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Posted: 6/22/2011 1:42:17 PM EDT
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So, I searched the previous threads, but I was unable to find a satisfactory answer to this question. I had primers back out on two out of 100 rounds of reloads yesterday. Here are the stats:
Once Fired brass, mixed between LC and Winchester. Both the LC and Win had crimped primers, so I had to ream pockets w/ hand tool Winchester 55 grain FMJ-BT bullets Winchester WSR primers 24.5 grains Hodgdon H-335 powder Overall length approximately 2.170. I trimmed all cases to 1.750 and seated bullets to the depth that let the crimp fall into the cantelure. No other signs of overpressure such as dark rings around primers, flattened primers, etc. I made a dumb (rookie) mistake and threw the two pieces of brass in the trash before verifying the headstamp. Could I have simply had a couple loose primer pockets? Could I have reamed the pockets too much? I still do not have a great feel for the reaming. The primers go in okay, but there is still some crimp left around the pocket. I am thinking of getting a RCBS swager to mount on my press. What did I do wrong? Thanks again for the help. |
| Backed out primers is usually a sign of a Low pressure load, not high pressure. Loose primer pockets do not cause backed out primers. Are you loading on a progressive and is it possible that you had a couple undercharged weak loads? Over sizing and excess headspace can cause flat primers or backed out primers. |
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Backed out primers is usually a sign of a Low pressure load, not high pressure. Loose primer pockets do not cause backed out primers. Are you loading on a progressive and is it possible that you had a couple undercharged weak loads? Over sizing and excess headspace can cause flat primers or backed out primers. I was confused about the backed out primer. My Lyman manual said it was a potential overpressure sign, but many other sources said under pressure loads will cause this. It is very possible that I had a couple under pressure loads. I do not use a progressive press, but I had a half-dozen lower-powered loads that were left over from my initial load work-up that I threw in with the batch to get rid of. Once they are loaded in 30 round mags, it is hard to keep track of which is which. Bad reloading practice, I know, but I will chalk it up as a lesson learned. I am sure that my headspacing is not an issue. Many sources state that excessive headspace and too little pressure can cause backed out primers. Can someone please explain, on a micro level, what happens to the case in each of these situations that causes the primer to back out. |
| Low pressure causing primers to back out: Firing pin force pushes the case forward in the chamber until the shoulder contact the forward part of the chamber, ignition and pressure causes the case to grip the chamber, case stays gripped to the chamber and doesn't expand rearward, primer backs out of the case until it contacts the bolt face. The amount the primer backs out depends on the headspace. Sometimes the rearward movement of the primer will flatten it slightly giving false pressure signs. A normal pressure round, the primer can back out until it contacts the bolt face but the case expansion to fit the chamber will reseat it flush with the case head. Primers that back out from low pressure shouldn't be protruding out of the case more than .002-.008". |
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I had similar issues with the identical load, and I fixed it by reducing the headspace to minimum specs using a Dillon gauge and a Hornady headspace measuring kit.
Now I can even run cases that have minimal primer pocket tension without a problem 24.5gr of H335 is my pet load for 55gr Hornady bullets, but I use the Hornady recommended COL of 2.200" and no crimp |
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Low pressure causing primers to back out: Firing pin force pushes the case forward in the chamber until the shoulder contact the forward part of the chamber, ignition and pressure causes the case to grip the chamber, case stays gripped to the chamber and doesn't expand rearward, primer backs out of the case until it contacts the bolt face. The amount the primer backs out depends on the headspace. Sometimes the rearward movement of the primer will flatten it slightly giving false pressure signs. A normal pressure round, the primer can back out until it contacts the bolt face but the case expansion to fit the chamber will reseat it flush with the case head. Primers that back out from low pressure shouldn't be protruding out of the case more than .002-.008". Makes so much sene that I feel dumb for not figuring it out myself . . . |
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Loose primer pockets can cause them to back out, or even fall out. To find out for sure, manually deprime it (in your hands, not on a press) and see how much pressure it takes to push the primer out, if you are doing it by hand with a depriming punch it should take a pretty good lick, if it pushes out easily its trash. Take the depriming punch out of a universal deprimer to do this. |
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Which priming method are you using? Press or hand tool?
You should be able to "feel" a loose primer issue with a hand tool. It is still possible to get feedback from a press, but you have to pay attention. If you detect a problem, such as too low of a force to seat a primer, stop and do as suggested. Investigate how much effort is required to remove the primer by hand or by tapping the case. If you think it is spooky, it probably is... Get a gage pin and see what the primer pocket diameter measures. Also, compare to a "good" one. The dimensions are listed. Crimp reamers should only cut a chamfer where the crimp was. At worst case, you may create an enlarged chamfer. Unless the tool is cutting the pocket diameter, it shouldn't cause a problem. If it is touching (cutting) the bore, it may be the problem. So, with 24.5 Grains 335 you probably don't have a hot load, but each gun is different. In all probability, you probably had an oversized primer pocket. Too bad you tossed them without the measurement. You will get better at diagnosing as you go. |
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Headspace could be an issue, it could be the shoulder is bumped back to far. Check the length of your trimmed cases as well OP. If you're under spec that could do it as well. You aren't showing any signs of pressure other than that, so it's not likely that it's overpressure. Are you seeing powder burns at the case mouth running down towards the shoulder more than with other ammo? That would be a sign that your load is low pressured, and the case isn't expanding and sealing correctly.
If you have pics post them, that will help. |
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Which PP reamer are you using? Lyman. I have heard some say that the Lyman removes too little crimp, but never too much. I have a Lyman PP reamer. I never use it as it doesn't work. Get a Hornady PP reamer. Link |
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