Help with possible pressure signs.

[Mike25]

Hello. I'm looking for some help with a .308 load. Being relatively new to reloading I am still trying to finalize a few things and make sure that I am safe.

First a little background;

I am shooting a TRG-22, purchased new, and have been very happy with it.

I ran an OCW test and settled on a load of 44.8 grains of Varget pushing a 175 SMK. I went up to 45 grains (published max in Hodgdons manual) and saw no pressure signs on any of the rounds that I used. I used CCI 200 primers and Lapua, Norma and Federal brass. I did one complete OCW test with each brand of case to make sure that they all worked, and saw no difference between them. The Federal brass was from previously fired FGMM commercial rounds. I did not have access to a chrono.

I have been using these loads and had not noticed any issues with them until this past weekend where I shot a 600 yard club match. This was only my second time actually shooting a match and the Temperature was 40 degrees, the winds were 24-30 with gusts around 40. I shot a 565-13 and considering the conditions I was happy with my score. The vertical dispersion was better than I expected so my only issues were reading the wind, so I was very happy with the performance of the ammunition.

I did not notice any issues with any of the rounds (all were Federal cases on their third loading) until I was almost finished with the third string. With about five rounds to go I noticed that the bolt for one round seemed to lift a little different than it had up to that point. Not really sticking, but I did notice a difference. It did not happen again with the remaining rounds. When I got home I checked the rounds and noticed that on 10 of the 66 there were light marks on the head stamp from the ejector, and on a few I could see a mark from the extractor. None of the primers were cratered and in fact they all looked normal to me. The marks on the head stamps seemed to be shiny and not indented, but they were visible.

My reloading procedure has been the same for all of the rounds I have loaded. I de-prime each case then tumble clean them. (I have since obtained an ultra sonic cleaner but have not reloaded any of the rounds that I have cleaned in it) I then full length size them. I set up the sizing die by having it against the ram, then turning it one full turn up and backing it down until the cases seat in the chamber. I then locked it down and have not touched it since. I then re-clean them to get the lube off and trim them to a length of 2.005. I then de-burr and chamfer the cases and then they are then primed. I then throw the powder into the tray and put it into the scale where I trickle powder into it to bring it up to 44.8 grains. I then seat a bullet. I have been seating the bullets well short of the lands (rifle measures 2.896 with a Hornady gauge and I have been loading to a COAL of 2.801) so I don't think that is a problem. While I'm sure that I can improve on it, at least for now I did not have an issue with the accuracy. I have done this for each and every round that I have loaded. I have also noticed that the Federal cases are MUCH harder to size then any of the other cases.

My question is could this be a problem with the cases as opposed to my procedures or the charge I'm using? Especially since I only noticed this issued with 10 of the 66 rounds I fired.

I have about 250 rounds loaded up now (mostly Lapua and Norma) and I'm wondering if I need to break them down or if I should go ahead and shoot them. Up until this past weekend I have not noticed any issues at all with these rounds, and I have been very pleased with their accuracy.

There were no other marks on any of the other Federal rounds that I shot that day, nor have I seen any marks on any of the previous (300) rounds that I had loaded.

Any help or insight would be greatly appreciated.

Thanks.

[Clark]

CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.
The 308 uses a case developed for the 1889 7.65x53mm Mauser [or the 1893 7x57mm Mauser, which ever you think came first] built with a large Boxer primer.
The limit for avoiding loose primer pockets in those cases for mass produced ammo was for a long time thought to me 65,000 psi, but the more recent 260 Remington was registered it with 62,000 psi.
The same dimensioned case, built with a small Boxer primer for the 6mmBR is good for ~~ 85,000 psi when the primer pierces because the pocket is stronger.
But in an individual rifle with handloads for Mauser case heads with large Boxer primer pockets, the threshold of loose primer pockets in a few shots will be ~ 72,000 psi.
Reducing ~4% powder charge as a margin for variations in charge per throw, bullet weight, seating depth, dirty chamber, temperature, etc, will produce about 62,000 ~ 69,000 psi in Quickload when the chrono matches the prediction.
From what I have seen, Varget modeling by Quickload is right on the money without adjustment.
At 2.8" OAL and not touching the lands, I would expect a few primers slightly easier to seat, starting at 47 gr 72 kpsi 2727 fps in the 20" TRG-22 and 2864 fps in the 26" TRG-22.
Backing off 2% to 46 gr for margin [Varget is temp stable], I would expect 67kpsi, 2672 fps in the 20" 2810 fps in the 26" barrel.
I would expect if you just load ammo and do a work up, it will waste time:
47 gr ok
48 gr ok
49 gr maybe ok, but bolt is hard to lift.
50 gr, primer falls out.

Better, but not perfect:
47 gr next primer hard to seat
48 gr next primer slightly easier to seat
49 gr next primer almost falls in
50 gr will not hold a primer

An even better way to do it is take dial calipers to the range and measure around the extractor groove before and after firing.
47 gr no extractor groove growth [egg]
48 gr .001" egg at one point rotating around the groove.
49 gr .005" egg
50 gr .015" egg

The best system is to make smaller increments and take dial calipers to the range, that way it all done in one trip to the range.

47 gr .000"
47.2 .000"
47.4 .000"
47.6 .000"
47.8 .001"
48.0 .001"
48.2 .001"
48.4 .002"
Quit
Then when I get back to the reloading bench, calculate the margin from 47.8 gr threshold.

What does it all mean?
SAAMI registered pressures are a crude approximation of a margin lower than loose primer pockets. The individual handloader can do better.

[F. Guffey]

Mike, I have suggested ‘time is a factor’ not a problem but on most reloading forms that does not fly, then there is the theory brass work hardens meaning if nothing changed and it did not happen on the first firing? It should not have happened on the third firing, I have fired cases that were safe on the first firing and over-pressure on the second,. same powder, same bullet same weight, same primer etc..

Something like first time firing to form then neck sizing can increase pressure, seating a bullet out against the rifling can raise pressure, failure to clean the neck of a chamber can cause an increase in pressure, I do not know if the 10 suspect cases were fired first or last.

F. Guffey

[mehavey]

Originally Posted by Mike25

...Federal brass...

That may be the source of your pressure-sign problem, as opposed to overpressure in fact.

I'll check QL tonight, but the IMR/Hodgdon site indicates 175SMK/Varget/45 = 48,600 CUP.

Compared to ANSI/SAAMI Standards:

Cartridge ANSI CUP ANSI PSI
308 win   52000     60000

You should be < (48.6/52)*60,000 ≈ <56,000psi ...not near enough to start (normal) brass flow.

[mehavey]

Getting home, I looked at QuickLoad. It does say you are ≥ max pressure (61,000psi).

It also says you're running 2650-ish, about 100fps over normal M118 Match velocity of 2,550.
`You sure you can't drop back to ~43gr/Varget & check w/ a chrono?

[243winxb]

A maximum load may expand the web area a small amount each loading. After 3 loadings this area may not spring back. FL dies do not size the web area. Take measurement of the web in front of the extractor groove. Compare with SAAMI drawings > http://www.saami.org/specifications_...ex.cfm?page=CC This is my guess.

[mehavey]

Read this first, though.
http://www.shootingsoftware.com/ftp/...%2019%2004.pdf
(Start w/ the conclusion)

[Mike25]

Thanks for all the replies. Lots of information and I'm not sure that I understand all of it, but I'm working on it.

Clark, that is some great information, but if I'm reading your posting correctly I should be fine with my load of 44.8 grains of Varget pushing a 175 SMK? I have not gone above 45 and that was only for OCW testing.

While I do not have a Chrono I have tried to work the data backwards and doing it that way gives me an approximate MV of 2675. At least that is where my data is correct.

I measured the web as per the SAAMI drawings and where I think I should be getting .409 I am seeing .405 for the web area. Not sure what that means though but I don't see any that are different than that.

The majority of the rounds that showed the marks were in the last string, but two of them were during the first. I have never seen any of these signs in any of my earlier firings with the Federal brass, and none with either the Lapua or Norma brass. I will check and see if the chamber is clean and post it here.

I have shot this load before and everything was great, even with the Federal cases. Could this be a headspace problem with the Federal brass? Just trying to figure this out.

Thanks again for the help.

[243winxb]

.4703" is the maximum diameter for what i am calling the "web" http://www.saami.org/PubResources/CC...Winchester.pdf

[mehavey]

SAAMI Web: 0.403"

My 308Win/M1A:
WW Case: 4X-fired: 0.466"
Lapua Case: Unfired: 0.465"

I'd put little faith in absolute web dimensions unless you know what you started with/unfired.

I'd also not suspect headspace problems sufficient to cause brass flow into the ejector cut-out unless cases were also stretching like mad,*** and primers flattening due to head slam into the bolt face as a result.

Without a chrono to test velocity, I'd drop at least a grain+



*** BREAK, BREAK: What are the case lengths of the overpressured cases?

[Mike25]

Even though none of my previous loads with this recipe showed any signs of pressure? Not saying I will not take the others apart and re do them, I'm just trying to understand what is going on.

If it is a problem with my recipe/procedures/rifle, then why did only 10 of the 66 show any signs? Why didn't any of my previous loads show any?

Like I said, I've been loading for less than two years and I still don't have everything locked down in my head, but I am working on it.

Thanks for your patience.

I'll check the case length right now...

[Mike25]

One of the cases with the pressure signs is at 2.0045, the rest are between 2.0055 and 2.010.

[mehavey]

Have you been trimming them? (I'm surprised that they're that short otherwise)

I was 'hoping' that the cases would be long -- 2.025+. That would at least explain why you never had pressure spikes before, and were only "starting" to get them now with a few cases starting to experience an interference fit in the leade as things stretched over repeated firings.

The only other thing (I can think of) that might be playing out here with those symptoms is the necks thickening up due to forward brass flow. That would begin to cause that same interference fit between the bullet and a tightly-cut chamber neck area over time.

[243winxb]

SAAMI Web: 0.403"

I am still trying to fiqure out where you got this? It would seem to be the extractory groove?

I checked the rounds and noticed that on 10 of the 66 there were light marks on the head stamp from the ejector,

This is common on factory ammo. Yours might be from some lube remaining on the brass. Bolt thrust would be higher lubed. Running maximum loads reduces brass life to as little as 3 loading. Depends on how much difference between dies and chamber.

[Mike25]

Yes, I trim every case to 2.005. I guess I got a little firm with the one that ended up at 2.0045.

I am puzzled as to why only ten of these cases showed any signs. I have been meticulous about my case preparation and my loading procedures. I'm not saying that my procedures are perfect, just that I focus on each and every case to be exactly as the one I did just before it.

I thought that I was close to publish max for my recipe, but I wanted to have one load that I could use anywhere between 100 and 1000 yards so I didn't have to have multiple recipes. After doing the OCW test - which showed a node at 45 grains - I figured I would back off .2 grains just to give myself a margin of safety, and up until last weekends shoot everything seemed to be working great.

Given the problems I was having with sizing the Federal brass, I was thinking that whatever problem I was having could be caused by, well, something with the Federal brass. At this point I'm thinking whatever I do, it will not involve Federal brass anymore.

Again, thanks for the help.

[Mike25]

243,

Yes, I guess I was using that grove...

Sorry, I thought that was what you were referring to.

Maybe those marks don't mean what I thought they did. I'm hoping that is the case here as I really don't want to have to break down the rest of my prepared loads, but I also want to be safe and not damage my rifle.

Thanks.

[mehavey]

I am still trying to fiqure out where you got this? It would seem to be the extractory groove?

Would you believe... 0.4703 ?

[243winxb]

mehavery

Would you believe... 0.4703

Yes, i will buy that. Your right about taking a measurement of the web before firing.

[Mike25]

Okay, I think I got the correct location for this measurement, and all of the cases with marks on them were between .4715 and .4720. Most of the cases that did not have marks on them were below .4710.

These cases are all on their third loading and were from Federal Gold Medal Match rounds.

Does that help?

[F. Guffey]

“I'd also not suspect headspace problems sufficient to cause brass flow into the ejector cut-out unless cases were also stretching like mad,*** and primers flattening due to head slam into the bolt face as a result”


“due to head slam into the bolt face as a result” ? Reminds me of the NYPD COP asking the Priest about an accident he was involved in. “Now tell me Father, how fast was the Rabbi backing up when when he hit you”?"

and, so, I ask, how fast was that primer backing-up (OUT) when it hit the face of the bolt?

Someone tell me the sudden top of the case head against the bolt face did not cause case head expansion and or imprinting on the bolt face.

http://www.eurooptic.com/sako-trg-22-rifles.aspx


F. Guffey

[Ridgerunner665]

Weigh those 10 brass that had the ejector mark...odds are they are a tad heavier (thicker)...which will sometimes cause what you are seeing when the load is near max.

Slightly smaller combustion chamber = higher pressure.

[243winxb]

Okay, I think I got the correct location for this measurement, and all of the cases with marks on them were between .4715 and .4720. Most of the cases that did not have marks on them were below .4710.

These cases are all on their third loading and were from Federal Gold Medal Match rounds.

Does that help?

This can be a sigh of high pressure. To best use this web measurement, it would help to know the diameter before firing. 40 years ago, if the web expanded .001" the load was too hot. Now benchrest shooters have special dies to return the web to it orginal diameters. Brass life is short. Different Components=Different Pressure. Watch for loose primer pockets on the next loading. When the case head expands ,so does the pocket. On firing, watch for gas leakage past the primer.

[F. Guffey]

“between .4715 and .4720. Most of the cases that did not have marks on them were below .4710”

On the third firing, measuring the case head for case head expansion is, at best, nice to know, I have tested receivers that expanded case heads .010 thousands, first firing, measuring case head expansion is a discipline when using the information to determine maximum load with control case head expansion, and that is just before pressure signs became visible.

The case head that expanded .010 also expanded the flash hole, and shortened the case head from the case head to the bottom of the cup, or top of the web.

And then there is the tool used to measure case head expansion, the variation you have posted can be caused by the tool. The bladed micrometer is said to be ‘the tool’ for measuring case head expansion, case head expansion is measured in .0001 thousands, a good start would be .002, again after 3 firings consider the case head has been worked and has hardened, some are excited about that.

Case head expansion, once fired, measure, then compare the measurement after firing another new case, unless, you want to do busy work, new, unfired brass does not behave in the same manner as 2nd and third, etc., all the up beyond 6 time fired brass.



F. Guffey

[F. Guffey]

"When the case head expands ,so does the pocket" and the flash hole, also, the case head shortens from the head of the case to the top of the web, and I have shell holders that are not alike.
F. Guffey

[243winxb]

F. Guffey, do you think he should pull the bullets and reduce the load? Or shoot them?