I had, and occasionally still have, the same problem you have, D.
For me, it's a simple fix IF I remember to do things correctly. When I hit the armguard, it's because my elbow is down at 5 or 6 o'clock. (I'm a lefty. For a right-handed shooter, it would be 6 or 7 o'clock.)
When I rotate my arm so that the elbow is at 3 o'clock (that's 9 o'clock for a righty), the problem goes away.
That's all there's to it. Hope that helps.
Mark