I have the same basic problem. But for me it only hurts during that last couple of centimeters. What I do, instead, is push the cartridge as far as comfortable, then use the next one to push the previous cartridge all the way in. Then, I only have to push really hard on the last round (#6).
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face