Standard 6.5/55

[Laurie]

However, a good thing to keep in mind is that the Swedes switched from the long M96 rifles with their 29" barrels.

But not for target shooting. Scandinavian prone rifle competition shooting used this rifle until the adoption of the Sig-Sauer STR 200 across all Nordic nations in the 1990s due to the increasing difficulties of sourcing and refurbishing original Swedish Mausers and Norwegian Krags. The STR 200 has a DIY QD barrel change system and barrels are made in 670mm (26.4"), 700mm (27.6"), and 740mm (29.1") lengths in 6.5X55mm chambering.

to the M38's with 24" tubes

......... as battle rifles in line with nearly every other European country during the 1920s and 30s who'd all found that 29-inch barrel rifles were extremely restrictive in WW1 trench warfare, and the ballistic potential of powerful cartridges and long barrels were never utilised. It also allowed standardisation on a single model / length for all 'arms' - ie infantry, artillery, bicycle, engineers, signaller, cavalry troops. In fact, British and Commonwealth forces started to switch from the Long-barrel Metford and Lee rifles to the SMLE 'universal rifle' as early as 1905 and it is widely recognised as one of the best battle rifles of the period.

 

[pintopete]

It seems that if you want to use the heavier bullets, as the OP stated, a longer barrel would provide higher velocity. If you can’t tolerate a 26”, then a 24” seems like a good compromise. The 2” increments will probably be less than 100 fps per step. But, if you are hunting, and want the best performance, longer seems better in this regard, especially in this cartridge. I went with a 26”, but haven’t finished the project yet. You could always shorten it, as others have said. 1:8 seems to be a good choice for those bullets. I think the ‘96 Swede’s were approx. 1:7.7~ twist. That twist stabilized those round nose 156gr bullets adequately.