From the late 1600s till 1830 the British used the Brown Bess Flintlock Smooth-bore musket. The "round" for the Musket came in a linen cartridge consisting of a Lead ball and black Powder. You loaded the weapon by first biting the Cartridge tearing it open and than priming the pan of the Flintlock and than loading the rest of the Powder and the ball down the barrel (And than using an wooden than than iron ramrod pounding the ball onto the powder). At that point you cocked the flint lock and hopefully the musket fired (Misfire rates appears to have been as high as one out of six rounds). These weapons were all smooth-bore firing a lead ball a little smaller than the barrel. The reason for this is that if you did have a misfire you could clear the weapon in 20-30 seconds by simply turning the weapon upside down and leaving the ball and excess powder fall out of the barrel (unlike a rifle where you had to pull the ball out of the weapon when it misfired which could knock out a rifle for up to five minutes).
Now in 1830 the British replaced the Flintlock system with the more reliable Percussion System (misfires in an 1830 test had been one out of a Thousand rounds fired compared to the one out of six for the Flintlock in the same test). While the firing mechanism was changed the 1830 musket was still a smooth-bore weapon. In 1848 a French Officer by the Name of Minnie invented a lead bullet for Rifles. This lead bullet was smaller than the bore of the barrel so could be loaded like a smooth-bore musket, but it had a hollow bottom with a wooden plug in the hollow. Upon Firing the wooden plug would pushed against the lead walls of the hollow base to engage the rifling. Thus you had a rifle that could be loaded as fast as a smooth-bore musket and with the percussion firing system you no longer had to worry about to many weapons being out of order do to misfires (in 1854 the US would adopt the same system but drop the wooden plug, the US found it was not needed, the powder itself would expand the hollow base to engage the firing).
Now the Minnie Ball concept had been invented in previous centuries, but never adopted do to the problem of the Rifle being out of actions do to misfires. The Percussion cap solved the problem of Misfires and once solved the Hollow Base Bullet was the next logical adoption.
I went into the above because the adoption of the New Hollow base firing Percussion Rifle in 1856 was the trigger mechanism for the 1857 Great Indian Mutiny. When Britain adopted the Minnie Ball in the early 1850s the British first issued them to their Regular Units. These new Rifles were found effective in the Crimea War of 1854. With the success of the New Enfield Rifles the British decided to issue the new rifles to their Indians units. It was this issuance that sparked the Great India Mutiny.
Now the cause of the Great Mutiny was more complex. Britain had less conquered India than moved in and took over. During the 1700s and early 1800s Britain thought nothing of using its Army to take over India and to put down any local who objected to British Rule. Given that the British ruled through the British East India Company, the British prefer to rule through local India rulers (Including the Great the Great Mongol Sitting in New Delhi, some of these Rulers, but Not the Great Mongol, survived till Indian Independence in 1947).
Now Britain wanted trade more than it wanted tribute, thus it rule was lighter than previous foreign rulers (But it also did less for the average resident of India than previous rulers, even permitting many of them to die if that was the best way to keep cost of Government down).
At the same time previous to the 1850s most British living in India tended to stay in India they whole life often marrying into the local population. In the 1840s and 1850s things started to chang as more and more British in India were they on temporary assignments AND BROUGHT THEIR FAMILIES ALONG. Thus you had less and less interlocking families connections between the British and the Local population.
Foreign threats had also diminished over the previous 50 years given that the French had finally been kicked out of India during the Napoleonic wars and England ruled India alone (except for the Portuguese Colony on the West Coast, but Portugal was a loyal Ally of England so not a threat). The British East India Company's primary concern was making money NOT ruling (but did run the country for that was the best way to make money). Thus you had a situation were India was still technically ruled by the Great Mongol in New Delhi but in fact all of the important decision were being made by his "Assistants" from the East India Company (Except in the areas of India independent of the Great Mongol where the British East India Company ruled through the technically Independent local Maharajahs).
To back up the East India Company the British Government maintained troops in India, but the East India Company over the previous 100 years raised it own local troops AND taken over various Troops from not only the Great Mongol but the other "Independent" Indian States. These Indian Units were both Moslem's and Hindu and retained a good bit of their connection to the population the troops were raised from. The British had had previous Mutinies but these had always been local units and Britain could also rely on Muslim units to put down Hindu Units and Hindu units to put down Muslim units. Thus the Mutinies were NOT effective. The Great Mutiny saw BOTH Muslim and Hindu units working TOGETHER for the first time in the British History of India. The underlaying cause was the misrule by the British but the trigger was the introduction of the New Enfield Rifle.
As stated above the Enfield Rifle Introduced in 1857 had been in use since the early 1850s in British Units in Britain and the Crimea. The British when it adopted the new weapon modified the traditional Cartridge, instead of using plan linen the British started to Encase the paper Cartridge with a coating of grease. Britain had just started to use corn base grease which was much cheaper than grease from Pigs and Cattle. The new Corn based grease was so cheap that the British believed the extra cost of coating the Round to improve their water proof-ness was worth the extra treatment. It was these nw Grease Cartridges that was to be the trigger for the Mutiny.
When the Indian Units were issued the new Enfield Rifles in 1857 a rumor started to go among the Troops that the Grease used in the Cartridges were from pigs and cows. The Moslem's in the Units were offended by having to BIT into the Cartridge and thus taste pork. The Hindus units members were also offended for by biting a Cartridge their believe their would be tasting beef. This caused various Muslim and Hindu Units to Mutiny and than unite and march on New Delhi to restore the Great Mongol to his rightful position as absolute ruler of India.
Thus the reason for the Mutiny had to do with British Mis-rule, the Grease was only the trigger. Now once the trigger had been pulled the resentments of the previous 50 years came to the surface and many of the same units that had revolted do to the Grease, used those Enfield Rifles in the subsequent revolt. Thus the point of this letter, pork/beef was NOT the cause of the mutiny, but only the trigger but it was a trigger that caused Britain to reform and re-think its rule of India. The real effect was to cause Moslem and Hindu units of the East India Company to act TOGETHER against the British, something the units had NEVER done before and would not do again.
A very anti-British site regarding the above (More extreme than I would go in evaluating British Rule of India but a good source of Data regarding British Rule):
http://members.tripod.com/INDIA_RESOURCE/hist-2nation.htmlList of Indian "Independent States" prior to 1947 Independence:
http://rulers.org/indstat1.htmlA very pro-Mutiny view of the Great Mutiny
http://www.freeindia.org/biographies/greatlkings/jhansi/page11.htmA BBC presentation on the Great Mutiny
http://www.bbc.co.uk/history/state/empire/indian_rebellion_01.shtmlA soldier's personal Recollection"
http://www.manfamily.org/PDFs/Indian%20Mutiny.pdf#search='The%20Great%20Indian%20Mutiny'A brief background on the Mutiny:
http://www.kamat.com/kalranga/itihas/1857.htmOther Readings on this subject:
http://www.eblanchette.com/_supportdocs/History%20Britain%20and%20India/Indian%20Mutiny%20Background.htmhttp://homepage.ntlworld.com/haywardlad/indianmutiny1.htmlhttp://members.tripod.com/~INDIA_RESOURCE/1857.html