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October 13th, 2014
by Philip Mahin, Sierra Bullets Ballistic Technician
This article first appeared in the Sierra Bullets Blog
The ANSI / SAAMI group, short for “American National Standard Institute” and “Sporting Arms and Ammunition Manufacturers’ Institute”, have made available some time back the voluntary industry performance standards for pressure and velocity of centerfire rifle sporting ammunition for the use of commercial manufacturers. [These standards for] individual cartridges [include] the velocity on the basis of the nominal mean velocity from each, the maximum average pressure (MAP) for each, and cartridge and chamber drawings with dimensions included. The cartridge drawings can be seen by searching the internet and using the phrase ‘308 SAAMI’ will get you the .308 Winchester in PDF form. What I really wanted to discuss today was the differences between the two accepted methods of obtaining pressure listings. The Pounds per Square Inch (PSI) and the older Copper Units of Pressure (CUP) version can both be found in the PDF pamphlet.
Image by ModernArms, Creative Common License.
 CUP Pressure Measurement
The CUP system uses a copper crush cylinder which is compressed by a piston fitted to a piston hole into the chamber of the test barrel. Pressure generated by the burning propellant causes the piston to move and compress the copper cylinder. This will give it a specific measurable size that can be compared to a set standard. At right is a photo of a case that was used in this method and you can see the ring left by the piston hole.
PSI Pressure Measurement
What the book lists as the preferred method is the PSI (pounds per square inch or, more accurately, pound-force per square inch) version using a piezoelectric transducer system with the transducer flush mounted in the chamber of the test barrel. Pressure developed by the burning propellant pushes on the transducer through the case wall causing it to deflect and make a measurable electric charge.
Q: Is there a standardized correlation or mathematical conversion ratio between CUP and PSI values?
Mahin: As far as I can tell (and anyone else can tell me) … there is no [standard conversion ratio or] correlation between them. An example of this is the .223 Remington cartridge that lists a MAP of 52,000 CUP / 55,000 PSI but a .308 Winchester lists a 52,000 CUP / 62,000 PSI and a 30-30 lists a 38,000 CUP / 42,000 PSI. It leaves me scratching my head also but it is what it is. The two different methods will show up in listed powder data[.]
So the question on most of your minds is what does my favorite pet load give for pressure? The truth is the only way to know for sure is to get the specialized equipment and test your own components but this is going to be way out of reach for the average shooter, myself included. The reality is that as long as you are using printed data and working up from a safe start load within it, you should be under the listed MAP and have no reason for concern. Being specific in your components and going to the load data representing the bullet from a specific cartridge will help get you safe accuracy. [With a .308 Winchester] if you are to use the 1% rule and work up [from a starting load] in 0.4 grain increments, you should be able to find an accuracy load that will suit your needs without seeing pressure signs doing it. This is a key to component longevity and is the same thing we advise [via our customer service lines] every day. Till next time, be safe and enjoy your shooting.
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October 7th, 2014
The digital archives of Shooting Sports USA feature an interview with Olympic smallbore shooter Lones Wigger. This constitutes the third and final part in a series by Jock Elliott on pressure during a match and the methods top shooters use to handle their nerves. Read Part I | Read Part II.
The Fine Art of Not Cracking Under Pressure – Part III
by Lones Wigger, Smallbore Rifle Olympic Medalist
 It’s pretty complicated — this subject of dealing with pressure. I’m a precision shooter and have learned to excel in that discipline. You’ve got to learn to shoot the desired scores at home and in training. And once you’re capable of shooting the scores, you may not shoot the same way in the match because of the match pressure. As a result, it takes 3-4 years to learn how to shoot, and another 3-4 years to learn how to win — to deal with the match pressure. It takes several more years to learn how to do it when it counts.
To win, there are several things you have to learn how to do. You have to do it from within. You have to learn how to train just as if you were in a big competition. You work on every shot. You have got to learn to treat it just like a match — to get the maximum value out of every shot. You have got to use the same technique in practice and in training. A lot of shooters have a problem because they change their technique from practice to the match. In competition, you work your ass off for every shot. You have to approach the training the same way.
A second way to combat pressure is to shoot in every competition you can get into so that you become accustomed to it.
Do Everything Possible to Prepare
The third technique is preparation. Before you are going to shoot in a big competition, train hard to do everything you can to raise your scores. So when you’re in the match, you know that you have done everything humanly possible to get ready for the competition. If you have self-doubt, you will not shoot well. You have to have the will to prepare to win.
When Gary Anderson was a kid, he couldn’t afford a gun or ammunition. He had read about the great Soviet shooters. With his single shot rifle, he would get into position, point that gun and dry fi re for hours at a time in the three different positions. He had tremendous desire. He wanted to win and he did whatever he could to get there. When he finally got into competition, he shot fantastic scores from the beginning.
Visualize Winning to Train the Subconscious Mind
A little bit of psychology: You picture in your mind what you want to do. You have to say, OK, I’m going to the Olympics and perform well. Picture yourself shooting a great score and how good it feels. You are training your subconscious mind. Once you get it trained, it takes over. A coach taught me to visualize the outcome, and it worked. Eventually you train your subconscious and it believes you can win. At first I didn’t know about teaching the subconscious to take over, but now I do it all the time. And it certainly worked for me at the 1972 Olympics. What it really takes is training and doing the same thing in training as at a match. If you are “just shooting,” you are wasting your time. READ MORE….
CLICK HERE to READ FULL ARTICLE featuring interviews with Brian Zins, Bruce Piatt, Carl Bernosky and Ernie Vande Zande. (Article take some time to load.)
Story courtesy The NRA Blog and Shooting Sports USA.
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April 1st, 2014
Ever wonder why fine wine is always stored on its side? That’s not just for looks, or easier access when the sommelier (wine steward) visits the wine cellar. Wine bottles are stored horizontally, at a slight angle, to prevent the wine from oxidizing:
“By intentionally storing a wine on its side, you will help keep the cork in constant contact with the wine. This will keep the cork moist, which should keep the cork from shrinking and allowing the enemy of wine, oxygen, to seep into the bottle. When oxygen comes into contact with wine the result is not good – the wine starts to oxidize and the aromas, flavors and color all begin to spoil“. — About.com
Ammunition Should Also Be Stored Horizontally
So what does wine have to do with shooting? Well, it may surprise you, but over time, our cartridges can spoil, just like wine can — though not for the same reason. We don’t have the issue of oxygen seeping past the bullet (the “cork” as it were). However, when ammunition is stored nose-up or nose down, problems can arise. In a nose-up or nose-down configuration, over a long period of time, the powder column will compress, and the powder kernels can actually break down. This can lead to erratic ignition and/or dangerous pressures.
To avoid the problems associated with powder column compression and kernel break-down during long-term storage, take the time to orient your cartridges like wine bottles, i.e. placed flat on their side. Of course, this really isn’t necessary if you burn through your ammo relatively quickly. But, if you are storing cartridges “for the long haul”, take the time to arrange them horizontally. That may require a little extra effort now, but you’ll reap the rewards down the road.
This tip courtesy Anette Wachter, www.30CalGal.com.
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March 5th, 2012
by James Calhoon
(First Printed in Varmint Hunter Magazine, October, 1995)
In the course of talking to many shooters, it has become clear to me that the manufacturers of primers have done a less than adequate job of educating reloaders on the application of their primers. Everybody seems to realize that some primers are “hotter” than others and some seem to shoot better for them than others, but few reloaders know that primers have different pressure tolerances.
Primer Pressure Tolerance
When loading a .223 to the maximum, I was getting primer piercing before I reached case overloading. I don’t know what prompted me to try CCI 450s instead of the 400s which I had been using, but I did. Presto! No more piercing! Interesting!? A primer that has a hotter ignition and yet withstands more pressure! Thats when I decided that it was time to do a dissection of all primers concerned. The chart below shows my results.
By studying the numbers (Cup “A” thickness), one can see which primers in the small rifle sections should be more resistant to primer cratering and/or piercing. Primer cup diameters are all similar and appear to follow a specification, but check out the cup thickness in the small rifle primers (Dimension “A”). Some cups are quite a bit thicker than others: .025″ for CCI 450 vs. .0019″ for Fed 200. Large rifle primers all appear to have the same cup thickness, no matter what the type. (As a note of interest, small pistol primers are .017″ thick and large pistol primers are .020″ thick.)
If you are shooting a 22 Cooper, Hornet, or a Bee, the .020″ cup will perform admirably. But try using the .020″ cup in a 17 Remington and you will pierce primers, even with moderate loads.
Considering that cup thickness varies in the small rifle primers, it is obvious that primer “flatness” cannot solely be used as a pressure indicator.
Another factor which determines the strength of a primer cup is the work-hardened state of the metal used to make the primer cup. Most primers are made with cartridge brass (70% copper, 30% zinc), which can vary from 46,000 psi, soft, to 76,000 psi tensile strength when fully hardened. Note that manufacturers specify the hardness of metal desired, so some cups are definitely “harder” that others.
What does all this mean to the reloader?
- Cases that utilize small rifle primers and operate at moderate pressures (40,000 psi) can use CCI 400, Federal 200, Rem 6 1/2, or Win SR. Such cases include 22 CCM, 22 Hornet and the 218 Bee. Other cases that use the small rifle primer can use the above primers only if moderate loads are used. Keep to the lower end of reloading recommendations.
– Cases that utilize small rifle primers and operate at higher pressures (55,000 psi) should use CCI 450, CCI BR4, Fed 205 and Rem 7 1/2.
– All the large rifle primers measured have the same thickness. Therefore choose based on other factors, such as accuracy, low ES/SD, cost, cup hardness, and uniformity.
Hope this clears up some primer confusion. If you want more information about primers, priming compounds, or even how to make primers, the NRA sells an excellent book called “Ammunition Making” by George Frost. This book tells it like it is in the ammo making industry.
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April 25th, 2011
Selection from BARNES BULLETS’ Tips, Tools, and Techniques
by Ty Herring, Barnes Consumer Service
The purpose of this month’s Tip from Barnes is to make you aware of valid pressure signs in most centerfire rifle cartridges so you can keep yourself out of hot water. Following the Barnes Manual should do exactly that. Below are photos of cartridges that definitely had too much pressure. Fortunately [they] were fired in controlled circumstances and no one was injured. But this shows what can happen if you are not careful….
 High-Tech Pressure Testing Equipment
At Barnes Bullets, we use some of the best equipment when we develop load data for you. Ours is state-of-the-art with a specialized “conformal” pressure system. This set-up uses a high-tech SAAMI-spec pressure barrel with a hole bored into the chamber area and a piezoelectric transducer is installed. As the pressure peaks under firing, the gauge that is specially calibrated reads the pressure and sends a signal to the control box where a technician can see the results.
For many years hand loaders have used the old fashioned trial and error method, hoping that by adding another grain of powder you don’t blow yourself up. Certain “guidelines” have been the standard — such as when the primer gets flat, or when the bolt locks up — you should stop and reduce the charge. These methods have worked for many, but some of them are more myth than reality. I’d like to go over some of these common pressure signs to help you avoid the pitfalls.
Pressure Signs That May Be Unreliable or Deceptive
When I first started hand loading centerfire rifle cartridges, I was told that when the primer flattens I should back the load down. This is one of those semi-myths. Some primers will flatten under high pressure and others will not. I’ve had some Remington primers that have blown right out of the case without ever showing any sign of flattening and on the other hand I’ve had Winchester primers that flatten with only a starting charge. I believe this to be a function of the thickness and hardness of the primer cup. The other myth that seems common is primer “cratering”. Cratering of the primer can be caused by a hot load. But it can also be a result of a slightly large firing pin hole in the bolt or a firing pin that is a bit too long or excessive headspace. Split or cracked cases are another area where it’s assumed that high pressure is the cause. Again this is only myth. Although it can be a result of high pressure — split or cracked cases are more likely caused due to a flaw in the case, improper head space or just simply from being sized and fired repetitively.
[Editor’s Note: Flattened Primers, Primer Cratering, and Cracked Cases CAN DEFINITELY BE CAUSED by excessive pressure. Accordingly, you SHOULD be careful when you see any of these conditions. If you see very flat primers or deep cratering be alerted that you may have exceeded safe pressures. Ty Herring simply makes the point that these telltale pressure signs may sometimes occur even when pressure levels are “normal” or moderate — due to the presence of other problems. Hence these indicators may be misleading. Nonetheless — all these signs (flattened primers, cratered primers, split cases) CAN be valid warnings. If you see these conditions, exercise caution because you may, in fact, have excessively hot loads.]
Valid Pressure Signs You Should Understand
So what are valid pressure signs? I’d say the most common and repeatable pressure sign that one can visually see is the “ejector groove mark”. It shows itself on the bottom of the case [between the edge of the rim and] the primer. It is caused when the pressures within the chamber force the case against the bolt face. On most bolt faces there is a round spring loaded ejector pin. On others there is a rectangular groove to eject the spent round. Under very high pressure the brass case will flow into this groove thereby causing the “ejector groove mark”. If and when you see this mark, it is a sure sign of high pressure. Some of the new high pressure cartridges such as the WSMs are made to run at these higher pressures and some factory loads will manifest the ejector groove mark even though they are within their pressure specification.
Older-Generation Cartridges
Some cartridges have very low maximum pressure ratings such as the 45-70, 30-30, 416 Rigby along with many others that will never show an ejector groove mark. Or should I say, they should never show one. By the time you reach that high of pressure in one of these rifles, it is likely the gun will be in pieces and the bolt may become part of you.
Sticky Bolt Lift and Difficult Extraction
Another common and very real high pressure sign is heavy or sticky bolt lift or extraction. This is caused due to the brass flowing and swelling in the chamber under tremendous pressure. However heavy bolt lift is not always a sign of high pressure. It may be caused by a variety of other issues. Knowing your gun and how it usually extracts a cartridge will be a clue as to whether or not you are actually getting high pressure.
This article appears courtesy Barnes Bullets. The article originally appear in the June 2011 Barnes Bullet-N Newsletter. Story tip from Edlongrange.
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August 1st, 2008
With the relentless pursuit of more velocity and the “next higher node” by many reloaders, it is important to pause and think about safety. And one has to remember that most brass will not hold up to high pressure the way Lapua or RWS does. Many readers have asked us: “How does one detect excess pressure?”. Well first, one can obviously monitor the primer pockets and measure the diameter of the case near the web. Excessive stretch or pocket loosening is a sure sign you’re running too hot. There are also many visible signs of over-pressure which you can see. Reader ScottyS provided this comparison photo of cases, showing the tell-tale signs of over-pressure.
Scotty tells us: “These samples were from a lot of Federal soft-point hunting ammunition that were fired in a custom .308 with a chamber on the tight side (although still allowing a .308 Winchester GO gauge). Among the pressure symptoms were heavy recoil, sticky bolt lift, and the left case had to be manually removed from the boltface. This demonstrates why: 1) you should never assume that all lots of factory ammo are the same (and safe); and 2) you should ALWAYS wear eye protection. This also shows how high pressure can spike once you approach maximum load levels.”
Scotty noted that there was a big pressure difference between the left case and the right case, although both were fired sequentially, and both were from the same lot of ammo. So take heed–always take precautions when testing new ammo, even if it is factory-loaded.
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