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Lake City .223 or 5.56 brass?

27K views 48 replies 11 participants last post by  The Expert 
#1 ·
HELP!!! Will someone answer this for me. I have been swagging military brass. I have noticed that the lake city brass has the NATO symbol on some and not on others. What is difference between the two cases? Are they both 5.56 cases or is one .223. Thanks Fin
 
#3 ·
so all are 5.56?
 
#4 ·
Or they are all .223.


Again, just to be repetitive, again, one more time (this isn't the only message board).

.223 Remington and 5.56 ARE ONE AND THE SAME CARTRIDGES.

The ONLY cartridge dimension specification that exists, is for .223 Remington. I have looked, I have challenged others to look, for a 5.56 spec cartridge dimension set. None found.
The 5.56 is the metric, military designation of the cartridge as it was adopted by the US military back in the 1960's.
.223 Remington is the civilian designation of the cartridge as it was released to the public for purchase.
They use the same dies.
The have the exact same maximum pressure limitations (something around 55,000psi without looking it up).

The ONLY difference, in current times, is in the rifle chambers, and the only difference THERE is in the cutting/shaping of the rifling Leade, the throat.
This aspect of the chamber has been CHANGED due to recent popularity of the very heavy bullets in current mil. use. The rifling moved away from the chamber slightly
The 50-55gr bullets in the 1968 M-16's did not use a different chamber throat as they were a mil FMJ version of the civ. cartridge.
 
#5 ·
Lake City marks its cases differently for different purposes. Those 5,56 cases marked with "NATO" mark are for official US ( Nato) Military use; those without the Nato mark are for Military Aid etc to Non-Nato countries. Of course, they can become mixed, even in US Use.

The Specs are the same....a Military case is a Military case...and whilst the Case outside dimensions are the same ( 5,56 vs.223) the Case weight and internal volume are different...the Military 5,56 case is heavier. ( and tougher) than the Civilian .223.

Regards,
Doc AV
 
#6 ·
About 10 years ago my friend bought a case of 40 S&W, each case was marked "LC". The box said Lake City, but it wasn't lake city arsenal, a unrelated private company like Lake City maufacturing or something. Maybe they made more than 40's?
 
#7 ·
Thank you Docav, that was exactly the answer I was looking for, and I appreciate your positive reply.
Fin
 
#8 ·
Ran into this about .308 vs. 7.62 NATO. Not really relavant to .223, but he touches on the marks on the bottom. I would assume from reading it that if not marked with the cross in a circle, then it isn't "certified" to be NATO spec. Can still be 5.56 though.

http://www.cruffler.com/trivia-June01.html

Also similar to that article 5.56 brass has extra thickness in it, which means the powder capacity is reduced. This can make a safe load in a .223 commercial case unsafe in a 5.56 case.

There are differences as well in maximum allowable pressures between 5.56 and .223, and minimum and maximum chamber dimensions that can make shooting a 5.56 round in a .223 chamber very unsafe.

I have a ar-15 I shoot and have searched extensively for info between the two cases but as has been said before, I haven't found any dies or reloading data specifically made for 5.56 rounds.
 
#10 ·
There are differences as well in maximum allowable pressures between 5.56 and .223, and minimum and maximum chamber dimensions that can make shooting a 5.56 round in a .223 chamber very unsafe.

I have a ar-15 I shoot and have searched extensively for info between the two cases but as has been said before, I haven't found any dies or reloading data specifically made for 5.56 rounds.
Have you taken into account that the US Mil. spec for 5.56 pressure and the SAAMI spec for .223 pressure are measured at 2 DIFFERENT locations, by 2 different methods?
SAAMI has.
The mil. method (a direct-pressure-impingement through a hole in the barrel at the case mouth), if measured the SAAMI way (piezoelectric strain gauges against the side of the brass case), develops the SAAMI pressures. Same-same, no difference.

The short throat of a .223 chamber, if heavy-bullet 5.53 ammo is chambered, will jam the bullet into the rifling, spiking pressure very high.
"Old" 5.56 from the 'nam period (later 60's, most of the 70's, prob. well into the 80's) will not do this due to it's 55gr bullets.
THIS has blown up more than a few .223 rifles.
There is NO DIFFERENCE in the chamber machining specifications between the 2 cartridges.

Hornady and Sierra both (in my manuals) have 5.56 data specifically, in addition to and separate from, .223 Remington data.

The .223 data stops at about 55gr bullet weight or so 40-55 or so.
The 5.56 data goes up to around 80-gr or so due to current popularity.

Those manuals also have specific data for M1 Garand as separate from 30-06 due to it's gas-system specific requirements.
 
#9 ·
Quote:
""There are differences as well in maximum allowable pressures between 5.56 and .223, and minimum and maximum chamber dimensions that can make shooting a 5.56 round in a .223 chamber very unsafe.""

Can you give one example of a factory produced round to back this up?

While the peek working pressure of the 5.56 Nato is slightly higher than the .223 Rem. it is no where near "very unsafe" !!
Your are going to have to post some proof on that one.
Motor
 
#30 ·
Wow, lots of comments since I was on! OP sorry, seems your thread has gone awry a little, but lots of great info.



I don't have any hard mil-spec sheet that says this. I have read it before, and seen it written since. In fact in reading this thread on the accurate shooter link above there is this line:

"While the external cartridge dimensions are essentially the same, the .223 Remington is built to SAAMI specs, rated to 50,000 CUP max pressure, and normally has a shorter throat. The 5.56×45 is built to NATO specs, rated to 60,000 CUP max pressure, and has a longer throat, optimized to shoot long bullets."

Now does that make it gospel, no. Please see the link from Zippy to read it in its entirety. It does bother me that I can't find an actual spec, but in my work I have found that you have to pay to view many of the relavant specs out there, making them hard to find.


Have you taken into account that the US Mil. spec for 5.56 pressure and the SAAMI spec for .223 pressure are measured at 2 DIFFERENT locations, by 2 different methods?
SAAMI has.
The mil. method (a direct-pressure-impingement through a hole in the barrel at the case mouth), if measured the SAAMI way (piezoelectric strain gauges against the side of the brass case), develops the SAAMI pressures. Same-same, no difference.

The short throat of a .223 chamber, if heavy-bullet 5.53 ammo is chambered, will jam the bullet into the rifling, spiking pressure very high.
"Old" 5.56 from the 'nam period (later 60's, most of the 70's, prob. well into the 80's) will not do this due to it's 55gr bullets.
THIS has blown up more than a few .223 rifles.
There is NO DIFFERENCE in the chamber machining specifications between the 2 cartridges.

Hornady and Sierra both (in my manuals) have 5.56 data specifically, in addition to and separate from, .223 Remington data.

The .223 data stops at about 55gr bullet weight or so 40-55 or so.
The 5.56 data goes up to around 80-gr or so due to current popularity.

Those manuals also have specific data for M1 Garand as separate from 30-06 due to it's gas-system specific requirements.
I did know they used two different specs, which does make me doubt some of the info on accurate shooter. But I have never seen SAAMI write anything saying they were the same, in fact I have seen this missive out on several places, but can't (again irritatingly) find it on SAMMI's own site.

"
Here is their 31 January 1979 release, with some minor errors corrected: "With the appearance of full metal jacket military 5.56 ammunition on the commercial Market, it has come to the attention of SAAMI that the use of military 5.56mm ammunition in sporting rifles chambered for Caliber .223 Remington cartridges can lead to higher-than-normal chamber pressures and possible hazards for the firearm, its user and bystanders." Tests have confirmed that chamber pressures in a sporting rifle may be significantly higher in the same gun when using military 5.56mm ammunition rather than commercially loaded Caliber .223 Remington cartridges, according to SAAMI. SAAMI points out that chambers for military rifles have a different throat configuration than chambers for sporting firearms which, together with the full metal jacket of the military projectile, may account for the higher pressures which result when military ammunition is fired in a sporting chamber. SAAMI recommends that a firearm be fired only with the cartridge for which it is specifically chambered by the manufacturer."

Link to full quote: http://www.rainierarms.com/?page=shop/basics (Bottom of Page)

I am by no means the experts of experts just repeating what I have seen and heard from what I hope (or at least currently believe) to be decently reliable sources.

My Hornady 8th edition handbook lists .223 data, and then .223 service rifle data, but does mention in the blurb on the front the 5.56 cartridge, which I find confusing. Why not call it the 5.56 service rifle data section.

finfin as others have stated, when using 5.56 brass, I work up a new load from scratch starting with minimums. That way I can ensure the load is safe in that brass.

Apologies if I offended anyone by my earlier post, we are all learning together I think.
 
#11 · (Edited)
FinFin .. folks are talking apples and oranges here ... The circle with the cross, "The Nato Mark" just means the ammo, as originaly loaded, meets Nato specs as to bullet weight , velocity, and pressure for one of the standard offical Nato loadings, and will shoot within Nato specs using the sights on any official Nato weapons regardless of what Nato country made the ammo or the weapon.

Doesn't mean it is maxed out in pressure by any one standard or another, doesn't mean it is .223 or 556 or 9 mm or 7.62 x51 or .308, which all have , if they meet Nato specs, the mark that says they meet Nato specs, the circle with a cross. The specs are slighly different for tracer or AP or Ball ammo in all Nato offical calibers, because different types of bullets have different weights , need diffrent types of powder loads etc but if they meet Nato specs for Nato ammo they get the Nato Mark.

Just talking .223 /5.56 here for a minute , one can assume that Nato ammo is safe and within the proper milspec to fire out of any Nato approved weapon in that caliber. Lots of different .223 out there can't get the Nato mark for a variety of reasons , uses a expanding bullet outlawed by various Law of Land Warfare treaties, lot of .223 varmit ammo uses powders that have pressure peak at the wrong place in the barrel to be within spec on Nato semi or full autos, great for .223 bolt action varmit shooting though, maybe uses a VLD 75 grain longrange competion bullet that won't fit in a magazine. Doesn't matter why, not in milspec, doesn't get Nato mark.

Nato ammo has a spec sheet and a "M" designation, regardless of caliber.. 120mm Tank rounds that meet Nato standards have the little Nato mark.

That all said, milspec brass is a little heavier in weight and thickness because Nato said that is how they want it in the contract.. I assume that is as an addition safety measure, or maybe so the brass will still be shootable after being dropped out of a helicopter, or maybe to slow cookoffs in a burning vehicle... not that it really matters.. you meet the spec or you lose the contract and don't get the Nato mark.

And all semi and full auto's have some restrictions on what powders and loads will work in them , not all as strict as the requiremets for the Garand, some just need enough pressure and power to function the action, but ammo that won't function the action in a semi , will work fine in a bolt gun. Ammo that could wreck a semi can be safe in a bolt gun.

Garand is a good example though, you can use bullets up to 170 grain with the right powders and not hurt the rifle .. but if the Ammo says it is M2 Ball 30-06 it is a 150 grain spire point flat base lead cored cupronickel jacketed bullet being pushed by enough 4895 powder to make the bullet go 2740 fps. There are IIRC some very limited authorized substitutions to that spec. The spec ain't near max allowable pressures for the cartridge itself, it is delibertly downloaded from earlier M1 ammo spec ( not to be confused with M1 rifles of various types) because of the cost of having rifle ranges that are big enough to shoot M1 spec ammo safely, and M2 30-06 made to exact US specs will never have a Nato spec mark because 30-06 is not a Nato approved caliber, and thus Nato has no spec for 30-06 to meet to get the mark.
 
#14 ·
Thank you for your expertly written synopsis, Ammosgt . So that leads me to my next question. Drum roll please. What do I do with all the military brass I own? Can I use a reduced load for the .223 safely using this brass?
Thanks Fin
 
#15 ·
You are welcome. You are going to have to be a bit more specific on what you mean by "reduced load" and what powders you plan on using.. some powders are better than others for a reduced load, and some powders cannot be reduced safely ( H-110 comes to mind, but H-110 is not used in .223)

General rule of thumb is that military brass is thicker than commercial brass, this can be confirmed by weighing and finding out how much heavier it is than any commercial brass you currently have loads worked up for.. if it is indeed heavier than the commercial brass you are currently using then you reduce your starting load by an additional grain or so over and above the standard reduction of 10% of ublished max load for that weight bullet and powder , and work the load up from there. remembering the general safety rule that anytime you change a component from a known load , you start all over and work up from at least 10% below max. That includes changing to a different brand or even headstamp of brass. This is for safety as well as accuracy.

If it is military brass it will, in all likelyhood, have a crimp holding the primer in, you will have to remove the crimp before you can reprime.

Keep in mind, if you are using the brass in a semi auto, you need to full lenght resize which will give you approximately 5 reloads before you need to scrap the brass... 5 is a generic typical life span, brass my last longer with light loads and not last the full 5 with heavy loads/ near max.. at any rate you must inspect the brass of excess stretching and incipient cracks each and every time before reloading. You also need to develop some way of marking the brass or otherwise knowing how many times it has been reloaded.

Any good reloading manual will have full instructions on how to reload and how to inspect brass and what to look for and the most likely places to find it. ... there are several threads on this forum on the pro's and con's on various methods of removing a primer crimp.
 
#18 ·
izzy good catch, my bad, he did say he was swaging primers.. I forget why I left my study and went to the kitchen again. But I am sure he was asking about reduced charges.. and that can mean many things... and military brass... hopefully we will have some specifics from the OP by morning...
 
#19 ·
While I do not laod .223, I load .308 and use mil. 7.62x51 brass exclusively.

In this cartridge, I have found the same velocities with roughly 2-gr less powder to be required due to the difference in internal case volume.

Long ago I took a 166gr Rem. case and a 184gr LC case, filled both with a powder charge (like, 48gr of WW748BR) and looked at the difference in filling height (the sole purpose of this).
There was a quite marked difference in the amount of room left in the case, both charges had been weighed, so were within a few granules, so had the same volume.
Spherical powder I used negates any "varied filling" common to stick powders.

The LC case was full TO the base/bottom of the neck.
The Rem case was full pretty much to the base/bottom of the SHOULDER.

Similar results I would expect from .223/5.56 brass BUT (like so many things on the 'net), there are claims that wide brass variance among the different makers of 5.56 brass really negates this and throws case volumes all over the place.
 
#21 ·
Adding to Oldstuffers excellent advice, If you are loading for a AR , you would want to keep the loads close enough to standard loading to properly and reliably function the action. If you want to go cat sneeze or light cast load you need to get a bolt action.
 
#22 ·
Quite correct, and very often a gas-action autoloader will NOT FUNCTION at the lowest, the "minimum", starting loads.

Knowing this and my rifle's behaviors, which decidedly dislike the light loads accuracy-wise, I now start about mid-way up the charge range and go from there.
 
#23 ·
Well i am glad I have started a good conversation between members. I am reloading only civilian brass right now, I have a boat load of military brass that I DO NOT want to give to MOTOR :laugh:. As for my question on reduced loads, I was specifically talking about military case used in a ar semi-auto with less powder (i use primarily varget) so 1) brass is not wasted, all has been swagged, 2) where is the starting point in loading these safely( i do not want to be a statistic on a govt. chart i.e. oldstuffer's story) ammosgt gave me a great start on that portion, 3) I am more concerned with accuracy then velocity, 4) I just want to enjoy the process and have a accurate and safe load to out shot my father in law's ar. And the bottom line is I just want to have a blast, no pun intended.

This is where I am at in the reloading process.
Brass has been swagged, sorted by mfg, fl resized, cleaned of lube, pockets cleaned, trimmed and measured for col, I have chosen to start with my Federal .223 cases about 400, I plan on using varget powder, also I plan on making 10 rds for each lowest start point and adding a half grain till I get to max . I will be using 53gr sierra match bthp. Hopefully this weekend at the Dulles show I will pick up a big box of 69gr sierra match bthp. Also some tools like a comparator and maybe a headspace gauge.
As always if I have forgotten anything, please let me know.


Thank you again fellows for all the help
Fin
 
#24 ·
Hey guys. Have this to add to the confusion. I am seeing more and more commercial "".223"" brass that IS CRIMPED. I recently purchased some brass from a member here that is a range warden and he confirmed this observation.

Fin's comment about "reduced loads" did need defined. I thought he my have been speaking of "backing off" because of the mil spec case but waited to see for sure.
Fin. You can use the "start load" safely with either case commercial or military. Like the others said the difference is usually no more than 2gr in change equivalent.
Motor
 
#25 ·
As noted finfin, you can merely start with the "starting loads", they should be plenty safe, yet, may OR MAY NOT function the AR's gas system.

You should find similar velocities (and thus pressures) as the "full-power" 55,000psi loads at between 1 and 2 grains less powder than in civ. cases.

Weigh some civ. cases to get a baseline and then weigh some GI cases, see exactly what you are dealing with.

Once both civ. and mil. cases are sized the same, trimmed the same, any difference in weight translates to inside volume (because the outside is the same size).

Same weight equates to same volume, heavier case equates to more brass = less empty space volume = slightly more pressure with the exact same load parameters.
 
#26 ·
What they said .. plus "reduced" load usually means going MORE than 10% below max, 10% less than max being a starting load not a reduced load. and 10% usually will not only NOT be accurate but it also will plague you with jams or misfeeds.. work up to where you get reliable function , clean ejections and reliable feeding and then work for accuracy.
 
#27 ·
Guys,
Over this past few days we have processed about 1000 .223/5.56 cases. I just got through weighing some sample lots and what I am finding is a maximum of only 7 grains and that is few and far between. Last year I went through about 400 commercial Remington cases. The average case was around 92 grains and the spread was around 90 to 94. The heaviest military case I found tonight was 97gr. Is what ever this possible 7 grain difference in brass weight which may result in a corresponding lower case capacity really enough to cause concern????

I haven't pulled out The Machinery Handbook to look up the weight per cubic inch of brass yet but 7 grains of brass can not make that much difference. Maybe in the 7.62x51 the difference was more hence the reputation mil. vs com. I don't know. I think I will need some volumetric proof before I buy into it for the 5.56 vs .223.
OH yeah. Apples to apples. Federal commercial (with crimp and .223 Rem on head stamp) VS Federal Military (with FC and year on head stamp). NO DIFFERENCE in weight. At least in what I have. They all averaged 92 grains as did most of the LC I have both with the circle and cross and without.
Motor
 
#29 ·
Motor, I would call those cases "weighing pretty much the same".

I would break them into 2, or perhaps 3, groupings:

90-92gr, 92.1-94gr, and 94.1-97 gr.

This is where an elec. scale is of great value over a beam.
 
#31 ·
Thanks zippyhuntin and viking traveler, excellent threads. i was not offended viking traveler. Motor when you sort your brass by weight do you use the higher weight cases for the lower of the load and vice versa? Thought of that as I was trimming brass today.
Thank you guys
Fin
 
#35 ·
Motor when you sort your brass by weight do you use the higher weight cases for the lower of the load and vice versa?
Thank you guys
Fin
I do not alter the load specifically to the case weight.

I do like motor, assemble a group of close-weight cases, and develop whatever load I desire in those cases, mostly my hunting ammo, again, like Motor, any possible gains from this "uniformity" of the cases, is welcomed, not a hard thing to do (match a batch of 50 cases).

If/when I run out of those cases, IF I have , say, another group of 50 the same weight, I test the load. If acceptable, I use it. If it needs "tuned", I do so.

If I next use a slightly lighter set of cases, I test the load, tune as need be.

If, conversely, I use a slightly heavier set of cases, I drop the load SLIGHTLY, test, tune as need be.
 
#32 ·
Fin,
I only weighed my brass to put together 2, 50 round lots that were +/-.5 grain for my hunting ammo. I hunt varmints and any accuracy gained is always welcome.
Besides that, I honestly don't pay any attention to it. Most of the loads that I shoot for fun are at least a grain under max and there is no way, (in you know where) that what ever volume in case capacity 7 grains equivalent of brass weight makes is going to cause any significant increase in pressure. And 7 is the extreme that I have found. If your worried about it weigh some cases and work up your load with the heaviest. Then you will always be at or below that pressure.
Like I said in my earlier post. I want to see some volumetric proof. Rim design, primer pocket shape and depth, and I'm sure if you looked very close there are other things that will effect case weight and not capacity.
One thing I would not do. Take a max load that was worked up in a commercial case and load it in a military case. But any time you are using a max load you shouldn't change components anyhow.
Do a little experiment. Measure a .223 case. Then trim it until it is 10 grains lighter. Then measure it again. See what the difference is. You then can use the formula for displacement to see how much you decreased the capacity. Keep in mind that doing it this way **IS** actually having a direct effect on capacity.

Motor
 
#33 · (Edited)
SAAMI points out that chambers for military rifles have a different throat configuration than chambers for sporting firearms
Yes indeed. It is the throat configuration, very short on a commercial .223 Remington chamber, which is very much incompatible with a current-issue 5.56 ammunition cartridge loading.

The un-rifled "throat" is significantly SHORTER in .223 Rem, and the end of the rifling that is angled from throat to full rifling height is much shorter/steeper.
Conversely, the 5.56 throat has a longer un-rifled area and the rifling is cut flatter and longer making a more gradual entrance, and more effective "room" for a bullet's sides to stick foreward.
The un-rifled section of the 5.56mm throat is specified to be .073" long forward of the case neck.
The .223 is .040", just a bit over 1/2 as long.
The distance the rifling is angled for bullet entry on the 5.56 throat is specified as 0.164" long to full rifling depth, a 0.427 degree angle.
The distance the rifling is angled for bullet entry on the .223 is spec'd at 0.045" long to full rifling depth, a 3 degree-10 minute-40 second angle.

This makes the entire throat section from maximum forward case mouth to full rifling engagement a mere 0.085" long. Between 1/16 and 3/32" long.
On the 5.56mm throat, it is 0.237", very nearly 1/4" long throat, 2.7 times longer.

lessee if the picture transfers:
Nope.
Here's a message board thread that STARTS with a chamber cutaway picture that shows this throat difference:
http://m4carbine.net/showthread.php?t=55149

Many other good machinist drawings show the comparisons as well.

If you look on SAAMI, you also will not find specification for 7.62x51mm, unless you look up the specifications of .308 Winchester. Same reason, same cartridges.

The pressure difference issue:
NATO EPVAT test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI.
The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ.
This difference in measurement method accounts for upwards of 20,000 psi (140 MPa) difference in pressure measurements.
This means the NATO EPVAT maximum service pressure of 430 MPa (62,000 psi) for 5.56 mm NATO, is reduced by SAAMI to 55,000 psi (380 MPa) for .223 Remington.
In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO.
 
#34 · (Edited)
The biggest "hitch" out there in the 'net when this discussion gets into 7.62 is that there are several copies of a MAJOR typo on the internet.

The PSI specification of .308 Win. is, if I remember correctly (haven't looked at SAAMI just now (time to eat)), 62,000psi Maximum Average Pressure.
The "older" CUP specification (in more than a few of my loading manuals), is 55,000CUP.

There is a major typo that has people thinking, and quoting, and pasting onto message boards AND VARIOUS WEBSITES (that really ought to research things deeper), 7.62x51 as a 55,000PSI cartridge, which it is not, it is a 55,000CUP cartridge (a major difference, 55,000CUP is NOT equal to 55,000PSI).

The one time I found an accurate spec. for the GI ammo, was 60,000psi, which, if you consider some of the very hot areas it has to be fired in without being seriously overpressure, is perfectly "more of the same" as .308.

There is no real "math formula" to do a CUP-PSI conversion, it is different @ 50,000CUP than it is @ 40,000CUP, than it is @ 30,000CUP, you just have to dig around until you can find both specs on the same cartridge.
 
#36 ·
Here is more than most people will ever want to know about measuring cartridge pressures:

A May 1999 trades article.

http://archives.sensorsmag.com/articles/0599/0599_p93/index.htm

Although ANSI and SAAMI (Sporting Arms and Ammunition Manufacturers Institute) document the conformal sensor as a Voluntary Industry Performance Standard for ammunition pressure measurements, NATO still uses the direct gas measurement method with a sensor located at the case mouth or over a drilled cartridge.


The direct-read method the mil. uses:
Quartz Sensors. Ballistic quartz pressure sensors have been used since the mid-1960s in both research and production testing for measurement of ammunition and gun barrel pressures. These sensors are installed at either a case mouth location or over a drilled cartridge and measure gas pressure directly from the burning powder. One advantage of this method is that a single sensor can be moved from barrel to barrel to fit a machined recessed mounting port in a variety of calibers. However, both case mouth and drilled cartridge installations have inherent limitations, especially with the gas passages associated with recessed mounting.

To protect the quartz sensor from flash thermal effects, an ablative diaphragm coating must be applied and frequently replaced. Another disadvantage is that the recessed mounting port affects the operation of both the gun and the gas dynamics of the measurement process. With smaller caliber ammunition, such as .22, .38, and 9 mm, the sensor's recessed mounting port adds significantly to the volume inside the cartridge and always results in lower pressure readings. Furthermore, the gas passage in front of the sensor may become restricted or plugged and require frequent cleaning.

Drilled cartridge location. The shell case must be drilled and the hole in the case taped to keep powder from falling out. During installation, the hole in the shell case must be carefully aligned with the gas passage leading to the sensor. Preparation is clearly a time-consuming process. When the gun is fired, there is always some gas leakage around the cartridge case. This leakage, combined with the added gas passage volume to the sensor, results in a lower-than-actual pressure reading.

Case mouth location. With this method, the sensor does not actually detect the pressure until after the bullet leaves the shell case and passes by the gas passage to the sensor. The pressure measurement therefore takes place after the maximum pressure is reached inside the cartridge case. Furthermore, copper or lead material from the bullet that is shaved off in the gas passage can restrict or clog the passage, affecting not only the measurand but also necessitating frequent passage cleaning.
The ANSI/SAAMI method:

The Conformal Pressure Sensor


The conformal pressure sensor, designed in cooperation with members of SAAMI, is intended for semipermanent installation in a test barrel for rapid-fire production testing of ammunition. It incorporates a curved diaphragm machined to match a specific gun chamber diameter and taper at a predetermined location. Installed in a test barrel, the diaphragm can be looked at as an integral piston that acts on the quartz sensing element due to the exploding gas pressure generated in the cartridge. It has no effect on the operation of the barrel or the measurement process.
A set of washers of variable thickness is supplied to help adjust sensor depth so that the diaphragm is mounted flush with the chamber walls. A borescope is used to inspect the installation to ensure that the sensor curvature conforms to the chamber walls.
Operation. When the cartridge is fired, the shell case expands and comes into contact with the sensor diaphragm. A uniform ring-shaped pattern of the conformal diaphragm is embossed on the cartridge case. The pattern has a fine, even outline indicating where the shell case expanded during contact with the diaphragm. A raised pattern on the shell case indicates that the sensor diaphragm is not flush with the chamber walls. A gouge on the case indicates that the diaphragm is not properly aligned with the gun chamber wall and is cutting into the cartridge case.
Test measurements can be made as rapidly as the ammunition can be loaded and unloaded. There are no gas passages to clean or ablative diaphragm coatings to apply, and the sensors' longevity means they do not have to be replaced in the middle of a test lot. Feedback from the field indicates the conformal sensor, when correctly installed, outlasts the test barrel.
 
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