{"id":132,"date":"2015-09-14T12:44:33","date_gmt":"2015-09-14T16:44:33","guid":{"rendered":"http:\/\/www.floridareloading.com\/?p=132"},"modified":"2017-02-04T21:30:57","modified_gmt":"2017-02-05T01:30:57","slug":"reading-pressure-signs","status":"publish","type":"post","link":"https:\/\/www.floridareloading.com\/index.php\/2015\/09\/14\/reading-pressure-signs\/","title":{"rendered":"Reading Pressure Signs"},"content":{"rendered":"

Most reloaders know that cartridges should never be loaded with powder charges above the maximum or below the minimum charge weight specified in the reloading manual. \u00a0 However, some reloaders do not understand that excessive pressure can result even when a load is safely within the recommended charge weight range.<\/p>\n

How is this possible? There can be a number of contributing factors. \u00a0 The data in the reloading manual was tested by the manufacturer to be safe using the powder, case, primer, bullet, and importantly – the firearm specified. \u00a0 If you change any of these parameters, the pressure developed by the cartridge will change. \u00a0 If you change more than one parameter, you run the risk of ‘stacking’ a number of slight increases in pressure that add up to an unsafe level.<\/p>\n

Start low, work your way up, and watch for pressure signs.<\/b><\/p><\/blockquote>\n

The above mantra has been repeated – ad nauseum – by every reloading instructor and author since the first shooter reloaded the first cartridge, but it is still the most sound advice one can give to somebody working up a load. \u00a0 This article will describe some of the most common of these pressure signs.<\/p>\n

Establish a Baseline<\/b>
\nIn order to read pressure signs from your reloads; you first need to know how a ‘normal’ round behaves in your gun, and what a ‘normal’ spent case looks like after you shoot it. \u00a0 To establish what is normal, you should fire some factory ammo through your firearm – preferably with a similar weight bullet and the same headstamps as your reloads.<\/p>\n

While you’re shooting, take note of the operation of the firearm. \u00a0 Try to gage the amount of recoil, and pay particular attention to extraction and ejection. \u00a0 For bolt or lever action rifles, take note of the force required to lift the bolt\/operate the lever after firing a round. \u00a0 With semi-autos, get an idea of where your brass lands after ejection. \u00a0 With revolvers and single shot firearms, get to know the force required to eject or remove the spent cases. \u00a0 If you have a chronograph, record the velocity of the rounds.<\/p>\n

Retrieve your spent cases and note the condition of the primer, the shape and characteristics of the firing pin impression left on the primer, take note of any marks or impressions on the case head, and inspect the condition of the rims on cases.<\/p>\n

It is a good idea to clearly mark and retain at least one fired factory case from each manufacturer. \u00a0 This will allow you to better compare the condition of the fired brass from your reloads with fired factory brass – without having to rely on your memory.<\/p>\n

Now that you have your benchmark, you’re ready to look for pressure signs. \u00a0 Keep in mind that there are no absolutes when it comes to pressure signs. \u00a0 There are exceptions to every rule, and some calibers\/firearms may exhibit no pressure signs until catastrophic case failure. \u00a0 Often times, something that looks like a pressure sign can be caused by excessive headspace, or by a problem with the firearm. \u00a0 If you suspect excessive pressure, stop firing until you determine what is wrong.<\/p>\n

Keep in mind that there are no absolutes when it comes to pressure signs. \u00a0 There are exceptions to every rule, and some calibers\/firearms may exhibit no pressure signs until catastrophic case failure.<\/b><\/p><\/blockquote>\n

Excessive Recoil<\/b>
\nSometimes, the first noticeable indication of a pressure problem with your reloads is excessive recoil. \u00a0 If the bullet weights are similar, and the recoil is noticeably greater with your reloads vs. \u00a0 factory ammo, it is possible that you’re pushing the envelope. \u00a0 Keep in mind however, that recoil is the least reliable indicator of over-pressure.<\/p>\n

Recoil is subjective, and you may be paying closer attention when firing your reloads, causing them to seem stronger when they’re not. \u00a0 Bullet weight contributes more to felt recoil than pressure, so if your reloads have heavier bullets than your benchmark rounds, heavier recoil should be expected. \u00a0 Also, if your benchmark factory rounds were inexpensive ‘bulk-pack’ handgun ammo (which is often loaded notoriously light), a bit more recoil from your handloads is probably normal.<\/p>\n

Hard Extraction<\/b>
\nUnlike recoil, extraction and ejection problems are very reliable indicators of excessive pressure. \u00a0 When a cartridge is fired, the case expands to seal the chamber. \u00a0 Excessive pressure causes excessive expansion, which causes difficult extraction. \u00a0 Harder-than-normal bolt lift on a bolt-action rifle or sticky lever operation on a lever gun are classic signs of over-pressure.<\/p>\n

A change in the way that cases eject or failures-to-eject can indicate excessive pressure in semi-auto firearms. \u00a0 The same signs can also indicate lower than normal pressure in a semi-auto, so you’ll need to look for additional pressure signs or use a chronograph and let the velocity tell you whether the pressure is too high or too low. \u00a0 Harder than normal extraction from a clean revolver or single-shot firearm is also a good indicator of excessive pressure.<\/p>\n

Flattened Primers<\/b>
\nA flattened primer is the most widely known pressure sign. \u00a0 Unfortunately, it is also one of the least reliable pressure indicators. \u00a0 When new, the bottom edge of a primer cup is slightly rounded. \u00a0 This creates a small bevel between the bottom of the primer and primer pocket. \u00a0 When the round is fired, the primer slams into the breech face and flattens out. \u00a0 The theory on flattened primers is that if the pressure is excessive, the primer will ‘flow’ into the bevel, with the round edges of the cup becoming squared off when the primer fills the open space.<\/p>\n

The amount of flattening is going to vary according to the firearm and the brand of primer, so taken by itself, a flattened primer will tell you little about the pressure. \u00a0 This is where you need your benchmark rounds. \u00a0 Compare the condition of the fired primers on your reloads to those on the benchmark cases. \u00a0 If the reloads are significantly flatter, it’s possible that the pressure is too high.<\/p>\n

The photo below shows three different .357 Magnum rounds fired from the same revolver. \u00a0 The round on the left was a low-velocity ‘powder puff\u201d load. \u00a0 The CCI primer shows almost no flattening whatsoever. \u00a0 The round in the center is a full power load with a Federal primer. \u00a0 Although the primer has flattened out some, this is perfectly normal for this particular revolver. \u00a0 Although many ‘experts’ would say that this primer is ‘too flat’ and indicates high pressure, it is virtually identical to a fired case from a round of Federal factory ammo.<\/p>\n

The case on the right shows a severely flattened primer that clearly indicates an over-pressure condition. \u00a0 Also notice that the firing pin impression gets progressively shallower when the pressure goes up. \u00a0 This is because the pressure is partially ‘popping out the dent’.<\/p>\n

\"\"<\/a><\/p>\n

The Severely Flattened Primer On The Right Indicates That The Load Was Too Hot<\/em><\/div>\n

Often, a flattened primer indicates excessive headspace rather than high pressure. \u00a0 If a cartridge fits loosely in the chamber, the primer will flatten out when the case head slams back against the breech face during firing. \u00a0 This can happen even with low pressure loads. \u00a0 The primer brand can also have an effect on the amount of flattening. \u00a0 Federal primers are soft, and will flatten more than other brands with everything else being the same.<\/p>\n

Extruded Primers<\/b>
\nAn extruded or ‘cratered’ primer occurs when material from the primer cup is forced back into the firing pin hole in the breech face during firing. \u00a0 Usually, this is caused by a loose fit between the firing pin and the opening. \u00a0 If this is the case, your benchmark rounds will show some degree of cratering. \u00a0 If no trace of extrusion exists on your factory rounds, but your reloads exhibit it, it can be indicative of excessive pressure.<\/p>\n

\"\"<\/a><\/p>\n

An Extruded Primer Can Indicate Excessive Pressure<\/em><\/div>\n

The primer in the photo above is from a neck-sized .308 reload with a maximum powder charge. \u00a0 A normal round from this rifle shows no cratering at all, so the extruded primer is a good indicator of over-pressure. \u00a0 Notice that because of the tight headspace of the neck-sized round, there is very little flattening of the primer. \u00a0 The rifle’s bolt was hard to lift after firing this round \u2013 further indication that it’s time to back off.<\/p>\n

Pierced Primers<\/b>
\nIf your firearm is in good condition, you should never see a pierced primer on a fired case. \u00a0 This pressure sign in particular is unmistakable: If the primer is pierced where the firing pin hit it, the pressure was too high. \u00a0 If you experience a pierced primer, stop firing the rounds immediately. \u00a0 This problem is more than a minor inconvenience; it can cause serious damage to the firearm. \u00a0 When a primer blows out, a high pressure jet of super-heated gas blasts out of the hole. \u00a0 This can cause erosion of the firing pin, breech face, or any other part of the gun that gets in the way. \u00a0 After piercing a primer, you should have your firearm inspected by a qualified gunsmith before firing it again with any kind of ammo.<\/p>\n

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This Pierced Primer Is A Sure Sign Of Over-Pressure.<\/em><\/div>\n

Missing Primers<\/b>
\nThere are two possible causes for missing primers on your spent cases: Loose primer pockets or higher-than-normal pressure. \u00a0 If your brass is from a high-pressure cartridge (like .38 Super or .223\/5.56) and it has been reloaded several times, then chances are good that the primer pockets have loosened up, and it’s time to retire the cases. \u00a0 If the brass is new or once-fired, a missing primer can be an indicator of over-pressure, and will often be accompanied by additional pressure signs. \u00a0 The photo below shows a once-fired 9mm case that was loaded to an overall length that was too long for the bullet\/chamber combination. \u00a0 The bullet was pressed into the lands when it chambered, resulting in excessive pressure upon firing. \u00a0 In addition to the missing primer, the case features another telltale sign of over-pressure that is described later in this article.<\/p>\n

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There Are Multiple Pressure Signs Exhibited On This 9mm Case, Including a Missing Primer<\/em><\/div>\n

Sooty Ring Around the Primer<\/b>
\nAlthough it is often listed as a pressure sign, this one is probably the least reliable. \u00a0 An obvious sooty discharge emanating outward from around the perimeter of the primer is a sign of gas leakage. \u00a0 More often than not, the leakage is caused by a stretched out primer pocket. \u00a0 The easy way to tell is to decap the case with a universal decapping die. \u00a0 If the primer pops out more easily than on a ‘normal’ case, you’ve found your problem. \u00a0 A universal decapping die should be used instead of the sizing die because it will allow you to better feel the force required to pop out the primer. \u00a0 If you don’t have a universal decapping die, you can use the sizing die for a larger caliber cartridge.<\/p>\n

One more thing: I underlined the word ‘obvious’ above because when this condition exists, the leakage is as plain as day and will look much different than a normal spent case. \u00a0 A little bit of crud left in the beveled recess between the primer and the case head is probably a better indicator of a filthy gun than it is gas leakage.<\/p>\n

Case Head Extrusion<\/b>
\nWhen a cartridge is fired, the breech face supports the case head. \u00a0 With the exception of break-action and some single shot firearms, the breech face does not totally cover the case head \u2013 there’s a cut-out in the breech for the extractor. \u00a0 Excessive pressure can cause brass from the case head to extrude into the extractor recess in the breech, leaving a raised bump on the case head in the shape of the extractor cutout.<\/p>\n

\"\"<\/a><\/p>\n

These .308 Cases Show Severe Case Head Extrusion Marks From The Extractor Recess<\/em><\/div>\n

If this extrusion does not show up on your factory ‘test’ rounds, but is present on your reloads, it is a very reliable indicator of over-pressure. \u00a0 Keep in mind that all brass is not created equal, and some brass cases (especially Federal) are softer than others. \u00a0 It is not uncommon to see a trace of the extractor recess impressed into the case head of factory Federal rounds, but a prominent extrusion that will catch your thumbnail is always a sign that there is something very wrong.<\/p>\n

Bent Rims<\/b>
\nEarlier in this article the various extraction\/ejection problems associated with over-pressure in a semi-auto were described. \u00a0 The reason for the ejection problems it that excessive pressure can cause the case to over-expand and grip the chamber walls much tighter than normal. \u00a0 When this occurs, the force necessary to extract the spent cartridge from the chamber increases.<\/p>\n

In addition to causing extraction problems, this increase in force can cause the extractor to bend the rim of the case. \u00a0 A rough finish inside the chamber (or other problem with the firearm) can also cause bent rims; so you should retest with some factory ammo to rule this out.<\/p>\n

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The Bent Rims And Deep Ejector Marks On These Cases Are A Good Indicators Of Excessive Pressure<\/em><\/div>\n

The photo above shows bent rims on some .308 cases caused by excessive pressure. \u00a0 Also note that there is a slight extrusion mark on the case head from the ejector. \u00a0 Neither of these conditions exists when factory ammo is used, so they are good indicators of excessive pressure.<\/p>\n

Unusual Velocity<\/b>
\nThe chronograph is a very useful tool for diagnosing pressure problems. \u00a0 In fact, a chrono can tell you that a pressure problem exists even if the rounds exhibit no visible signs. \u00a0 Before firing your reloads, it’s a good idea to consult several reloading manuals to get a general idea of the velocity to expect. \u00a0 Be sure to take into account the firearm used by the manual’s publisher for testing. \u00a0 For example, if the reloading manual states that the .357 magnum cartridges were tested in a universal (closed breech) receiver and a 10\u201d barrel, you should not expect to match the velocity with your 4\u201d revolver. \u00a0 If you do reach the stated velocity even though you have a shorter barrel and a pressure-relieving cylinder gap, you’re probably running too hot.<\/p>\n

Use the chronograph to measure the velocity of your rounds as you work up a load. \u00a0 An increase in the powder charge should increase the pressure; and an increase in pressure should cause an increase in velocity. \u00a0 If it does not, it can indicate that some dimension inside the case or the firearm is stretching when the rounds are fired. \u00a0 If you increase the powder charge and do not see an increase in velocity (or worse yet, see a drop in velocity), you should stop immediately and find out what is wrong.<\/p>\n

Final Thoughts<\/b>
\nAs you’ve probably figured out by now, reading pressure signs is part art, and part science. \u00a0 Many of the conditions described in this article can be caused by factors other than excessive pressure. \u00a0 You’ve probably also noticed that excessive pressure often results in more than one of the signs being exhibited. Any time you suspect higher than normal pressure, it is prudent to back off and reassess. \u00a0 The rule is, as always: Start low, work your way up, watch for pressure signs, and never exceed the charge weights listed in the manual.<\/p>\n","protected":false},"excerpt":{"rendered":"

Most reloaders know that cartridges should never be loaded with powder charges above the maximum or below the minimum charge weight specified in the reloading manual. \u00a0 However, some reloaders do not understand that excessive pressure can result even when a load is safely within the recommended charge weight range. How is this possible? There<\/p>\n","protected":false},"author":2,"featured_media":115,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/posts\/132"}],"collection":[{"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/comments?post=132"}],"version-history":[{"count":3,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/posts\/132\/revisions"}],"predecessor-version":[{"id":258,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/posts\/132\/revisions\/258"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/media\/115"}],"wp:attachment":[{"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/media?parent=132"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/categories?post=132"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.floridareloading.com\/index.php\/wp-json\/wp\/v2\/tags?post=132"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}