Home Forums Reloading Big Game Rifles Cratered and Pierced Primers - Advice Needed

The copper crusher system was designed to give results in PSI, and at lower pressures, it does pretty well. When piezo measurement gear became available, it was found that at higher pressures the copper crusher system seriously underestimated PSI. Still, back in the day, copper crusher numbers were commonly reported in PSI. P O Ackley's book is full of "PSI" numbers that were produced on a copper crusher system. If you see an old standard or number, it's hard to tell whether it's from the old system or the new one, since both are reported in the same units.

The military did not use the SAAMI copper crusher system. They had their own way of doing it. Military copper crusher numbers are not the same as CUP.

Exercising a bit of Google-fu: SAAMI puts the piezo transducer in the middle of the cartridge and rests the piston on the cartridge case. CIP in Europe drills a hole in the cartridge case so that the piston is in contact with the gas, with no brass in the path. NATO EPVAT puts the transducer at the mouth of the cartridge. The US military used the SCATP method, which is similar to SAAMI.

So, there you have four different piezo methods, and at least two different copper crusher methods. Small wonder it's confusing.

Now, is the 223 loaded to the same pressure as 5.56? I have believed that they are not. However, in light of today's exercise, and the fact that brass in the pressure path reduces readings by about 5-7000 PSI, I suspect that Ramshot's 5.56 loads might be in error. It seems possible that they have used the CIP number and the SAAMI test procedure.

So the definitive answer will probably come from someone chronographing American Eagle 223 ammunition vs. American Eagle 5.56 ammunition. They are both made at Lake City, and if anyone understands military vs. SAAMI tests, it would be them.

The military did use the copper crusher system of taking chamber pressure. If you look at military SCATP standards it simply states that SAAMI standards will be used for taking chamber pressure readings.

And as I stated earlier I have the milspec requirements for commercial contract ammunition made for the military. And the requirement lists 52,000 cup or 55,000 psi for 5.56 ammunition.

The only difference between the .223 and 5.56 are the throats. Now look at the first information at the link below for my Savage .223 throat that is longer than the throats in my AR15 rifles.

HOLLIGER ON .223/5.56 CHAMBERS (Savage .0566 and AR15 .0500 throat length)
http://www.radomski.us/njhp/cart_tech.htm





The throat in my Savage is big enough for the M855 cartridge with room left over for the Savage company lawyer. Meaning its the shorter throats that will cause the pressure spike when firing 5.56 ammunition.

And you do not need to test any ammunition yourself, it has already been done, and all you need to do is read.

5.56 vs .223 – What You Know May Be Wrong
http://www.luckygunner.com/labs/5-56-vs-223/

That Lucky Gunner article is very helpful. Thanks for posting.

The author makes the point that he used two different 5.56 chambers during testing, and his first pressure graph does not stipulate that he used the same FN chamber for comparisons of 223 and 5.56 pressures. But from the context, it appears that he probably did.

If so, 5.56 is loaded to higher pressures than 223. That is what I had believed, but started to question in light of my recent suspicion that the Ramshot used CIP/NATO spec numbers and SAAMI test methods, which is a no-no.

The one big error I see in the Lucky Gunner article is that he did not appear to control barrel and ammo temperature. When I do strain gauge measurements, I stick a thermocouple to the barrel just ahead of the receiver. That gets rid of a substantial amount of measurement system error.

I have a note in to Ramshot. Maybe we can get some clarification from them on how they did their data.

Back in '02, when I did my article about converting CUP and PSI, the 223 Rem 55,000 PSI:52,000 CUP data pair was an outlier that did not conform with the rest of the data. Since it was the oddball of the data set, I took it out. In general, 55,000 PSI is equivalent to 48,300 CUP. I have no idea what kind of jiggery pokery produced the 52,000 number.

Anyway, although we're having great fun, we've drifted far from the original question.

OK, one last bit of info... then I gotta go earn a living.

Ramshot wrote back:



So they are not mixing CIP/NATO numbers with SAAMI test procedures.

5.56 is loaded hotter than 223, and it's OK. The snail is on his thorn, God is in His heaven, and all is right with the world. Well, except for our politics....

When you fire a 5.56 M855 cartridge in a military chamber with its longer throat the chamber pressure is 55,000 psi.

When you fire a civilian .223 cartridge in a civilian chamber with a short throat the pressure is still 55,000 psi.

Meaning military 5.56 ammunition is not loaded to higher chamber pressures. "BUT" if military ammunition is fired in a civilian short throated .223 the chamber pressures will be higher. And the throats are what cause this change in pressure readings. And the European CIP considers the .223 and 5.56 cartridge to be one in the same.

The SAAMI interchangeability warning between the .223 and the 5.56 did not come out until 1979. And it was at this time the military introduced the M855 cartridge and M16 rifles with a longer throat.

The SAAMI sets guidelines for chamber dimensions and the gun manufactures are free to change chamber and throat dimensions as they see fit.

I can load my Savage .223 hotter than listed loads in reloading manuals because it has a longer throat than either of my AR15 rifles.

And the max load for the .223 with 55 grain bullets in the Hornady manual is 23.2 grains of H335. And the max load for 55 grain bullets and H335 in the Sierra manual is 27.5 grains.

I will take a wild ass guess and say the difference in these two .223 rifles is throat length. And a good reason why they say to start low and workup when reloading.

Now look below at all the different throat lengths and diameters. My off the shelf factory Savage .223 has a .0566 length throat the same length as the PTG and JGS NATO chambers. And its the .0250 length throats that will cause the higher pressures and possible problems. And not by people guessing about how the pressure is measured in what type chamber.

That sounds reasonable, within the limits of measurement precision.

But you are confounding two variables, throat length and cartridge load. That needlessly confuses the issue.

A simpler way of stating it is, for any given chamber, 5.56 loads will produce higher pressure and velocity than 223 loads.

Throat length is a separate variable. Shorter throats produce more pressure and longer ones produce less, all other factors equal.

If the Lucky Gunner author had been just a trifle more clever he could have done a balanced experimental design and cleanly separated those two variables.

And I do think the issue is a bit overblown. When I was working on an M855 problem at Lake City, we ran thousands of rounds heated to 150-160F, with the rifles at the same temperature. We weren't testing MV or pressure, but those temperatures had to be producing some serious out of limit conditions. We had no problems. I suspect that the SAAMI spec may be pretty conservative compared with other cartridges.

I suspect you are right.

55k PSI is pretty anemic in a modern rifle.

Good discussion. Interesting points have been brought up that beg for definitive answers. I want to be right, but I'm not so sure I'm really that close. I'd like to see all these disparities resolved, but simply in the interest of truly knowing, which isn't the same thing as believing. You guys have a great evening.

Let me piggyback on what has been an interesting thread here if I may. Ramshot moved the target on me. I have an older Ramshot loading pamphlet. It lists a max load of TAC in 223 (not 5.56) pushing a 60 grain bullet at 26.7 grains and a starting load at 25.4. I split the difference and built some loads with 26 grains using Remington 7 1/2 primers. I haven't fired any yet. Today I was skimming TAC loads on the Ramshot download and it lists a max charge of TAC pushing a 60 grain bullet at 24.8. Similarly I built some loads using 50 grain bullets and those loads too are beyond current Ramshot max loads. My launch platform is a Remington SPS.

I spent a while looking at TAC loads on various forums and have found some that show my loads as OK and have found some that show my loads as over max. Any thoughts?

Nosler also lists 24.8 grs TAC with 60 grain bullet rem 7 1/2 primer. So its your call. personally I would load up some lighter charges and work up and see what happens. Again its your call.

Paul, I'd start with the latest Ramshot online loading manual. They provide data for both .223 and 5.56 loads. Keep in mind, bullet selection matters. As an example Hornady Vmax typically have a greater bearing surface then a Nosler Ballistic tip of the same weight. Consequently, if I work up a load with NBT's, I'll back off a grain if I switch to the VMAX.

My apologies, I stepped away from this project for a while and neglected to see that there was still ongoing discussion here.

I searched around a bit and came to the same conclusion that I should try a different cup thickness. One of the sources was the James Calhoon article that I believe is also the source of one of the charts you posted. http://www.jamescalhoon.com/primers_and_pressure.php

This past week I had a chance to make some new loads and to swipe by buddy's new magnetospeed chronograph. I used the same mid-range 556 load (according to Ramshot data) that was causing cratering, but I loaded them with CCI 41 primers. With the thicker cup I got zero cratering, primers that still had a radius on the edges, and groups under 3/4" at 100 yards. When I put the magnetospeed on the barrel I got readings of 3090, 3097, and 3095...which is exactly what I had expected (and hoped for) based on the pressure that should be there.

Thanks again for the advice. These loads will only be used for hunting. I wanted the extra velocity of 556 pressure to make sure that the Barnes TTSX opens up out to 300 yards. All of the plinking and practice will be done with my usual 223 reloads...which are mild and do just fine with CCI400s.