I was reading a book on reloading and it showed a picture of some shot brass that went from the correct pressure to very high pressure. It said to note the differences of the primers as pressure got higher. Problem is, I could not tell a difference Maybe it had to do with the pics being in black and white or its just me. Anyhow, what are some other ways of telling when a load pressure is too high?

what i have seen is when the primmers are flat and i meen flat thats a sign.if your bolt is hard to open after the gun is fired that is sometimes a sign.and last is if you are splitting once fired brass that can be a sign.i hope this helps some just be carefull when you load i always check each charge 2 or 3 times just to be sure.

Yea I have loaded a couple thousand .40 and not one problem but since switching powders I have more "pop" when they are fired. Probably just not use to the different powder.

Here's a pretty good pic that shows some clear and detailed images of some high pressure signs.
over pressure pics

One observation I've noticed about flat primers: Different brands of primers are harder or softer than others. The hardest will take considerable more pressure before starting to flatten than the softest will. The pic in above link shows a pretty good example of what a partially flattened primer looks like. I've seen some that were a whole lot flatter than that one - almost completely filling the radius at edge of primer pocket but still didn't show the ridge around the primer indentation or any other pressure signs. Those were some soft primers I was using, and the flat ones were often the most accurate in the loads I was fooling with. They were not over pressure, but were what I considered max for me. That raised ridge or cratering as they call it shown in the pic is one I've been told to particularly watch out for because a little more can result in a pierced primer. I personally think that the fit of the firing pin through the hole in the bolt face has as much to do with that cratering ridge business as high pressure does but I have no proof of that. I'd bet that the rifle that fired the cases shown in this pic took a pretty good whack with something to get the bolt open judging by the spot on the case head where the brass flowed around the ejector. If this one happens, it's real easy to see because that spot really will be very shiny compared to the rest of the case head. I've never experienced the loose primer pockets and suspect that probably takes a pretty healthy dose of over pressure to stretch them that much.

There's also ways you can measure with a micrometer at a certain spot. Google search for "high pressure signs in fired brass" will yield all sorts of additional information about what to look for. A lot of the time, these signs start to show up when people are looking for that place where their groups start shrinking back down the second time as charge weight is continually increased which can be getting quite close to the edge of messing up. Likely well beyond what modern loading manuals list as max load. It's bound to be hard on the rifle and risky to body parts as well.

Here is my example of a "flat" primer. This was shot in a T/C Encore so there are no extractor marks but I felt it when it happened. Hope this helps.

One more thing. Look at the edges of the primers. Notice the difference? The one on the left is "pushed" out to the edge of the primer pocket.

yea look at the primer...you will be able to tell a flattened primer....also look at the indintation where the firing pin stikes the primer....if there is a ridge around where the firing pin strikes the pressures are a little high also.

Aside from the usual signs of high pressure mentioned above, a chronograph can be a good indicator of pressure conditions. Velocities over published data for any given bullet weight/powder charge combination can be an indicator that you are pushing toward the redline or well above it.

Pictures are usually tough to tell the differences. Black and white pic's make it even tougher IMO.

You could also feel the light tension or none at all when installing the primers w/ a hand primer. If the primer came out and then was slammed back into the brass the opening can enlarge and not be able to put tension on the new primer.

I kinda agree w/ the chronograph to a degree. Even though the velocity could be lower than the book doesn't mean it is still not building up too much pressure.

Bullet seating (too long) can contribute to higher pressures w/o much change in the velocity.

Also an under charged load can cause even higher than normal pressures. Seen this w/ folks trying to make their own reduced load.

The perfect reason to get an updated manual that lists the bullet and powder combo you plan on using that has a suggested starting load and max load. I'd also recommend using a reloading manual that list reduced loads.

BTW, the pic's above in ilike2hunt2's post is a little decieving to me. Reason being they are different makes of brass (can cause a psi change also). The one on the right appears to have flattened so much it stretched the primer pocket. The primer diameter appears to be larger than the one on the left. Not sure why the left was noted to be too high of pressure?? Are my eye's playing trick's on me or is it a typo? Help!!

Forgot to mention that I've had some firing pins contact the primer to make the little crater like they are pointing out in Jon's post. So, this isn't always a good sign.

10-4. This is your best tool to tell you whether you're pushing it too hard. Of course, to make use of this method you have to understand that what you're looking for is reasonable velocity considering the powder and bullet weight being used...just because you're getting 3400 fps with a 50-grain bullet in .223 does not mean you're okay---you would be if you were loading H335, but not Alliant 2400.

You can stare at primers and measure case head expansion all day long, but still not have any real, reliable idea whether your load's too hot or not.

Cast rifle loads, using pistol powders like unique, can produce over pressure loads but with low velocity.

I just started reloading a while back. I have had some signs of pressure and backed down. My friends rem 7-08 was showing signs of pressure with factory loads, he ended up selling it and he gave me the cases. I was loading some for my 7-08 and noticed that some of the primer pockets were a little loose, how loose is too loose ?

If you are getting blow by (gases escaping around the primer)then they are too loose.
If the primer falls out after fireing the it is definetly to loose.