308 and 6.5 case capacities

[BillinNH]

Although I've chased down several leads from Google I can't seem to find the case capacities of .308Win and 6.5x55 Swede. Hard to believe there's nothing on the 308. I found two for the Swede but they were both obviously wrong (30 and 80 gr. of H2O). So if you know the case capacity of either of these cartridges, whether cc's or grains of H2O, please post them as well as your source. Many thanks.

Bill

 

[Jim Watson]

56 grains of water FOR BOTH .308 Win and 6.5x55, according to "Some Simplified Interior Ballistics for Handloaders" by Wm. C. Davis, Jr. in the NRA 'Handloading' manual of 1981.

That is the full case volume with no allowance for the space taken by a normally seated bullet.

 

[BillinNH]

Thanks Jim. However, over on hand and reloading, someone came up with 3.68 cc for 6.5 and 3.43 cc for 308.

Hmm. Let me do some conversions here.

BTW, this issue is not critical, it's to settle an argument about relative case capacities. One of the questions was 308 vs 6.5x55.

Bill

 

[USSR]

Actually, the Swede has a bit more case capacity than the .308 (57.7gr H2O vs. 55.0gr - 56.0gr H2O depending upon mfg.), that's how the 6.5x55 can generate more velocity than the .260Rem, which is based on the .308 case.

Don

P.S. - The Swede measurement is an actual measurement of my Lapua brass.

 

[BillinNH]

The 3.68 cc for 6.5 and 3.43 cc for 308 were cited from Richard Lee's 2nd edition. But it was pointed out that this was for "useful" case capacities which I guess takes bullet seating into account.

Looks like 6.5 and 308 are close enough that bullet seating might make the difference. The Lapua measurements are convincing, though, so barring further input I guess I'll declare 6.5 to have one smidgeon more case capacity than the 308. Have to end the argument somehow ;-)

BTW, don't ever start the same thread on two different forums. It gets very confusing. This is also on hand and reloading. Sorry 'bout that.

Bill

 

[Jim Watson]

I guess they are making 6.5x55 bigger now than in 1981. But let's see, now:
3.68 = 3.43 + 7%
57.7 = 56 + 3%

One gunzine writer says that velocity changes as 1/4 the change in case volume. Vihtavuori shows that velocity changes almost but not quite as much as case volume. Either way, 3% on case volume is not much. You could probably see 7%, though.

 

[USSR]

Jim,

Granted, it's not much of a difference. But there is another factor that often comes into play when we are talking about case capacity of a loaded round: In most cases (no pun intended), the .308 or .260 is chambered in a short action, and the bullets are seated deep to enable magazine feeding. Since the 6.5x55 is always in a long action, the bullets are seated out and do not intrude so much into the case, thereby allowing even more "as loaded" case capacity.

Don

 

[BillinNH]

I think I agree with Don on this point. Personally, I never understood the attraction to short actions.

Bill

 

[Jim Watson]

Well, if you need the magazine AND a little extra velocity.
MY .308 is a single shot and I load it longer than standard.

 

[lencac]

Question, why are we checking the volume between dissimular rounds? I can see if you are checking say for different types of brass for 308 or different brass for 6.5x55. But why are we trying to compare apples to oranges?
But nevertheless if I need to check case volumes I use something like H380 powder. Fill the case to heaping, level off with business or credit card and weigh the contents.

 

[BillinNH]

<Question, why are we checking the volume between dissimular rounds? I can see if you are checking say for different types of brass for 308 or different brass for 6.5x55. But why are we trying to compare apples to oranges?>

See post #3 in this thread. It isn't of practical consequence, I just wanted to settle an argument.


<But nevertheless if I need to check case volumes I use something like H380 powder. Fill the case to heaping, level off with business or credit card and weigh the contents.>

Using water for this purpose has become standard because it is widely available and doesn't change its properties and is generally not compressible. By multiplying (or dividing) by the right constant the weight of the water is directly convertible into volume.

BTW, the argument was about rank ordering the following cartridges by case capacity. I have listed the water weights for each. The Swiss was a surprise.

30-06 66.58
7.5x55 Swiss 65
7.62x54R 64
8mm Mauser 63
6.5x55 Swede 57 app.
308 56 app.
303 Brit 55.7
7.62x39 35.5



Bill

 

[USSR]

Bill,

Don't know where you got the 66.58 for the .30-06, but it's not even close. Winchester holds 70.4gr and Lapua 69.4gr.

Don

 

[BillinNH]

Don -

The 30-06 data came from a surplus.com article on the LFAD loading calculator software. Elsewhere in the article it gave various case ranges (different brands) ranging from 65 to 68.5 gr. So I guess my data needs to be refined. Are your figures from your measurements or another source?

At any rate , thanks for the correction. And at least we know that the '06 has the greatest case capacity of the cartridges under discussion.

Bill

 

[lencac]

Water is messy, H380 is neat and meters like water. Try it you'll like it

 

[GunTech]

According to QuickLoad 3.3

6.5x55 57.0 gns H2O
308 56 gns H20

Naturally, the brass manufacturer makes a difference

 

[USSR]

Are your figures from your measurements or another source?

Bill,

My measurements. I refuse to just give data found floating around on the Internet, unless I know from personal experience that it is true. I see it all the time; somebody posts something that has no basis in fact, and then guys go passing it on as factual data for years.

Don