released from and not achieve ignition and conversely the ALL FIRE height which is the lowest point the ball can be released from and give 100% ignition reliability.
As stated above primers need to be hit hard and they need to be hit fast. Lets say the ALL FIRE drop height is achieved with 2 ounce steel ball dropped from 20 inches which will give you 40 inch ounces of energy . Now lets take a 20 ounce ball and drop it from 2 inches. It will also give you 40 inch ounces of energy but you will not have the first primer fire because the ball has not achieved the velocity at point of impact the 2 ounce will achieve free falling from the 20 inch height.
Once the ALL FIRE height is learned a copper cylinder to very demanding specifications is placed in the fixture and the 2 ounce ball is dropped and this results in the striker indenting the copper in much the same way as it would hit a primer. The copper is removed and placed on a bench inspection fixture which has a dial indicator gage and the indent is measured with a hemispherical pointed probe that will contact the lowest point of the indent and the difference noted in thousandths of inch on the dial indicator. This is known as the ALL FIRE COPPER indent which for large rifle primers is .012”. The ALL NO FIRE COPPER Indent is about .009”. It is much lower for handguns as outlined above. Between these two numbers misfires become more frequent.
How does this relate to a firearm? In the US firearms industry coppers are inserted in copper holders which appear to be the same thing as headspace gages but they do not have the same GO, NO-GO data on them. Some are marked, some are not. They are expensive to buy. I bought my last one fifteen years ago for like 165.00 and that is only half the problem. Getting the coppers is also very expensive and 30 years ago they were like 1.00 each. I have copper holders for 5.56, 7.62 and 30.06.
The firearms industry now has a standard of .016” indent for large rifle and it used to be .020”. I have a 1911 Swiss rifle that gives .022” and had a La Corona Mauser that gave .024” indent. About five years ago I got two new rifles from Santa Claus and both had copper indents of .015”. I packed them up and off they went to factory with letters addressed to the Chief Engineer. One took two trips back to get it right and the other came in with three coppers packed in plastic bag showing .020” indent. I checked with one of my coppers and got the same reading. I had a third rifle and learned this firm had not checked striker energy in a number of years.
Why is the WEAPON COPPER indent much deeper than the ALL FIRE COPPER indent? Unfortunately weapons tend to collect trash in striker channel. Some are greased (cosmolene). Some have a design than tends to drag on the striker as it moves as can be easily seen by taking down the bolt action rifle, removing the striker spring and looking at inside surface. You will most likely see flats worn on the inside of the spring which was completely round when new. As the flats develop spring energy is deteriorated so one does not have the same striker diameter as new.
Many misfires occur in cold weather because the bolt has not been taken down and degreased thusly the grease tends to harden in cold weather retarding the striker velocity.
Military rifles tend to be exposed to other unpleasantness such as dust, mud, corrosion, extreme cold, etc and you need all the extra energy you can muster to make sure it goes bang.
I hear guys say, “My rifle really hits primers hard and shows me a fired case.” THE INDENT ON THE PRIMER OF A FIRED CASE HAS ABOLUTELY NO RELATION TO STRIKER ENERGY.
The indent does however tell us several more interesting things. As we all know center fire ammunition are used in all rifles however the term “center” does not necessarily describe where the striker actually hits the primer and more often than not gives off center hits. Does this matter? Yes.
Many years ago Frankford Arsenal did a multi million primer ignition reliability study on primers with various amounts of off center distances purposely machined in on the drop test fixture to give increased off center strikes. The results were amazing. Zero (absolute dead center) to .020” offset gave no increase in misfire rates. (Note: most US strikers for large rifle and magnum rifles are .060” in diameter with hemispherical nose)
Once the offset passed .020” the misfire rate started to rise and the further the offset the higher the misfire rate. The industry and military standards allow for one half the striker diameter offset and I have seen even more than this in military production rifles. Why? Obviously to meet high production demands with the gamble that some will misfire at a rate of say 1 in 100,000 or 1 in 10,000. Personally if my life depended on it, it would be dead nuts but achieving this is almost impossible.
I have one 303 Brit round that was snapped, reinserted and hit again in a different area way off center and neither time did it ignite. I keep it as a demonstration round.
The appearance of the striker indent is deceptive and one needs a measuring microscope to determine the actual center of the striker indent. The eye will not allow sufficient accuracy to determine a dead center hit.
How do I know if my striker has enough energy/velocity? Good question. What we did at Aberdeen Proving Ground when we tested weapons was to disassemble when new and record the lengths of all coil springs in a relaxed state and every so many rounds thereafter the measurement was taken and differences recorded. Thusly if we experienced misfires (rare occurrence) we measured the copper energy, spring lengths and if energy deterioration was experienced the stoppage would be charged to the spring and not the entire weapon system. As well all magazines were numbered and rotated through all weapons. If a malfunction occurred we recorded the round number in the magazine and the number of the magazine and you could pretty well track if it was a mag problem as it would do it again and again in that or several weapons, thusly the stoppage would be chargeable to the magazine and not the weapon.
Spring Engineers will tell you a properly made spring will never take a set however you don’t know if it is properly made until you use it to hell and gone and see what happens.
On my target rifles I do not have a copper holder for about all I can do is to disassemble when new, record the spring length, reassemble and at the end of each season I re-measure. Also I buy extra energy springs which are stronger than original design springs from Wolff Springs as they generally have one or two energy levels higher available for the most popular designs.
Is there anything else to look for? Yes there is. Homer Powley (a past friend now at the big range in the sky) did an exhaustive test study at Frankford Arsenal and he reduced the striker energy in rifles by cutting coils off the striker springs making them have less energy. Reducing the striker energy past a certain point results in erratic primer ignition which first shows up in increased standard deviation. This was confirmed in testing at Aberdeen when rifles were fired with the same lot of ammo and a firm standard deviation established for that lot in that rifle. A coil was cut and the same numbers of rounds were fired again.
The first thing to show up was increased standard deviation and rifles still showed 100% ignition but started to exhibit vertical dispersion at long range immediately.
The same thing occurs in our flashlights. When new the batteries give us a bright light and will do so for awhile then we notice the light is not as bright but still keeps us from stepping in bad places in the dark. A multimeter check of battery voltage as new and periodically thereafter will confirm a voltage drop thus a decrease in the amount of light. It then becomes a matter of just how much light loss or standard deviation increase you are willing to accept.
Instead of a multi-meter the chronograph will tell us the “good news” as the Brits say well before there is any “drama”.
Thusly for best long range performance one needs to load several hundred rounds of ammo when a rifle is new and fire it say 30 continuous rounds at the same firing interval recording ES, SD, temperature etc. Then every say 1000 rounds repeat at the same temperature and check the SD. 200 rounds of control ammo will last you 6000 rounds. At Aberdeen we did this every 1200 rounds and took chronograph readings and shot dispersion (accuracy) at the same time on indoor range with same lot of “control ammo”.
There is another thing such periodic testing will reveal which is barrel wear. As the barrel throat gets burned away average velocity starts to drop. The rule of thumb is if velocity average drops 200 fps or more the weapon fails or in the case of ammo, the ammo fails.
Many top long range shooters install new striker springs at first of every season but this may or may not be often enough.
Thusly the title of this thread is Primers are like light bulbs.
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03-29-2012, 11:01 PM #2Valued Member
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- Mar 2012
hard core info!!!! i've been reloading for years, and have learned more in the last couple weeks, then I had thought possible. Thanks for sharing the knowledge HummerSi Vis Pacem, Para Bellum