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I am loading for a 7mm using Lee Dies and was surprised to see a big difference in accuracy by adding a Lee Factory crimp die. I am loading hunting rounds so crimping is necessary. The bullet seater die does not crimp at all. Both targets are 5 rounds single load at 100 yards with, new WW Super brass, 139 gr Hornady SST,62.2 gr of RL 19, C.O.L. 3.36, shot out of a browning A bolt Medallion with a boss set to 2.5. Hornady Manual says 3000 fps for this load. I do not have a crono yet so I could not check. The tight group is with the crimp loose group without. I did load 4 other loads in .5 grain intervals to 63.3 gr with crimp none shot as well as 62.2 gr load. I could probably tune the boss to the other rounds but do not see any reason to with the max gain of 100 fps +-. any thoughts?
 

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Try loading for 44 mag with win.296 and a 240gr swc and no crimp , or very little. It will make a mess of your revolver.
 

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I was also surprised by an increase in accuracy using the Lee Factory Crimp Die in 7.62x54R. I didn't expect it and was a bit worried about the die damaging the bullet. I have bought the dies for some of my other rifle calibers now but I don't often use them.
 

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In just my very limited tests with the LFC die, I noticed that it did make some improvement when loading bullets that are, shall I say, less than match grade. For example, I have some pulled M855 62g .223 bullets that when I loaded them without crimp, they averaged around 3 MOA out of a rifle (Colt AR Govt A2) that will shoot cloverleaf groups when using 77g Sierras. After running the rounds through a LFC die, the groups of the M855 loads shrunk to an average of just over 2 MOA. Trying the LFC die on match bullet loads didn't seem to show any appreciable improvements in grouping on paper. This led me to guess that with bullets that are less than consistent in size and contour, a light touch with the LFC die gave consistent neck tension and helped align the rounds. Can't prove that, just my theory.
 
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