snowman
Member
All for naught, too, since the guy I was working for never reimbursed me a cent anyway(didn't even offer).
Andy
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Rant: Another gun rag gets .308 vs 7.62 NATO wrong
- Thread starter LVSteve
- Start date
All for naught, too, since the guy I was working for never reimbursed me a cent anyway(didn't even offer).
Andy
Eddy's Shooting Sports
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Everytime I have to explain the 308/7.62 223/5.56 nonsense I feel like my head is going to explode. I wish we could go back to the 80's when nobody gave to bits and there was no such thing as a 77gr 5.56NATO. it was a non-issue until the internet.
LVSteve - thanks for good informative article. A shame so much BS followed it. Interesting question on the .223 VS 5.65 - if you have this comparison, would appreciate seeing what you turn up. Get the feeling the results are similar to the 308 VS 7.65 pressure measurements. Would be good to see all such data on a common base, but we can't seem to go from the old English measurements to Metric which is a better system for calculation. Again thanks for useful data.
Who likes exponentiation?! 
Try THIS on for size:
piezo = crusher * ( 1 + ( crusher^2.2 )/30000 )
This formula is supposedly good for converting CUP values between 0-60 ksi. Beyond 60 ksi, conversions become progressively more inaccurate. Not that converting CUP to PSI was ever an exact science to begin with...
Does your head hurt yet?
Try THIS on for size:
piezo = crusher * ( 1 + ( crusher^2.2 )/30000 )
This formula is supposedly good for converting CUP values between 0-60 ksi. Beyond 60 ksi, conversions become progressively more inaccurate. Not that converting CUP to PSI was ever an exact science to begin with...
Does your head hurt yet?
Thanks for the info Steve, but it seems like every time I try to read another article to finally get an accurate answer on the .308 v. 7.62 question, and if it is safe to use one in a firearm marked for the other, it reinforces one thought for me.
Get a 30-06.
Get a 30-06.
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Jack Flash
SWCA Member
Let's see what the equation gives us for 50,000 CUP (50 ksi):
piezo = 50 * (1 + 50**2.2/30000) = 50(1.18222) = 59.111 ksi[/FONT]
So it looks like that gives reasonably close results to the OP's statement that 50,000 CUP is roughly 62,000 piezo.
You're a better man than me. I tried testing the formula myself and felt like my head was going to explode when I attempted to solve the decimal exponent.
LVsteve: Thanks for that article. I had always heard that the two measures were not convertible, but felt that was not really accurate. This is great information and I appreciate your posting it.
mwtdvm
Member
I'll stick in my $0.02
Crushing copper pellets is peachy keen fine except we have moved on to the "Digital Age" and the transducer, which measures pressure can be hooked up to measure the peak pressure over time... And that's where things get interesting. The pressure peak may be so transient that the copper does not have "time" to sufficiently deform. And spikes like that can result in failure of components. So copper is out and digital is in. Learn to live with it and love it..
Crushing copper pellets is peachy keen fine except we have moved on to the "Digital Age" and the transducer, which measures pressure can be hooked up to measure the peak pressure over time... And that's where things get interesting. The pressure peak may be so transient that the copper does not have "time" to sufficiently deform. And spikes like that can result in failure of components. So copper is out and digital is in. Learn to live with it and love it..
Roadtrash
US Veteran
help Help my eyes have glazed over I can't see! Ahhhhhhhhh........Whew now where's that keyboard.
DR505
US Veteran
I'm confused: between .308 and 7.62, which is a CTG?
OP
LVSteve
Member
If you are talking factory ammo, it depends on the pressure curve of the powder. I've shot ammo Remington green box FMJ marked .308 from a FAL with no problems. Red-X marked Winchester does not work well at all as it has too slow a powder. Even the adjustable gas system on the FAL cannot cope.
rojodiablo
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I feel you are very on target with this. (Pun intended!)
From what I have seen recently, the chrono tells us that NATO 7.62 and a variety of 308 hunting ammo were not far off of each other; within 100-150FPS. As to what I have seen in hit power on the plates, all things being equal, they stack up pretty equally in the amount of penetration, the amount of swin the target does, etc.
Yet, with the rifle we tested the ammo on last, the Winchester XP did not cycle the last round and lock the bolt, but NATO ammo, and cheap Wolf ammo would. But the chrono said the Winchester was a little faster. I put this down to powder burn characteristics. Everything else was identical.
Good point!!
Straightshooter2
US Veteran
It's been awhile since I researched this, and my mind is still in a blur, but this is what I seem to recall...
The .308 and .223 were civilian versions of their respective military counterparts. Even though their pressures look different, even if measured in the same scale, they are not. The military specifications require the pressure to read at the case mouth instead of the back of the case like SAAMI does. When SAAMI set their specifications it was based off of military ammunition, that's the way SAAMI works.
The difference between rifles marked in the civilian calibers, .308 or .223, and the military calibers isn't the ammunition they shoot, it's a slight difference in the lead of the firearms chamber. The respective ammunition is similar and completely interchangeable.
The .308 and .223 were civilian versions of their respective military counterparts. Even though their pressures look different, even if measured in the same scale, they are not. The military specifications require the pressure to read at the case mouth instead of the back of the case like SAAMI does. When SAAMI set their specifications it was based off of military ammunition, that's the way SAAMI works.
The difference between rifles marked in the civilian calibers, .308 or .223, and the military calibers isn't the ammunition they shoot, it's a slight difference in the lead of the firearms chamber. The respective ammunition is similar and completely interchangeable.
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OP
LVSteve
Member
From my research sources, the the chamber leade/freebore spec for 308 Win and 7.62 NATO is the same, but 7.62 NATO has larger allowable headspace with the shoulder area of the chamber being about 0.013 longer. As stated before, this is a nod towards keeping a hot and dirty weapon running in combat. I have a reference .308 Winchester vs. 7.62x51mm NATO 7.62 NATO ammo is happy in the extra space due to its thicker case web. The same article claims that the CUP/PSI confusion was actually started by the Army, which if true is pretty darned funny.
There is a difference in the leade and free bore between 223 Remington and 5.56 NATO. 5.56 NATO is somewhat longer, so it gets away with using the long 77gr bullet without overpressure. Scroll down this page for the precise details. http://www.frfrogspad.com/ar.htm
After that we get into the Wylde and Noveske chambers which attempt to allow for long bullets and 5.56 NATO compatibility while retaining 223 Remington accuracy.
From all the references I can find .223 Remington and 5.56 NATO cases are identical. The Wikipedia article claims that NATO and US milspec pressures for 5.56 are equivalent and the difference in numbers is due to the US military allowing the use of the SAAMI measurement protocol. I can buy into that to some degree but others do not. Indeed, the latest and greatest Mk 262 77gr rather fast for a round that is supposed to be running at SAAMI equivalent pressures, and this tester even says "NATO pressure". MK262 clone 77Grain 5.56 load problems / updated OCW tests It has been acknowledged that the gas port pressure with this round is way higher than normal. How much of that is "boost" and how much is powder burn rate I cannot say. Special powder you cannot buy at Midway is suspected.
The US armed forces do play fast and loose when it comes to pressures, especially with special weapons like sniper rifles. The latest 300 Win Mag round uses a special brew that is well past SAAMI specs. This was done so that the round would not appear too inferior to the .338 Lapua.
They get away with it by using custom built rifles with new cases and load lengths matched to the gun. Even so I feel it would be prudent to put a "useful life" limit on such a tweaked weapon.
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sipowicz
Member
I just measured my inseam and it came out to 3 pianos from the 50s.
smutt
Member
You guys have just given me a belly full of laughs.
