View Full Version : .405 Winchester - Slow burning powder - Somchem S365

04-06-2014, 11:05 AM
Having seem some very nice CB loads with Somchem S365 (similar IMR 4350 /H 4350) for the .458 Winchester, and with the .405 having the very similar case vol/barrel volume relationship, and with a 330gr .405 having almost same SD as 405gr .458, looked to be a nice experiment...

The most interesting data was that Somchem S365 provides almost same velocity for same bullet and charge mass...but at approx 8000 lower psi. This would suggest a slower 'push' and less stress to the actual CB. Also burn efficiency was around 90% with the S365 vs. low 80% for other 2 powders

The relationship of .405 Win to .458 Win is approx 80% charge and 80% bullet mass ( same SD approx 0.35x). Loading data is approx 69 gr with 405 gr in .458 vs. 55 gr with 330 gr in .405 win...both at 100% load fill. Both forecast about 1900 fps with either calibre and approx 2100 with 110% load capacity.

Loaded up the .405 Win with RWS 5342 (mag) primer, Hornady brass, 55.0gr S365 and cast GC mountain mould bullet (actual 322gr / #2 mix). Gentle LEE FCD squeeze to close mouth belling and soft crimp into lead (no crimp groove). Bullet size 0.413 with Hornady gas check and HPR lube.

First shot from clean barrel, left the barrel (insides) looking like burnt candle smoke...nearly gave up there! Fired a few more shots, and with lube coating now working, barrel cleaned up nice and shiney with a few odd unburnt kernels remaining after each shot.

On target, shooting freestyle off a bench, first 5 shots easy under 2 MOA. Could do better with bags, but recoil of the 1885 Traditional Hunter's crescent butt limits much bench time.

Some very interesting technical stuff.

3 shots over chrono - 1910 , 1904 , 1921 fps (being shots 6,7,8)

Case base expansion - nil

Case ejection - easy

Fired case mouth - 0.438"
case thickness - 0.012 ea side
Cast bullet 0.413
Cast bullet gascheck sized would just not fit into fired case mouth.

Fired cases are much larger than NIB Hornardy unprimed cases, perhaps they are sized to fit .410 J-types, so approx 0.003 too tight. Are going to try and size to 0.437 by using partial RCBS .405W trim die, to keep brass close to fired spec (-0.001) with minimal belling at mouth to preserve brass life and prevent work hardening...

All for now