The British went to Concord to seize the militia stores, since well regulated militias kept stores of weapons, powder, etc., and met for training on a regular basis at specific locations.
Looking at earlier examples of militia laws like Virginia's, which the Militia Act of 1792 appears to have been based upon, and also considering previous proposals to bear arms for reasons other than use in a militia, it is clear that one cannot separate the right to bear arms from that of a 'well regulated militia'. In both examples below we see the requirement for a bayonet, mustering, training, etc.
The discussion of the right to bear arms when forming the bill of rights was a discussion of state militias vs a federal army, where the ideal of the militia was that no standing army would be needed. But, even during the Revolutionary War it was acknowledged that the militias were typically unreliable, they again proved so in the early years of the country, all the way up to the Spanish Civil War, after which legislation finally created the National Guard as a means to regulate the state militias.
http://en.wikipedia.org/wiki/Virginia_militia
A Well Regulated Militia During the French & Indian War
"WHEREAS it is necessary, in this time of danger, that the militia of this colony should be well regulated and disciplined...And be it further enacted, by the authority aforesaid, That every person so as aforesaid inlisted (except free mulattoes, negroes, and Indians) shall be armed in the manner following, that is to say: Every soldier shall he furnished with a firelock well fixed, a bayonet fitted to the same, a double cartouch-box, and three charges of powder, and constantly appear with the same at the time and place appointed for muster and exercise, and shall also keep at his place of abode one pound of powder and four pounds of ball, and bring the same with him into the field when he shall be required...And for the better training and exercising the militia, and rendering them more serviceable, Be it further enacted, by the authority aforesaid, That every captain shall, once in three months, and oftner if thereto required by the lieutenant or chief commanding officer in the county, muster, train, and exercise his company, and the lieutenant or other chief commanding officer in the county shall cause a general muster and exercise of all the companies within his county, to be made in the months of March or April, and September or October, yearly; and if any soldier shall, at any general or private muster, refuse to perform the command of his officer, or behave himself refractorily or mutinously, or misbehave himself at the courts martial to be held in pursuance of this act, as is herein after directed, it shall and may be lawful to and for the chief commanding officer, then present, to cause such offender to be tied neck and heels, for any time not exceeding five minutes, or inflict such corporal punishment as he shall think fit, not exceeding twenty lashes. .." [2]An Act for the better regulating and disciplining the Militia, April 1757.
http://en.wikipedia.org/wiki/Militia_Act_of_1792
"That each and every free able-bodied white male citizen of the respective States, resident therein, who is or shall be of age of eighteen years, and under the age of forty-five years (except as is herein after excepted) shall severally and respectively be enrolled in the militia, by the Captain or Commanding Officer of the company, within whose bounds such citizen shall reside, and that within twelve months after the passing of this Act. And it shall at all time hereafter be the duty of every such Captain or Commanding Officer of a company, to enroll every such citizen as aforesaid, and also those who shall, from time to time, arrive at the age of 18 years, or being at the age of 18 years, and under the age of 45 years (except as before excepted) shall come to reside within his bounds; and shall without delay notify such citizen of the said enrollment, by the proper non-commissioned Officer of the company, by whom such notice may be proved. That every citizen, so enrolled and notified, shall, within six months thereafter, provide himself with a good musket or firelock, a sufficient bayonet and belt, two spare flints, and a knapsack, a pouch, with a box therein, to contain not less than twenty four cartridges, suited to the bore of his musket or firelock, each cartridge to contain a proper quantity of power and ball; or with a good rifle, knapsack, shot-pouch, and power-horn, twenty balls suited to the bore of his rifle, and a quarter of a power of power; and shall appear so armed, accoutred and provided, when called out to exercise or into service, except, that when called out on company days to exercise only, he may appear without a knapsack. That the commissioned Officers shall severally be armed with a sword or hanger, and espontoon; and that from and after five years from the passing of this Act, all muskets from arming the militia as is herein required, shall be of bores sufficient for balls of the eighteenth part of a pound; and every citizen so enrolled, and providing himself with the arms, ammunition and accoutrements, required as aforesaid, shall hold the same exempted from all suits, distresses, executions or sales, for debt or for the payment of taxes."