Recognizing Pressure Signs

Load manuals and experienced reloaders frequently advise working a load up in small charge increments while watching for pressure signs. Many beginners are unaware of all the signs. Below is a partial list of them, along with alternate causes of the same signs where I am aware of them. No one particular sign can be counted on to become apparent in all guns, nor even to be consistent with any particular set of load components. There is also no way to tell which sign will show up first in your gun and with your load and component combination, so you need to learn to watch for them all. The standard recommendation, if you get a clear pressure sign, is to back the charge weight of the load down 5%. In most instances, persistent pressure signs do not occur until your pressures are already well above SAAMI MAP.

1. Case bulging excessively. (This is most often at an unsupported part of the case head.)
2. Case cracks along its side. (May mean excess pressure, but may mean brittle, defective, draw mark scored, or worn out brass.)
3. Case head expansion. (A.k.a., CHE. It most often means pressure too high for the lot of brass used, but an isolated example from a lot may mean nothing, as brass is often imprecise, so CHE can occur at pressures that differ by 2:1 within a brass lot.)
4. Case head separation. (May mean high pressure, but may mean excess headspace or worn out brass.)
5. Case splits in body in fewer than 10 reloads. Back powder charge down at least 2%; 5% if in the first two or three reloads. (May also be due to excess headspace, a once-fired case from another gun that was highly stretched at first firing (use paperclip probe to feel for pressure ring inside case and reject any where you can feel one), or is less commonly due ammonia vapor exposure or to a brass defect in an individual case.)
6. Case mouth split in fewer than 6 reloads. (May mean high pressure or ammonia vapor exposure, but more often simply means case needed neck annealing.)
7. Case mouth split in fewer than 4 reloads (May mean high pressure or ammonia vapor exposure, but more often means case got too hot during annealing.)
8. Case pressure ring expansion (A.k.a., PRE; not much more reliable than case head expansion but may mean pressure is excessive for the particular piece of brass or lot of brass it occurs with. It can, for example, happen with Federal commercial brass, but not with Lapua brass or with military brass at the same pressure.)
9. Case primer pockets getting loose in five reloads or fewer. (This is a version of CHE, but may be apparent earlier in pressure. Lowering charge, as in the introductory paragraph, may fix it. However, if the load seems reasonable or is an old standard, same as in 3 and 8, switching make of brass can fix it.)
10. Case stretching excessively. (This is usually visible as pressure ring area stretching which may be due to excess pressure or to excess headspace. Use a bent paperclip or other probe to feel for thinning at the pressure ring. In rear bolt lug guns, the whole case may lengthen before resizing and be impossible to rechamber without sizing.)
11. Case, extractor or ejector marks on head, especially after increasing powder charge to next higher increment. (Most common in semi-auto rifles, but can happen with any extractor and ejector. May be due to high pressure, bad timing in a semi-auto action, or may be due to an improperly fit extractor standing proud on the bolt face.)
12. Case, won’t fit back into chamber after firing. (May mean high pressure, but can also result from a chamber cut at an angle off the bore axis or by an out-of square bolt face. Test for the latter two possibilities by noting head stamp orientation at firing. If case fits back in at that same orientation but no other, then one of these two conditions obtain.)
13. Gas leak. (See Primer Leaking, below.)
14. Groups start to open up at or beyond a published maximum load.
15. Hard bolt lift. (This often indicates excess pressure, but can also result from only one bolt lug making contact until peak pressure is reached (lugs need lapping).)
16. Incipient case head separation (Starting or partial case head separation or signs of it. Can also be a problem with excess headspace.)
17. Increase in powder charge achieves unexpected velocity. (Average velocity will tend to increase by the same number of feet per second per grain of additional powder over the normal operating pressure range. If your next charge increment fails to produce the expected additional velocity or produces too much additional velocity, pressure may be high. Poor grouping usually accompanies this symptom. It is also caused at reasonable pressures by uneven bolt lug contact (lugs need lapping), in which case still further charge increments go back to producing orderly velocity increases and grouping improves. Suspect this last situation if the charge at which the velocity anomaly occurs is in the middle of a published load range. Otherwise, back the charge off 5% from where the issue started.)
18. Primer blown loose. (Primer falls out when gun is opened; same as loose primer pocket, #9, above.)
19. Primer cratering. (May mean high pressure, or it may mean a worn firing pin or firing pin tunnel, or may mean you have a new production Remington bolt with chamfered firing pin tunnel.)
20. Primer flattening. (May mean high pressure, or may mean long headspace; some loads always make flat primers; softer primer cups (Federal) flatten more easily than harder ones (CCI), so it may mean nothing at all.)
21. Primer mushrooming; i.e., primer cup fills out radius at primer pocket perimeter. (May mean high pressure, or may mean excess headspace.)
22. Primer piercing. (May mean high pressure or may mean incorrect firing pin protrusion or incorrect firing pin nose shape.)
23. Primer leaking gas around edges of primer pocket. (May mean high pressure, may mean loose primer pocket in case, may mean damaged primer was inserted, may mean excessive chamber headspace.)
24. Case, short life - back load off at least 2% (under 10 reloads in non-self-loaders, or under 5 loads total in self-loaders before pressure ring is detected with paperclip probe.)
25. Case, sticky or hard extraction. (Especially in revolvers, this is a positive sign to knock the powder charge down at least 5%. In rifles also look for chamber ringing.)
26. Case, torn or bent rim. (Caused by hard extraction, see #24 & #25, above).
27. Case, primer pocket expanded. (A.k.a., PPE; this is the same, in principle, as #9 above, but can be made apparent by measuring with gauges before primers actually are loose. It is a somewhat more sensitive measure than O.D. CHE measurements.)
28. Primer loose or falls out when opening the action or after seating. (See #9 & #27, above).
29. Case, increase in required trimming frequency. (This refers to a sudden increase in case length growth per load cycle. It is actually a less acute version of #10. It can be caused by excess pressure, but can also be a sign of increasing head space due to some other problem. It is especially common as a pressure sign in lever action guns because the greater span from bolt face to rear lug allows more steel stretch when pressure gets excessive.)
30. Case, increase in apparent headspace. (This means the cases are coming out longer, including between the casehead and shoulder. It can mean bolt lug setback, which is usually an extreme pressure sign. It can also mean a loose barrel or an improperly set up Savage barrel. Whatever the cause, the gun should go straight to the gunsmith for inspection.)
31. Gas or Flame Cutting of revolver top strap. (Can also be due to excessive barrel/cylinder gap that needs correction.)
32. Gas or Flame cutting of rifle bolt face by gas leaks around primer pocket or at bolt face perimeter. (Can also be result of occasional leaks from normal rounds firing, as is observed in many military gun bolts.)
33. Velocity higher than manual maximum load velocity reported for same powder charge and barrel length. (May mean excess pressure or a “fast” barrel, but often is actually a chronograph error due to screens being too close to the muzzle blast, bad lighting conditions (watch for ground reflection), or a low battery. In one instance, though, a fellow loading a .243 Win load in the Speer manual and still one grain below the manual maximum was getting velocity readings 200 fps higher than the manual claimed for the higher maximum load. His single-shot action was also popping open at every shot. With QuickLOAD, we were able to calculate he had about 77,000 psi.)
34. Flash hole diameter growing. (This is a more sensitive version of case head expansion. See #3, #9, and #27, above. It can be checked with pin gauges in the form of numbered drill bits or by special gauge.)

Excellent list!

From the Pressure Trace testing I did last month, the "Classic" signs are really a poor indicator of actual pressures. We had some 308 rounds that were reporting 75,000psi with NO primer issues, or hard extraction.
IF you feel you MUST exceed book loads, watch your Chronograph guys!! In our testing an extra 100 fps, equated to approx 12,000 PSI additional pressure.