Over pressure on 2 out of 184 rounds?

[6BRinNZ]

What is the FB of your reamer?
The bore groove dimensions of the barrel will greatly influence pressure relative to a specific charge.
IMO primers alone are a terrible gauge for pressure its the combination of two signs together that is the warning.
It could be worth (if you haven't already) running the magneto on a club day under the hot conditions with match length strings. If your 2765 - 2780 was based on a smaller sample at 100 yards then you could easily be up at 2790+ with heat and fowling. IME this climb is worse with tighter barrels and longer strings.
I use the bolt drop method for checking if I'm in the lands or not and the fact that you are seating out a little further now is possibly a clue to the sudden appearance of the problem (what was the last thing you changed ). I have dealt with an example recently where a shooter thought they were jumping but kept running into pressure issues later in the day. Using the bolt drop method it was found they were actually into the lands. But they didn't have to remove an ejector to run the test so it was a very easy method to use.

 

[sdneil]

Holy Cow Alex...with all the talk about 2 bad primer pockets I guess you wont be at the match this Thursday...Just kiddin... I know I will see you at the line...Neil

 

[jlow]

Other considerations.
• The barrel may be getting a bit worn (2700 rounds now), and when I measured the bolt-to-lands after 2000 rounds, the distance had enlarged by approximately 0.005, so I started seating the bullets about this distance further out, did some testing, and this worked fine.

The big uncertainty I have, which I was avoiding bringing up as it has been discussed ad nauseam, is how to measure the distance to the lands. I started to write my concerns on this, which involve using the Stoney Point tool method as well as the split-case method, but it is too long of a subject, so I will start another thread at the risk of being pelted with the expected "Oh, Not Again!" comments.

Thanks!!!!!!

Alex

From the above, I would agree that if you are not sure of how far you are seating out and you are seating them longer, I think 6BRinNZ nailed it, i.e. they ended up touching or being jammed into the lands. I generally do not get too much closer than 10 thousands based on measurements because there are lots of things that can give you errors.

 

[Alexander-M]

Background

• 308 W, 200 rounds, Lapua brass fired twice in the same rifle
• All cases were processed together the same way, F/L sized, chamfered, etc.
• Trim length was 2.006 ± 0.001
• While seating the bullets, I did not detect any that required higher effort to seat
• I used Tula KVB-7’s, 44.40 gr of Varget, and Berger 185-gr Juggernauts
• Bullet seating depth was 2.013 ±0.001 CBTO
• I stored the 200 rounds in two, 100-round boxes
• Fired 184 rounds in a match; 92 each day, and kept them separate in their own boxes
• A day later, I fired the remaining 16 rounds

First concern (from original post)
Two of the spent cases had a thin black ring around the primers and ejector imprints. Over pressure? Why?

Second concern– different case OAL’s! (17 July 2016)
After full-length sizing the 200 spent cases while keeping them separated in the original 100-case sets, I found that one set (all 100) had an overall length of 2.010 and the other set (all 100) had an OAL of 2.015. The only difference between the two sets was that one was fired on a Saturday, and the other on the following Sunday. Why did they have different OAL's by 0.005?

Third concern– the three cases in question had shorter OAL
The two cases with the black rings around the primer, AND one other case, were shorter: 2.005, 2.006, 2.005. I discovered the third shorter case while trimming the cases, as this particular case did not engage the Giraud TriWay timmer, which I had set to 2.006. This third case, by the way, also had the extractor imprint, but did not have the black ring around the primer. I admit that it is possible that when I original trimmed the cases, a few (three?) may have been a bit shorter, perhaps 2.002 or 2.003 instead of 2.006. I check every 10 cases to insure that they remain ±0.001 of the set dimension.

Fourth concern– the three cases in question had enlarged primer pockets (as may be expected?)
I have my primer pocket gage set to Ø0.2015, and if it drops in the pocket without any interference, I pitch the case. I use CCI-200's for brand new and once fired cases, and KVB-7’s or CCI-250’s henceforth as they are larger by about 0.001.

I gauged 30 of the 197 cases (the original 200 cases minus the three in question), and all had good primer pockets, but the primer pockets of the three questionable cases measured Ø0.2114, Ø0.2118 and Ø0.2118 – way too large. I did not detect any primers seating without proper pressure when I primed the cases. In the rare occasions when I have detected a primer that seats too easily, I mark the case and set it aside.

To recap:
(1) Why did three cases show signs of over pressure?
(2) Why did I end up with two distinct sets (100 and 97) of fired cases with different OAL's when all started the same?
(3) Why did the three cases that showed signs of over pressure, have a shorter OAL than all the rest?
(4) Why were the primer pockets of these three cases enlarged? (I am 99% sure they were the same as the rest to start)

Thanks for taking the time to read all of this! Your opinions are welcome, as always!

Alex

 

[Average joe]

Once had a couple of shots during a match wth noticeably more recoil, and high impacts. Went home and inspected the rest of the unloaded, prepped brass.
Found some had clumps of tumbling media stuck in them. Had tumbled them after turning necks with lots of lube. I now wipe them with qtip after turning.

 

[jlow]

Second concern– different case OAL’s! (17 July 2016)
After full-length sizing the 200 spent cases while keeping them separated in the original 100-case sets, I found that one set (all 100) had an overall length of 2.010 and the other set (all 100) had an OAL of 2.015. The only difference between the two sets was that one was fired on a Saturday, and the other on the following Sunday. Why did they have different OAL's by 0.005?

Alex

You have a lot of things going on here, some of it may be related, others maybe not. One thing I have found in my career doing troubleshooting is never discount the fact that more than one bad thing is happening at the same time. This can be confounding and the only way I have found to deal with this is to deal with each problem as you find it, fix it and see what happens, if there is still a problem, keep looking.

So just taking the “Second concern” for a second. I find it very odd that you are FL sizing and they are consistently 5 thousands different. One thing people should know about FL sizing is if there was no shoulder in the sizer, all sizing cause an increase in OAL of the case because squeezing the body of the case with the sizer, that stuff has to go somewhere and since the only place to go is up, it goes up and increase the length of the case. So for the final OAL to be 5 thousands different even after FL sizing, means one set was sized quite short BEFORE it was fired. This last bit of course is hard to address since all the cases now has been fired and sized.

Have you checked the headspace of the two lots to see if they are different?

 

[Alexander-M]

Joe,
I suspected that very possibility as I also tumble the brass in media, which may stick to the inside walls of the cases.
After I am done doing all the prep to the cases, but before tumbling them, I put them in a can with mineral spirits. I shake them a bit, drain the mineral spirits, and then put them in the tumbler. I just did this last night, and with a Q-Tip checked the inside of the cases for evidence of tumbling media, but found none. But it still is a possibility, so I will check them 100% from now on.

Jlow,
Yes, a lot going on, and not easy to assign cause and effect to each.

I had not checked the cases for headspace, and now they are all mixed after trimming, cleaning, etc., and tumbling. After I read your post, I check the case lengths to the shoulder of 50 cases using a Hornady cartridge headspace gage bushing. The longest was (1.1685) 1.6185, the shortest (1.1665) 1.6165, and most were 1.6175 and 1.1680, the three cases i question were 1.6175, 1.6175 and 1.6185. I don't believe this tells me much regarding what the problem may be or may have been.

Thanks!

Alex

Edited to correct typo of lengths

 

[CJ6]

Joe,

Joe,
The longest was 1.1685, the shortest 1.1665, and most were 1.6175 and 1.1680, the three cases i question were 1.6175, 1.6175 and 1.6185.

Thanks!

Alex

Thanks!

Alex

Numbers mixed up?

 

[Alexander-M]

Numbers mixed up?

Yes, thank you!
I corrected the numbers, above., from 1.1685 and 1.1665 to 1.6185 and 1.6165

Alex

 

[jlow]

Joe,
I suspected that very possibility as I also tumble the brass in media, which may stick to the inside walls of the cases.
After I am done doing all the prep to the cases, but before tumbling them, I put them in a can with mineral spirits. I shake them a bit, drain the mineral spirits, and then put them in the tumbler. I just did this last night, and with a Q-Tip checked the inside of the cases for evidence of tumbling media, but found none. But it still is a possibility, so I will check them 100% from now on.

Jlow,
Yes, a lot going on, and not easy to assign cause and effect to each.

I had not checked the cases for headspace, and now they are all mixed after trimming, cleaning, etc., and tumbling. After I read your post, I check the case lengths to the shoulder of 50 cases using a Hornady cartridge headspace gage bushing. The longest was (1.1685) 1.6185, the shortest (1.1665) 1.6165, and most were 1.6175 and 1.1680, the three cases i question were 1.6175, 1.6175 and 1.6185. I don't believe this tells me much regarding what the problem may be or may have been.

Thanks!

Alex

Edited to correct typo of lengths

Actually that is kind of interesting since your case OAL after FLS (before trimming?) were 2.010” in one set and 2.015” in the other with 5 thousands different, whereas your headspace in the mixed batch had a maximum variation of 2 thousands, so that would mean at least 3 thousands increase in length in your OAL were due to neck lengths. Also if your original trim length was 2.006, then they grew by 4 and 9 thousands - that's quite a bit….

Was it significantly hotter or raining on one of the days of the match?