Read back for the previous two articles on my reloading experiments with the 8x58RD.
Last post I was looking at the implications of using 7,62x54R case as an alternative to the 8x58RD. Lunch time I slugged the bore of the rifle (S&L Model 42) and checked the dimension, the bore comes up at 8,15mm/.321″ however the rifling definition is not particularly crisp. One of the issues with military 8x58RD ammunition is it often uses potassium chloride in the construction of the primer. This leaves a minute deposit of the hygroscopic potassium chloride salt in the bore after a cartridge is fired. Being hygroscopic the salts attract and hold moisture which leads to corrosion/rusting unless one pays particular attention to the cleaning of the bore after use. This is why you will sometimes come across a lovely looking Krag or S&L with a bore that has been all but destroyed due to the owner putting a few rounds of milsurp through the rifle and then returning it to the cabinet uncleaned.
It is always sad to see such a rifle.
Back to the reloading experiments. The 54R brass is easily expanded to suit the new bullet and chambers perfectly after a full length size, in fact it chambers unsized and you could probably load a 54R round in the 58RD, fire it and end up with a perfectly formed 58RD case – not that I would ever advocate such an action! (Wear your safety glasses if you really must try this)
One interesting feature of the sizing die I use is it not only opens the neck to suit the 8mm bullet it also allows you to flare the mouth of the neck slightly if you wish. This gives two benefits, one is it gives an easier lead when seating the bullet which is especially handy with cast bullets as there is less chance of shaving the lead, it also means you can flare the case neck mouth to a size where it aligns itself with the chamber neck which is something reloaders looking for accuracy with cast bullets will require.
Next step is to source some bullets, fire form the cases and shoot the thing in anger.
In my last post I looked at the idea of using 54R brass as an alternative to 8x58RD so lets have a closer look at the two cases and consider if this really is a viable option. Below are the drawings for the two cases with the 7,62x54R at the top and the 8x58RD at the bottom, I have red ringed the key dimensions.
Starting from the head and moving towards the neck lets compare the two.
|Head to shoulder
|Neck outer diameter
|Case base diameter
|Case shoulder diameter
A closer look at the table shows the rim diameter is smaller on the 54R however not enough to be significant. The head to shoulder is shorter on the 54R so it will fit however the Alpha shoulder angle is very different however again this should not cause issues as only the front of the shoulder will be set back and then only marginally. Luckily the case is rimmed so no worries about building over length to hold the case in the chamber for first firing.
The 54R case finished length is 4,03mm shorter which is a bit of a problem and the cartridge overall length of the 58RD is 4,77mm longer than the 54R – this is an important detail and does mean we will be jumping the bullet quite a bit regardless of if it is cast or jacketed.
What I cannot predict although it can be calculated is the developed length of case after the first firing, it is at times like this it is worth considering fire forming without a bullet, to do this you use a low charge of faster powder, add a filler and then plug the end of the case with something – soap works well for this and it means the associated pressures with firing are drastically reduced, wear your safety/shooting glasses regardless of predicted chamber pressures.
So that is my musings on the use of 7,62x54R brass in the 8x58RD. Looking at the dimensions the case is going to fit quite nicely and should blow out to conform to the chamber without issues. I would suggest using a reasonable make of brass, Lapua springs to mind. Having written this I am tempted to open the 54R brass out to 8,0mm with a mandrel stage followed by passing the case through a full length sizing die and then fireform with a plugged case.
Pictures to follow..
Well at long last we have some 8x58RD Dies, they are new, robust and of unknown maker however they are dies and that is a good start as far as I am concerned so the next thing is get some rounds built.
I had planned on taking standard Berdan primed brass and either converting it to boxer or just reloading them as Berdan. The only downside with Berdan primed brass is removing the primers and that is no real hardship as they are easily removed hydraulically or you can always mess around with other techniques if so desired. Hydraulic removal of primers is a wonderful process, find a lump of wood and drill a shallow hole to match the diameter of the cartridge head or rim, now drill a smaller hole to allow the primer to drop through. Now fill the case 3/4 full with water place it in the hole in the wood, find a suitable piston which in this case is a length of brass that fits fairly snugly through the top of the case, insert the piston, hold it firmly (Gloves are good if it is a bit on the short side) now give it a smart rap with something and voila, the primer is pushed out with the hydraulic action, you get a bit wet and the case is ready to be cleaned and sized before priming. You will need the correctly sized primers however that is not a real problem. I much prefer to do this outside on a sunny afternoon and find it quite therapeutic…
The problem is I do not have any fired 8x58RD brass right now so what are the alternatives? Well there is some new Bertram brass available however it has a reputation for splitting even when annealed and it is very expensive. Certainly other cases such as the 45/90 can be necked down however this involves trimming and annealing and again the brass is not cheap. There is a third option and that is to use 7,62x54R brass which is something we have a fair few of here having shot various Russian rifles in the past. Now one of the issues with 54R brass is it is going to come up short once it has been opened up to suit the 8,0mm however it does have a reputation for working fairly successfully and also means as I am reloading I can keep the MV’s down to something sensible.
Now to the choice of bullet, standard jacketed bullets of around 200 grains would be a good start however given that the two rifles have less than perfect bores I am inclined to use cast bullets which means I need to slug the bore first to confirm the best choice of bullet. Slugging is the process of taking an oversize to the bore lead slug or ball and forcing it down the bore, this does sound rather harsh however it is surprisingly easy. Lubricate the bore with some oil, take the slug and tap it down into the bore from the muzzle end and once it is in the bore it will tap down with very little effort, I prefer to use lengths of oak dowel however others will use a single length of suitable round bar, I found this method less easy as the rod will bow during the process if you are not careful plus if you are working with a 30″ barrel you end up having to stand on a chair to start the process. The lengths of oak dowel have worked perfectly many times in the past and I will continue to use them.
Once the slug drops out of the other end it can be measured and used as an indication of the diameter bullet to be used. Of course at this stage it is worth taking a cast of the chamber as well so you have a better idea of what you are working with but I am not going to pursue that avenue in this post as accurising cartridges for cast bullets is a whole subject on it’s own and way beyond this article.
I guess the next job is to decide on what sort of powder load to go for. A serious consideration is the maximum safe pressure for the rifles in question is going to be around 3200 Bar/46,500 PSI – CAUTION!! This applies to the later 8x58RD such as the S&L M.38/M.42 and not to the earlier rolling block One thing I do not want to do is overly stress the rifle so I suspect I will be looking at a fairly modest load of N140 or similar. Time to do some more research in this area meanwhile I will machine a mandrel, open up some 54R brass and see how it looks.