Am new to duplex loads and would like some opinions, have a Low Wall (original action) with new barrel and have been using 42.o grains of Curtis & Harvey (U.K.) FFF powder, behind a 245g moly coated & lubed projectile, with good results at 100 yards. Am now loading Buffalo Arms 325g projectile with 4.og of Hodgdon Universal (Aussie equiv. AP-70N) under 42.o of Curtis & Harvey FFF, before firing would like to know if this is a safe load for my rifle. This powder load completely fills the case but when seating the projectile compresses to allow the projectile to seat down to top of the canelures, i.e. proper depth. Any feed. Thanks.back greatly appreciated

The recommendation is generally not to use any compression when duplexing black.
Without a strain gauge it is almost impossible to say whether your load is safe or not.

I would be hesitant to use a cartridge that Winchester years ago chose not to chamber in the low wall but here we are today seeing their name on low walls with high intensity cartridges being chambered. Modern steels and better testing methods may be the reason but for my top knot's safety I would not be firing a 38-55 in a old low wall, too many high walls out there to be flirting with a possible disaster.

A LW in 38/55 is safer to shoot than a LW in 38/40 or 44/40, assuming the same pressure and barrel weight.

The case head on modern 38/55 is .416 and the case head on 38/40 & 44/40 is .471 and much thinner.

I don't think that the OP will have any problems IF he keeps is bullet selection at 240 gr or less and uses the low end smokeless powder charges developed for the 255 gr bullet and BP, behind the 240> gr bullets.

Why is it I never hear complaints about about how dangerous, using the LW's in 38/40 and 44/40? Loaded to the same pressures with the same SD bullets, the 32/40 and 38/55 are safer, because of the smaller case head and use stronger brass.

The OP's rifle is already built and has probably been shot, to some extent. My LW was 357 Mag when I got it, rebored from a original Win 32 cal barrel. It had been shot for at least, a few years, before I got it, 25 years ago.

It's not in stock but, this would be a good bullet for this LW:

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Frank