MESSRS EDITORS—On page 214, present volume of the SCIENTIFIC AMERICAN, I find a challenge from Lieut J C Symmes, addressed to all inventors of breechloading'guns I am ready to accept the challenge, upon the conditions that at least three hundred shots shall be fired without cleaning the guns This will give a fair test of their accuracy of fire, and at the same time test the working of the machinery This last test I consider the most important feature in connection with breechloading firearms GILBERT SMITH Buttermilk Falls, N Y, March, 1858 [We admit Mr Smith's card in response to the challenge of Lieut Symmes, as it is the first one which we have received, and it specifies conditions which are important in judging the utility of this class of firearms Parties propose to enter upon this contest will future address their responses to Lieut inmes, at the Watertown (Mass) Arsenal, instead of to us—EDS