Trying to use memcpy to continuously update an array, but failing - c

Question

Just some premilinary info, the below code is part of a user space HID driver Im building, so Im going to try my best
to skip over the sections relating to device conectivity, etc...
I have two main arrays that I focus on which is the buf[] array and the buffer[] array.
The buffer[] array will be comprised of ranges of hex values that are taken from the buf[] array and appended on to it.
With the purpose of the buffer[] basically holding a large number of bytes that can then be consumed else where.
But I seem to be running into issues with buffer size growing past 1400, I also feel as though my logic as far as adding
to the buffer is flawed and not working as I think it is. Is there another way that I should be going about trying to acomplish this end goal?
If this code does not show enough PLEASE let me know and I will make the neccesary edits, Im desperate for the help
and still very new to C. Thank you!
full code found here if necessary http://pastebin.com/cyawpXCq
int int main(int argc, char const *argv[])
{
unsigned char buf[64];
unsigned char buffer[1400]; //1400 is the max size this should ever be
int i;
size_t buffer_length = 0;
for (i = 0; i < 24; i++)
{
// in this loop I add elements to the buf[]
// these elements are sent to the device
// which then returns the buf[] with new elements
// in it.
// I then want to push a range of these elements
// into the buffer which I am attempeting like so
// I skip the first 7 elements and take the
// next 16 elements which follow and append those to
// the buffer[].
memcpy(buffer + buffer_length, buf + 8, 16);
printf("\nStored Buffer - \n");
for (size_t i= 0; i < sizeof(buffer); i++) {
printf("%02X ", buffer[i]);
}
// add another 16 to the length
buffer_length += 16;
// loop breaks based on another condition
break;
}
// This condition comes next and does a similar
// thing as above
if(true)
{
// buf[] gets returned to
// me containing hex values from a device. I now
// want to append these values into the buffer[]
// and take the 30 elements which come after the
// first 7.
memcpy(buffer + buffer_length, buf + 8, 30);
printf("\nStored Buffer - \n");
for (size_t i= 0; i < sizeof(buffer); i++) {
printf("%02X ", buffer[i]);
}
// add another 30 to the length
buffer_length += 30;
}
// this loop can can return up to about 200 unique buf[] arrays
// and again is doing a similar thing where buf[] is filled with device
// data
for( int address = 0x0370; address < 0x0370 + 1400 + 1400; address += 28)
{
// I want to append 28 elements following the 7th element from buf[]
// to the end of the buffer[] on each iteration
memcpy(buffer + buffer_length, buf + 8, 28);
printf("\nStored Buffer - \n");
for (size_t i= 0; i < sizeof(buffer); i++) {
printf("%02X ", buffer[i]);
}
// add 28 to length each time.
buffer_length += 28;
printf("buffer_length = %zu", buffer_length);
}
return 0;
}