Blown Primer Cause?

[Gary L. Griffiths]

CAUTION: The following post includes loading data beyond or not covered by 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.

I have been working up some .223/5.56mm loads in the 60-65 gr. bullet weight category, attempting to duplicate the ballistics of the 5.56mm Carl Gustav 62-gr. LAP round with a hunting/varmint type bullet. I set QuickLoad to 30.0 gr. water weight, corresponding with the unfired Lake City 13 cases I'm using, with a weight factor of 0.4, which experience has shown most closely corresponds to the velocities I have been observing with my loads. Plugging in an Armscor 62-gr. FMJBT, using 25.1 grs. (weighed) of AR-Comp, QuickLoad computed that I should get 3048 fps. With 54570 PSI. Hot, but by no means approaching the 5.56mm pressure limit of 62,366 PSI.

I test fired 20 rounds, 10 each using unfired LC-13 cases with CCI-41 primers, and 10 using twice fired LC-13 cases with CCI-400 primers. The batch with the CCI-400 primers averaged 3062 fps., while the CCI-41 primed cases averaged 3042 fps. I discovered, however, in the middle of the string, one of the new cases blew the primer! This round was the highest velocity in the string, at 3073 fps., but one clocked 3072 fps., and two clocked 3060 fps. Moreover, two of the CCI-400 loads were faster, at 3083 and 3080 fps.



The top row of cases is from the CCI-400 primed batch, all of which show some signs of pressure with slightly flattened primers and the beginnings of some cratering. The center row is from the CCI-41 primed batch, showing the blown case and others with signs of pressure similar to the top row. The bottom row ends and center are factory Carl Gustav 5.56mm cases showing
the same characteristic primer flattening and cratering as the handloads, while the two cases flanking the center of that row were milder loads of 24.5 grs. AR-Comp with 55-gr. FMJBT bullets.

Ordinarily, a blown primer is a sign of greatly excessive pressure, but in my experience that also produces correspondingly greater velocity. In this instance, the velocity was well within the norm for the load being tested. Could this be the result of an anomalous soft case, or one with a slightly larger than spec primer pocket? I can thumb-set a new primer in the pocket of this case, so it definitely was expanded.

Since I'm in the 5.56mm velocity/pressure range, in my .223 Wylde and 5.56mm ARs, should I just abandon this pressure level and confine myself to lesser performing loads down in the .223 pressure range? All thoughts appreciated.

[mehavey]

Forget the primers
Look at all the ejector/brass flow marks.

You are at least 15,000psi over max.

[WESHOOT2]

You work upward in your gun; you start low and work up slow.

Except you worked up too far; your load is blowing primers in your gun.

[reynolds357]

That is some of the most over pressure ammo I have ever seen. You using the wrong data for your powder? Seriously, that stuff is DANGEROUS. You are going to see some rifle parts flying before long. Don't pay velocity any attention when trying to determine pressure. Tolerance of barrel and length of barrel determine velocity.

[243winxb]

CAUTION: The following post/title includes loading data beyond or not covered by 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.

.223 Wylde and 5.56mm ARs

What chamber was the brass/load fired in? How was the crimp on the primer pocket removed, if any? Longer bullet bearing surface will increase pressure. [IMG][/IMG] Click photo for larger view.

milder loads of 24.5 grs. AR-Comp with 55-gr. FMJBT bullets.

This is more inline with Alliant loading data. http://www.alliantpowder.com/reloade...5&cartridge=46 and SAAMI pressures. http://www.saami.org/specifications_...essure_CfR.pdf

should I just abandon this pressure level

Yes, till you buy pressure testing equipment.

[243winxb]

5.56 X 45MM NATO
CIP COMMERCIAL AND NATO/MIL SPECIFICATION (62,350 PSI)http://www.accuratepowder.com/ Find load data and powder here, that are for the higher pressure loadings. Note the barrel length being used. (24)

[skizzums]

25.1 gr shouldn't be exorbitantly hot. I can't agree that you are 15kpi over max. BUT, you definitely need to do a more proper work-up.

[Gster]

Everything you wrote after that Q was answering your own Q.

[mehavey]

"...Plugging in an Armscor 62-gr. FMJBT, using 25.1 grs. (weighed) of AR-Comp, QuickLoad computed ....."

What am I missing here?

{edit: the image violated the board policy on posting copyrighted materials and had be pulled.}

Just offhand I'd up the resultant boat-tail pressure effects to 70ksi to be conservative

[Gary L. Griffiths]

What am I missing here?

Weight factor of 0.4 instead of 0.6. This factor is consistent with the velocities I've been getting with my rifles. Also, 16.5" bbl.

[mehavey]

Using a 16.5" barrel -- and Wt Factor still at 0.6 as shown -- I get 3,080fps which is
consistent with your velocity ...and still in the very high 60 thousands pressure.

... which is also consistent with the condition of your fired cases.

[4runnerman]

Call me silly here,but what is it you are trying to do?.Get over 3000 FPS with a 60 gn bllet?.

[Jimro]

The general consensus is that you are over pressure. I agree.

What is telling is that the milsurp CG loads are also overpressure in your rifle.

Since your rifle already has Wylde or 5.56 chambers, yes you should abandon that pressure level with AR-Comp. Or you should have your rifle inspected to make sure that it does in fact have the advertised chambers to see if that might be a factor.

Give CFE223 a shot in that bullet weight, leave ARComp for the 55gr bullets.

Jimro

[mehavey]

To give the devil his due....

QuickLoad does tell me that AR-Comp is the best powder for velocity/burn/pressure/barrel length w/ that bullet -- BUT -- at 23.8gr for SAAMI max @ ~2,950fps.

That last 100-120 fps you want over that is costing you at least 15,000psi more.

[F. Guffey]

Your primers have craters meaning you have brass flow around the firing pin.

My opinion, you need discipline, the primer pocket has expanded, if the primer pocket has expanded the flash hole has expanded, increased in diameter. If the flash hole and primer pocket expands the case head expands and the case head is crushed/shortened from the top of the cup above the web to the case head.

A disciplined reloader would measure the case head before firing and again after firing. I have a flash hole micrometer. When the first NT cases came out I almost lost the gage when it fell through the large flash holes

F. Guffey

[Hummer70]

It would appear you would benefit greatly from the Quickload Program.

I try to keep my pressures curves in or slightly below the yellow line on that program.

If you get primers looking like that with yellow line pressures is a pretty good indication you have a striker energy problem.

I had the exact same appearance on a Rem 7615 with M193 military ammo. I check striker indent, it was not to spec, called Wolff and got new hammer spring and the problem went away immediately.

[F. Guffey]

If you get primers looking like that with yellow line pressures is a pretty good indication you have a striker energy problem.

I have to ask which primer? I would say he has close to 6 that look nice. Meaning the pressure in the primer removed the dent then conformed the primer to the protruding firing pin. Then there is that problem with the cratered primers, they just don't look right. They have the appearance of brass flow back against and around the firing pin, by all means get new hammer spring.

I suggest more discipline and consistency and accuracy. Same head stamp, same primer, same powder charge and weight of bullet should not give him primers with dents that go from nice to cratered to completely missing.


Did I mention I have a flash hole gage, a very few reloaders start with uniform diameter flash holes, the logic has to be explained, shouldn't be that way.

F. Guffey.

[Slamfire]

Your loads are clearly overpressure for the gun, case, powder, primer, bullet, barrel, chamber. Cut your loads by a half grain and retest . If you are still popping or piercing primers, cut again by a half grain. I had to cut some of my loads by 1.5 grains so they would stop popping primers in my Kreiger barrel match 223. The same loads were hot, but not overmax, in a Wilson match barrel.

Quickload, computer models, are guides based on someone else's data. One should never assume they are calibrated models of your equipment. Your equipment is very different and you should expect different results.

The slope of the smokeless pressure curve is exponential. Move it, change the slope, and pressures change exponentially. What that means is little changes up front will create big changes in pressures. Since humans do not think in exponential terms, they think in linear terms, people are baffled by the outcomes of exponential events, because it does not "make sense".

Velocity, I have not seen enough pressure/velocity data to know just how much pressure increase it takes to produce X more feet per second. I am of the opinion that the pressure increase is orders of magnitude higher than the velocity increase. Because F = ma, there will be a velocity increase with higher pressures, but I can't quantify a number. Pressure also varies much more than we realise, and that is because there are no good databases of pressure tested data. The numbers we see are a number, not a matrix of velocity and pressure for a string of shots. I regularly test over a chronograph and I do see wide velocity spreads, I believe the pressure spreads are even wider. We know that SAAMI pressure requirements are a mean plus 20%. That is a lot of ammunition whose high end pressure extreme is 20% over the SAAMI recommended maximum average pressure should be scrapped. That much variation in pressure was quite an eye opener for me.

[mehavey]

For small increments (10-15%), Pressure goes ~ as the Velocity-ratio cubed

Using that:

V1: 2,950fps (direct extrapolation from Alliant pressure test data/matched to QuickLoad baseline, then barrel shortened)
P1: 55,000psi (SAAMI max)

V2: 3,180fps (Op's reported)
P2: 69,000psi (V2/V1)cubed * P1

[44 AMP]

What am I missing here?

From the screen shot of the loading program, I'd say what you are missing is the red letters in the bottom right that say, "

DANGER! ....DO NOT USE THIS LOAD

Since missing that helpful hint and using the load, NOW you wonder what happened?

It doesn't MATTER WHAT the book says, nor what the computer program says, what matters is what your rifle and ammo does, and the load you used is just too hot for your combination of gun and components.

What velocity you get with what bullet is machts nichts. It matters not. Cratered primers, bolt face markings on the brass, blown primers, means its TOO HOT!!!! It doesn't matter if the data says it should be ok, you have physical proof it isn't.

Stop there, and rethink things.

Or be prepared to pay for gun repairs, and may be medical bills. It's your choice.

[Gary L. Griffiths]

Appreciate all the replies and advice. Agreed, regardless of what any program says, the cases say, "TOO HOT!!!" I'll cut the load to 23.0 grs. and see how that goes.

Interesting observation on flash hole size. Hadn't thought of that, but it makes perfect sense: A larger flash hole allows higher pressure to affect the primer.

Again, thanks to all. Really appreciate the info and the concern.

[F. Guffey]

Interesting observation on flash hole size. Hadn't thought of that, but it makes perfect sense: A larger flash hole allows higher pressure to affect the primer.

Forgive, not my intention to confuse.

A very few reloaders uniform the diameter of their flash holes. The best answer is: "I do it just in case it matters or makes a difference". Using the flash hole gage allows a reloader to track the diameter of the flash hole, it is not something that is used obsessively. When developing loads that are on the high side it must be understood there is something beyond 'primer signs' when my flash hole increases in diameter, the primer pocket increases in diameter and the case head expands, to expand the case head must shorten between the cup above the case web and case head.

F. Guffey

[Gary L. Griffiths]

...not my intention to confuse.

No confusion here. Understood, if the case head expands due to excess pressure, the flash hole will expand correspondingly. However, it would seem logical that if a new case has a flash hole that is at max spec, or even out-of-spec large, more pressure will be placed on the primer than the same load fired from a min or nominal spec flash hole.

[Jimro]

Just to clarify, a larger flash hole does not allow more pressure. A larger flash hole allows pressure to equalize faster. The size of the hole has nothing to do with the amount of pressure on either side, only the rate at which it can equalize.

Jimro