What High Pressure Looks Like

[Slamfire]

Sometimes new folks don’t know what high pressures look like. Last week I had the privilege to be squadded with some the finest shooters in the world at the Camp Perry National Matches. I picked up brass from both the USMC rifle team, and the Army Marksmanship Unit (AMU). These gentlemen were shooting match quality M16’s.

Both of these elite shooting teams shoot commercial loaded ammunition out to three hundred years. The AMU armorer told me they were using 72 Bergers out to 300 yards, and the 80 Sierra at 600 yards. This year, the Marine I was squadded with told me that the ammunition they were using all the way back to six hundred was Factory Black Hills Ammunition. Loaded to USMC specifications. If my recollection is right, the USMC was using 77 Sierra’s at the short range. Of course using 80’s at the back. There was a slight departure from the past as both the AMU and the Marines use to have their long range Ammunition loaded by their Ammunition Technicians. The AMU used to used new factory primed cases, the Marine Corp did this, and sometimes reamed the pockets and inserted the primers. I could not find an Ammunition Technician to talk to this year, undoubtedly they were under cover from the heat and the rain squalls. And I did not bug the AMU people around me, so I am not sure what their current ammunition practices are.

Their short range ammunition is fine, the brass is reloadable, but when you get to their long range ammunition both of these units load hot ammunition. The WCC cases are AMU long range, the BHA are USMC. As you can see, the case heads have flowed into the extractor hole, and there is evidence of gas leaking around the primers. Even though the primers are not all that flattened, the pressure is too high. You have to remember, primers lie!, they are not good indicators of pressure. Overall what you are seeing is positive indications of excessive pressure .

USMC Brass



AMU Brass



Both of these elite shooting teams have the financing to replace bolt heads, firing pins, and anything else on their rifles. For me, I can’t afford a new bolt face every couple matches.

This long range brass was unusable and I tossed it out.

 

[Harley Quinn]

This long range brass was unusable and I tossed it out.
*************

Did you follow it up a little and see if the brass flowed forward and made it longer at the neck? I know some of the over pressure items are a one time shoot.
But if the brass and primer are marked like that it could be other problems, as in not keeping your chamber dry and too smooth, so the cartridge moves back when fired??? I know they move back but not until fired and then going out the eject area.

Several things to look at, did you? The reason I ask is the primers are not that bad, IMHO, any other comments???

HQ

 

[Vern Humphrey]

Look at the ejector marks on the case heads! The AMU shooters have three assigned rifles per man -- one to shoot, one in the shop and one in reserve. And no wonder!

 

[The Bushmaster]

Now THAT is a sign of high pressure...!!!

 

[Harley Quinn]

Look at the ejector marks on the case heads! The AMU shooters have three assigned rifles per man -- one to shoot, one in the shop and one in reserve. And no wonder!
***********

I can also see the ejector marks, but the stamping is clear on the case and the primers are not slammed tight. I think it would be interesting to see them if they were in a bolt.
Like I am saying they are moving backwards from a slippery chamber wall I figure to help extraction and the out come is not as simple as it looks. Unless you are very well qualified and expert in the fact that they are at a higher pressure which seems not normal practice.

Maybe a heavier projectile for the distance or a tight crimp. I am not totally convinced it is more grains in the case. Oh well not a biggie.

Going to follow it up with an e-mail to Black Hills ammo. Funny things happen and are not always what they seem. But then again it could be all of the above

HQ

 

[Walkalong]

Yep. The primers look fine, except for the AMU brass primers and the flow around the pin in the fireing pin hole, but the brass tells the tale. You can see not only the ejector mark, but the brass flowing into the extracter cutout.

 

[Harley Quinn]

Yep for sure, it looks like two of them in the bottom picture might be from a different rifle. (wcc 06) Got some black around the primer and the indent is more severe, some gas escaped there

Hmmm

 

[Slamfire]

Did you follow it up a little and see if the brass flowed forward and made it longer at the neck? I know some of the over pressure items are a one time shoot.

Dude: I have all this Camp Perry fired brass that I have to size, trim, and remove the crimp from, I do not have the time to measure brass that I am not going to use.



Actually the AMU is firing lighter loads than around 2002-2003. Sometime around then I picked up AMU shooter's Troy Street's brass, (I was squadded next to him) the day before he won the 1000 yard Service Rifle Trophy . Out of 20 cases, fired at the 600 yard line, 17 had completely blown primers!

I remember discussing with an AMU shooter the next year that I thought their cartridges were too hot. This shooter informed me that their cartridges were not hot enough!. Well back at 600 yards, the Range Gods enacted their evil, this poor guy had a blown primer and it jammed his trigger mechanism. I remember him holding his lower in his hand and pounding it on the firing point, trying to dislodge that primer. When he reassembled everything and fired his next shot, the wind had changed and he shot an eight. At his level of competition, he was done for the day, might as well go home.

 

[Harley Quinn]

Dude: I have all this Camp Perry fired brass that I have to size, trim, and remove the crimp from, I do not have the time to measure brass that I am not going to use.

So you are pretty close to this I'd say.
I thought there was an e-mail to BHA, but alas not. Only phone and street # thought I'd send this link to um and see what they had to say.

The trim is the feature I was curious about. Since that is the overall I was mentioning.

HQ

 

[RexDart]

Both of these elite shooting teams shoot commercial loaded ammunition out to three hundred years.

Good Lord! If they're getting relativistic velocities, no wonder the brass is showing pressure signs.

 

[Slamfire]

The USMC does not tell the shooters what powders, powder charges, used in their ammunition. That is because too many civilians went home and copied the formula and blew up rifles. My shooter was told the velocity of his bullet, which helps him to figure windage.

His 600 yard ammunition was 200 fps faster than mine, fired in a 24" barrel. His was the standard 20" barrel. If I increase my ammunition charge by a little bit, I will have pressure problems. I have no doubt that their stuff would be overmax in my rifles.

The USMC and the AMU control the configuration of their rifles so that ammunition is interchangeable throughout the respective teams. They will use one type reamer for the team, barrels are all different makes, but they do what they can to ensure everyone can fire one type of ammunition. Still, there are variations, and it is possible that another USMC shooter's barrel would not have leaky primers.

As for the commerical ammunition shot out to 300 yards, in past years both teams shot Federal Gold Medal Match. For almost a decade the AMU shot 69 Sierra's in the Federal Gold Medal match. When the 77 Sierra came in, both teams tried that.

For those who discount factory ammunition, one of the Armorers told me "I don't know why we are not using the 69's, I set a number of national records with that." I have observed the rapid fire groups of AMU and USMC shooters and can tell you, premium factory ammunition will shoot perfect groups. Wish I had a camera which could show you the knots these guys shoot.

 

[solvability]

SF1 you think the temperature on the line - pushed the pressure over the top?


You going to B&G on Sunday - I got a new SW 686 to shoot on steel?

 

[Slamfire]

SF1 you think the temperature on the line - pushed the pressure over the top?

That brass was picked up by me off the firing line on Thursday. That day was a totally wet weather day. Violent rain squalls. Everything I had got wet. My scope fogged up. The Marine I was squadded with put his poncho over his gear, and just let the rain run over him. I don't like being saturated so I wore my poncho. I guess that is why I am a civilian. My recollection was that he shot a 196, and I shot a 189. He did very well considering he was blowing water out of his rear aperature. I thought I did pretty good considering I could not see the target frame for at least four shots!

Even though Camp Perry was running into the high 90's that week, the day that brass was shot, it might have gotten into the 80's, and those relays were fired in the rain.

The young Marine did tell me that in hot weather he had had pressure problems. You have to understand that these service rifle teams push that long range ammo to the limit. The service rifle shooters are supreb wind readers, having been taught by the best in the business, but even so the wind ballistics on a .223, even with an 80, is pretty insignificant compared to a 6mm or a 6.5. So they are trying to get the most out of the cartridge. And if that means they fire new brass once, well it is all part of the cost of doing business.

 

[shu]

"..he was blowing water out of his rear aperture." (!?)

perhaps he should have used his poncho to cover himself, as you did.

 

[Walkalong]

Actually the AMU is firing lighter loads than around 2002-2003.

Just more proof primers will lie. The fit of the firing pin to the fireing pin hole, the quality of the finish on the fireing pin, and the strength of the fireing pin spring all make a big difference on that little flow ring on the primer showing up.

 

[peterotte]

.....it could be other problems, as in not keeping your chamber dry and too smooth, so the cartridge moves back when fired???.....

.....they are moving backwards from a slippery chamber wall.....

Harley Quinn, I'd say that a rough chamber at those pressures would cause head separation! A gentleman did a software simulation of bolt face thrust with varying degrees of case to chamber friction and showed that the differences were small but that if case head separation occurred, the bolt face thrust would nearly double. He also showed that while a lubed case would reduce friction - particularly in a rough chamber - it did not reduce the friction that much. (Oil in the chamber will likely cause diesel detonation - a different kind of animal altogether).

It's most likely, those guys are using a strong primer to withstand the pressures. That would be why they don't show the same pressure signs the cases do. It would be interesting to see the case elongation associated with the case head pressure signs. Just measuring those fired cases won't tell much. You would need before and after measurements.

Regards
Peter

 

[Harley Quinn]

Harley Quinn, I'd say that a rough chamber at those pressures would cause head separation! A gentleman did a software simulation of bolt face thrust with varying degrees of case to chamber friction and showed that the differences were small but that if case head separation occurred, the bolt face thrust would nearly double. He also showed that while a lubed case would reduce friction - particularly in a rough chamber - it did not reduce the friction that much. (Oil in the chamber will likely cause diesel detonation - a different kind of animal altogether).

It's most likely, those guys are using a strong primer to withstand the pressures. That would be why they don't show the same pressure signs the cases do. It would be interesting to see the case elongation associated with the case head pressure signs. Just measuring those fired cases won't tell much. You would need before and after measurements.

Regards
Peter

Peter thank you for taking time to relate this information.

I am still wondering about the heavier bullet weight and adding powder. Both of those items will increase pressure ( I understand you know this just mentioning it).

It is a good discussion and I thank all for the information Nice insight into the "elite shooters" and their tricks of the trade. The 80 sierra is what design projectile? The reason I ask is it is going to take up move space in the case and pressure will rise there Hmmm this is a real tricky situation to say the least.

 

[FM12]

Well, all I can add here is that I once saw a program on tv highlighting the AMU. One tv shot showed a young soldier handloading on a Bonanza CO-AX press like I use. IIRC, he was loading 300 cal ammo. Gotta love those Bonanzas. Seems like that's what them Cartrights loaded on, out on the Ponderosa.

 

[Slamfire]

Well, all I can add here is that I once saw a program on tv highlighting the AMU. One tv shot showed a young soldier handloading on a Bonanza CO-AX press like I use.

Probably on History channel, probably "Tales of the Gun".

In Shooting Sports, about 1996 or so, there was an article on the USMC reloading. They were reloading for long range for the 308. There was a picture of a guy seating bullets on a Bonanza Co-Ax. Guess they like that too.

Another picture showed an Ammo Tech sorting Sierra Match Kings by weight!.

Previous LR ammunition I picked up from the Marine Corp, the Ammo Techs had reamed all the pockets to depth. I have no idea if they did flash hole trimming, but you never know. Absolutely no case neck turning. And all with new brass.

The last I talked with a USMC ammo tech, they were true believers in straightness. They want to get the runnout in the cartridges to nothing.

When you talk with the bunch, every couple of years you get a new bunch of guys, and they have a few new magical hoo doo's. From lubes to whatever.

Great Guys. You ought to meet them.

 

[peterotte]

....they were true believers in straightness. They want to get the runnout in the cartridges to nothing.....

My personal approach to straightness is to not resize. Instead, I use a paper sabot to hold the bullet in the case. I also lube the bullets by placing a smear of bullet lube on a cardboard wad that goes under the sabot. It seems to work quite well, particularly with the long necked hornet. The barrel stays shiny clean with no burnt powder particles left behind. I no longer clean the bore after a shoot. I do monitor it often in the damp climate I live in. So far, no rust. (Long storage will still gets Hoppes treatment).

Peter

 

[Vern Humphrey]

Seems like that's what them Cartrights loaded on, out on the Ponderosa.

As I recall, Hop Sing did all their reloading.

 

[redneck2]

Ever notice that the Cartwright's always wore exactly the same clothes for every single episode? Hop Sing was probably busy doing laundry.

 

[Harley Quinn]

Peter:
That is interesting about resizing. I can see that in a bolt action.
But this thread is about semi auto shooting Bullet, projectile, sabot are you using these as I believe they are as in rifles and shotgunsOr have you mixed them somewhat
Might just be the sunday morning cobwebs.

 

[Walkalong]

Wake up Harley

 

[peterotte]

Harley Quinn No, not cobwebs - I wasn't very clear. What I called a sabot is a little paper cup thingy made from paper hand towel that takes up the gap between the unsized case neck and the bullet to give it grip. I would not try this with an auto-loader as the bullet grip is much less than with a neck re-size. (It grips a 303 bullet pretty tightly). And anyway, far too much effort for bulk loading. I was just commenting on the straightness issue. (It also holds the bullet straight in line with the bore and theoretically keeps it that way as it jumps the gap - proof of that is still to be, well, demonstrated. But it looks good so far at least).

Regards
Peter