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Old September 17, 2010, 05:19 PM   #1
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Overpressure signs

I did some test firing for some load workups and am wondering if I'm getting overpressure signs.

.308 Winchester
Bullet: 168 grain Sierra HPBT Matchking
Primer: Federal 210M (match)
Brass: LC Match, 2.005" trim length
Powder: load #1 40.0 grains IMR 4064, load #2 41.5 grains IMR 4064
Load Data: Lyman Reloading Guide

Load #1 is the start load in the Lyman Guide, but load #2 is the start load on the Hodgdon website.

This first picture shows a comparison of the primers with load #2 in the first row (obvious flattening) and load #1 in the second row (obvious backing out).

This second picture shows the case walls with load #1 at the top and load#2 at the bottom. I also ran the paperclip test with no indication of a pressure ring inside the case wall. There was some stiffness in the bolt for most (but not all) of the rounds from load #2, no stiffness with load #1.

These next two pictures show an angle on the case heads where you can see the obvious backing out from load #1 and the flattening from load #2.

This is the first reload after swaging the primer pockets which were also cleaned with a Sinclair primer pocket tool. I can't explain the backing out with the cooler load unless the pockets are overly large now. The flattening alone didn't worry me as much as the accompanying bolt stiffness. The two together bother me a bit. I would appreciate the the collective wisdom of the m ore experienced.

BTW, load #2 gave me sub-MOA groups (.471") and load #1 about MOA (.915"). I'd like to be able to use load #2.

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Old September 17, 2010, 06:24 PM   #2
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I can't explain the backing out with the cooler load unless the pockets are overly large now.
Low pressure loads routinely push primer out.

The primer is pushed out and the pressure never gets high enough to stretch the case enough to seat it back.

If those are a starting load and a higher load, you appear to have taken a very large step.
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Old September 17, 2010, 06:29 PM   #3
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I'd go back and verify all settings, calibrate my scale and recheck everything. Load number 2 looks hot. Flatened primers and a stiff bolt lift are signs you are way over on pressure. Also (and this is unlikely) be sure your not seating the bullets out so far they are into the lands when the round is chambered. This will raise the pressure.
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Old September 17, 2010, 06:35 PM   #4
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I just took another look at your pics and noticed you are using military brass. Someone correct me if I'm wrong (as I never use mil brass) but I seem to recall military stuff has a thicker wall and most of the load data in manuals is for civilian brass. This can cause higher pressure too. Brickeyee brings up a good point though. I would move up in powder by 1/2 grain at a time. You may have gone from too light a load to too hot a load in one jump.
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Old September 17, 2010, 08:16 PM   #5
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Load #2 looks hot to me. As said before you could check your bullet to land relationship. I set mine up to just barely touch the lands. I usually smoke the first 3 or 4 dummy rounds to make sure my setting is correct.
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Old September 17, 2010, 09:38 PM   #6
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While I'm doing some experimenting here, this is not the first time I've used 4064 for the .308. I've loaded some up to 42.5 grains in the past with none of these indicators. But that was with civilian brass.

I appreciate the explanation of the primers on the starting load, that makes sense.

I'm using 2.8 - 2.81" as my OAL. I'm pretty certain I'm not contacting the lands just yet. I used a loose bullet set at 2.85 and chambered it with no push back. I could be wrong about that, but I'm doubtful that contact with the rifling is contributing to the problem.

I did work up some loads with Lapua brass (same powder charges) and did not have the flattened primers.

Could this be related to the relatively soft Federal primers? I usually use CCI or Winchester because I like a harder primer than Federal.

I realize the jump from 40 to 41.5 is fairly large but what I was selecting was the midpoint between the start and the max load from the Lyman Guide. I've used 41.2 of 4064 as my accuracy load in the past, but to be frank I wasn't paying as much attention to the rounds I was loading then. If it went bang and printed tight groups I was happy. I'm trying to master the craft of accuracy reloading for the .308, so now I'm paying attention to everything.

The LC brass averages about 6 grains heavier than the Lapua and most definitely has thicker neck wall. Could this be caused by a longer grip on the bullet before release that is allowing the internal pressure to build more?

The rounds chamber without resistance, but they feel snug. I'm wondering if the bullet is being held longer as the neck begins to expand with the LC cases.
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Old September 17, 2010, 09:49 PM   #7
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The LC brass is not the problem. I use nothing but LC brass in my 308s and it works just fine even with max published data. I think you might be a little too long on the COL. If the bullet is touching or is sitting on the lands of the barrel, when pressure starts to build the bullet runs a hair forward, becomes wedged and pressure spikes occur. The increase in pressure then moves the bullet again but you're also creating max pressures because the bullet is having to start, stop, and start again, all the while the pressure is building. You might just chamber a loaded round or a sized round with a bullet in it at your current COL and when you pull it out, look for signs of rifling on the copper jacket of the bullet. I'd push them back to 2.775 if it were me. That's the max COL as shown in the Lyman book using that bullet.
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Old September 17, 2010, 09:50 PM   #8
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Low pressure loads routinely push primer out.

That's what I have found with 8 x 57 loads I made up for a Comission rifle.

IMO, the second load does not look terribly hot. Warmish. Primers flat, but not flowing around the pin (cratered). The sticky bolt is a stop sign, though.

I'd reduce the charge if using the .mil brass.
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Old September 17, 2010, 10:10 PM   #9
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I would say the the Fed primers are softer but if the bolt is lifting hard you still have high pressure. I use Fed primers in rifles and if I saw them that flat I would back off. Each rifle reacts in its own way to a load. Just because one rifle is okay with thicker brass another may not be and while it may not be the entire cause of your pressure I'd bet it is a contributing factor. I'm sure you can use the LC brass but if it were me I'd back off my charge.
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Old September 17, 2010, 11:34 PM   #10
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They look plenty normal to me.
Most factory loads flatten the primers like that.

The fact that you have the primer backing out indicated a loose headspace. Probably
not enough to hurt anything.
Add a little more pressure and the backed out primer gets splattered.
Its a false pressure indicater.

I just realized that it was Federal 210 primers. Federal primers are believed to be softer than most of what is on the market today.
I believe that the old softer primers got lawyered up in other brands because
some people were blowing the primers with too much pressure.
I find Federal factory loaded cases at the range that look exactly like yours.

Last edited by lwknight; September 18, 2010 at 03:28 AM. Reason: More on that
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Old September 18, 2010, 12:07 AM   #11
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I'll take a swing....

1. Cases too long or not resized to fit chamber.
2 Measure the fired cases to compare with SAAMI specs. Case head should be .473. If it's .005 larger, danger.
3. Buy a box of factory cheap WW or Rem @ Wally. Compare primer imprint.
4. Put a nickel between your die and shell holder and tighten down. This will prevent the shoulder from being sized.
5. The resized case should drop into the chamber. If not, trim to 2.005.
6. Unclenick may have some other input.
7. Like stated above, could be head thrust.

You didn't state the type of rifle.
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Old September 18, 2010, 07:30 AM   #12
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I think it's time to do some careful measuring, Ike. Knowing the headspace dimensions of your rifle, sized and fired cartridges and distance to the lands will be a necessary next step for you IMO. A careful analysis of these dimensions will result in a cartridge tailored to your rifle. Trial and error worked surprisingly well for me for many years but I now have the gauges and I'm not afraid to use them.
Good points above about reduced case capacity (and powder charge) for mil brass and taking smaller steps up from a starting load. Flattened primers alone, esp Federal, may not be a bad thing. Sticky bolt lift and other signs would make me back off the powder as well as check seating depth. Some accurate loads will flatten a primer somewhat with no other pressure signs. My latest 30-06 rifle shoots its best groups so far at a point just under where the primers move from what I call mild to moderate flattening. Previous rifle's pet load was over two grains hotter with almost no primer flattening from an accurate max load.
I watch my primers carefully but they can be misleading or at least misunderstood.
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Old September 18, 2010, 12:19 PM   #13
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Okay, I spent morning loading some more test rounds.

First of all I loaded some intermediate powder weights (40.5 & 41.0 of 4064) still at the COL of 2.8.

I also loaded a series with Varget in 0.5 grain increments starting at 41.0 up to 44.0. I hope I don't have to wind up pulling bullets on the higher loads!

Then I loaded some at 41.5 of 4064 (this is the load that flattened the primers) but set the COL at 2.775 per Loader9's suggestion.

I also have a Hornady LNL Case Length gauge coming since I really don't know the the chamber size. Now I will.

AND, I picked up my spanking brand new Winchester Model 70 Stealth in .308.

Our range is hosting the state Bend-in-the-Trail match/meet this weekend so it will be next week before I can get to the range. I'll report back with pictures of the cases after I've tested them.
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Old September 18, 2010, 03:10 PM   #14
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Originally Posted by Ike666
Powder: load #1 40.0 grains IMR 4064, load #2 41.5 grains IMR 4064
Load Data: Lyman Reloading Guide

Load #1 is the start load in the Lyman Guide, but load #2 is the start load on the Hodgdon website.
Next time you use the Hodgdon site, click on the button along the top named "print". You will get the barrel length, case, and primer used in the test loads. The cases are almost always Winchester, including the loads for .308 Winchester. Winchester .308 brass is a design developed originally for the 1992 Palma match to have more powder capacity than conventional .308 cases. They weighed an average of only about 156 grains last time I bought some new bulk Winchester. Lake City usually runs about 179 to 181 grains, or about 24 grains heavier on average. The specific gravity of 70:30 cartridge brass is just over 8.5, so that difference translates to 2.8 grans of difference in case capacity, which means around 1.5 grains less of most rifle powders will produce the same pressure in Lake City brass that it does in Winchester. So, reducing the Hodgdon load data from 41.5 to 40.0 to get a starting load for your LC brass is perfectly reasonable.

Federal loaded its Gold Medal Match 168 grain SMK load for years with 43.5 grains of IMR4064 using its own 205M primers. Federal cases (IIRC; can't seem to lay my hands on any here to double-check) were about like other non-Winchester commercial cases, and weighed around 170 grains. So you could expect 42.8 grains in your LC cases to give about the same pressure and barrel time performance as Federal's own 43.5 grain load. Just slightly less velocity (20 fps or so).

As to the primers, they do look a bit extra flat. That usually happens because the head mushrooms (the exposed part sticking out fattens) under pressure so that when the case heads stretch back to reseat the primer, they not only are flattened, but that swollen mushroom head is squashed wide to fill the radiused lip of the primer pocket.

However, the edges of the primer firing pin indentations are not squared, much less cratered, so I doubt the pressure was actually excessive (though primers are not the most reliable indicator; just a convenient one). It seems more likely the very flat spread is due either to cases sticking to the chamber walls more firmly than usual so that the head stretching back is delayed a little, which will grow the primer mushroom head, or to excess headspace. One way to check would be to neck size some of these cases, load them singly and gently (chamber fast with a bolt can shorten them), and then run the same load. That way the primer won't have any headspace to back out into, and you can see if that extreme flatness is mitigated?

I would also take a depth mic or use the head step of a caliper to measure how far out your first set of primers are sticking? That should tell you how much bigger your headspace was than the sized cases were. I can't tell if it's really excessive from the photos because of the rounded edges of the primers, but it looks like it might be on the long side, which could also cause the broadly flattened primer by letting it back out farther enough than normal to mushroom more than normal. Figure that if you chambered the rounds slowly and without slamming the bolt, you shouldn't see those stick out more than about 0.010", maximum. This would be if the brass were sized to -0.002" under minimum chamber headspace when you started, as is fairly normal for new, unfired cases.

That leaves the sticking bolt. If some high pressure event is actually occurring, your velocity should be too high for the load with your barrel length (I don't know what that is?). So a chronograph is a good idea for a reality check here. Things other than high pressure can cause bolt sticking, though. We had a thread not too many months ago in which a fellow had some 1960's LC cases ('68, maybe) that were giving him sticky bolt lift even with starting loads. He had to back down to around 32 grains to get it to stop, IIRC. I sent him a few new, unfired LC cases, and he tried them with the same starting load and had no sign of sticking. We never did figure out what had happened to the old LC cases? Had someone over-annealed them, leaving them too soft to spring back after exposure to normal chamber pressure? They sure behaved that way. I don't think he knew who fired the brass originally or how many times or if it had been annealed. Or perhaps that brass had simply been stretched too far by extraction in a machinegun and gotten to too thin to spring back from the breech? Don't know. We just know the sticking stopped when he used known good cases. It wasn't caused by of exceeding normal pressure for the round. It was just excessive pressure for those particular cases.

So, based on the above, I would do the same cross-check. Get some new cases and load them per their weight and see if sticking stops and primers are any less flat? The way to calculate weight for constant barrel time (pressure moves just a couple hundred psi in QuickLOAD this way, so not significant) is the simple linear equation below. Note that this only applies to mimicking the barrel time of the Federal Load with the 168 grain Sierra Match King seated to 2.800" COL and using a Federal 210 or 210M primer, and is not for any other combination:

Adjusted IMR 4064 Charge = 55.1 grains – (0.0682 × case weight in grains)

Thus, a 186 grain IMI Match case should be charged with:

55.1 gr. – (0.0682 × 186 gr) = 55.1 gr – 12.7 gr = 42.4 gr IMR 4064

A 180 grain LC case should be charged with:

55.1 gr. – (0.0682 × 180 gr) = 55.1 gr – 12.3 gr = 42.8 gr IMR 4064

A 156 grain Winchester case should be charged with :

55.1 gr. – (0.0682 × 156 gr) = 55.1 gr – 10.6 gr = 44.5 gr IMR 4064
QuickLOAD says these are not maximum loads and should be running in the vicinity of 52,600 psi, give or take a few hundred. That agrees well with Hodgdon's data on the Winchester case, for which the maximum is given by them as 1.4 grains higher (45.9 gr).

So, to test if the LC cases may be bad, get whatever new case you can or even use a good condition range foundlings or cases from commercial load that were fired in your chamber for the first time and did not stick would be better still. Size and decap and clean these. Weigh them. Calculate the above load, knocking the result down 5% and working up in 3 steps to arrive at the above load. 5% and 3 steps rather than the usual 10% and 5 steps should be good enough in this situation as we are not working up to a maximum. You should not get case sticking at any level.

If you prove to yourself that the sticking is gone, then run Dan Newberry's round robin to fine tune to the very best load. That varies with the gun. If you wind up running in the pressure range of the old Federal load (they now use Reloader 15, BTW), that will be good for excellent barrel life.

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Last edited by Unclenick; September 18, 2010 at 03:29 PM.
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Old September 18, 2010, 09:26 PM   #15
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Nick: Again, thanks. I did fire some similar loads with the Lapua brass. There was some flattening of the primers - not as pronounced as the LC. Used the same two loads (40 & 41.5 of 4064). More importantly there was no stiffness in the bolt with the Lapua brass. Also, on the start load there was no primer backing out.

The rifle is a Rem 700 PSS with a full 26" barrel.

The LC cases were in the 179 grain range, and the Lapua are in the 172 grain range. So, with the Lapua I'd match the Federal load with about 43.4 grains of 4064 (load=55.1-(0.0682 x 172)). That is sure a bit more than the max of 41.5 I had loaded in them.

I'll take the chrono with me to the range when I next go.

Interestingly, I just bought my first pound of Rx15 and loaded my first 5 rounds with it.
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Old September 18, 2010, 10:03 PM   #16
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Is anyone checking case head expansion as a pressure sign? It should be a more reliable indicator than primers.

I recall my older manuals suggested dropping 2 grains for starting loads with military cases from commercial cases because of reduced volume which increases pressure. Do the manuals not suggest that now?
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