Learning pressure signs
- Thread starter Schnittker
- Start date
“Learning Pressure Signs” an addendum.
More discussion on:
ejector marks,
gas leakage,primer cratering,
case head expansion,
primer pocket expansion,
cold welding@ Schnittker and others’ discussions on pressure and it’s affect on primers is excellent. One would do well to study his photos and discussions in depth. To assist in understanding all of the above, several members have contributed their knowledge of the topic to try to make this post a one-stop-shop of information for those who are new to hand loading center fire rifle cartridges.
Let’s start with more photos of fired cartridges, showing light to strong ejector marks and gas seepage which can occur when nearing too much pressure or when primer pockets are getting worn out and beginning to leak. Gas leakage can be damaging to a rifle and can result in gas cutting/etching of a bolt face (undesirable).The first photo is of various degrees of ejector marks, from light to rather severe.
In the second photo, primer cratering is noted in the top right case and the one below it.
Clearer view of gas leakage, flattening primer and primer cratering.
(See Attachments below)
Case head expansion is yet another indication of pressure. This measurement is taken at the “200 line” from SAAMI specs on a cartridge case. It is a measurement of how much the web of the cartridge case stretches due to internal pressure. The web (base) of the case is the strongest portion of a cartridge case. Stretching here directly impacts the primer pocket. It is also a measurement which tells you when the primer pocket is done for and will no longer reliably hold a primer. There is also a tool which will tell you this.
When you fire form a cartridge to your chamber, you remove excess clearance which comes with all new factory brass. New brass is somewhat undersized so it will fit in any chamber cut to that specific cartridge. On the first or second firing, new cases typically expand around .002 (2 thousandths). After that initial expansion, future expansion is shortening the life of the cartridge case/primer pocket. If one shoots mild loads, it’s not uncommon to get multiple loadings on a piece of brass. If you shoot loads on the upper end of speed/pressure, it is not uncommon to only get 2-3 loadings from a piece of brass before the primer pocket is stretched to the point it will no longer hold a primer reliably. Fingernail polish or moisture barrier sealant (same thing) can be used a time or two before gas leakage typically begins – and gas leakage should be avoided. It’s best to trash the brass when primer pockets are ruined/stretched.
First photo is of dial caliper measuring new brass at the 200 line. Initial measurement on this cartridge was .528. After first firing, the web stretched to .530. After 3-4 firings the primer pocket was trashed and the web measured .532.
A safe rule of thumb is keep web expansion to less than1.5 thousandths (.0015) if you want to make your brass last.
(See attachments below)
There are also tools to measure your primer pocket. These are primer pocket go/no go gauges. The one pictured is from Brownells. If the gauge will not enter the primer pocket, the case will hold a primer snugly. If the gauge goes in the primer pocket, it’s time to trash the brass. The beauty of this tool is it eliminates you trying to seat a primer that's not going to stay, or tells you when finger nail polish is in order - (or not).
(See attachments below)
Cold welding primarily affects new brass or brass that has been cleaned excessively. The most common example comes from an individual who loads up a bunch of new brass and then leaves it on the shelf for a couple of years.
If the brass has been fired and the carbon in the neck is not completely removed, cold welding is typically not a problem. The carbon in the neck isolates the bullet from direct contact with the case walls and cold welding is prevented. If the carbon is completely removed by brushing vigorously with a bronze brush or case cleaning with stainless steel pins, cold welding can occur if the ammo sits for an extended period of time.
The photos show a ring of oxidation (?) in case necks and on the base of the bullets after they sat for 2 years waiting for the next prairie dog hunt. This was new brass, waiting to be fire formed while shooting Pdogs. (sorry for the poor quality of the photos. This was from a few years ago)
(See attachments below)
The following are excerpts from other threads. If you have additional pieces that are pertinent to this thread, please add them here or send them to me. This should be very useful to new hand loaders.
Old PDR vs new PDR
Muddyboots
Moderator
@BFD,This is what has seemed to worked for me. Once brass is ready for FL sizing, I brush neck with bronze brush couple swipes to "clean of of debris" not remove carbon, swab neck (CAREFULLY without slobbering it up) with lubricant (I use STP) which I feel helps neck sizing consistency no matter what I use. I then use the "magic" acetone by dipping neck area into small bottle to dissolve the lube out of neck. It dries INSTANTLY ends up squeaky dry. Fast forward to bullet seating, I swirl bullet in graphite, seat bullet, crimp. The graphite statically attaches to bullet so it is there during seating. All I can say is ES SD is very low and loads are accurate. No cold weld. YMMV
BFD
Cold Weld Insurance:New brass could use a thin amount of dry graphite applied to the necks or bullet bases to prevent cold welding.
Fired brass will already have enough carbon residue to provide this thin film between metals. Hence the acetone is only to remove the case lube/neck lube as Muddy stated in his process. (*Considering you don't clean the brass with stainless steel pins or some electrolysis gadget that removes all carbon. Then you would need to add graphite to the fired brass necks)
Precision and Proper Application:
The wet type lubes caused my groups to open considerably. It mimicked groups I would get when firing the initial fouling shots on a clean barrel.
The dry graphite opened the groups a little, but I added too much graphite and skewed the results. Benchrest competition champions use dry lube in the necks, and do so properly, so I trust their results and reporting. (Think of rather a dusting of the dry lube, and not clumping)
Graphite in the Barrel:
Applying dry graphite in the barrel, after a thorough cleaning, will minimize considerably, if not totally eliminate the POI shift of first round shots on a cleaned barrel. This is done by embedding graphite on a patch and then running a combo of short & long strokes through the barrel. Every barrel I've done this graphite treatment on has me printing the first rounds with no discernable difference with POI.
I once set myself up for a blind test of the graphite treatment. I purposefully left a barrel raw after cleaning to gather more data on this procedure. Well, I forgot I did that and ended up shooting it without the graphite treatment. This was an excellent way to eliminate experimenter bias! I was WTF on the first 4 rounds fired and got worried I did something wrong with the load development...then I remembered what I forgot and started laughing at myself. "OK, this graphite thing has become like a law of physics for me!"
Carsyn.22
Brad when you talk about lube in the ID of the neck does that include the LEE sizing lube that dries? That’s what I’ve been using and just leaving it in there… then again I ain’t no bughole shooter like you!
I have methyl hydrate and graphite so I could try a test between the Lee lube and graphite sometime
BFD
Yes. Lee, Imperial sizing wax, Hornady one shot, anything slippery wet. No good.On the graphite. I started using the Aerosol version of lock ease. It would dry after a while, so I would allow a day to 3 to shoot. The lock ease in the liquid form wasn't drying even after a week or more sitting in the barrel. I blew primers on the first two rounds because the liquid was still in the barrel. So, I just use dry graphite in a dish with .177 BBs. Use a pair of needle nose pliers and push the patch around in the graphite till covered black.
Koda
Not a consensus.
Cold welding and case cleaning are two separate subjects.
As far as i know there isn't a consensus on either subject just a discussion on how and why individuals are including these steps in their process.
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Question for all of you smarter than me! Im in the process of loading for my 300 win mag with 154HHT. As ive read in this forum to do a pressure test then back off a grain or so and shoot for groups. Heres my pressure test starting low and working up with the grain and velocity produced in picture. I eventually got to 78gr of H4350 (the highest I loaded) and those are the 3 rounds with what i believe to be slight ejector marks (at top of each case slight half moon) bolt lift is still easy and smooth. Would you guys call this pressure and to stop increasing powder charge? I feel like this velocity is a lot more than what i was expecting to get too before i would run into major pressure signs but I havent. Also this is without a crimp, Im running .002" neck tension here, I will start adding 1/8 crimp to these rounds and see if i can tighten the group up. Where to go from here?
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BFD
Hammer Time Executive member
Yup, pressuring stoutly with flat & cratered primers. Pop them out and also look at the sides of the primers for belling out on the tops. Lapua supports the primer all the way, so the hourglass look will be another indication of most likely over pressure.
Most importantly measure the primer pocket diameter. You decide how long you want your brass to last. FWIW I only got to 76gr of XMR 4350 with 137HH in 300WM for a brass longevity load at 3350fps 24”.
^^^^x2
I run same load but found best accuracy with 1/4 crimp so don't be shy of increasing crimp. Let rifle tell you what works versus our noise!
I run same load but found best accuracy with 1/4 crimp so don't be shy of increasing crimp. Let rifle tell you what works versus our noise!
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So my question is now where do I start testing for group sizes? If were calling 78grains signs of pressure how far should I back it down and shoot 5 round groups?^^^^x2
I run same load but found best accuracy with 1/4 crimp so don't be shy of increasing crimp. Let rifle tell you what works versus our noise!
LightTheTower
Hammer Time Executive member
Because you’re adding in crimp now, I would drop to 76.5 ( I like the looks of your speeds @ 76 to 77).
BFD
Hammer Time Executive member
So the common ramp up to pressure then back-off method would have one beginning the precision testing of the first load that didn't show over pressure and reduce .5gr per increment loads till one or more are showing precision.
Benjblt
Member
I'm farely new to reloading. I'm shooting new peterson brass, N560, 125 grn HHT's out of my Seekins 6.5PRC with a 21 inch barrel. Attached are pictures of brass from three different powder levels, 58 grains (3,140 fps), 58.5 grains (3,160 fps), 59 (3,190 fps), and 59.5 (3,120 fps). FPS are averages with some fairly wide spreads except for at 58.5 grains where there was only a 6 fps spread between 4 shots. . . . I see marks on the head around the case head, or face, whatever you call it around the primer pocket. Sometimes its the round ejector marks and some times its small partial circles near the rim. For reference it was 65 degrees outside. What are you'alls thoughts? ... BTW, accuracy was about a half inch group except for the 58.5 grain load which was closer to an inch.
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aratliff
Hammer Time Executive member
I would not sweat this ejector marks unless there is also accompanying primer flattening.
The gas leakage is a sho’nuff big deal, though.
Best I can tell, primers look good on that 58.5 charge. Pop them out and examine them, too. There is a stickied thread about what to look for. Measure the primer pocket growth as well and compare it to a new, unfired case if you have some. (If not, let me know and I will measure when I get home later today).
And forgive me if I am possibly insulting your intelligence, but re-work your load when you begin the second firing, because, as @Muddyboots has taught me, the brass will not absorb as much of the pressure on the second firing.
Edit to laugh at myself, as this is that stickied thread! Me=dumba$$!
The gas leakage is a sho’nuff big deal, though.
Best I can tell, primers look good on that 58.5 charge. Pop them out and examine them, too. There is a stickied thread about what to look for. Measure the primer pocket growth as well and compare it to a new, unfired case if you have some. (If not, let me know and I will measure when I get home later today).
And forgive me if I am possibly insulting your intelligence, but re-work your load when you begin the second firing, because, as @Muddyboots has taught me, the brass will not absorb as much of the pressure on the second firing.
Edit to laugh at myself, as this is that stickied thread! Me=dumba$$!
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Good guidance above.
Primers are still well rounded on the edges, no flattening.
Don't see/can't tell if there is any cratering on the primers.
At first glance, thought I saw some gas leakage around primers (as noted), on closer inspection, it's hard to tell.
Re-fire (2nd loading) and see what pressure signs you get (as noted).
With ejector marks on 1st firing, you're likely close to pressure. Peterson is strong and masks pressure well. With ejector marks, you'll likely only get a few loadings before the primer pocket wears out (stretches , loosens).
And welcome from NE Alabama!
Primers are still well rounded on the edges, no flattening.
Don't see/can't tell if there is any cratering on the primers.
At first glance, thought I saw some gas leakage around primers (as noted), on closer inspection, it's hard to tell.
Re-fire (2nd loading) and see what pressure signs you get (as noted).
With ejector marks on 1st firing, you're likely close to pressure. Peterson is strong and masks pressure well. With ejector marks, you'll likely only get a few loadings before the primer pocket wears out (stretches , loosens).
And welcome from NE Alabama!
BFD
Hammer Time Executive member
Review the first post in this thread, really go review this entire thread, and show us what you got. You are wanting a totality of the clues available to make your analysis. Visual of case heads and primers is just a start.
Benjblt
Member
I have no ego when it comes to reloading.. . so you're in no danger of insulting my intelligence. I asked anyhow. I did read much of this entire thread. I don't see the gas leakage nor did I notice them. I will look again closer when I get home.I would not sweat this ejector marks unless there is also accompanying primer flattening.
The gas leakage is a sho’nuff big deal, though.
Best I can tell, primers look good on that 58.5 charge. Pop them out and examine them, too. There is a stickied thread about what to look for. Measure the primer pocket growth as well and compare it to a new, unfired case if you have some. (If not, let me know and I will measure when I get home later today).
And forgive me if I am possibly insulting your intelligence, but re-work your load when you begin the second firing, because, as @Muddyboots has taught me, the brass will not absorb as much of the pressure on the second firing.
Edit to laugh at myself, as this is that stickied thread! Me=dumba$$!
Benjblt
Member
Thank you! I thought the primers looked good myself. I'll examine closer when I get home. Currently my 6.5 PRC die is 70 miles away so I'll have to wait on a second reload. The bummer is the higher the powder charge the better my groups got. Steve had told me to start at 57 grains and work up with the N560 and I was hoping to get some good velocity. He thought I could get 3,400 fps not knowing my barrel was 21". Obviously I'm responsible for working up my own, safe load. I will own that. I'm just knew and trying to keep it safe mostly. . but also looking for accuracy and performance. The Hornady book has all the bullets within the 120 to 135 grain weight at the 58+ grain powder charge with N560. If I look at the HHT load data from this site I see that OG-Danimal worked up some loads with N560 and I'm running 30 fps faster, roughly, at the same powder charges with a 3" shorter barrel. Not sure what that means.
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aratliff
Hammer Time Executive member
You probably do not have gas leakage. It was very early this morning (for me) when I was looking at this earlier. I was scrolling through the pictures and most likely saw someone else’s since all pictures within the thread were there. Since I had to wake up very early, I was not sharp enough to catch that.
Mea culpa.
BFD
Hammer Time Executive member
Those primers are pretty, but an ejector smear on a bolt gun case head is not good. There's a slight chance your ejector spring is stout, but 99% of the time this is over pressure.
That is common in stout to over pressure loads. Common occurrence. Means a different powder should be selected.
N570 is a pretty slow powder for your application. I should think N560 & N165 will bring you on home. Interesting to see the Hornady data showing only a grain difference between N560 & N165. These two powders are currently a mystery to be solved recently on Hammer Time.
Ya'll know I'm getting serious when I'm breaking out the color codes!
