Excellent advice from Taterhead and Any Cal. These guys have a lot of experience and know what they are talking about. Reading primers can be useful, but it can also be confusing.
There is a lot that can be said about reading pressure signs and load work-ups. I will add two more things to what has already been said. First, don't try to make a powder that is too fast work with top end 10mm loads. If you shoot a lot of 9mm and 45, and you only have two powders on hand, that's fine. You can probably find some safe load to use in 10mm for Power Pistol, Unique, etc. But those are NOT top end loads! I see this quite often where someone wants to drive a 180gr bullet at 1300fps out of the stock G20 barrel with Power Pistol. Can it be done? Probably. Can it be done safely without exceeding SAAMI pressure limits? NO! So don't even go there. If you want top end performance, use the powders that are going to get you theren safely, like Longshot, 800-X, A#9, and maybe Blue Dot. These are the powders you want to be using if you're going to make serious 10mm ammo. Leave the Unique, Power Pistol, HS6, etc. for the low velocity plinker loads.
Secondly, I STRONGLY advise doing load development with a chronograph. Yes, they are going to cost you $100, but you can use them with every caliber you load, and the data you collect from various chronographed loads is an invaluable tool. A chrony provides feedback for what you are trying to achieve. If you are getting 1300fps with a 180gr. bullet using Longshot or 800-X with standard primers, you are probably not going to see any smiles. I have worked up 180gr bullets to 1300fps with both Longshot and 800-X using both a LWD and the G20 barrel, using "soft" Starline brass, and still have not had a single smile (note that the 6" LWD barrel fires the exact same 1300fps 180 gr load from the G20 barrel at 1400fps from the 6" barrel). Without a chrono, how do you know where one powder does better than another? How do you know you have achieved "full power 10mm loads?" You don't. You are flying blind, trying to read primers and guessing. There is plenty of data that has been compiled by the handloaders here that back up a 1300fps 180gr. loading with Longshot and 800-X, but you probably won't find those loads in any reloading data book. So my advice is to stick with book loads and book loads ONLY if you don't chrony your test loads. Trying to achieve an unknown velocity with an unknown amount of powder is a recipe for disaster.
So, if you don't have a chrony, stick with book loads. Even then, you aren't 100% safe, so work up from a safe point backed off of the maximum listed loads. A conservative loader will consult 4 different references, and take the "max load" from the most conservative reference as his guide. An unwise loader will look at the 4 different references and try for the highest value that he sees. The unwise loader is the guy that gets the smiled brass. The loader with chrony sees the trouble coming from a long way off, and rarely ever gets to the point of smiled brass, unless he chooses to push it to that point.
BTW, all of the 10mm ammo that I load runs fine out of both the stock G20 barrel (22lb spring) and 6" LWD barrel without any smiles or other problems. Not only is it possible, but I believe if you are loading within SAAMI pressure specs (maybe with a small but responsible amount of margin) it should be expected.
Good luck and be safe!
A handgun is only good for fighting your way to a rifle.
Last edited by TDC20; 01-10-2013 at 00:02..