#1
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20 VT primer issue on Cooper 21
Primers CCI 400 -These primers are probably 5 to 8 years old. Always kept in my reloading table in the reloading room in my house.
Nosler 221 FB cases (new) I have a new to me Cooper 21 in 20 VT. I loaded up several rounds recently and went to the range today. When I work up a new load, I always look at each case after firing to see if any issues are starting to come into play. All the rounds fired were weighed and trickled up to the load I wanted. I started off with 32 VMax and 39 Sierra BK using 18.2 grs of Rel 7. No primer issues. I shot 6 rounds of each. I then switched over to the 34 Varmint Nightmare. This is where the problem started. I used the same primers and brass mentioned above along with Rel 7 and H4198. H4198 - Started at 18.0 grs and worked up to 18.5 grs Rel 7 - Started at 17.5 grs and worked up to 18.5 grs Notice on the case below how very flat the primer is. Also notice the mark on the primer and slightly on the case in the 9 o'clock position. More on this mark a little further down on this thread. 18.2 grs H4198 I continued my testing and the extreme flatness of the primers continue and now the primers have started backing out slightly. The primer below backed out .02. 17.5 grs Rel 7 I fired a few more rounds and the flatness of the primer continued along with the 9 o'clock position starting to get worse. I have never had a blown primer that looks like this one does, but it does appear to be a blown primer. The dark dot in the center of the primer is a shadow not a hole. 17.8 grs Rel 7 When I received the rifle I did notice the rifle did not "eject" a test round but laid in the tray. This was okay, since I would rather pick out of there than off the ground. The rifle extracted each round without issues. While shooting the test rounds I also looked at the bolt face. Looking at the bolt face, in the 9 o'clock position is the ejector. It does not protrude away from the bolt face, but is slightly recessed. I don't have a tool to measure the depth of the recess, but it is slight. Before I started testing today, the bolt face was clean and spotless. Now in the recessed area, it is full of imbedded brass from the base of the cases. In summary; 1. Am I loading these rounds too hot? 2. Did I get a bad lot of new Nosler brass? I'm going to send the bolt to Cooper to have them look it over. I also noticed the allen screw on the bottom of the bolt is missing. I know what it does, but not sure if that added to the problem. Comments welcomed. Thanks for the help. |
#2
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I have never used Nosler brass, just rem 221 or formed it from 223. I know I would stop shooting those loads in my gun. I do use h4198 with both 32 and 40 gr bullets ( for several thousand rounds ). I have settled on 17.8 gr with the 40's and 18.7 gr with the 32's. Primers look good with those loads in my guns. 1 is a Cooper 38 and the other is a Savage with a ER Shaw barrel, both are 12 twist. The capacity of Nosler vs what I use may be very different, I don't know. Have you checked your velocity with those loads?
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#3
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[quote=Have you checked your velocity with those loads?[/QUOTE]
No I haven't. Will do that another time. Too many people at the range today. |
#4
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20 VT issue on Cooper 21
I guess it could be a problem with the bolt, but from the looks of your photo's and the cartridge base, it appears it is a classic over pressure load. Hopefully Cooper can give you a answer when you send them your bolt and information. Bill K
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#5
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What Bill K said. A classic over pressure. Also, when the primer backs out like that, it usually means that the brass was a bit short when sized.
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#6
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I think it's over pressure as well. I don't think the bolt is the cause of the blow out. It probably contributes to it. It looks like the damage to the primer and case head occurs when the recessed are of the ejector smashes into the primer and case head.
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#7
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Thanks for the info. I check this out as well.
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#8
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Quote:
Measure the headspace of one of your unfired cases and one that you've fired. There will be a difference and the unfired will be shorter. Here's what happens. As the firing pin strikes the primer, the case is driven forward. Powder ignites and gas expands the case, gripping the chamber. Gas pressure forces the primer back. If the pressure raises slow enough that the brass hasn't fully gripped the chamber, the gas pressure forces the case against the bolt face. The set back smashes the primer flat giving false indication of over pressure. |
#9
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But the casehead was swaged into the ejector hole. An ejector mark is definitely an indication of over pressure.
__________________
Any citizen accused of a crime is presumed innocent until bankrupted beyond all reasonable doubt. In our country the lie has become not just a moral category but a pillar of the State. -- Aleksandr Solzhenitsyn Last edited by RareBear; 12-25-2018 at 02:45 AM. |
#10
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20 VT primer issue on Cooper 21
Precisely RareBear. That really added to my thought of over pressure. Waiting to see what RIO has to say or add, as he is well into Cooper's and their workings. Bill K
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