Obviously, I don't have your data set, either.
However, if you look at a couple different places, you can see an annual death rate of ~10 per 100,000 (or about 32,000 per year with our current population) over the past several years.
If this rate is consistent, which those sources seem to indicate, that means that per decade since the founding of the country (which I'll call 1790 for when the first census was done) has been about 2,600,000 (see table for math).
Census Population Avg/Yr of Decade Firearm Death/Yr Death Rate Total deaths
1790 3,929,214 4,618,849 462 10/100k 2,543,936
1800 5,308,483 6,274,182 627
1810 7,239,881 8,439,167 844
1820 9,638,453 11,252,237 1,125
1830 12,866,020 14,967,737 1,497
1840 17,069,453 20,130,665 2,013
1850 23,191,876 27,317,599 2,732
1860 31,443,321 35,000,846 3,500
1870 38,558,371 44,373,790 4,437
1880 50,189,209 56,584,488 5,658
1890 62,979,766 69,595,967 6,960
1900 76,212,168 84,220,332 8,422
1910 92,228,496 99,125,017 9,913
1920 106,021,537 114,612,081 11,461
1930 123,202,624 127,683,597 12,768
1940 132,164,569 141,745,184 14,175
1950 151,325,798 165,324,487 16,532
1960 179,323,175 191,267,551 19,127
1970 203,211,926 214,878,866 21,488
1980 226,545,805 237,627,839 23,763
1990 248,709,873 265,065,890 26,507
2000 281,421,906 295,083,722 29,508
2010 308,745,538 308,745,538 30,875
Total military deaths in the US Civil War were about 620,000 (some place this as high as 850,000).
Total military US deaths in WWII were about 405,000.
Total military US deaths in WWI were about 116,000.
Other conflicts rank below on that chart.
Just summing the top three wars we have been involved in, total military casualties come to about 1,141,000 (or maybe 1,371,000, if you use the larger guess).
Caveats
- The conclusions above are based on reverse extrapolation from data available from the last couple decades - which probably are pretty poor when it comes to the first several decades (at least) of the United States' existence
- None of the data I have found separate firearm deaths among the military from the general population in times of peace
- None of the data I can find separate civilian deaths by firearm from military deaths by firearm during times of war
- All of the data I can find puts the suicide rate at ~60% of the total death rate by firearm - IOW, of those about 2,600,000 firearm deaths, 1,560,000 have been suicides
- To echo @DJClayworth, all the deaths in the Civil War happened in the United States - which will wildly skew the total data (since you'd need to remove those ~620,000 deaths from the total of 2,600,000, which brings the total down to really only about 1,980,000 - still larger than the deaths from all wars we've been involved with, but a much much lower ratio thereto)
Conclusion
Based on the generic claim, "since the beginning of ... the United States ... more people died within the US due to firearms, than in all the wars the US ever fought combined" is at least plausible, if not actually correct.
