Refurbishing an Argentine RB - Part 9
Measuring the chamber
Joel, you have done a splendid job.:cheers:
To instantly put your mind at rest, the rifle appears to have a perfectly normal .43 Spanish chambering, with acceptable military tolerance. I see no evidence that it has been reamed. You can order the 43 Spanish reloading material without worrying that it might be wasted.
Quote:
Originally Posted by
killforfood
So Patrick, how did you know that this wouldn’t have a long throat when so many do?
All BPCRs have short throats to provide well-defined engagement of the bullet with the rifling. A long throat would let the bullet "jump the grooves" i.e. it would charge straight over a gradually tapered rifling, becoming partially stripped before finally engaging.
The comparatively long, gradual squeeze that can be used with jacketed bullets which already engrave with a thou or so of rifling will not work with soft lead.
We can now compare the meagre data I have on cartridge dimensions with your measured chamber dimensions: I have two sets of figures, one metric, one imperial. You will see that the agreement is not very close. I have no way of telling whether the figures are derived from drawings or measurements on original (unfired?) cartridge cases.
Quote:
Originally Posted by
killforfood
Overall chamber length from breech face to the beginning of the rifling is 2.660”.
Looking at your pics, the neck section ends about 0.15" short of the left-hand caliper jaw. This would allow a case length of nearly 2.5" before the neck jammed.
I have 56.58 mm = 2.28" or 2.25" as figures for total case length.
You are OK:thup:
Quote:
Originally Posted by
killforfood
Just ahead of the rim in the web area it was .526”
I have 13.31 mm = 0.524" or 0.516"
You are OK:thup:
Quote:
Originally Posted by
killforfood
The shoulder diameter is .512”
I have 12.77 mm = 0.503" or 0.512
You are OK :thup:
Quote:
Originally Posted by
killforfood
Groove diameter .442”
You will not be able to get a 452 slug down that bore with the brass rod method. 10 thou over groove size will NOT go. Even a "soft" lead pistol bullet will have a Brinell hardness of at least 15, more likely 20.
Quote:
Originally Posted by
killforfood
This gave me a groove depth of .006”. Subtracting two groove depths gives me a bore diameter of .430”.
So you not only have a rifle in chambering 43 Spanish, the bore diameter is actually 0.43". It is not always so.
Quote:
Originally Posted by
killforfood
The end of the neck is .460”
I have on record 11.54 mm = 0.454" or 0.455" for the cartridge.
You are OK :thup:
Quote:
Originally Posted by
killforfood
The neck just in front of the shoulder is .464”
I have 11.55 mm = 0.455"
You are OK :thup:
Finally, rim thickness. You have not measured that yet. My figures are 2.26 mm = 0.089" or 0.065". That's quite a difference, but all that matters is that the bases of the cartridge cases that you buy will actually go into the recess and allow you to close the block. Looks like your rim recess is about 0.09-0.10" deep. For rim diameter I have 16.54 = or 0.635. That is not usually a problem.
At this point, I must advise you not to let yourself be scared by headspace doom-and-gloom soothsayers who have no idea about BPCRs and who will try to convince you that your rifle is going to blow up if the headspace is not correct to the micron. In such old rifles the secret of using those expensive cases over and over again is neck sizing, and nothing else. Fortunately, in the case of 43 Spanish there is probably no SAAMI data available for the armchair experts to get steamed up about (at least I hope so).
So once those cases have had a first firing, they will have expanded to fill the chamber as is, not as should be, and the cartridges will thereafter be headspacing on the shoulder. This means, of course, that those cartridges are only suitable for that rifle. For instance, I have an 1871 Mauser rifle and an 1871 Mauser Jaeger, and must keep the batches separate for each rifle. Not your problem yet, but give it time...
The only thing which you MUST check is that the block really does lock up tight. As the block rotates in the action, any slackness will mean that the cartridge base will become skewed if the block opens a bit on firing and can rotate backwards.
Conclusions:
- with the usual precautionary AFAICTWAHTOIMH !
You rifle is chambered for 43 Spanish. It has not been rechambered.
You will need lead-tin alloy bullets with about 5% tin - 95´% lead.
The lead must be reasonably pure - lead flashing as used by roofers is OK. Wheel-weights from the local garage are most definitely NOT suitable. The easiest way to get the tin content is to mix in lead-tin solder in the appropriate amount. At this point, please read up the thread on the 1871 Mauser, if you have not already done so.
You now need to order a bullet mould.
RCBS 82040, for a 0.439" 370 gn. bullet or Lyman 2640186 / 0.439" / 370 gn. will both work as cast.
When you have gained some experience with BP reloading, and are tuning for maximum accuracy, then you could try RCBS 82093 for a 0.446" 370 gn flat-nose bullet, or 2640110 / 0.446" / 340 gn. But in both cases you will need to size the bullets down to no more than 0.443". The full 0.446" may well go through the bore, but could cause a neck jam in the chamber. To evaluate that possibility you must first have the brass, so that you can measure the neck wall thickness.
We have now gone as far as we can with theory at the moment. In the end, that muzzle and crown (or rather, lack thereof) is going to be a decisive factor. So could you please make a couple of pictures of the muzzle end of the rifling, as suggested in my previous posting?
End of Part 9
