Marking indicating conversion to .303 caliber.

The ones I have had were rebore/re-rifled using the original 6.5cal bbl.
The bbl was not set back on any that I owned,,just rechambered to 303Brit after reboring.
At first thought,,you'd think the 303 cartridge would 'clean up' the 6.5 chamber. But it does not.
It leaves the fired 303 empty cases with a distinct 2-step neck, the larger lower dia of the 303 neck being a portion of the original 6.5 chamber body.

People have argued that point with me in the past, but simply placing a 303 and 6.5 Dutch cartridge side by side will show where they do and do not overlap. I use to have a pic of both plus a fired case from one of my rifles for a comparison but it's long gone in a computer crash.

Springfield Sporters of PA used to sell a lot of these converted Dutch carbines in their ads in Gun List and Shotgun News. They were not expensive then. The big muzzle break on the end was an eye catcher to most. The butt plate on many was a rubber replacement a lot like the Enfield 'Jungle Carbine' 303 #5.
You don't see them much anymore, just like a lot of the surplus rifles from just a few years back.

I forget what the reason was for the conversion to 303 was. I was told it was something to do w/Australia it seems. Either the rifles were going to Australia for home defense (WW2),,or Australia was to provide 303 ammo since the 6.5 was no longer available from Europe.
Maybe that was all just conjecture,,but that seems to have been at least one reason for the conversions.

Of course the enbloc clip fits the 303 just fine and they function OK.
I will say they do kick a great deal more in 303 caliber than the same carbine in original 6.5
Most every one I've seen is severely pitted under the wood line. I suspect from the climate there.