Many, if not most, modern fly lines come with a factory welded loop for an easy leader connection. The problem is that if you’re using a straight shot of leader material that’s under 40lb. test, the diameter of that leader can cut into the the welded loop while fighting a big fish, trying to free a snag, or inducing any other stress that puts extreme pressure on the connection.
Solution: create a short mono butt section to act as a buffer between your welded loop and leader. I’ve been using a foot-long length of 50lb. or 60 lb. mono. Just tie a perfection loop (here’s a great tutorial from Animated Knots) at both ends, and you’re good to go! I’ve been using this system with my two-handed shooting head for over a year.
currentseams.com 
Great tip!
Thank, Scott! I got so frustrated with destroyed welded loops, and this has solved the problem. Be safe and be well.
Steve with your system doesn’t the loop still ware just not as much but it will still ware ? Why not just cut off the loop and use a nail connection with a loop knot? Bill
Hi Bill, no, it does not. 18 months into this system and the factory loop is virtually non-blemished, and certainly not cut into as typically happens with smaller diameter connections. In my experience, cutting off a factory loop and replacing it with a hard connection inevitably results in a cracked, hinged line at the junction point. So that’s my logic! 🙂
Sounds good . I’ll give it a try. Bill
I replace the butt section once a season. 🙂