Reloading for a 43 Spanish RB

[Steve L]

After much frustration searching various forums, until my head hurts, I’m bringing my question here to hopefully find advice that doesn’t scare me.

I picked up a very nice Argentine RB a couple of weeks ago. It’s a very nice example, but is one that doesn’t have the Argentine roll mark on the top barrel flat. The bore is in excellent condition, and on further inspection the breech block has no wear or signs of use, etc. The bluing is near perfect. Over run gun or Arsenal refurbished? Don't know. All of which made me a bit nervous, since I’ve seen a lot of stories about what Jimmy Bob did to his 43 Spanish rolling block out in the garage. I was fearful maybe this was lipstick on a pig, as the saying goes. And admittedly, the only reason I wanted one was because I inherited a bunch of new brass, three sets of dies, etc. I had everything to load for 43 Spanish, I just needed the gun. So for $600.00 to my door, I have one.

I chamber cast the rifle to make sure it was as advertised (see above...ha), gave it a thorough look over, and slugged the muzzle end with a .439” bullet to make sure I knew what I had. What I didn’t know, was that slugging it with a .439 bullet wasn’t very accurate because of the large groove diameter I didn't yet know about. The markings looked good on the bullet however. I measured the 5 groove rifling on the slug, though it was a pain with the thin end of my dial calipers, but it seemed to have a .433 bore so I ran with it. I loaded 28 grains of AA5744 into 20 cartridges and headed out to see how it shot. (Which is my load for a 71/84 Mauser I have that shoots great). Well it shot like crap.

With a 6 o’clock hold, at 100 yards, I put one dead center of the bullseye, one 8” at noon off the target, one 8” low at 6 o’clock off the target, two at 2 and 4 o’clock about 8” from center off the target, and I don’t know where the other ones went. Not on the cardboard box. After 17 rounds I stopped.

I don’t know if it shoots to the right, because of the trigger pull that equals my body weight, and the complete lack of a pattern. So tonight I took some new measurements. First, I slugged it with a .460 diameter ball. I then gently turned the ball with my thumb and forefinger in my dial calipers to get max groove diameter. To double check that number, I wrapped a .002” feeler gauge around the rifling marks on the ball, measured the diameter, and subtracted .004”. Both methods put my groove diameter at .445”. Then I used a split ball inside mic on the bore and came up with .431”. Not satisfied, I chucked up a half inch bolt in my jeweler’s lathe, and turned it down in steps starting at .437” down to .429”. I stuck it in the barrel the way you would check an M1 Garand. I again came up with a bore diameter of .431”. So I’m pretty confident the final numbers are a groove diameter of .445” and a bore of .431”. Seems like kinda deep rifling?

I ordered the Lyman die and sizer to cast my own bullets last night, and my thought was to NOT size the bullet and see if they drop at .441” or .442”, hand lube them and hopefully tighten things up. Tonight I had the thought, I have a custom neck sizing die and expander die that I made on my lathe for my German 71/84 Mauser, and it would work well on the 43 Spanish brass to accept my .446” diameter Mauser bullets that are the same weight, cast with Lyman #2 alloy. I prefer not to shoot black powder just to get the bullets to bump up better, and would rather close up what I know now is probably a leak around a .439” bullet going down a barrel with a .445” groove diameter.
Can I safely fire a .446” bullet down the barrel with a .445” groove diameter and a .431” bore without pressure issues? And I have replaced the trigger spring with one I made out of flat spring steel, bringing my trigger pull to 7 pounds to help out with that shooting toward the right thing. Thanks in advance!

[wlw-19958]

Hi There,

I have a couple of Spanish model rolling blocks and the groove
diameter can be all over the place. My first rolling block has
a groove diameter of .444" and my second one has a groove
diameter of .4395". I haven't measured the land diameter.
but .431" seems a bit too small.

Obturation is going to be based partly on the bullet alloy.
I use a use soft lead alloy (40 to 1) to mold my bullets. I
have only used black powder in my loads so I cannot com-
ment on smokeless loads. Soft bullets will tolerate shoot-
ing through an undersized bore if the difference is small.

Most of the Argentine rolling blocks were re-blued when
imported back into the USA. Originally, the frames were
in case colors but when they re-blued them, the frames
ended up getting blued too. Also, the Argentine Govern-
ment had a large supply of replacement stocks so most of
the refinished rolling blocks got new wood.

Good Luck!
-Blue Chips-
Webb

[Steve L]

The bullet mold will be here tomorrow. The one's I shot came from Western Bullet, and I have no idea what alloy or hardness they are. I'm not stunting the Western Bullet either, as I've shot their button nose wad cutter in .45 Colt, and haven't found anything more accurate. I'll drop some with the Lyman #2, which I've had a great deal of luck with in other antique rifles, and see where they land between .440 to .442. I've read where this solved the accuracy problem for a few guys. Maybe back off the AA5744 a grain or so too. I ordered the .439 sizing die, and I suppose if I can find a way to open it up to .444 by honing or boring, I could size down the bullets for my .43 Mauser two more thousands, and handle it that way without concern.

And I MAY load a few with black powder and take it out to compare results. I wish I had a block of ballistics gel laying around, so I could shoot the .439 bullets into it and recover them for measurement. Then compare the expansion between black powder and the 5744. All this because I had new .43 Spanish brass and dies handed down to me, and no rifle...lol.

[wlw-19958]

Hi There,

Have you checked the neck size? Increasing the bullet diameter
will increase the neck size so make sure your chamber will handle
the increase.

Cheers!
Webb

[Oscarflytyer]

my first Argentine 43 Spanish RB was much like yours sounds like. my research says they scrubbed them in the '50s to remove all the scales etc before putting them on the milsurp market. My first was well scrubbed/polished/ground down/edges rounded (I didn't know any better at the time...). AND the bore was VERY over-sized - enough that I bought 44/77 .446 molds.

I just gave up on it when I ran into a very reasonable 'nother example. Ironically, while it was in almost pristine shape/almost perfect blue/Argentine lettering on top of receiver super crisp - the damn barrel was bent (former mortar-man "strung" it and proved it to me!). A buddy bent the bbl back to fairly true. I am shooting it with .439" bullets and 26 gr of 5744 and am very happy.

[Steve L]

Just an update since I posted this. I loaded 10 rounds with BP, and also 10 rounds with AA5744 and IMR4198. Chronographed them for comparison, and was expecting to see a tighter group with the BP. All 30 rounds were right in the mid 1300 to 1400 fps range. All three patterned at about Small Dinner Plate MOA. It was very disappointing. On firing the BP, I even swabbed the bore twice (one wet patch followed by one dry) every round.

THEN, because I hate to lose, I spent some quality time alone in the garage jigging up the bullet mold in my benchtop mill. I finally came up with a way to make hollow base bullets with an end mill, and get the hole centered to within .001" to .002". I made three versions with different depths. The cavity was .220" in diameter, and depths of .100", .110", and .120". Very similar cavity to the factory hollow base bullets I have a few of. I loaded all 30 of them with 27.5 grains of 5744. They all shot fine, and they all shot the same, Small Dinner Plate MOA. (The one's at a depth of .110" actually did a bit better at 8 MOA.)

Again today, I checked my measurements again, but this time I used Cerosafe on a one inch section of the bore at the muzzle. I still came up with the same numbers I listed above: A .431 bore, and a groove diameter of maybe a few ten thousandths under .445". So, to the above subject of chambering a .446" bullet, I took a fired cartridge and put it in the expander die. There was of course no resistance, but I wanted to just barely flare it. I then took a .446" bullet for my 43 mauser, and slid it right into the mouth of the fired case. It went easily but yet I could tell it was contacting the inside of the case all the way down. I then put a very light crimp on it, just to hold it in place. I was able to chamber it with a gentle push of my index finger without any resistance and close the breech block without pushing on it. So, yes I could load the .446" and they will chamber fine. The bullets are cast from Lyman #2, about 15 Bh or so. Maybe drop my load to 25 or 26 grains of AA5744 and see if it pushes it out the door ok? If they were .445" I wouldn't think twice about it, but will the extra .001" over the groove diameter be an issue?

[Oscarflytyer]

Are your cast bullets ~15 bhn? If so/regardless - I would recommend something cast in 20:1 or 30:1 or 40:1, or even pure lead. The softer, the more it should obturate to fill the bore. I am thinking that is the problem. I was pretty sure it was with mine.

IF it is somewhere in the .446 size, might even consider it as a 44/77... That was the path I was on with mine before I found the pristine example I now have.

[wlw-19958]

Hi There,

This story seems to be typical. I experienced the same problems
with my first RB. I chose to go 40:1 and rely on obturation. Going
.001" over bore generally isn't an issue so long the bullets are cast
from a soft lead alloy.

Cheers!
Webb

[NDduckhunter]

I have an almost mint Remington made #1 in .43 Spanish/ .44-77 military rifle, it has a .446 groove, and the bore is like new. I also have an original model 1 sporting rifle in .44/77 and the chamber is almost identical but the bore is .453-.455. Rim and case dimensions, even the neck were almost the same. Which causes issues when you load the .44/77 with .455/.454 bullets as the neck causes the shell to stick.