I hope you don't mind the hijacking to your thread, Richmond
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I would say that, one reason for this period grenade fuze holes being larger than others was the need for some to be wide enough to introduce shrapnel, namely (lead) bullets ... resuming that thin holes were to fit simple matchcord and respective grenades to be filled with only gunpowder.
The British introduced the shrapnel grenade in Portugal during the Peninsular War, an invention soon adopted by Portuguese. Apparently Wellington had some doubts about the efficiency of such grenades, on grounds that their projectiles impeled by the bomb explosion didn't have enough velocity to penetrate and kill victims, only injuring them. But he appreciated the use of such shrapnel in heavy cannonry (24 pounder), with visible results in Badajoz.
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