Methods
Case Weight, Wall Thickness and Volume Capacity
Cartridge cases with and without primers/water were weighed on a RCBS Charge Master 1500 that had been calibrated and was accurate based on measurment of 10, 20 and 50 gr standards. Case neck wall thickness was measured with a Mitutoyo 115-313 tube micrometer. Three measurements were taken at three points around the neck, and the average was recorded. Case length and the neck diameter of the loaded cartridge were measured with a Mitutoyo 500-196-30 (CD-6" ASX) digital caliper. For neck diameter, three measurements were taken at three points around the neck, and the average was recorded.
Case volume was measured using a slight modification of the water method described in the QuickLoad manual. Water was dispensed
into cases that contained unfired primers using a 12cc Monoject injection syringe with a mounted Monoject 20 gauge needle with sharp edge ground flat. The cases with primer were weighed empty. Water was added to the case until it reached the neck. When water first enters the case, it forms a concave meniscus. As the level reaches the case rim, it goes from a concave meniscus to a convex meniscus so that it almost appears flat (SEE PHOTO 1). At this point, the water level is still slightly below the lip of the case. I add one more small drop so that the water forms a slightly more convex meniscus and the water reaches the rim of the neck (SEE PHOTO 2). The water-filled case is then weighed, and case volume (gr water) determined by the difference in case weights. The cases were emptied, primers removed, and cases dried by heat before loading.
Load Cartridges, Fire over Chronometer and Brass Preparation
Case priming was done with a 21st Century Shooting hand press. Primers used: CCI 41 (lot H22C201). AR-Comp powder (22.2 gr ± 0.02 gr) was dispensed with an AutoTrickler V4 system (Adam MacDonald, New Brunswick, Canada). 77gr Sierra MatchKing bullets were loaded with a Redding Competition Seater Die for 223 Remington with a Redding T-7 Turret press. Bullet seating gave a COAL of 2.255 inches and was assessed with a Hornady bullet comparator system and a Mitutoyo 500-196-30 (CD-6" ASX) digital caliper. AR-15 rifle had a 20 inch White Oak Armament 1:7 twist barrel with a 223 Wylde chamber. Muzzle velocity was measured with a MagnetoSpeed Sportster chronograph using Hi 1 setting at 147 ft, temperature 72-80F, Humidity 52-55%, 30.12 mm Hg.
Brass was deprimed with a Redding small depriming and decapping die, and fired brass was cleaned/polished for 4 hours in Frankford Arsenal treated corn cob media in vibratory cleaner. Brass was annealed with Annealing Made Perfect Mark II annealer using the setting provided by the analysis run for each type of brass. Full-length resizing was done following lubrication with a RCBS SB XL full size die for 223 Remington. Cases were not trimmed after confirming acceptable size with a L.E. Wison gauge. Measurements were completed on the cases for reloading as before. Loading and firing for reloaded cases was done as before.
Data Analysis
Data was recorded in Excel spreadsheet to calculate initial means and standard deviations data. SigmaPlot V.10 (Systat Software, Inc) was used to display data in graphs. SigmaStat V.3.5 was used for statistical analysis.