Fact or Fiction: Small vs. Large Pistol Primers in .45 ACP
August 26, 2014
I don't know if you've noticed, but several of the major ammunition companies are loading some of their .45 ACP ammo using Small Pistol rather than Large Pistol primers.
So what's the difference in performance between .45 ACP handloads using Large Pistol versus Small Pistol primers?
I had always assumed there couldn't be too much, or shooters would notice and avoid the Small Pistol primer factory loads, but I'd never taken the time to experiment and compare ballistic data.
Some Winchester, Federal, and CCI factory loads have appeared with Small Pistol primers. The Winchester headstamp includes an "NT" marking, which I believe indicates nontoxic (lead-free) primers. Some Federal factory loads also use a similar coding. CCI/Blazer, Speer, and other Federal brass loaded with Small Pistol primer pockets simply have the ubiquitous ".45 ACP" or ".45 Auto" headstamp.
Well, you ask, "So what?"
Obviously, it must be safe to do so or they wouldn't risk it. But it can surely play hob with your reloading routine. Trying to force fit a 0.210-inch-diameter (and highly energetic) disc into a 0.175-inch-diameter primer pocket can cause a significantly emotional event if it ignites. A friend of mine handloads on the automated Dillon 1050 progressive tool, and after experiencing several startling "pops," he now carefully examines any fired .45 ACP cases he picks up at the range and stores and reloads his Small Pistol primer brass separately.
It's just another example of why segregating your cases—by headstamp, number of times fired, etc.—is a good rule to follow.
My most significant brass recovery coup occurred at an InterMedia Outdoors writers' conference. Local range club members volunteered as range officers for the conference and usually divvied up fired cases from each day's shooting sessions. But the morning after several new .45 ACP pistols had been thoroughly wrung out, empties remained scattered all over the recovery tarps. I asked one of the early rising range members about it, and he responded, "It's all Blazer brass with Small Pistol primers. Nobody wants it." After I convinced him it could be reloaded with no problem, we quickly gathered up and split more than 2,000 bright and shiny cases. I still haven't loaded all of mine yet.
Large vs. Small
For this exercise, I chose five propellants and assembled several boxes of target loads using Zero 200-grain, swaged SWC lead bullets, Blazer cases with Federal 100 Small Pistol primers, and Federal cases with Federal 150 Large Pistol primers. I also used a couple of boxes of hotter handloads that utilized CCI and Speer brass primed respectively with CCI 500 (Small Pistol) and 300 (Large Pistol) primers topped with Hornady 185-grain XTPs. They were loaded with Ramshot Zip powder.
I load all of my .45 ACP ammo with Hornady Custom-Grade New Dimension dies. Unlike most "no lubricant needed" tungsten carbide sizing dies, Hornady's sizer die features a titanium nitride coated insert. To date I've loaded thousands of rounds and, if I clean it occasionally, expect it'll last many thousands more.
I've found that seating a swaged lead bullet, being softer than a cast or a jacketed one, requires a bit more casemouth flaring. But don't overdo it—just make sure the mouth clears the bullet base enough to avoid scraping lead as it is seated.
Most reloaders skip cleaning the primer pockets. I almost always do clean the pockets, and not wanting any adverse variable to affect the results of this evaluation, I did so when preparing these test loads. If I'm priming more than 100 cases, I typically use a handheld tool with a magazine tray; fewer test load groups are usually primed with an old RCBS ram-prime die arrangement. However, I always gauge primer seating depth by "feeling" the case head with my finger to assure they're at least flush and, preferably, two- or three-thousandths below flush.
Redding's 10-X mechanical powder measure usually dispenses very precise charges. It handled Trail Boss, Red Dot, and the other disc or flake propellantsâ€”with one exception. I wanted to vary charge weights by just a few tenths of a grain, and IMR 700-X just wouldn't "throw" close enough. So I individually weighed each charge to obtain the desired result.
I seated the swaged lead bullets first (COL of 1.24 inches) and then ironed out the casemouth flare in a Hornady taper crimp die to obtain a casemouth diameter of 0.470, +/- 0.001 inch.
I chose my Heckler & Koch USP Expert .45 ACP pistol to perform the range work. The magazine holds 10 rounds, so I could load five each of the Small Pistol and Large Pistol primer test loads and fire comparable groups back to back. The pistol also has excellent iron sights that my aging eyes can still discern well enough to shoot quite accurately.
As you can see in the accompanying chart, the results of the selected loads compare quite favorably. I prepared at least three batches of each target load varying the propellant charge weights as my evaluation of the velocity data (average and standard deviation values) and group size suggested.
I also checked in with one of my industry contacts to find out, if possible, just why they chose to switch from Large Pistol to Small Pistol primers in some of their .45 factory loads. We discussed the actual quantitative and chemical variables between their Large Pistol and Small Pistol primers.
Because the SAAMI specs do not dictate primer configuration, my source summed up the situation by simply saying, "Today's primer technology is so much better than before, a Small Pistol primer is now actually more suitable for the .45 ACP cartridge."
Practically speaking, you don't need to avoid handloading .45 ACP brass that have Small Pistol primer pockets. Just be sure to keep them separated from the Large Pistol primer pocket cases.