A friend of mine in Texas has 3 different older 404 Jeffery rifles, by Jeffery, John Roberts, and another. They will easily chamber his older RWS ammunition, but not the newer 404 Hornady loads. The new cases seem to be a mil or 2 longer. He's looking for a gunsmith in Texas (to avoid shipping) who could lengthen the chambers in these 3 rifles and set headspace.

I'd suggest he proceed carefully...Had issues with dimensions on 450 Rigby by Hornady just very recently...makes me a little "cautious"

Matt @ Hill Country Rifles.
Quality gunsmithing!

For what he will be charged to work on three rifles, just get a reamer cut to fit the Hornady ammo, and do it yourself.
Then sell the reamer for at least half what it cost.

RWS cases at 72mm in length are one millimetre shorter than other manufacturers, I'd be surprised the chambers are not cut for the standard 73mm length as this is what the original Kynoch cases were and the only other cases I have to measure are Parker Hale made by Norma, and these are 73mm in length. I have new in packet RWS cases (not loaded cartridges) and like the others I have previously used they are all 72mm in length.
I haven't tried any other later manufactured factory ammo in my 404 such as Hornady but it chambers Kynoch, Parker Hale and RWS no problem.

Thanks Eagle....good info. I wonder if he's tried any newer ammunition other than the Hornady.