Primer Blow Out with NO Over Pressure Signs?

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Originally Posted by 20X11

Flattened, loose primers also happen from excessive headspace (improperly adjusted dies setting the shoulder back too far). I read the whole post but haven't seen this mentioned or verified.

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Sorry, haven't checked into this thread in a while...

Yes, if you're pushing the shoulder too far and it's a light load, the primer can pop out. Several things at play... primer goes off and jumps out of the pocket. Normally the powder charge then expands the case and the primer re-seats flush with the base (we're talking fractions of a second here). With a light load and a headspace problem, there's too much room between the brass (that doesn't expand enough due to the light load) and the bolt face... potentially enough for the primer to come totally out. That explains the 38.0 grain load. I discovered this early on with start loads ridiculously low in Hornady #7.

Headspace problem plus powerful load usually means case head separation (almost always a headspace problem).

Forget what came with your die set. Normally, you can turn the sizing die down until it touches the shell plate and you're good to go. Most directions say to go 1/8 to 1/4 beyond that so it cams over. I have found this to be detrimental with autoloaders (bolt guns I just neck size, so it's never an issue). A case gauge is very much worth the money.

My only other advice is don't load to 42.8 grains. Find a different powder / bullet / primer / brass combination if it's not doing what you want.

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Originally Posted by Zombie Steve

Sorry, haven't checked into this thread in a while...

Yes, if you're pushing the shoulder too far and it's a light load, the primer can pop out. Several things at play... primer goes off and jumps out of the pocket. Normally the powder charge then expands the case and the primer re-seats flush with the base (we're talking fractions of a second here). With a light load and a headspace problem, there's too much room between the brass (that doesn't expand enough due to the light load) and the bolt face... potentially enough for the primer to come totally out. That explains the 38.0 grain load. I discovered this early on with start loads ridiculously low in Hornady #7.

Headspace problem plus powerful load usually means case head separation (almost always a headspace problem).

Forget what came with your die set. Normally, you can turn the sizing die down until it touches the shell plate and you're good to go. Most directions say to go 1/8 to 1/4 beyond that so it cams over. I have found this to be detrimental with autoloaders (bolt guns I just neck size, so it's never an issue). A case gauge is very much worth the money.

My only other advice is don't load to 42.8 grains. Find a different powder / bullet / primer / brass combination if it's not doing what you want.

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Now this actually makes sense. I have a headspace insert for my hornady comparator, so I'll measure up some brass tonight and see where its at. I used the Lee Full Length sizer, so I have no idea what the shoulder is at. I needed to fire form this brass before I could use my Lee Collet Sizer, and I don't recall what I did with the die setup, if I touched the shell plate, turned 1/8-1/4 more. I most likely followed the Lee directions.

I was just telling Belly in a PM, I'll probably load them to 2.825" (internal mag length is 2.835") and do another ladder test, starting at 39.0gr (or even higher) and working up to 42gr. Especially since 38.0-39.6gr was 2351 FPS - 2464 FPS, which is slower than I want to go, so I might as well save powder/bullets. That is, using the new Lapua brass and possibly other primers if I can find any in stock locally. I'm taking some WLR primers with me to work today to measure them with mics to see if they are truly undersized or within spec. If they're undersized, I might try calling Win and asking why they're undersized.

PM Returned.

I think we can change a couple things around to continue being nerds abotu this stuff that most likely doesn't matter.

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Originally Posted by BuffCyclist

Now this actually makes sense. I have a headspace insert for my hornady comparator, so I'll measure up some brass tonight and see where its at. I used the Lee Full Length sizer, so I have no idea what the shoulder is at. I needed to fire form this brass before I could use my Lee Collet Sizer, and I don't recall what I did with the die setup, if I touched the shell plate, turned 1/8-1/4 more. I most likely followed the Lee directions.

I was just telling Belly in a PM, I'll probably load them to 2.825" (internal mag length is 2.835") and do another ladder test, starting at 39.0gr (or even higher) and working up to 42gr. Especially since 38.0-39.6gr was 2351 FPS - 2464 FPS, which is slower than I want to go, so I might as well save powder/bullets. That is, using the new Lapua brass and possibly other primers if I can find any in stock locally. I'm taking some WLR primers with me to work today to measure them with mics to see if they are truly undersized or within spec. If they're undersized, I might try calling Win and asking why they're undersized.

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Amendment to my previous post - I shouldn't have said brass expanding (it does, but shouldn't much if it's sized right) - the powder charge going off pushes the brass back against the bolt face and essentially re-seats the primer.

FINALLY, I HAVE SOME ANSWERS!!! [WooHoo]

Was distracted this morning when I showed up to work, my chief engineer asked me what I was thinking so hard about, so I told him. He took me out to the machine shop and after searching high and low for about 10-15min, finally found them and handed me a pair of Starrett Small Hole Gages and a pair of Starrett Micrometers (0.0001" precision). Told me to borrow them for the night and I'd have my answer, whether it was out of spec primers or out of spec primer pockets in the brass.

So, as soon as I got home, I started measuring. What did I find? Well let me tell you!


I found the specs for primers as well as primer pockets ( http://ballistictools.com/articles/p...d-diameter.php ) and started measuring 10 each of LC LR 07 primer pockets, CCI BR2 LR primers, WLR primers, and some other misc brass.


All of this data was taken from measuring between 10-20 cases/primers, and recording the measurement 3 times, the writing down the average of those 3 for all cases/primers. The same measurements between cases were VERY consistent.

LR Primers
Min = 0.2105"
Max = 0.2130"

LR Primer Pockets
Min = 0.2085"
Max = 0.2100"

CCI BR2 Primers - 0.2111" (middle of spec)
WLR Primers - 0.2103 (lower end of spec)

LC LR 04 Primer Pockets - 0.2094" (in spec)
LC LR 07 Primer Pockets - 0.2106" (above spec)
LC LR 08 Primer Pockets - 0.2097" (in spec)
LC LR 10 Primer Pockets - 0.2100" (max spec)
LC LR 11 Primer Pockets - 0.2095" (in spec)
R-P Primer Pockets - 0.2098" (in spec)
Black Hills Primer Pockets - 0.2100" (max spec)

I STILL don't have the Lapua brass, not happy with SouthwestAmmunition for that, they were in-stock when I ordered, then they claimed they must have sold out after I ordered even though the page still hasn't changed like some other items that say "Requires an additional 1-2 weeks processing time)". Anyways, I don't have that brass in yet so I can't measure the primer pockets to see what they are.

What I think happened is that the LC LR 07 primer pockets were a few ten thousandths (as in, as much as 0.0003"-0.0005") larger than the primers, which caused less friction to hold the primer in place, so the primers were easier to unseat and blow out. When I get time, I'll be pulling the remaining 51rds, weighing charges to ensure that wasn't a contributing factor too but will then just load up the Lapua brass with a smaller range of powder charge and retest.

Oh and my Timney Trigger arrives today to fix the XMark Pro Trigger Recall problem. So that should be fun.