Primers - Small Rifle Primer Study

A Match Primer Study in the 6BR Cartridge
By Germán A. Salazar
This article was originally published in the June, 2008 issue of Precision Shooting

Primers are a frequent topic of discussion among reloaders and match shooters. However, we seem to know less about primers than we do about most of the other components we use in making our ammunition. I don’t claim any special expertise in primer design or manufacture; however, I have, over the years, paid close attention to the performance of different primers in my loads and developed a great interest in primers. What follows is a somewhat detailed presentation of my primer study using the 6BR Norma cartridge (hereafter 6BR), including some historical background into match primers that I hope the reader will find informative.

What do we seek in a primer? What characteristics will the ideal primer encompass? A primer, like most things in the industrial/mechanical world, embodies a number of characteristics which must be balanced with respect to each other in order to have a useful, manufacturable and affordable product suitable for sale to the general reloading market comprised of hunters, plinkers, tinkerers and match shooters. Our interest, as the title of this article suggests, is somewhat limited, we are concerned only with a primer’s performance in the competitive arena. Accordingly, we seek accuracy and we further seek an understanding of the factors which contribute to accuracy. There are no earth-shattering discoveries here, only a few more steps on the journey of inquiry into the invisible world inside the barrel.

Selecting a primer for a given load or cartridge is a task that every careful handloader faces with a large degree of uncertainty and some trepidation. Will the primer be compatible with the powder? Will it create higher pressures? Will it stand up to the pressure? Will it increase or decrease accuracy? We can obtain a fair amount of information about the burning rate of various powders and their suitability for a certain applications, yet most handloaders are in the dark when it comes to understanding the primer’s effect on the load. Manufacturers try to guide us by labeling primers as “Match”, “Magnum” , “Bench Rest” and other appellations contrived to catch our eye at the sporting goods store, but none of these terms tells us much, if anything, useful about the primer’s effect on the load. Do primers have an equivalent to a “burn rate”? Can we somehow predict a primer’s performance? Are there any shortcuts to shooting a lot of rounds over a chronograph and into a target? Is there a fuller meaning to the raw numbers we see from a chronograph? All of those questions plague us and we will try to address them in a manner that will guide the thoughtful handloader towards better performing loads.

Historical Background
The primer, while small, has always been an important part of the accuracy equation of match grade ammunition as it has an influence on pressure and velocity well out of proportion to its size. Reviewing references covering ammunition as far back as the 1923 Frankford Arsenal International Match load for the 30-06, we find that arsenal and civilian reloading authorities often stated that a “softer” primer gave better accuracy. We can only wish that the literature produced then provided a better definition of what they meant by “soft” or how they measured it but we have to live with that omission.

Just prior to the turn of the 20th Century, Frankford Arsenal was loading the .30 US Army (30-40 Krag) with mercuric, corrosive primers which used ground glass as a frictionator to help start combustion. As the fulminate of mercury rendered the brass cases unsuitable for reloading, the non-mercuric H-48 compound was adopted at that time. The Union Metallic Cartridge Company also introduced a non-mercuric primer at that time, the U.M.C. 9 1/2 (Modern Rifle Shooting, Walter Hudson, M.D., Laflin & Rand, 1903 at p. 107).  Fired cases were regularly sent back to the armory for reloading in those times, making this an essential change. In 1910, the mixture was again changed, to eliminate the ground glass which was found to increase metal fouling in the bores. The new glass-free FH-42 mixture was still corrosive and non-mercuric.

In 1917, at the peak of production for war needs, a large batch of the FH-42 mix (already loaded into ammunition) failed to perform as required, causing the recall of millions of rounds of ammunition, some already in France. The Winchester developed 35-NF formula was given to Frankford and subsequently adopted as the FA70 mix. The FA70 was used in those 1923 International Match loads was the archetypal soft primer. It was corrosive, non-mercuric, and was valued for the fine accuracy it delivered. All government match ammunition through 1940, when production of match ammunition ceased, was loaded with the FA70 mixture (the primer itself was actually called the FA26 but is often referred to as the FA70). This primer was the gold standard of that era.

Frankford Arsenal, as well as the other government facilities producing and testing match grade ammunition had facilities that we, as amateur handloaders, can barely fathom. Their testing comprised millions of rounds of ammunition and the search for accuracy in support of the National Match, International and Palma ammunition programs was relentless. The Frankford and Lake City Arsenals developed and tested the components and methods of manufacture that led directly to today’s match grade components from commercial manufacturers. I am unabashed in my reliance on their guidance through the articles and books which were generated from that vast store of knowledge.

For many years after their introduction, non-corrosive primers were considered harsher and less accurate and thus were not used in arsenal loaded match grade ammunition. Given the government’s facilities and test programs, we cannot doubt the conclusion that the softer primers were more accurate. Unfortunately, despite a great deal of research, I can find only minimal quantitative, anecdotal or illustrative definitions of the meaning of “softer” as applied to primers. One example can be found in the book: Complete Guide to Handloading by Philip B. Sharpe (Funk & Wagnalls, 1937). Mr. Sharpe, a highly regarded authority on reloading and other technical topics, sets forth load data for both corrosive and non-corrosive primers with the latter being reduced by 3.2 grains in one representative 30-06 match load with the 173 gr. bullet and HiVel #2 powder. Other loads were similarly reduced and there is a general warning to reduce all loads formulated with corrosive primers by 5% when using non-corrosive primers.

Another quantitative indication of the relative meaning of a “soft” primer can be found in Al Barr’s “Loads for the ‘06” (American Rifleman, April, 1949 p. 28). This was the period of transition, when non-corrosive primers were gaining wider acceptance and handloaders were becoming acquainted with their characteristics. In his reloading tables, which were compiled with the assistance of the H.P. White Labs pressure testing facility, Mr. Barr shows a 7,000 PSI increase in pressure with the substitution of the new Winchester 120 (non-corrosive) primer for the FA26 in a standard 30-06 match load with IMR 4895. In the text, Mr. Barr states: “The powder companies have always advised a powder reduction of about five percent when substituting non-corrosive, non-mercuric primers for corrosive Frankford Arsenal 70 or FA26 primers when using maximum recommended powder charges. The reason, of course, is higher pressure caused by hotter commercial (non-corrosive) primers.”

The recommended five percent powder charge reduction gives us some indication of the relative meaning of “soft”. Perhaps it tells us that accuracy is more easily found when the influence of the primer on the overall pressure of the load is minimized; or perhaps only that there is a pressure level that must be maintained in order to develop maximum accuracy. Certainly however, a five percent reduction in the charge of a 30-06 increased air space in an already overly large case and that alone would have a detrimental effect on accuracy. With the broad range of powders available today, one can almost always find a powder that develops the desired pressure and velocity while giving close to 100% load density. In the immediate post-war years however, choices were fairly limited, the old standbys being IMR3031 and the then ubiquitous Hercules Hi Vel #2. DuPont’s IMR 4895, IMR4320 and IMR4350 were all fairly new powders and 100% load density was not generally attainable.

The years between 1917 and 1950 were a bustle of activity in the primer field with efforts to develop non-corrosive primers such as the Swiss and German arsenals had developed being a top priority. Jim Burns, Remington’s primer expert, developed the hugely popular Kleanbore non-corrosive primer for rimfire and centerfire cartridges which was introduced in 1926. Remington held patents on some important non-corrosive primer formulas, but the government was not idle. Frankford Arsenal worked with Berdan priming in corrosive and non-corrosive formulations. The Berdan primers were tried because the available non-corrosive mixes required a larger amount of compound than could be put into the Boxer type primers. The Berdan experiments were short-lived, however, and Frankford continued work on non-corrosive Boxer primers labeled the T53. While match grade ammunition was not the focus of the Arsenal’s research, the controlled environment and relatively small lots of ammunition prepared for the National Matches (about 300,000 rounds annually at that time) provided a useful and frequent testing ground for new developments.

In 1950, all US military rifle ammunition production was ordered changed to non-corrosive primers and that process was complete by late 1951; however, no match ammunition was being produced at that time. In 1956 Frankford Arsenal resumed small scale match ammunition production. It is interesting to note that despite all of the resources at their disposal, six years after the general changeover to non-corrosive primers in arsenal loading and thirty years past the time commercial ammunition makers’ gradual changeover began, Frankford’s chemists still could not find a non-corrosive primer with the fine accuracy of the soft FA26. Accordingly, the corrosive FA26 primer was used in the then new 7.62 NATO cartridge for the 300 Meter events at the 1956 Olympic Games in Melbourne. This special ammunition, designated T275 and later T275E4 and headstamped FA 56 and FA 56 Match, was the only US made 7.62 NATO ammunition with corrosive primers. As it was intended only for International teams, it received very limited distribution. The very small quantity of FA 56 Match 30-06 produced that year became the last corrosive primed .30 caliber match ammunition produced at the arsenals.

Frankford resumed full scale production of 30-06 match ammunition in 1957 initially with the Remington RA70 non-corrosive primer mix. By 1958, Frankford had developed a non-corrosive lead styphnate based primer considered suitable to replace the famed FA26. Labeled the FA36, the new primer was reported to have soft ignition and gave excellent accuracy with velocity spread reduced by 20% and group size at 600 yards reduced by 10% over the FA26. Unfortunately, as the FA36 was not limited to use in match grade ammunition, it was quickly modified by the addition of zirconium to the mix to make it more suitable for extreme cold weather use, quite likely decreasing its accuracy potential to some degree.

Frankford was not alone in holding on to the old primers for match ammunition; Winchester-Western continued using that company’s corrosive and mercuric 8½ G primer in match ammunition (.308, 30-06, and .300 H&H) until 1960 when the 8 ½ G was finally replaced with the non-corrosive, non-mercuric number 120. Remington had long since switched to its non-corrosive Kleanbore primer in match grade ammunition. Thus, by 1960, all US made match grade ammunition was finally loaded with non-mercuric, non-corrosive primers in place of the old “soft” corrosive primers. (See: American Rifleman: F.A. T53 Primers, March 1955, p. 78; Frankford Arsenal and Match Ammunition, April 1957 p. 40; Ammunition for the 1958 National Matches, Sep. 1958 p. 29; FA 36 Primer, September 1959, p. 58; Match Ammunition Manufacture, Dec. 1959 p. 15; Barrel Life, Feb. 1960 p. 38; Corrosive Primers, June 1960 p. 60; Non-Mercuric, Non-Corrosive Primers, Jan. 1961 p. 34; National Match Ammunition, Aug. 1962 p. 22; 1963 NM Ammunition, Aug. 1963 p. 62; US Service Primers, Jan. 1966 p. 63; Non-Corrosive Dates, April, 1966 p. 63 and The Cal. 30 Cartridge in Match Competition, Sep. 1969 p. 42. See also: The Book of the Springfield, by Edward C. Crossman, Ch. 12 Ammunition Components, Small Arms Technical Publishing Company 1932; Muzzle Flashes, by Ellis Christian Lenz, Standard Publications, Inc. 1944 pp 651 – 760; Hatcher’s Notebook, by MG Julian S. Hatcher (various references), Stackpole Books 1962; Handloading by William C. Davis, NRA 1981, Non-Mercuric, Non-Corrosive Primers, p. 20; and, Ammunition Making by George E. Frost, NRA 1990, Primers and Priming p. 47).

With the foregoing background in mind, we set out to examine a sampling of modern primers. Our objective was to see if there is a correlation among several factors including visual flash, pressure, velocity and accuracy. While keeping in mind the historic significance of the soft primer, we approached this testing with an open mind as much has changed in 70 years.

Primer Flash Photos
The photos of the primer flash generated by each primer type are quite revealing, showing us a range in flash size of several orders of magnitude among frequently used match primers. Upon viewing the range from tiny flash to near blowtorch blast, with much in between, we were encouraged that we had a lead on the search for the modern day incarnation of the elusive soft primer. At a minimum, the range of visual flash suggested that there should be significant performance differences among the various primers.

While each primer type is represented here by a single picture, five to ten of each type were fired and photographed. Within a given lot of primers, the visual flash of each type was found to be very consistent. However, different lots of the same type of primer can show marked differences from one another. The lots used in the testing were selected randomly from those available, some were relatively new and some were quite a bit older (up to 20 years) but all had been stored in a temperature controlled, indoor environment.

Testing Methodology
At this point, planning for the firing tests began. With the assistance of Bob Jensen, whose knowledge of ammunition and primers is encyclopedic, a testing plan was developed which would allow a useful comparison of the various primers. Lapua (Nammo Lapua Oy) generously furnished components for our testing and their contribution to the project is greatly appreciated. Given that Lapua does not presently sell primers in the reloading components market, their support is a clear indication of their selfless interest in furthering the knowledge base of reloaders.

The results presented here should be are not meant to be determinative of a single “best” primer for all applications (or even for all 6BR loads). This is a study into some of the characteristics of primers and how, if at all, those characteristics may be related. While we tested a large number of primers, some of which are not available in the retail market, we will limit our presentation here to five types which are generally available to handloaders. These five are the Federal 205M, the Russian made PMC Small Rifle Magnum, the CCI BR4, the Winchester Small Rifle and the Remington 7 ½ Bench Rest. These primers present a fairly broad cross-section of visual flame production and we believe that a great deal can be learned from them. While some will be disappointed over our failure to include their favorite primer, we had to draw the line somewhere and these five present a useful range of performance.

With our test equipment in place, we began the pressure and velocity testing portion of this test. We first fired the reference ammunition provided by Lapua in order to verify the calibration of our equipment, an Oehler 43 Personal Ballistics Laboratory system. Our pressure readings were within 100 PSI of Lapua’s specification; this was determined to be well within acceptable limits. Having preliminarily established the accuracy of the system, and due to the relatively limited amount of the factory reference ammunition, we loaded a reasonably large amount of our own reference ammunition to approximate the factory pressure and velocity. This was done using new Lapua brass, Lapua 105 grain bullets and VihtaVuori powder. One of the test primers, which had previously shown a very high level of consistency, was selected to be used in our reference load. All primers were seated with the Sinclair tool which has proven to be the best tool for this purpose.

To the extent possible, SAAMI testing procedures were used as a guide for our testing. However, there are many variances from those procedures. Most notably our use of a strain gauge pressure measuring system (Oehler 43) rather than the SAAMI standard copper crusher or piezoelectric transducer method as both of these are beyond the scope of our budget and facilities. Further, as the 6BR cartridge is not covered by SAAMI standards, the exact location selected for placement of the strain gauge was based on our understanding of the principles involved and the study of similar cartridge specifications in the SAAMI guide. Despite these variances, we believe the results obtained to be reliable and repeatable. (See: Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Rifle Sporting Ammunition for the Use of Commercial Manufacturers, American National Standards Institute 1992, 1999).

Statistical Firing Tests
Firing our reference ammunition showed it to compare quite favorably with the factory product in terms of consistency and met our goal of having a larger supply of reference/calibration ammunition. While our reference load was slightly lower in pressure and higher in velocity than the factory reference ammunition, it was within CIP specifications for the 6BR Norma and produced very consistent pressures. This difference is most likely attributable to our unavoidable use of a canister grade powder as the factory powder is not available to reloaders. The factory reference ammunition was subsequently used to check the equipment prior to each session and our handloaded reference ammunition was used before and after each test to ensure that external factors such as ambient temperature were properly accounted for.

All testing for this article was done with a Borden action with new Krieger 1:8" twist barrel, 30" long chambered in 6BR by Lester Bruno and stocked in a MAK Enterprises Tubegun stock. The scope used was a Leupold BR 24 with the Tucker coil spring modification. Accuracy tests conducted prior to the primer tests showed this to be a very accurate rifle for its intended purpose: prone shooting at distances of 300 meters to 600 yards. The load used for the tests is the same as our reference load except for the primers, these being the only variable element. Each test firing consists of ten shots.

Table 1 summarizes the results of the test firings for pressure and velocity. Each primer test was fired twice, the test sessions being one week apart. Ambient temperature ranged from 70 to 74 degrees F at the first session (A) and from 67 to 72 degrees F at the second session (B). The primer tests were fired in inverse order in Session B to determine if barrel heat was a contributor to the noted changes in pressure. Nonetheless, in both tests, firing was conducted in a manner calculated to minimize the effect of barrel temperature changes and barrel temperature was closely monitored.

We collected data for muzzle velocity (gross, SD and ES), chamber pressure (gross, SD and ES), area under the pressure curve which is a measure of total energy produced, and rise time, which is a measure of the time from ignition to peak pressure. Both rise time and area under the curve were so close for all primers that much more firing would be needed to determine if there is any statistically valid difference among them. However, both muzzle velocity and chamber pressure showed the variances that reloaders have come to expect from different types of primers.

A glance at Table 1 will indicate a difference in average velocity between sessions for each load that is greater than warranted by the ambient temperature change between those sessions. That is just one of the many frustrations the amateur ballistician faces. Frankford Arsenal chronographed over permanent screens placed 100 feet apart with a tolerance of 0.01" in a controlled environment. We must make do with environmental changes, a much more modest (and manageable) separation of four feet and somewhat greater tolerance from session to session in both screen spacing and muzzle to screen centerline distance, especially the latter. Accordingly, I place more emphasis on the pressure readings and the variability of both pressure and velocity than in the absolute velocity figures.

The results of the firing data are presented below in tabular format and the reader may draw some inferences therefrom. I was immediately struck by the relatively low range of average peak pressure among the various primers; given the visual differences in the flash, I expected a greater range. Nonetheless, there is a direct correlation between the size of the visual flash and the pressure generated by each primer: the larger the flash, the greater the pressure. Velocity follows pressure within reasonable limitations, and since the only variable in these loads was the primer, we can see a very direct relationship there as well. As an initial point of analysis, we can broadly say that more flash equals more pressure and more velocity.

Perhaps more interesting is the data showing the variability of each load. While many reloaders focus on extreme spread (ES or range) of velocity, I much prefer to focus on the standard deviation (SD) as it is statistically a better measure of expected performance of any given shot. The same holds true for pressure data, the SD of the peak pressure readings tells us something useful about the primer’s ability to function in a consistent manner in a given load.

It is in this analysis of the data that our predicted correlation between flash size and pressure breaks down. Note that the “small flash” primers, Federal and PMC, had similar peak pressure SD figures. The “medium flash” primers, CCI and Winchester, however, did not perform similarly at all. The CCI was in line with the small flash primers whereas the Winchester produced the largest peak pressure SD of the test. And then appeared the biggest surprise of the test: the Remington with its ferocious visual flash and highest average peak pressure nonetheless produced the lowest SD of peak pressure; although interestingly just an average SD of velocity.

Accuracy Firing Tests
If the statistical tests had some small but unavoidable systemic flaws (environment, set-up), the accuracy testing presented even more of a dilemma. Our readership is a sophisticated group which understands the methods and standards of Benchrest competition. Ideally, the accuracy firing tests would be conducted with a return to battery rail gun at 300 meters. The problem is I am not a benchrest shooter, do not own a rail gun nor have access to one. However, I am an experienced prone shooter and have good equipment for that shooting discipline that serves every need of this testing procedure. Therefore, the most practical option open to me was to conduct the accuracy firing tests from the prone position. I added a scope to the test rifle as noted above in order to minimize aiming error but the human element is a distinct part of this portion of the test. Given that our test cartridge, the 6BR with a 105 grain bullet, is more commonly used as a prone and position shooting cartridge, than as a Benchrest cartridge, I don’t think that this is a significant flaw in our testing. Each accuracy firing test consisted of 15 shots.

How much variablity could we expect in accuracy from the primer differences? The staff at Frankford Arsenal was of the well grounded opinion that the bullet accounts for 90% of a cartridge’s potential accuracy, with the powder, primer and case accounting for the remaining 10% (“Factors in Accuracy”, American Rifleman July, 1958, p. 30). With that cautionary prelude firmly in mind, we began the firing tests.

Test firing was conducted at the Ben Avery range in Phoenix at 600 yards. Our focus was on vertical dispersion differences among the various primers. Given the range of pressure and velocity variations, we expected to see some vertical dispersion differences and that was indeed the result obtained. Table 2 summarizes the outcome of these firing tests. Interestingly, the order of the vertical dispersion of each load could almost be predicted based on its pressure/velocity/flash. However, once again, the Remington 7 ½ which had the larget flash and highest pressure performed better than predicted, winding up in the middle of the pack for vertical dispersion. Perhaps the low SD of pressure generated by the Remington is its saving grace; that will be an area for further investigation. Keeping the Remington exception in mind, we can otherwise see a pattern of lower pressure/velocity/flash being related to reduced vertical dispersion at 600 yards.

The study of primers is an ongoing fascination for me, as they are a vital, yet often overlooked part of the accuracy system. I will continue this work with a series of tests on large rifle primers, hopefully we’ll find something interesting there as well. What I hope you will retain from this article is that primers are sufficiently different as to merit testing in your loads and perhaps something about their history and characteristics. If you conclude from this article that A, B or C is the “best” primer, then I have failed because it is not my intention to make any such pronouncement, but to examine a variety of primers in a single load and a single rifle so that we may examine the primers themselves in as pure a manner as is possible. My objective is to explore and to learn, not to make absolute judgments.

This testing conducted for this article would not have been possible without the generous assistance of Lapua who provided us with factory loaded 6BR ammunition to use for pressure, velocity and accuracy baseline data as well as reloading components for the test. Our sincere thanks and appreciation goes to the good people of Nammo Lapua Oy. I must also acknowledge the contributions of Bob Jensen. Bob, who is well known in the Palma shooting community for his coaching skills and his memorable work loading of the 1992 Palma ammunition, has been a good friend and patient mentor to me in many endeavors and I am very grateful for that. Last, but not least, Jim Cobb and Nate Silverman’s technical assistance with many aspects of the testing was invaluable.

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