.45 ACP NT brass used large pistol primers when it first came out. The problem was the DDNT used has higher brisance (suddenness of explosion) than lead styphnate and made enough gas so quickly in a large pistol primer that it could back the primer out hard enough to flatten and pierce pistol primer cups. To solve that, they had to drill the flash holes out to a larger size. Later they just switched to small pistol primers because they make less gas and the diameter of a standard flash hole is large enough in proportion to the narrow diameter to vent the gas better, and the narrower SPP cup is more rigid than an LPP cup the same thickness. Today, all you see are the SPP DDNT pistol primers, but you still find the old large flash hole NT cases on occasion.
More recently, as with
the Federal Catalyst primers I mentioned, non-DDNT lead-free formulations are appearing. Perhaps the Sinoxid primers are among them. One of the problems with DDNT, in addition to the ignition delays, is moisture deterioration. There is a concern they won't have a great shelf life, though I believe this has been improved.
Here's
a rundown of what the DOD found.
Here's
the DOD-funded study.
Since the Sinoxid primer was the first to use lead styphnate, it is interesting to hear they are going lead-free. They will need to have an MSDS available and it may reveal what they are using. The article I linked to about the Federal Catalyst primer explains most of its ingredients, though a proprietary sensitizing mix is involved. What is fascinating is Federal is convinced it will ignite powder with the reliability of a magnum primer while producing the combustion consistency of a weak primer. It should add up to lower velocity SD's for all.