Forums.NitroExpress.com

4seventy:

I'm new here and didn't see this thread when I went through the old stuff. This is something I've noticed and wondered about - a lot - for long time.

I've just measured some old Kynoch factory .470 (loaded in 1972) and a few of same fired in a Rigby best boxlock ejector built in 1910. Length to shoulder of the loaded round is 2.450" and length to shoulder of the fired case is 2.455". I've never measured this before with respect to this particular rifle and I'm amazed. I've never seen those two measurements that close between old Kynoch and the chambers of a pre-war English double rifle before.

I've stared in wonder many times at the obvious difference in that measurement when shooting factory Kynoch in English doubles. With respect to my current .450/.400 3" the length to shoulder difference between old Kynoch and a case fired in my chambers is .100". The difference in my old .450/.400 3 1/4" is .200". The difference for my .400/.360 Purdey is .120". With virtually all of the other nitro doubles that I shot or loaded for, the difference was quite visible.

I bought my .450/.400 (3" & 3 1/4") and .400/.360 dies off the shelf (non-custom) from RCBS. All three sizing dies, screwed all the way down, just kiss the shoulder of cases fired in my rifles - it doesn't get any better. Since factory ammo is such a loose fit, I've always wondered how RCBS got their specs so close to the chambers.

I take the CIP standards with a 10 pound sack of salt. They are an attempt to establish standards 100 years after the fact. Based on what I've seen, the pre-war Brit gun and ammunition makers simply did not adhere to any collective standardization trade-wide. Britain did not become a CIP member until 1980. Chamber measurements, groove diameters and bullet diameters bounced from hell to breakfast. Trying to standardize it now is a joke. I'm sitting here looking at an old Kynoch (loaded in 1967) .450/.400 3" NE and a new one from the new Kynoch (Kynamco) loaded to CIP standards in 1997. At a glance, then a double take, then a REALLY close look....nope, one of those boxes is labelled wrong. Excepting the headstamp, no experienced shooter would conclude that they are the same cartridge. Shoulder diameter of old vs new is .515" vs .495" and there is a 1/4" difference in the length of the neck (and yes, overall case length of the new is 3", not 3 1/4")! If the new cartridge is at CIP spec, original Kynoch would not chamber in a new CIP spec chamber - at least not without a 10 pound hammer! Small wonder to me that RCBS .470 specs changed so much when they switched to CIP specs.

To summarize the above disjointed observations, here is what I think happened. The US is not a member of CIP. Standards here are SAAMI. There are no SAAMI standards for the .470 Nitro Express or any of the other British flanged nitros, or at least not until very recently, and as I said above, there doesn't appear to have been much agreement about what the standards were within the British trade itself until CIP. When folks started reloading for the flanged nitros here, dies were custom shop items and were made from cases fired in the customer's rifle. When the need to make die sets for stock arose due to increasing demand, my guess is that RCBS probably reviewed the custom specs and arrived at a "standard" that seemed to have worked for most of their customers. I think this is why my dies fit so well, even though the dimensions of the sized cases differ so much from old Kynoch. When that "standard" didn't work for someone, custom dies were made. In recent years, I've known a couple guys who had to do it this way, but most of the time the standard dies work fine. I used standard RCBS dies when I loaded .470.

It sounds like your rifle is chambered a tad tighter than most and that may be because it is from a continental maker. Who knows? Time for a custom sizing die. Good luck.
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"Serious rifles have two barrels, everything else just burns gunpowder."