Shotshell Case Life and its Effects on Ballistics (1998)
by: Tom Armbrust
Posted: 06/03/2008
One of the many questions that is directed to me at the various trap and skeet clubs I visit in my travels is: "How many times can a shot shell be reloaded and what effect, if any, does it have on velocity and pressure?" A very good question I thought to myself. Morris Buenemann, a honcho at Winchester, (427 N. Shamrock Street, East Alton, Il 62024, phone 618-258-2000) has worked in the shot shell ballistic lab helping develop reload data for Winchester AA target loads. They found out some very interesting information. When a brand new primed empty hull was substituted for a once fired hull, velocity and pressure were somewhat reduced. The explanation seems to be that the heat scored rough interior of the once fired hull creates more friction on the plastic wad and shotcharge as the new smooth interior has much less grab on these components. My question was after repeated reloads, would reduced crimp strength and hull deterioration become a problem, playing hob with velocity and pressure causing excessive variations, possibly weakening target breaking ability due to pattern reduction.
My outfit "Ballistic Research" carried out an extensive test series, recording velocity and pressure after each series of shells had been carefully reloaded 12 different times. Velocities were recorded on an Oehler M35P chronograph. For more information on Oehler's excellent line of velocity and pressure test equipment contact: Oehler Research, Inc., PO Box 9135, Austin, Texas. 78766, phone 800-531-5125. Dr. Ken Oehler has supplied Ballistic Research, my company, with state of the art test equipment for many care free years. Pressure was recorded in PSI on a PCB 165A02 Piezo electric transducer in conjunction with a PCB Model 462B52 ballistic charge amplifier, and Model 451A07 digital peak meter.
Popularity with reloaders plus long case life resulted in my selection of these first two hulls for testing. They were the 12 GA Winchester AA, compression formed and the Remington STS Premier hulls. All tests used the Winchester-209 primer, again due to its popularity and minimal ballistic variation. Alliant powder was kind enough to donate American Select for this test series. This new powder is fast becoming a big hit with clay target shooters due to its very clean burning characteristics, lack of felt recoil, and most excellent patterns. This is due in part to a somewhat longer time pressure curve, and slightly lower pressures. For more information on the complete line of Alliant shotshell powders contact Mr. Dick Quesenberry, Alliant Techsystems, (New River Energetics, PO Box 6, Radford, VA 24141, phone 540-639-8503). The Green Duster wad GT 9210-12 was also selected for its popularity, excellent ballistic uniformity, uniform pattern results, from past testing, plus its very economical price for the cost conscious shotshell target reloader. For more information and prices contact (Micro Technologies Inc. 1405 Laukant St., Reedsburg, WI 53959, phone: 608-524-9977 or www.dusterwads.com.
The 12 GA Remington STS Premier and Winchester AA shells were loaded as follows:
Shell: 12 GA 2-3/4" Remington STS Premier
& Winchester AAPrimer: Win-209 Lot - MDL 542 Powder: 19 GR Alliant American Select Wad: Greenduster GT 9210-12 Shot: 1 oz 7-1/2 lead Lawrence Mag
All powder and shotcharges were weighed on a Denver Instruments Accurate Load III Electronic scale. All shotshell hull resizing, priming, wad seating and crimping were carried out on a Mec Sizemaster press at Mayville Engineering Inc. Dave Kern, (715 South Street, Mayville, WI 53054, phone 920-387-4500) for their extensive line of shotshell reloaders and prices. On the first loading the Remington STS Premier hulls averaged 1219 FPS extreme variation 12 FPS, 10120 PSI EV 500 PSI. A most interesting recent ad in Trap & Field showed the Remington STS shells reloaded a dozen times and still the crimp looking very good, and with excellent tight recessed closures. If this were true, Remington's research and design shotshell crew have used the most modern plastic technology to come up with one of the most reloadable shotshells to date. You shotshell reloaders who shoot the small bore skeet and sporting events don't feel left out, as now the excellent Remington Premier STS shotshells are available in 20 GA, 28 GA and .410 bore, with extended reloading life!
Case deterioration was very minimal with this hull not showing any cracks or case mouth splits until the 10th reload, as one hull suffered a case mouth split. By the 12th loading all five shells showed very slight splits, crimps were still very firm resulting in uniform ballistics averaging 1207 FPS EV 15 FPS, 9980 PSI EV 1200 PSI. No ballistic problems with these Remington STS shells resulted after 12 loads!
Winchesters ever popular AA shells averaged 1216 FPS EV 9 FPS, 9860 PSI, EV 1700 PSI on the first loading, with the same set of components as the Remington STS shells. By the 10th loading, one of the shells developed a full length case mouth split, with a second shell developing two partial splits. Crimp strength was becoming weak by the 12th loading as a slight crimp bulge was noticed. Case mouths were also very black from powder soot. Yet ballistics were still very close to the first loading at 1209 FPS EV 32 FPS, 9200 PSI EV 1300 PSI.
Next in our test series came the excellent line of Federal hulls. Federal's paper target Gold Medal has been loaded by Federal for many years. Legendary popularity with handicap trap shooters due to its lack of felt recoil, at a 3 dram velocity level of 1200 FPS. This is due in part from the soft paper tube design expanding on powder ignition, to exactly fit your shotguns chamber dimensions. In an upcoming article for Trap & Field, I will discuss the excellent high density long range patterns achieved at 45 yards, by the factory paper Gold Medal loads and the ever popular all plastic Gold Medal target loads. For more information on shotshell loads and reloading components contact Jason Nash ATK (Federal Cartridge Company, 900 Ehlen Drive, Anoka, MN 55303, phone: 763-323-3878 or Jason.nash@ATK.com
All three of the Federal hull designs were loaded as follows:
Shell: 12 GA 2-3/4" Federal Paper
& Plastic Gold MedalPrimer: Win-209 Lot - MDL 542 Powder: 19.5 GR Alliant American Select Wad: Federal S3 Pushin Cushion Shot: 1-1/8 oz 7-1/2 lead Lawrence Mag
Federal's Gold Medal paper averaged 1174 FPS EV 41 FPS, 10760 PSI EV 1100 PSI on the first loading. On the second load velocity decreased by 25 FPS and pressure decreased by 1300 PSI. Slight pin holing was observed just above the brass head on the 4th loading. Small cracks were also starting to appear in the paper base wad. By the 5th loading powder burn through was casing larger pinholes, and small particles of paper base wad material were now missing. The primer pocket was also starting to expand causing a loose primer fit, with some powder gas leakage evident. By the 6th load crimps were starting to bulge as the paper was becoming soft. Yet on the 6th loading ballistics still had not fallen off adversely, they averaged 1138 FPS EV 52 FPS, 8960 PSI EV 1300 PSI. To be on the safe side the reloader should expect no more than four loadings from the paper tubed Federal Gold Medal shell. After the first loading, the powder charge can be increased by a half grain to achieve similar velocity on the next three loadings.
Federal's excellent all plastic Gold Medal shell averaged 1171 FPS EV 23 FPS, 9580 PSI EV 800 PSI. This shell went through 12 loads with very little deterioration. Very tiny case mouth splits were starting to appear by the 9th loading with very little change to the case mouth by the 12th loading. Crimp depth strength decreased somewhat by the 6th loading with a very slight case mouth bulge becoming visible on a couple of rounds by the 10th loading. By the 12th loading ballistics were still uniform with very little decrease averaging 1151 FPS EV 37 FPS, 9460 PSI EV 900 PSI. All things considered and yes, a few more reloads could have been squeezed from this hull!
Last but not least was Federal's plastic paperbase hull. It has had various names such as, League and Top Gun with a 8 fold crimp, and Game Load with a 6 fold crimp. On the first loading this hull averaged 1142 FPS EV 27 FPS, 8580 PSI EV 1000 PSI. Very tiny case mouth splits were observed after the 8th loading with very little change by the 12th loading. Again like the Gold Medal hull crimp depth slightly relaxed by the 6th loading, with a slight case mouth bulge visible by the 10th loading. No gas leakage around the primer pocket was evident even up to the 12th loading. Slight paper base wad cracking was visible after the 6th loading with tiny base wad particles being torn loose. Ballistics still had not deteriorated to a low level with this hull after 12 loads, averaging 1115 FPS EV 23 FPS, 8566 PSI EV 800 PSI. It is interesting to note that the Federal plastic paper base hull would require about .07 of a grain of powder to achieve similar velocity and pressure results as the Federal all plastic one piece Gold Medal hull. This hull is a real bargain for the reloader, as they can usually be gotten from local trap and skeet clubs for your time involved in picking them up. This shell is a real sleeper with its long loading life for the cost conscious shotshell reloader.
I would like to thank Jim Heggeness (2406 9-1/2 St. North, Fargo, ND 58103) for his hard work in preparing these velocity and pressure graphs used in this article.
In closing, I would like to make a couple of comments regarding case life and pattern test data (see data sheets). Patterns were shot at 40 yards through a Browning BT-99. Its bore measures 0.7415, with .041 choke constriction, with a parallel section length of 0.440. First once fired Federal Gold Medal one piece plastic hulls were primed with the Winchester-209 primer. Ninteen point five GR of Alliant American Select powder was topped with the Federal S3 wad, and 1-1/8 oz of 8 Remington lead magnum shot, running 460 pellets to the 1-1/8 oz shotcharge. Crimps were firm and well closed running 0.055 in depth. Velocity averaged 1171 FPS, EV 23 FPS, pressure averaged 9580 PSI, EV 800 PSI. 309.4 pellet hits were contained in the thirty inch circle for 67.2 percent extreme pellet variation was a tad high running 53 pellets for 11.5 percent. The twenty inch core held 184.2 hits, the five inch annular ring had 125.2 hits.
After reloading the Federal Gold Medal hull twelve times velocity averaged 1162 FPS EV 37 FPS. A fall off of only 9 FPS from the first load. Pressure averaged 9660 PSI EV 900 PSI and an increase of 80 PSI. Reloading these hulls for the thirteenth time resulted in crimps becoming somewhat weak. Crimp depth relaxed to about 0.020 with two shells showing a very slight case mouth bulge. Yet patterns were hardly affected. This time 299 pellets were contained in the thirty inch circle, for 65 percent with an extreme pellet variation of 11.6 percent. A pattern reduction of 2.2 percent, resulted. The twenty inch core contained 185.8 pellet hits, with the five inch annular ring catching 113.2 hits. So the annular ring gave up 12 pellet hits to the once fired shell. I would have thought the relaxed weakened crimps with less crimp depth should have lowered ballistics resulting in slightly denser patterns for the 13th reloaded shell, yet the pattern tests did not prove this out. A difference of ten pellets in the annular ring is pretty meaningless for good clay target coverage.
Well, the next time you hear a fellow trap shooter blame his numerous reloaded shells for missing an easy trap target, due in his mind to inferior ballistics, excessive EV's or reduced pattern percentages. My test series says he better find a better excuse! As none of these problems arose even after loading the hulls 12 times! Yet just the opposite is true when using slowburn rate powders, behind heavy shotcharges of lead or steel shot. Hunting load hulls should be in first class condition to promote utmost crimp strength and depth, achieving uniform ballistics, due in part to the resistance of a firm strong crimp. I must admit though, I get quite a psychological boost from once fired hulls, reloaded with excellent factory type crimps, whether in the hunting field or on the clay target range.