I have been handloading and shooting like a mad man all summer long. I have a question about pressure signs. What is the order that you will start to notice too much pressure. Like will you see cratering primers first, then with more pressure you will start to see blown primers.

The reason I ask is two fold. First of all, the only "signs" I think I have ever had with my hand loads is VERY small primer cratering. I am talking very small here. Once I see that, I don't go any further.

The second reason I am asking is for safety. I have read in the reloading part of this site that Saeed will sometimes have a hard time opening the bolt after shooting some very high pressure loads. To me that seams like WAY too much pressure. I always though that once you get to that point you are getting close to blowing up your action.

If you can educate me further on pressure, I am all ears.

Thanks, this site is great!!

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Monyhunter

Cratered primers are the least likely to tell you anything about pressure. Any rifle with a firing pin hole that is oversized gives you a cratered primer without any excess pressure. The curvature of the edges of the primer can give a bit better indication but because of differences in materials used for the cladding, they are also highly suspect. Hard bolt lift and extraction, or ejector or bolt face marks on the head of a case are probably the earliest indicators of excessive pressure.

I agree with Bob. Cratering of the primer tells you more about the fit of the firing pin than the pressure of the loads -- except with the same gun and primers, cratered versus uncratered indentations do indicate higher pressures.

The radius of the primer edges also has more to do with the headspace of a particular brass case in your chamber than with pressure. Low pressure loads fired with longer headspace show extremely "flattened" primers, whereas higher pressure loads fired with very tight headspace may show little primer flattening at the radius if the primer cups are "hard" or thick.

First indication: Sticky bolt lift. This will happen before bolt face imprints.

Second indication: Expanded case head measured at the rim or belt. This is tricky to measure, and remember, the original case may not be perfectly round so you have to measure at a pre-referenced place. I don't even start to believe that guys who claim they can measure 1, 2, or even 5 one-thousandths inch expansion. But if you get measurable expansion, you load is too hot.

Third indication: Losened primer pockets. Directly related to above, but easier to detect, especially with a hand seating tool, which you should always use.

Fourth indication: Case head engraved with mirror image of bolt face, such as ejector hole or slot mark, etc. If you see such, you are definately too hot (and probably had to use a rubber mallet or the heel of your shoe to hammer the bolt open).

Finally, look at the pressure ring near the head where the brass becomes thick enough that it does not expand to fit the chamber, but holds the pressure itself. On lighter loads, this ring will be further forward (toward the mouth of the case). As pressure goes up, this ring will move progressively rearward toward the head. There is no "gauge" or objective measurement for the pressures involved, but using new brass from the same lot, the pressure ring will be further aft with higher pressure loads than with lower pressure loads.

There is a tremendous margin of safety with modern bolt actions. Even with weaker action types, the brass case usually gives up long before the integrity of the action is breeched. So, what you worry about with high pressure is how does the action handle the high-pressure gas spewing from the primer hole or from a crack in the case head (not about the bolt lugs shearing off and sending the bolt back through your cheek). And in practical terms, you worry about slick feeding and not having to hammer the bolt open as that wounded elk tops the ridge on its way to the next state.

The best thing to do is get a strain gauge, expensive though.

The most practical way is to measure case expansion at the junction of the case wall and solid head. Get a base line from factory ammo. Measure to four didgits with a mic. Do this at several radial loctions, pick the largest one. Your chamber might not be perfectly round. Ok, now you have measurement like o.4735". Check your handloads the same way. Those that give a measurement of 0.4735" are the same pressure as factory. Larger is higher pressure samller is lower. For most cartriges I load to factory pressure. SAMI and the factory boys have more resources for load developement that we can imagine. I figure that I want safe ammo that shoots straight so I make it like they do.
Measuring the expansion at the rim is probably not the best since by the time the solid head is flowing you have gone way to far. Primer eyeballing is un-reliable for many reasons. Sticky bolts fore tells bad stuff, that is way to hot. I am a bit skittish about pressure. I have trashed a couple of rifle by eyeballing and winging it. Since I started doing it his way, I have not had a single primer fall out or a bolt get sticky. Best part is that you can plot your pressure against velocity and see trends and avoid disaster. You will actually see velocity gain slow as you increase the charge past a certain point.
Check out "Pet Loads" by Ken Watters, it goes in to detail regarding this method.

Scot, I disagree a little bit about your measurement advice as it does not take the individual chamber dimension into account.
My idea about a safe and reasonable procedure goes like this:
Measures are taken right above the end of the web.
Measure factory cartridge before firing (1) and after(2).
For reloading, use a reduced starter load in the neck sized (and tuned in several ways) shell, size still (2). After firing it should still be (2).
Now you work up your load and may find that a load which expands the wall more than (2) will yield the results you are after. Now your case reached reached stage (3) and should not further exceeded.

As the material changes its properties (elasticity, thickness of walls) with continuous firings, the procedure is not as simple as it seems to be, and it needs the experience of a Ken Waters who could judge by measurement how hot a cartridge had been loaded.

I agree with most of what has been said here except to say that measuring case head expansion is fraught with difficulty and even if it should be done correctly, the horse is already out of the barn, as far as the avoidance of > high pressure goes. Not for beginners, at any rate.

Primers can tell you something if components are routinely used but, as stated above, they can be misleading.

Knowing your factory load pressure ring dimensions and using them as a barometer is a good way to go. With belted cases, I have a jig that allows consistent measurement of the forward half of the belt only, which serves the same purpose as micing the pressure ring on beltless cases. Ken Waters' system is a good one but it relies very heavily on the consistent use of specific components, for which, one will "get a feel for" over time.
Bob Hagel had a similar but more aggressive system which was better suited to the belted magnum cases. His is the method I use most, with a bit of my own stuff, thrown in.
I recommend Hagels' book "Guns, Loads & Hunting Tips" along with Waters "Pet Loads" mentioned above.

I would be willing to bet that not 1 or 2 shooters out of 500 or so that "mike" their case heads either measure expansion in the right place or more importantly can use their micrometer with sufficient accuracy and precision (not the same thing) to get any useful information.

The only "rule-of-thumb" I'm willing to use when I suspect excess pressure is getting close is to reload the same case 5 or 6 times with a load....if the primers still seat firmly I don't worry. If the pockets show any sign of becoming loose I back off.

The pressure signes mention apply for the most part to modern bolt rifles, with older bolt guns, most lever actions, and handguns it would be best to stay well within reccomended load data and not push it until you start seeing pressure signs because your first one may be a gun in two pieces. Not trying to be a smart aleck but you never mentioned what you were loading for so I just thought I would give you a warning that may or may not apply.

Micing cases is the best route, but few can actually do that...so to simplify life I believe one could go until he gets an extractor mark then back off one or two grains. A sticky bolt usually comes two grains after the extractor mark...

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Here is a variation on the miking procedure, that requires no tools. Use clean polished cartridges. Eyeball how far case wall of the cartridge expands and disturbs the polish, toward the rim. The pressure ring. Compare that to factory. Make your reloads with the same brass as the factory ammo. Since the solid head tapers into the case wall, higher pressure equals closer to the rim. More pressure expands thicker brass. No tools required. Just give your cartridge a steel wool polish before you fire it. Grab and twist. You can readily see the expansion progress toward the rim as you increase the charge. You can write on the fired cases with a fine marker to keep them straight later. Just line them up on a flat surface in the sunlight and look. It is very easy.
Some one mentioned case head expansion not being calid because chambers vary. Use the same rifle for all of this!!!
It may be true that few bother with this. You really should. If for instance you use bench rest primers, the first sign of excess pressure can be gas in your face. All I am suggesting is a practical way to see it coming and load safely. If you use surplus powder you need to learn these things. I do this when I work up loads. I keeps notes and paste them into my relaoding books. This is great stuff to review later. Five years from now you will have no idea of what worked in your rifle, unless you keep notes. You will spend less time trying random things if you know what ground you have covered. It saves lots of time to be organized an be able to estimate relative pressure. I am older and wiser than years past. Back then when I loaded picked random loads from manuals and eyeballed primers, I trashed a few rifles. I am to old for that kind of exitement.

[This message has been edited by scot (edited 10-17-2001).]