7.62x39 Bullets .308 vs .311 Real testing with pics

Status
Not open for further replies.
R

R.W.Dale

Member
Joined
Oct 14, 2005
Messages
11,652
Location
Northwest Arkansas
It's been pretty hotly contested as to how much diffrence there is between loading 7.62x39 using .308 bullets vs .310-.311 so here it is. I tested this today and here are the results.

The rifle is a CZ527 carbine topped with a 3x9x40 redfield accutrac scope. The bore measures .300 land to land and .3105 in the grooves

The ammo was loaded with 150 gr Sierre soft points 10 rds of .308 and 10 rds of the same bullet sized .311. Cases were Remington CCI 400 , The powder was 23.5grs of Re-7 with a COL of 2.310

It was about 65 degrees today with a light varible breeze of 15 mph

Shot string 1
.308 bullets

1851
1826
1852
1827
1846
***************
Shot string 2
.311 bullets

1935
1904
1937
1912
1925
****************

Shot string 3
.311 bullets

1953
1888 !?
1915
1932
1925
***************

shot string 4
.308 bullets

1852
1855
1869
1844
1873
 
Hpim0697.jpg

All velocities were taken at 25 feet.

As you can see there is very little diffrence in group size. About the only real measurable diffrence in using the .308 dia bullets is that they are somewhat slower in the FPS department.

Of course your mileage may vary.
 
Nice, this clearly shows that, unless you are shooting "balls to the wall" loads, there is no real danger shooting .308 or .311 in a 30 caliber rifle. Thanks for the test.
 
Been wondering about that for a long time. The test you did has been on my "round to it" list for several years now. THANK YOU for sharing your work!
 
krochus

Crosshair while I agree with your assesment , you may want to note that I was shooting .308 bullets in a .310 bore for this test.

Oopsie,:eek: Guess I read the bore dimensions wrong. Boy do I feel stupid. (Note to self: Learn to read numbers.)
 
So does the higher velocity from the .310" bullets represent a higher pressure or better gas seal in the barrel?

Also, the .308 and the .310 bullets were both 150 grains, but the .310 has a slightly thicker diameter. Are the .310s some fraction of a grain heavier, or is the length slightly reduced to match the weights?

Nitpicky, I know, but I'm always curious how alike alike is. :scrutiny:
 
Interesting test - thanks. Since your test was with a CZ boltie, you took advantage of the fact that you can use an OAL that is longer than SAAMI spec for your test load. I'd be curious as to how the pressure curves would be different with a shorter OAL (2.250), and if that would appreciably alter the peroformance of the 308 Sierras.

On a side note, have you tried any loads for the 150's in a 7.62x39 using H4198? The RE7 velocities look low, and I'd be curious if H4198 or RE10 would be more appropriate?
 
So does the higher velocity from the .310" bullets represent a higher pressure or better gas seal in the barrel?
Click to expand...

To answer a question that has languished for years, it'd have to be both. Better gas seal means less blowby, which necessarily increases pressure. More gas behind the bullet, more pressure.

I think I've seen a test of .308 and .311 bullets in a .308 bore, too, but I can't remember.
 
I've noticed the lower FPS in loads useing .308 slugs for my M30 Ruger.
I haven't got any accuracy useing .311 slugs at all. .308's do better.
.310 slugs in particulaqr the Hornady V-Max 123 gr shoot fine. Graf's has them on sale and when they are gone that's it they will be dis-continued.
they shoot as good as Lapua Match in my M30 with careful loading.
good luck with the X39 loading.
 
Another thing to keep in mind was his bore dimensions.

No two rifles are going to be exactly the same, unless from the same Mfg. and model, and from same barrel mfg eqipment with same tooling.

The .300" bore diameter tells the whole story here. If the bore was a .303" which is more typical of the .310-.313" crowd, the results would have been somewhat different. (ie: much lower velocity and poor accuracy).

I for many years shot cast bullets of .308-.309 through my various .30 cal rifles (.30/30, and .30/06). When I finally tried a .311" sizing die that I obtained for producing .32acp ammo, voila! my accuracy in the micro-groove Marlins vastly improved. Ditto with a .360" sizing for my .35Rem. I also saw some marginal improvement with the .30/06 as well.

I shot a LOT of cast bullets through various SKS's I had through the years, and a .311" bullet always shot just fine there too.
And, the 125gr Nosler BT's and Sierra PtSP's always gave excellent accuracy too.

I did try some .311" 150gr Sierra Spts in a .308wcf once, just to see. They wouldn't chamber in that rifle, so, that answered that question. Again, though, it was probably the rifle, (a Remington Mohawk600), which had a tight chamber. Might have worked through a 7.62Nato chamber though.......
 
Status
Not open for further replies.
Back
Top