Author Topic: 7.62x54r not as efficient as .308?  (Read 3427 times)

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122andy

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7.62x54r not as efficient as .308?
« on: January 10, 2011, 04:28:51 PM »
You always hear guys saying 7.62x54r as being "in between a .308 and 30.06". I was looking at the Lyman manual and found some interesting numbers. Cross-referencing the load data using a 150 grain bullet and looking at the data for XMR-2015, RX15, Varget and N-140, the .308 produces faster velocities with LESS powder than the 7.62x54r. Interestingly enough thats even with a 2" shorter test barrel for the .308. The IMR-4895 produced much closer results. In general it appears the .308 is a more efficient round and that the 7.62x54r is def not in between .308 and 30.06 in the performance category. I still like it tho! Comments?

SamStafford

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Re: 7.62x54r not as efficient as .308?
« Reply #1 on: January 10, 2011, 04:44:55 PM »
To me? I think the 7.62x54 is a little more than the .308, but less(just a little)than the 30-06. Now, people will state that you can make one more powerful than the other...could be true. Just my 2 cents.
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122andy

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Re: 7.62x54r not as efficient as .308?
« Reply #2 on: January 10, 2011, 05:08:24 PM »
To me? I think the 7.62x54 is a little more than the .308, but less(just a little)than the 30-06. Now, people will state that you can make one more powerful than the other...could be true. Just my 2 cents.
Thats what I am getting at. This is mechanics, not what people "think" or "feel". Im basing this on load data, not opinions. You should check it out the numbers for yourself if you have a load book, its very interesting. Keeping all things equal(same powder and bullet weight) the .308 consistently produces higher velocities with less powder than the 7.62x54r.

res45

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Re: 7.62x54r not as efficient as .308?
« Reply #3 on: January 10, 2011, 06:24:37 PM »
Not a whole lot of difference with a basic 150 gr. load,most reloading manuals have a good bit of CYA built into there loads anyways. The intended target want know the difference.

308 Win. 150 gr. Nosler

150 gr (9.7 g) Nosler tip     860 m/s (2,820 ft/s)        3,590 J (2,648 ft·lbf)


7.62 x 51mm

9.7 g (150 gr) FMJ             850 m/s (2,800 ft/s)        3,504 J (2,584 ft·lbf)


7.62 x 54r 150 gr. FMJ

9.7 g (150 gr) FMJ             865 m/s (2,840 ft/s)        3,629 J (2,677 ft·lbf)

j20owner

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Re: 7.62x54r not as efficient as .308?
« Reply #4 on: January 10, 2011, 07:01:37 PM »
Pressure level is what you're not seeing there, guys.  Max for the .308 Win is something like 62,000 while .30-06 is actually only at like 58,000.

Ok, from Wiki(maybe not the best source, but probably right):

.308Win-62,000psi
.30-06 - 60,200psi
7.62x54-57,000psi

Hope that explains it a little bit.
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allesennogwat

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Re: 7.62x54r not as efficient as .308?
« Reply #5 on: January 10, 2011, 09:38:19 PM »
When Poland joined NATO they did testing comparing their reference cartridges to NATO reference cartridges. The testing included, pressure, velocity and accuracy. One very interesting thing about it is their maximum allowed pressure for 7.62x54R is a bit higher than the pressure limit for 7.62x39 but their reference cartridges in their own testing resulted in a lower pressure for 7.62x54R than 7.62x39.

5.56x45 - limit = 380 MPa - measured = 328 MPa - velocity = 915.7 m/s @ 24 meters

7.62x39 - 275 MPA - 261 MPa - 714.6 m/s @ 25 meters

7.62x54R - 285 MPa - 255.1 MPa - 825.1 m/s @ 25 meters

7.62x51 - 365 MPa - 330 MPa - 830.7 m/s @ 24 meters

Note the NATO cartridges were measured at 24 meters and the Polish cartridges at 25 meters.


noyb72

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Re: 7.62x54r not as efficient as .308?
« Reply #6 on: January 10, 2011, 09:56:02 PM »
You have made a discovery that physicists and cartridge designers have known for a long time. In any 2 enclosed spaces of different sizes like 2 cartridges, it will take less propellant to make a larger increase in energy in the smaller space than the larger.

A well loaded 30-06 can come real close or even beat some 300 H&H loads because of this. Especially if you load the 06 to the same pressure as the Holland.

Ron
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122andy

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Re: 7.62x54r not as efficient as .308?
« Reply #7 on: January 10, 2011, 10:01:57 PM »
I wasnt even really looking at pressure...I was just noting that when using the same weight bullet with the same type powder that from starting load to max load the .308 acheives a higher muzzle velocity with less powder than the 7.62x54r.

122andy

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Re: 7.62x54r not as efficient as .308?
« Reply #8 on: January 10, 2011, 10:04:23 PM »
You have made a discovery that physicists and cartridge designers have known for a long time. In any 2 enclosed spaces of different sizes like 2 cartridges, it will take less propellant to make a larger increase in energy in the smaller space than the larger.

A well loaded 30-06 can come real close or even beat some 300 H&H loads because of this. Especially if you load the 06 to the same pressure as the Holland.

Ron
Makes sense, thanks for noting that Ron.

wrightbrigade

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Re: 7.62x54r not as efficient as .308?
« Reply #9 on: January 10, 2011, 10:10:32 PM »
IN all practicality can anyone put this into real world perspective, if my guess is right its not enough a difference to matter?
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j20owner

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Re: 7.62x54r not as efficient as .308?
« Reply #10 on: January 10, 2011, 10:24:22 PM »
Do you think a deer or other 'critter' hit with a bullet at 2500fps can tell a difference than if the bullet was traveling 3000fps?  No.  The only thing that it makes a difference on is trajectory and energy at extended ranges.

But yes, all things being equal, a .308 Win is more 'efficient'.  It takes less powder in a smaller space to create the same amount of 'push'. 

If you would load any of these cartridges to the same pressure, required charge weight would show a linear progression proportionate to case size.  Does that make sense? 
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noyb72

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Re: 7.62x54r not as efficient as .308?
« Reply #11 on: January 10, 2011, 10:26:01 PM »
The difference is felt in your arm and your wallet. If you load an 06 and a 308 to the same pressure with the same bullet, you will use less powder in the 308 to get the same velocity up to the 308s max velocity. The extra powder costs more if you reload alot and the extra mass increases recoil. Their is DEFINATLY a noticable difference in recoil between the two above loads in guns that weigh the same.

Their is a point where the bigger case gains the advantage. That is with big bullets and slow powders. The extra capacity allows enough slow powder to move the bigger bullet. This is why the classic 06 load is 180@2700 and the 308 usually uses 150s or 165s. The 06 has the case capacity to move the bigger bullet.

Ron
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noyb72

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Re: 7.62x54r not as efficient as .308?
« Reply #12 on: January 10, 2011, 10:30:30 PM »
Do you think a deer or other 'critter' hit with a bullet at 2500fps can tell a difference than if the bullet was traveling 3000fps?  No.  The only thing that it makes a difference on is trajectory and energy at extended ranges.


500 fps is a hell of a lot of speed! Yes, the deer will know the difference. It will know the difference because the bullet will either blow up at the faster speed or drive a heck of alot deeper and transfer a heck of a lot more energy. Both shots may make the deer dead eventually but the faster round, with the right bullet, will increase your chances of a quick kill.

Also, 500 fps is going to DRAMATICALLY increase your max point blank range and reduce your need to holdover on longer shots. 100-200 fps your argument holds water but 500 is a lot of speed.

Ron
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j20owner

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Re: 7.62x54r not as efficient as .308?
« Reply #13 on: January 10, 2011, 10:52:53 PM »
No, my argument is valid.

Untold numbers of deer are shot with .30-30 lever action rifles, with 150 grain bullets traveling around 2400fps at the muzzle.  You can also shoot a .30-06 with a 150gr bullet at 2900fps.  

How far are most deer shot when shot with a .30-30?  I'd wager on the low side of 75 yards, and that's generous.  At 75 yards, the .30-30 should have around 2085fps.

How about most shots with the .30-06?  Let's say 150 yards.  With the exact same bullet(not something very likely, but possible if you handload), velocity at 150yards is about 2200fps.  

So, there would be a difference of 115fps between those two instances.  How many people are actually hunting with cartridges whose impact velocities are anywhere near their starting velocities?  It's the golden rule of hunting, know the capabilities of the shooter, the weapon, and the cartridge as loaded.  That's what matters when it comes to stuff like this.  Would you take a .30-30 lever action out hunting in the wide open of Kansas?  Probably not.  Would you hunt in thick timber with a .30-06 if you knew your shots were going to be under 100yards?(I know people who shoot deer with .300 Mags at under 100yards-silly)  If it's your only option, it's more than likely going to happen.  But, I've seen deer hit with the .300 Mag at 50 yards travel 3 times further than a deer hit at 50 yards with a 7.62x39.  The reason is bullet construction.  There's so much more to shooting than just velocity.  Of course, speed sells so whatever is faster must be better.

But you already knew all that, didn't you?
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noyb72

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Re: 7.62x54r not as efficient as .308?
« Reply #14 on: January 10, 2011, 11:21:01 PM »
We can play situations all night long. I think you agreed with me though. In your first example the velocity difference at impact was 115 fps, I said your argument made sence at 150-200.

I also said 500 fps may cause the bullet to explode. I could have included not expand. A 300 Mag with a super premium bullet is not going to expand in a deer at 50 yards anywhere near what a conventional soft point in a 7.62x39 would. The lack of energy transfer may allow the deer to stay on its feet longer. I'd argue a deer notices the difference between walking around dieing and being dead. With an impact speed difference of 500 fps (which is the ONLY speed the deer cares about,) making the argument equal by assuming the same bullet, the deer will know the difference.

Ron
"In all the years I've sat on this bench...I heard lots of things that give me grave doubts about the human race. This ain't one of them". Judge, All the pretty horses.