Shipbucket

I dont think merely upsizing the roller block mechanism will work. There is an x/y axis graph of mechanism robustness versus lightness with the larger the calibre nad the higher the ROF requiring greater robustness. This is why the MG213 and all later revolver canon are used to achieve reliablly high ROF.
The FN HB had ROF up to 570rpm. The MG131 was electric and a lighter bolt and 950rpm.
You must decide wether you want a free hand pintle type mount, eg the MK103 was often field mounted on a post driven in the ground. For all high ROF you will need a codesigned mount to give accurate tracking and stability - the 5cmFk41 downfall. Whether you can use a MG42/45 mechanism to achieve 700rpm in 30mm is questionable. The MG151 had 650rpm
The MG42 was a peculiar piece, yes we all know its place in history as the first truly mass produced infantry weapon using stampings etc for ease of manufacture. But it was a product of a political decision not a rational technological choice. The MG32 and MG81 both came earlier and had equivalent ROF. The fundamental flaw is waste of ammunition and drift of the whole weapon during sustained use at up to 1500rpm. The bipod had to be held to the ground and the tripod was usually sandbagged. The successor MG45 of up to 1800rpm would have been useless in a LMG role. The BREN, long regarded as the best LMG of all time, had 500rpm but less because of mag changing. But it was accurate and a good team timed mag changes to suit sweep or target shift.
A succesful weapon is not always the most efficient or effective, with cost always being a major factor and the search for the ideal is ongoing. What time period tech are you envisaging?
ciao

Also, what application is the weapon for?
Where the weapon is mounted can often mean the difference between a 'good' design and a 'bad' one... with one weapon having both qualities, depending on how it is used. The Oldsmobile 37mm cannon that was despised in the P-39 Aerocobra became absolutely adored by the crews of PT boats- so much so that a 'field expedient modification' became a standardized upgrade package!

There's a lot to consider in making an autocannon this large.

Its supposedly meant as a weapon of higher fire rate than magazine-fed weapons, to be used for the same applications (AA/Shore Bombardment) as the other weapons. But, the big thing is that it would potentially replace the weapon for a 3-for-2 basis.

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