308 blown primers question

[358WCF]

From what era ?
There was some weak runs a few years back.

The defective WLRs... not WLRMs... "weak runs (?)"... were, as far as I've heard, cracks on the radius of the cup which pinholed even with low pressure loads. The primer does not disappear, & the case is still usable/reloadable even if a bit ugly at the edge of the primer pocket. This is a different problem than the OP is having.

 

[Homerange]

The defective WLRs... not WLRMs... "weak runs (?)"... were, as far as I've heard, cracks on the radius of the cup which pinholed even with low pressure loads. The primer does not disappear, & the case is still usable/reloadable even if a bit ugly at the edge of the primer pocket. This is a different problem than the OP is having.

Sorry, yes I overlooked the OP is using Magnum Primers.

The WLR's I've seen fail OTOH were in hot but safe loads worked up by experienced handloaders whom after having their bolt faces eroded vowed to never use a Winchester primer again.
That was something like 10yrs back and they may have got their shit together.

 

[Webster]

. Maybe it's me, but the 3 with primers from the 44.8 dont look over pressure to me - but like i said im new to this.

No matter what the manual says max load it isn't a fixed number. I believe ejector swip mark can only come from high pressure. The case head is getting pushed into the hole. Strange you have low fps. I would try a different powder. Look at the load maps in the technical section. No obvious answer. You might have a tight barrel?

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[steves86ta]

What's everyone's opinion on having the bolt bushed?

I found a few videos and articles that said howas struggle with this issue because of how large the firing pin and hole are

 

[Ned Ludd]

A larger-than-necessary firing pin hole would be more likely to cause pierced rather than blown primers, and I'm not seeing the kind of cratering in your original primer pics that might be expected from an over-sized firing pin hole. Nonetheless, it is a good idea to have it bushed if you think it is part of the problem. It won't hurt anything to have that done.

 

[steves86ta]

I went out today and loaded up 35x rounds at 43.8 grains of the staball Match powder. This was the middle of my node from previous testing

I was testing for seating depth and loaded up 35 rounds 5 groups each .005 farther from the lands. I loaded up 3 batches each with different primers. Winchester, CCI and federals

Out of the 35 in each batch, I blew at least one primer in each batch of 35. Groups were best at .030 off the lands for all the primer types

I plan to download my chronograph data when I get home but from what I saw the velocity was all in line.

Again no pressure signs on anything except the ones that blow a primer out.

I know to try varget have not found it in stock locally yet. Don't really want to spend hazmat for one or two pounds from the manufacturer. But I will if I have to.

I also got a recommendation for a local gun Smith that I have a call out to. Plan to ask him about bushing the pin and also looking into rebarrelling

 

[steves86ta]

Next, you need to start taking and recording some critical measurements, if you haven't done so already. The taking and recording of accurate measurements is sometimes the only way one can readily troubleshoot problems such as this, and it's generally just a good practice. For example, measure the case diameter at the datum line just above the extractor groove (circled in red on the following .308 Win Cartridge/Chamber diagram from SAAMI). Doing this before/after firing can provide some idea of how much case expansion is taking place in your chamber.

View attachment 1451925

In addition, taking and recording base-to-shoulder (BTS) measurements can also be critical. It is sometimes possible for the case shoulder is bumped back excessively during the re-sizing process (i.e. > .002" or so). When the firing pin hits the primer cup, it drives the case forward until the case shoulder "bottoms out" in the chamber. If the case BTS dimension is too small (i.e. the shoulder has been bumped back too far), this can create an excessive gap between the base of the case and the bolt face as the firing process proceeds, allowing primers to "pop out", even in cases where the pressure may not be over MAX. It may not seem like a tiny gap of only a few thousandths could cause this to happen, but I can assure you it does. For this reason, it is not uncommon to observe popped primers when fire-forming virgin brass, which is usually much shorter (BTS) straight out of the box than it will be after the first firing/re-sizing cycle. Seating bullets long to prevent this tiny gap from opening up may help with virgin brass, but it's not really where you want to be with fire-formed brass, where optimal bullet seating depth is absolutely necessary for good precision. Make sure you are sizing your case back at the shoulder by no more than .001" to .002" during the re-sizing process.

@Ned Ludd

Im not a machinist - so bare with me here.

If I am reading the drawing correctly, the base to the shoulder should measure 1.634 -.007

Does this mean the Minimum base to shoulder should be 1.627 and max is 1.634?

Mine measures right about 1.620. After firing - Both the one that popped the primer and one that did not.

I do not have any factory 308 ammo here to measure what that looks like

 

[Coyotefurharvester]

The hornady comparator body is MORE than likely NOT making contact with the case shoulder in the correct position. You would need a headspace gage to zero your caliper/comparator on to measure the difference between fired brass and the SAAMI numbers.

 

[Ned Ludd]

@Ned Ludd

Im not a machinist - so bare with me here.

If I am reading the drawing correctly, the base to the shoulder should measure 1.634 -.007

Does this mean the Minimum base to shoulder should be 1.627 and max is 1.634?

Mine measures right about 1.620. After firing - Both the one that popped the primer and one that did not.

I do not have any factory 308 ammo here to measure what that looks like

It will depend on the chamber specs and the caliper inserts you're using. For example, I use the steel inserts from Sinclair and brass fired in chambers cut with the reamer [print] illustrated below routinely yields a cartridge base-to-shoulder (CBTS) measurement of 1.5600"m (average of 10 pcs). Re-sized brass averages 1.5585". My understanding in that the measurement taken with the beveled insert are supposed to index in the middle, but I'm not a machinist either, and I've never quite gotten that whole shoulder measurement thing/index point thing figured out. In your specific circumstance with whatever caliper insert you're using, it is the difference between the brass before and after firing that will be critical. Likewise, you generally want the CBTS after re-sizing the brass to be no more than about .0015" to .002" shorter than it was in the fired brass; i.e. it fits into the chamber readily and the bolt closes easily, but it is not over-sized.

 

[358WCF]

I went out today and loaded up 35x rounds at 43.8 grains of the staball Match powder. This was the middle of my node from previous testing

I was testing for seating depth and loaded up 35 rounds 5 groups each .005 farther from the lands. I loaded up 3 batches each with different primers. Winchester, CCI and federals

Out of the 35 in each batch, I blew at least one primer in each batch of 35. Groups were best at .030 off the lands for all the primer types'

A wise man told me many years ago that the definition of insanity is doing the same thing over & over but expecting different results. Stop it. The 1st time was an accident/mistake. The 2nd & 3rd times were not. I dont know you but wouldn't want you to ruin a perfectly good rifle, or tear up a not replaceable eye.

I plan to download my chronograph data when I get home but from what I saw the velocity was all in line.

Again no pressure signs on anything except the ones that blow a primer out.

The Hornady data was shot with Win cases. The Winchester brand is rather well known to usually have more internal capacity than other brass. Lapua brass is smaller inside which will yield higher pressures. Why are you working down from a max load to start (in your 1st post) ? Start loads are called start loads for a reason.

To blow a primer out... gonzo... not there... you have already passed the threshold of marginally safe by 15-20K psi. The ejector scrubs show up around 10Kpsi over safe max. I dont care what some jamoke on the internet, your brother in law's cousin, or U-tube says, primer appearance is not a real good way of determining pressure unless you are very familiar with the characteristics of the particular lot of primers you're using. It seems you're not. Unless you have some way of measuring pressure you're treading in dangerous territory. Being new at this, but not heeding what your rifle &/or brass is trying to tell you is foolish at best. Slow down & think. Formulate a smart & safe plan of moving forward rather than the Rick-o-shay Rabbit method of problem solving.

Have you called Hodgdon to see if there is a hot batch of Staball Match? It's a relatively new powder. Maybe some #s got transposed in the manual? Shit happens. I locked the bolt on a 35 Whelen a while back with a start charge of 4320. It happens. Reloading manuals are but guides. Almost guaranteed that my stuff is different than your stuff which is different than the stuff they shot in the pressure gun at the lab. Max is not necessarily what the book says.

I know to try varget have not found it in stock locally yet. Don't really want to spend hazmat for one or two pounds from the manufacturer. But I will if I have to.

That would be my next experiment rather than the aforementioned insanity. Start at the start.

Like all else, there's a learning curve. It doesn't happen all at once. Keep asking questions.

 

[steves86ta]

A wise man told me many years ago that the definition of insanity is doing the same thing over & over but expecting different results. Stop it. The 1st time was an accident/mistake. The 2nd & 3rd times were not. I dont know you but wouldn't want you to ruin a perfectly good rifle, or tear up a not replaceable eye.



The Hornady data was shot with Win cases. The Winchester brand is rather well known to usually have more internal capacity than other brass. Lapua brass is smaller inside which will yield higher pressures. Why are you working down from a max load to start (in your 1st post) ? Start loads are called start loads for a reason.

To blow a primer out... gonzo... not there... you have already passed the threshold of marginally safe by 15-20K psi. The ejector scrubs show up around 10Kpsi over safe max. I dont care what some jamoke on the internet, your brother in law's cousin, or U-tube says, primer appearance is not a real good way of determining pressure unless you are very familiar with the characteristics of the particular lot of primers you're using. It seems you're not. Unless you have some way of measuring pressure you're treading in dangerous territory. Being new at this, but not heeding what your rifle &/or brass is trying to tell you is foolish at best. Slow down & think. Formulate a smart & safe plan of moving forward rather than the Rick-o-shay Rabbit method of problem solving.

Have you called Hodgdon to see if there is a hot batch of Staball Match? It's a relatively new powder. Maybe some #s got transposed in the manual? Shit happens. I locked the bolt on a 35 Whelen a while back with a start charge of 4320. It happens. Reloading manuals are but guides. Almost guaranteed that my stuff is different than your stuff which is different than the stuff they shot in the pressure gun at the lab. Max is not necessarily what the book says.



That would be my next experiment rather than the aforementioned insanity. Start at the start.

Like all else, there's a learning curve. It doesn't happen all at once. Keep asking questions.

I get that I really do

I'm really leaning towards a hot batch or something. I did call hodgdon Friday and left a voicemail. I plan to call tomorrow again

When I worked up the 175's it was with 2 pounds I bought individually. It worked so well I bought the 8lb keg in working from now.

The thing I don't understand, is coal, charge weight, bullet and brass is all the same. My velocity is lowish for the spec and it's not every round or even every 5

The rounds I took today were down to 43.8 which is quite a bit lower than the ones I was having issues at before and still popped a few.

I plan on calling hodgdon first thing tomorrow and am really at this point hoping they tell me it's a hot batch

Fwiw today while I was out I also brought some of the 175's I had loaded with the powder I bought before this keg and they all shot great. They are at 44.6 gn which is quite a bit hotter than I was loading the 168's.

I know I come across like an idiot. I've been loading for this thing for almost a year now and have had no issues until now. That's why I'm perplexed.

 

[Doom]

Unless you have changed something in you brass preparation its unlikely that is going to be the issue. It would take a significant change in the case datum dimension to "blow a primer" out of the case. If that were the case you most likely would not see ejector marks. The primers are loose in the pocket because the case head is expanding. So you are left with the likely suspects of powder lot or bullet change. In this case I suspect the problem if it exists is in that area.

Since this is a commercial barrel/chamber I would forget about 20 thousandth and load to 2.800" COAL The reason is to insure that you have enough bullet in the case to prevent premature release and lodging the bullet in the lands. I'm suspicious that this is the case from looking at your cases. You show clean brass than your ugly cases. This make it look like an inconsistency (large) between the fired rounds. If you still have pressure signs at this level I would think the powder data is suspect.

 

[steves86ta]

Unless you have changed something in you brass preparation its unlikely that is going to be the issue. It would take a significant change in the case datum dimension to "blow a primer" out of the case. If that were the case you most likely would not see ejector marks. The primers are loose in the pocket because the case head is expanding. So you are left with the likely suspects of powder lot or bullet change. In this case I suspect the problem if it exists is in that area.

Since this is a commercial barrel/chamber I would forget about 20 thousandth and load to 2.800" COAL The reason is to insure that you have enough bullet in the case to prevent premature release and lodging the bullet in the lands. I'm suspicious that this is the case from looking at your cases. You show clean brass than your ugly cases. This make it look like an inconsistency (large) between the fired rounds. If you still have pressure signs at this level I would think the powder data is suspect.

I just got off the phone with Hodgdon and he suggested the same thing.

He said that im probably right on the edge of the bullet wanting to stay in the case and then lodging in the lands. It's become a problem with the 168's because they are a smaller bullet than the 175's.

He gave me some things to measure and i will measure today. I also plan to start at 2.800 and look from there.

He also said to not use Magnum primers - said this can cause the pressure to increase too

 

[dryhumor]

This picture is a progression of charge weight. Might or might not be useful to you. The far left is where I started, the far right is where I stopped. Varget and 163 gr projectile. The far right had the start of heavy bolt lift. Note the edge of the primers, moving from rounded to squared. .4 grain increments. Pretty subtle indication of pressure increasing.

 

[Flouncer]

Define "popped" primers. Popped to me means they were not in the case after the shot. Did the primer fall out of case during brass ejection? They can't really come out of the pocket while the bolt is still closed. Popped could also mean what most call blown, ie: a hole in the primer where the firing pin indentation is and lots of smoke. Either way the ejector marks signal high pressure.

Frank

Frank, I dont see ejector marks in his pics. I have seen mine, and there is an obvious cylindrical scratch from rotating the bolt. Easy to spot and obvious. Can you clarify on his pics ?

 

[steves86ta]

As an update to the thread - Thank you everyone for all of the advise.

I bought a Hornady OAL gauge and modified case. I also have the tap and drilled/tapped a Lapua fired case from my rifle.

They both measured the same and that my chamber is 2.950 +/- .005 to the lands

this compared the the method i was using, means i was basically putting the bullets into the lands (was loading to 2.940ish

I will be going out to the range Saturday, and will be starting at 'ground zero' again. I will load to load data length which puts about a .150 jump to the lands.

I will start at the bottom again and work my way up. The rifle is as clean as it's ever been so there should be no carbon induced issues.