6.5x55 Case Length

[Foxyboy43]

Crikey! A casual flick through this post makes me think of Hitler and Von Braun’s plans for the V2! Or is it just me…….

 

[NP435]

Simplistic.

That's just SAAMI's sort of rule of thumb, (i.e. difference between min. and max. of 20/1000"), to give their clientele (ammunition manufacturers, not reloaders), something to aim for, in a voluntary way. Probably not based on any analysis or testing, but rather a practical round number that is readily achievable in mass production. Anywhere in that ballpark will do.

That's when they aren't trying to draw up, retrospectively, chamberings that they played no part in the standardisation of, many of which existed long before SAAMI existed. And others were defined outside of the US, but nonetheless SAAMI attempt to take them over.

E.g. study the 338 Lapua Magnum. Not invented there. Nevertheless they have drawn it up, hedged about with yellow, and red, warnings. OMG, we aren't prepared to just translate the CIP spec, oh no, we will make up our own ideas, disregard others, and add a few (the ones in yellow). What a dogs breakfast they made of that.

View attachment 238759

Yet again we see the same old rule of thumb "- 0.020" tolerance on case length. Plucked from the air.

Together with their shoulder position (Junction Cone) measurement approach, unchanged since they first began. As in, drill a hole specified to 0.001" (0.476") and then try to measure the distance between where it's knife edge might touch upon some point on there, yet specify that "headspace" to within 0.0001" (2.2550"), even though the shoulder angle will further multiply any such imprecision. Farcical.

If you use a Hornady case comparator, that's what you get, a cylindrical hole drilled into aluminium. Fair does, that's how SAAMI specify it. Whereas if you buy a Sinclair bushing it is conical, cut to the precise shoulder angle of the case for which it is to be used. Both do the job, as comparators. But as an engineer I know which is the superior approach for actually measuring something.

It's details like this that seem nonsensical to me, and of no useful applicability to reloaders.

Contrast that with the proper original CIP drawing. Finland being a CIP nation.

View attachment 238771

L3 applies. Only the max. specified. No minimum. No arbitrary 20/1000". And, for the interested, L3 for the chamber (minimum, no max.). With the tightest combination allowing 0.25mm clearance.

Again, CIP specify the shoulder position in a way that can actually be measured, using conical bush cut to the precise shoulder angle of the case. alpha. 40 degrees + 45 minutes, minus 11 minutes.

I do have a pet gripe about SAAMI's habit of sometimes converting to inches with rounding error, then reverse calculating back again into into mm and putting the mm figures in brackets. It is quite the other way around. Since the 1950s the inch has been defined as exactly 25.4mm.

Even in the US, in precision industries, things are usually drawn up and measured in SI units, have been for many years. Since the standardisation of the "metric yard". 0.9144 m. And the precision machinery usually calibrated that way.

BTW, here is the pukka drawing for the 6.5 x 55 SE. NB. L3 is 55.00mm. Maximum. Not 54.991mm (doh, they got it wrong by nine microns) as SAAMI would have you believe. minus 0.51mm (AKA 20/1000") I think they just made that bit up, because it's expected, what they always have done..

View attachment 238780

Sir you made the point for me thank you. My hope is the op has some food for thought.

 

[Milligan]

I think the op may contemplating his existence and place in the universe when all he wanted was some assurance that he would be ok.

 

[Kiwiguy]

Which would be incorrect.

Technically, of course, you might describe the chambering as 6.71 x 54.991 mm. Or maybe 6.71 x 80.01

Can you please explain why you are quoting figures for the 6.5x55 Swedish from the SAAMI drawings which were only standardized in 1993 rather than the much older CIP drawings?

 

[Rutland lad]

I reload a few different calibres. Some for me, some for friends. I was surprised to find that there are calibres that never seem to need their cases trimming, and calibres that always seem to need their cases trimming.
Now I know that, it saves me lots of time and effort. Every day is a learning day.

 

[Sharpie]

Can you please explain why you are quoting figures for the 6.5x55 Swedish from the SAAMI drawings which were only standardized in 1993 rather than the much older CIP drawings?

The OP is "reloading 6.5x55" Which is the SAAMI designation for what they also call the 6.5x55 Swedish. Hence why I referenced the most recent SAAMI drawing for that, dated 1993. Doubtless there were previous versions prior to 1993, nevertheless this is the current revision. SAAMI don't publish change-logs for the public to see, so quite what changed in the latest revision I have no way of telling. Wherein the case length is specified as 2.165" Or 54.991mm. (i.e. 2.165 x 25.4 = 54.991).

Hence why I corrected your observation that "Considering it is the 6.5x55mm there is a strong possibility that the maximum case length is 55mm" Whilst being a "strong possibility", it is, actually incorrect. The OP called it the 6.5x55. Not 6.5x55mm. Besides, 6.5x55mm is the designation of the original 1893 cartridge. The CIP designation is 6.5 x 55 SE.

The US 6.5x55, AKA 6.5x55 Swedish, is an all-imperial invention, 2.165" long. I am guessing that that particular dimension has not altered since it's inception, whenever that was.

As to when CIP first released their specification, I would not know that either. Their current drawing is dated 1984. That was when it was first issued. The current version was revised in 2016. On October 18..

I admit, this is extreme pedantry on my part. And I'm sure we can agree that the nine micron difference is, literally splitting hairs. (Human hair is approx. 70 microns thick). And utterly irrelevant when considering where to trim to.

6.5x55mm is the designation for the original cartridge, jointly developed by the United Kingdoms of Norway and Sweden, standardised in 1893. Unsurprisingly I couldn't find a contemporary drawing for that.

From Wikipedia:

While the original and colloquial cartridge name is 6.5×55mm, there are some variations in chamberings. In addition to the original 1890s specification, three modern chambering and ammunition pressure variations also exist.

6.5 × 55 SE is the European C.I.P. designation with SE being the Swedish two-letter ISO country code.
6.5×55 Swedish is the American SAAMI designation (official SAAMI abbreviation 6.5×55).
6.5 × 55 SKAN is the Scandinavian designation used by the Scandinavian shooting associations DFS, DGI and SvSF.

Maximum pressure (C.I.P.) 380.0 MPa (55,110 psi)
Maximum pressure (SAAMI) 351.6 MPa (51,000 psi)

Also see 6.5x55

I'd better stop there, I have work to do trying to count how many angels can dance on the head of a pin.

 

[Stalker62]

I'd better stop there, I have work to do trying to count how many angels can dance on the head of a pin.

You have already done enough.

Herewith is the answer to that little question...

 

[Milligan]

Can you please explain why you are quoting figures for the 6.5x55 Swedish from the SAAMI drawings which were only standardized in 1993 rather than the much older CIP drawings?

You really had to ask? Really?

 

[Jelen]

I reload a few different calibres. Some for me, some for friends. I was surprised to find that there are calibres that never seem to need their cases trimming, and calibres that always seem to need their cases trimming.
Now I know that, it saves me lots of time and effort. Every day is a learning day.

Yes. .308 stays pretty much the same. 6.5x55 grows like grass.

 

[Rutland lad]

Yes. .308 stays pretty much the same. 6.5x55 grows like grass.

That’s really interesting.
The LAPUA cases I’ve reloaded don’t seem too bad at all so far.

 

[Jelen]

That’s really interesting.
The LAPUA cases I’ve reloaded don’t seem too bad at all so far.

I forgot to add 'in the winter' LoL.
You will notice the difference between the 2 calibres much quicker if you only neck size your cases. I then full length resized for both and the growth was less pronounced, but the 6.5x55 still needs trimming sooner than the .308, or .243 for that matter. It could be because I load hotter, or the chamber size?