Check which primer your cases use. In the past, 45 ACP was all large pistol primer, and most still is, but not always these days. You should be able to tell if primers are a different size by looking at a piece of each brand you are using. The last Blazer I shot was large pistol primer, but it's been so long since I bought any ammo I don't have a clue if it is still the same. You might also call who you ordered the 500 nickle cases from, and ask them which primer it takes- that way you would know what you are comparing to.
With primers so dear these days, it would really suck to finally find some in stock and get the wrong ones.
Have fun, 45 ACP is a great round to load. There's tons of load data out there for it.