Finn M39 reloads help

[Bruce_in_Oz]

I am keen on bullets that "fit" the groove size, even to the point of using "oversized" bullets on occasion; like "soft" .311 soft-points in a particular .30-06 that shot exceptionally well with them.

"Bore-riders" are not a new thing, as indicated by the longevity of the .303.

They may also not be an ideal thing, but you get that at times.

Furthermore, gas-bleed is MUCH greater with boat-tails of the solid based (like most "sporting" projectiles), than with "open-based", FLAT based FMJ types. Hit an "open-based" bullet up the rear end with 40,000 plus PSI and it is unlikely to stay at the original diameter for very long. Has anybody got the article, I think it was in the British "Guns Review", that detailed experiments with ULTRA short rifle barrels and reaming out the bore itself?

My recollection is that the recovered bullets showed measurable expansion at their tail-end when fired in short, slightly-oversized, smooth-bored barrels. The rather rapid burn-rate of traditional Cordite may have been a contributing factor.

This feature is a direct carry over from the earlier, muzzle-loaded Minie ball of P-53 Enfield, etc., fame, i.e., a "bore-rider" with an expandable "skirt" that sealed the rear and also helped "scrape" out the residue from the previous shot. Earlier editions of this bullet design had a small "plug" inserted into the hollow base of the lead bullet. this was designed to be driven into the slightly-tapered recess on ignition and force the "skirt" out into the grooves. It didn't take long for someone to discover that this plug was not necessary as gas pressure, even from a black-powder load, was sufficient to do the job.

Going to the .577-450 Martini Henry bullet introduced a few new "funnies".

Henry's original bullet design tapered from .450" at the base to .439 near the nose. Experiments carried out by a certain Dr. Mann, from about 1890 to 1910, strongly indicated that the best bullet for black powder was a bore-rider, with a rear band increased to groove size.

Kynoch production up until the 1960s, kept this idea and their bullet measured .452 at the base and .446 at the nose. with a thin paper patch, this came out to .460" and .455 respectively.

Using more traditional "cartridge" paper, these days fashionably referred to as "artists" paper, the diameter at the base comes out to .470", conveniently assisting the fit of the bullet into the case. Like the bullet, the case NECK is nominally tapered, from .516" at the rear, just forward of the "shoulder", to .507" at the mouth. Thus, it seems that the patched bullet was dropped into a "partially" formed case and sat on the powder load topped with the beeswax "wad" before the case was sized down onto the bullet.

Oddly enough, this concept carried over to the .303 round. This, of course, was originally loaded with black powder, but this was not dribbled into a fully-formed case. The case was basically "straight" sided and looked a lot like a .444 Marlin. Into this, a "pellet" of compressed black powder was inserted, a "glazeboard" wad followed and THEN the final taper and neck were ALMOST finish formed. The bullet was inserted on top of the wad and the whole thing then sized and the bullet crimped in with annular or stab crimps that lined up (hopefully), with the cannelure.

The Cordite loads were done in much the same way, with the little bundle of propellant inserted BEFORE final case forming. Ever tried to get the Cordite out intact?

The other trick with the Martini bullet was in the Henry's rifling, which is a marvel to behold: It is "nominally" seven-grooved, but there are actually fourteen "lands" of two different widths and ALL "lands and grooves" are radiussed. The "theoretical" .464 inch "groove" diameter does not appear as such, much the same as in the seven-"grooved" Metford and five-grooved Enfield rifling on the later Lee based rifles. Nominal "bore" size is .449", a lot closer to .450" than .38 (special) is to .357"

Anyway, we have veered a bit away from loading for the Finn M-39