Barrel on the Aussie HB rifles was to the same spec as the barrels on the old Long rifles. In other words, same outside diameter as the barrel on a Number 4.
At least, that went for the single rifle I was able to inspect closely. they really are not all that thick on the ground in this country.
As to the Ross, my views are well known (TOO well-known, some would say!).
The problem was not really British-standard ammunition, but rather British NON-standard ammunition which would not make it into the chamber of an SMLE. People have forgotten that the British increased Chamber diameter of the SMLE (very quietly) about the same time as the Ross was being (very loudly) cursed in public. There was a LOT of politics involved in the whole sad affair.
The men I knew who used the Ross in the Gas Attack at St. Julien fired literally hundreds of rounds that day..... with no trouble. I do not know what ammunition 8th Batt was using.
Captain George Dibblee DCM (5th Batt CMR) told me that the Ross was "unpopular, due to its length and weight; you couldn't get into a dugout with your rifle slung". He attested also that 5 CMR had NO problems with the Ross Rifle and attributed this to their standard of maintenance.
I have used a Ross Rifle Mark III myself in a timed, high-speed match with 40 reactive targets on rolling ground, distances unmarked, ranges from 80 yards to 590. Two Rosses cleared the range in 8 minutes 30 seconds, beating out a pair of MINIMIS. Not bad for old junkers! One was my HMS Canada rifle, the other a Bubba Special with a full-length barrel. We used 78 rounds total.
In 1939, Canada held more Ross rifles than Lee Enfields in stores. They were used for training throughout the War.
The bad 1915 ammunition was from a single contractor, whose ammunition unfortunately was what was issued at a critical time. It was problematic in Ross and Lee Enfield rifles.
McBride reported that Cdn machinegunners would pass every round through the T-slot on the face of their Brownings' breech blocks before loading the checked cartridges into belts.
And like I said earlier, I've personally experienced a "jamming" Ross on the range. Spotlessly clean rifle, SAAMI-spec modern commercial-grade ammo that worked perfectly in every other .303 rifle I ever fired it in. Ross would jam as soon as it was fired enough to heat up the rifle.
So with all due respect, I personally do NOT believe that the problem was solely "non-spec' or "bad" British ammo. That undoubtedly exacerbated the situation, but the problem was definitely more than that - or it wouldn't have been felt necessary to retro-ream every chamber of every Ross in the system.
I think part of the problem was that the Ross was never ever a fully developed battle rifle. It was adopted at an early stage in its development and issued to the Militia. And it developed a sterling reputation as a superbly accurate service 'target' rifle - everything built to match-grade specs (including the barrelling
and the chambers) and performed superlatively with match-grade Canadian ammo. Didn't do so well when it got into dirty service conditions using non-match-grade war-service ammo.
But if you look at the history of the Ross, one of the things that really stands out is that Sir Charles Ross never ever stopped tinkering with it. That's the reason there are an endless number of marks and variations - and trouble sometimes telling them apart. The Mark II and Mark III, for example, are for all intents and purposes entirely different actions.
The other thing, of course, is that the Ross rifle, in all its variations, was essentially built to the same size specs as the British
Long Lee Enfield - hence the complaints about its size and weight.
Originally, the British followed the age-old pattern of issuing full-length Long Lee Enfields to infantry and very short Lee Carbines to cavalry. One of the major improvements that came out of their experience in the Boer War was the decision to equip everyone with an intermediate-sized rifle, the Short Magazine Lee Enfield. The Americans followed the same pattern soon after with their Springfield, and the Germans eventually did the same with the Mauser Kar98k. The Ross rifle was never developed in a 'short rifle' pattern. And that, by itself, might have been enough to make the troops want to dump it for the SMLE.
The Ross bayonet was absolutely superb however. Reportedly, when used as a bayonet, it was somewhat wobbly on the rifle. On the other hand, as both a fighting knife and all-round utility knife, it was so much better than the SMLE's Pattern 1907 bayonet (and just about every other bayonet issued to anybody until the 1990s or thereabouts) in both quality of design and materials that it wasn't funny. I think a lot of them went "missing" when the troops exchanged the Rosses for SMLEs.