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04-25-2017, 01:45 PM
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Reloads, Primers and Pressure signs - an FYI
It's commonly recommended to examine fired primers for "signs of pressure" when working up top loads.
I'm not suggesting that it's a bad idea, but it's definitely not a tell-all either.
Pictured (T to B) are 2 Magtech 115gr FMJ factory cases, 2 reloads using Win WSP and 2 reloads using Federal No. 100 primers, fired in my M&P 9c.
Reloads are 124gr Gold Dots with the same powder charge, "approaching +P".
Note that all show obvious extrusion around the firing pin.
Note also the similar appearance of the Magtech factory primers and the Win reload primers as compared to the much more flattened Federal reload primers.
Had I fired only the Federal primed loads I would have not felt comfortable with this load due to the flattening seen.
But comparison of the Win primers and the Magtechs shows that the load is in fact not excessive - the Federal primers apparently just have a softer cup than the Winchesters.
I'm not suggesting that Federal SP primers should be avoided, I'm simply passing on what I see and my conclusions for consideration.
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04-25-2017, 02:50 PM
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Yep, unless primers are completely flat, no radius at all, they are not a conclusive indication of pressures...
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04-25-2017, 03:02 PM
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Reading pressure signs on mild straight-walled cases like .38 Special can be grossly misleading and often a waste of time.
I can load a +P+ .38 Special cartridge and fire it in a Model 686 with no particular definitive pressure signs, and no danger.
The identical cartridge in a WWI .38 special revolver may only show ONE pressure sign: the top strap hitting the ceiling.
Reloading tables and chronographs are your friends.
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04-25-2017, 03:04 PM
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None of those primers are close to being flattened, but it doesn't matter as primer appearance is not a reliable means of determining pressure. Using pressure-tested published handloading data and chronographed velocity in your gun is crude, but is a more reliable method of judging safe pressure.
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04-25-2017, 05:42 PM
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Those primers on the Magtech 9mm ammo are very common. Also 9mm Glocks seem to smear primers quite a bit. I like to use CCI primers in my 9mm handloads and Federal primers in my competition revolver handloads. There are people who will swear there's no real difference in primers from brand to brand but I know there is.
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04-25-2017, 06:49 PM
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Yeah, I find that more than Glocks leave a signature on the primer too. My Beretta 92 and my P4X Storm subcompact both leave a design on the primer even with lower powered rounds.
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04-25-2017, 07:12 PM
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I'm unfamiliar with the term "signature" is as it refers to expended brass cases, but wouldn't such markings indicate a gun problem?
I just examined some fired 9mm cases (Winchester) that were primed with CCI small pistol primers. They were fired in three pistols: a Walther P4, Beretta 92 FS, and a Sig P226. All have normal round firing pin indentations.
Last edited by rockquarry; 04-25-2017 at 07:14 PM.
Reason: spelling
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04-25-2017, 07:21 PM
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"Signature" is the term for the distinctive marks left on a primer, brass or bullet by particular firearms designs.
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Last edited by wha-tah-hey; 04-25-2017 at 07:33 PM.
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04-25-2017, 09:34 PM
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Looks like the OP is new to the world of M&P semi-autos. The marks on those primers are caused by the relief cut in the breach face. It's part of the design of the M&P's and has nothing to do with pressure.
Primers are a lousy way to tell whether or not your handloads are over pressure, particularly in a handgun.
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04-25-2017, 09:40 PM
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Too many factors......
Hardness of primer, size of the firing pin hole and firing pin diameter... With all of those variables it just doesn't tell you much.
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04-25-2017, 10:03 PM
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Quote:
Originally Posted by MichiganScott
Looks like the OP is new to the world of M&P semi-autos. The marks on those primers are caused by the relief cut in the breach face. It's part of the design of the M&P's and has nothing to do with pressure.
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Actually, this is my 2nd M&P, the 1st going to my youngest son a couple of years ago, and I am aware of the facts you mention.
Please note in my original post that I didn't say those marks were anything other than common to the cases shown.
However they do, in fact, have something to do with pressure, that being what caused the metal to flow into the breech face relief cut, 'though not necessarily excess pressure.
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04-25-2017, 10:05 PM
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If the primer blows out of the pocket, the pressure is too high. I've had that happen with rifle loads, but I don't remember having any blown-out handgun cartridge primers. But I have encountered unusually loose primer pockets probably as the result of high pressure loads.
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04-25-2017, 10:17 PM
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How about when you start blowing holes in primers? Surprisingly, no one has mentioned this scenario.
Last edited by bluetopper; 04-25-2017 at 10:23 PM.
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04-25-2017, 10:24 PM
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The primer on the bottom right has more flattening than I'd like to see - Federal primer or not.
Also that brass looks like it's past it's useful life. The headstamp is worn thin and there are extractor nicks all the way around the rim. I have .357 and .38 special cases with reload counts in the 20's and pieces of 9mm brass that have been loaded at least a dozen if not 20+ times. I rarely toss brass, but those would get thrown out.
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04-25-2017, 10:27 PM
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If needed, replacement of pistol by rifle primers simply requires safely working up the load again from a safe minimum load.
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04-25-2017, 10:29 PM
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Quote:
Originally Posted by bluetopper
How about when you start blowing holes in primers? Surprisingly, no one has mentioned this scenario.
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Yep, saw that in some factory PMC 357's back in the 80's when PMC ammo was pretty new to the area. Severely overpressured; had to tap the extractor on my boot to eject the cases. Thank God I was shooting in a 27 with those factory overloads.
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04-25-2017, 11:28 PM
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Was shooting with a retired LEO one afternoon in 2006. He had a beautiful 4in Colt Python from '55 I believe. I was shooting a 586. We had fired some 38 spl and a few Federal .357 when he hauls out a factory fresh box of SuperVel 357. I hadn't seen a yellow-red box of supers in years. I asked him could I just buy 'm, "Nope", said he wanted to remember the days on the force when he carried this every shift. Well, the first round locked the gun up. He got it open, and while I was reminding him of the signs of over pressure-- he touches off another one. Yep, LOCK UP, and this time it stayed locked, he had to take it home. I believe that in both instances the lock up was sure sign of " too mucha PSI ".
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04-25-2017, 11:33 PM
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Quote:
Originally Posted by reddog81
The primer on the bottom right has more flattening than I'd like to see - Federal primer or not.
Also that brass looks like it's past it's useful life. The headstamp is worn thin and there are extractor nicks all the way around the rim. I have .357 and .38 special cases with reload counts in the 20's and pieces of 9mm brass that have been loaded at least a dozen if not 20+ times. I rarely toss brass, but those would get thrown out.
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Reddog, you're seeing a lack of contrast in the pic due to the bottom part being in shadow, also some fuzziness due to lack of depth of field in the close-up.
The reloads are #5 for that brass.
I toss if I find loose primer pockets (rarely in pistol brass) or split necks due to work-hardening.
The flattening you note is the basis of my post - I would normally be concerned if the Win primers hadn't shown the load to be acceptable.
But since a primer gets only one use it's not an issue for me.
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04-26-2017, 01:35 AM
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The model 686 and..
The first model 686 and other models of the same series extruded the primer around the primer pin and locked up the pistol with hot loads. Very soft foreign made primers were blamed but S&W did a recall anyway to alleviate the problem with a new firing pin and bushing because S&W wanted their guns to work with all ammo that is out there. When the recall work is done, they stamp an 'M' next to the model number in the yoke.
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04-26-2017, 09:29 PM
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Also when one chamber gets bulged and brass sticks in that one chamber from now on. That's a sign of over pressure also.
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04-27-2017, 11:08 AM
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Quote:
Originally Posted by bluetopper
Also when one chamber gets bulged and brass sticks in that one chamber from now on. That's a sign of over pressure also.
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Not only is a bulged chamber a sign of over pressure, it's alos a sign of a ruined gun.
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04-27-2017, 11:40 AM
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Yep, its one tool but not the best tool. Case head exp, case head & extractor marks better. Along with a chrono, it all works to keep you honest.
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04-27-2017, 02:25 PM
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There are no reliable signs of overpressure in most handgun cartridges. Just because you're seeing them doesn't mean there's an overpressure condition, and just because you're not seeing them doesn't mean all is well.
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04-27-2017, 06:49 PM
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Quote:
Originally Posted by DWalt
If the primer blows out of the pocket, the pressure is too high. I've had that happen with rifle loads, but I don't remember having any blown-out handgun cartridge primers. But I have encountered unusually loose primer pockets probably as the result of high pressure loads.
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Loose primers can also be a sign of very low pressure. When firing, the sequence of events can go like this:
* cartridge fires
* pressure unseats primer
* case thrusts backwards under pressure against recoil shield, reseating primer.
If the pressure is too low, step 3 might not happen, leaving an unseated primer.
I load a lot of target loads (.45 auto, 3.9 gr Bullseye + 185 gr LSWC). I've seen flattened primers using Federal primers, according to the data that load is probably under 10k psi.
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04-28-2017, 10:05 PM
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All cartridges working at or around 20K/PSI won't show signs of overpressure by reading the primer cup.The 9mm working at a little over 30K might give some.
A chrono will give a much safer indication since velocity is most of the times(not always)directly related to pressure. Brass expansion is the safest sign to measure but not an easy one(very small increments mean a large difference;thus one needs accurate measuring instruments).
But a primer that has changed shape,except for the firing pin indentation(harder vs softer primer cup material,firing pin hole much larger than the firing pin,harder vs softer spring strenght,etc,)must always be analysed and taken into consideration since this is normally the first readible sign.And when in doubt,don't go any further and seek good advice.
Keep the sport safe!
Qc
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