345 DeSoto said:
I'd like some more info on the increase in accuracy of loading light
I started reloading because I shot USPSA matches and wanted to save money on ammo over factory rounds and many match shooters claimed reloaded match rounds were more accurate than factory ammo. Many match shooters held the notion that in theory, accuracy "should" improve as you work up your loads from start charge towards max charge due to increase in chamber pressures for more efficient powder burn.
Well, my reloading and shooting mentor was a bullseye match shooter and he threw that notion out the window. Unlike the rapid fire "action pistol" match shooting of USPSA where double taps and faster stage times trump over surgical precision of each shot, slow fire bullseye match shooting requires utmost accurate loads and trigger control. He told me optimal accuracy will result from "consistency" of reloading variables. Of course, he taught me the virtues of scraping the bottom of FMJ lead base so all the bullets weighed the same, hand sorting brass by headstamp and hand weighing the powder charges but these reloading variables are for another thread discussion.
We developed various match loads that met USPSA power factors (major and minor) using slower Universal, HS-6 and WSF along with faster burning W231/HP-38, Titegroup, WST, Clays and Bullseye. Range testing was done using modified Norinco 1911/Sig 226 (my match pistols before switching to Glocks) off sand bags at 7, 15, 25 and 50 yards. We found many accurate loads not necessarily at high-to-near max load data as I anticipated, but at mid range load data using faster burn rate powders. Since surgical precision loads were not needed for my USPSA "action pistol" match shooting, I went with W231/HP-38 loads that produced less snappy felt recoil for more comfortable double taps.
Over the years, what I found is that slower burn rate than Unique/Universal powders tended to produce optimal accuracy at high-to-near max load data while faster burn rate than W231/HP-38 powders often produced accurate enough loads at mid range load data and sometimes at lower powder charges. So when I conduct load development, I often dip below the published start charges to see if the powder I am using can produce lighter yet accurate loads. Powders like Bullseye downloads well to produce accurate loads and probably explains why many bullseye match shooters use it. Clays is another powder many use for lighter and cleaner loads. Some match shooters like WST/Titegroup for lighter loads but when I switched to 40S&W, many match shooters commented on spikey pressure build up with WST/Titegroup so I stayed with W231/HP-38 even though it is more temperature sensitive.
While 165 gr FMJ/JHP Montana Gold with 5.0 gr W231/HP-38 was my favored match load, going from Limited to Production allowed for lighter recoil minor loads with 125 power factor. With 180 gr bullet, you only need 700 fps to make 126 power factor and that is easily done with below start charge. For Glock 22 and even for G23/G27, 3.8+ gr of W231/HP-38 with 180 gr Berry's/PowerBond/Rainier/X-Treme plated bullets will start to reliably cycle the slide and 4.0-4.2 gr will produce 9mm like mild recoil for fun and comfortable plinking/training drills with max charge being at 5.0 gr.
especially the .45 ACP loadings. It never occured to me that "light" loads for the .45 could be just as accurate, if not more so, than full power loadings.... Tell me more....
With 45ACP, you are only limited by the recoil spring rate as to how low you can go with your powder charge and many bullseye match shooters use lower spring rates like 10/12 lbs. With typical factory 16 lb recoil spring, fast burn rate powders will still cycle the slide at start or below start charges. 4.0 gr of Red Dot/Promo is below start charge (Lyman #49 lists 4.4-5.5 gr) yet with 200 gr SWC bullet, still reliably cycle the slide and produce accurate enough groups. It is likely from fast burn rate powder that can build enough initial chamber pressures for consistent enough muzzle velocities that results in accuracy. With 10/12 lb springs, many use even a lower charge of 3.5 gr Bullseye (Lyman #49 lists 4.9-6.0 gr) with 185/200 gr SWC bullet and obtain accuracy and reliable slide cycling.