There has been some discussion concerning Delrin or metal spring guides.

1 1/4" diameter PEEK costs a bit over $100/foot and is more expensive than 1 1/4" diameter Ultra-Wear-Resistant AMPCO 18 Bearing Bronze which costs a bit over $98 a foot.

PEEK is a good high strength, high temperature plastic (14,000psi and -20F to 480F service temperature), however, since
1 1/4" diameter Delrin rod costs about $8 per foot.........I'll continue to use Delrin!

I've used 6/6 nylon for guides (the molly filled stuff) and it works OK. The issue for me is that the nylon machines into long strings that fly everywhere (especially around the spinning chuck) and it isn't as stiff as Delrin. Delrin is slicker than standard 6/6 nylon but similar to molly filled 6/6 nylon.
6/6 nylon nylon coefficient of friction .25 (molly filled "Nylatron" .20)
Delrin coefficient of friction 0.20

Anywhoo.....6/6 nylon is stronger than Delrin and less brittle which also makes nylon less stiff, plus 6/6 nylon can change dimensionally if it absorbs water from the air.

Bottom line (IMHO), leaving all the "minutia" behind, both are fine for airgun spring guides. I simply prefer the machining properties of Delrin.

Just ordered a "new to me" Delrin 150 rod which is rated at 11,000psi.
http://www.plasticsintl.com/datasheets/Delrin_150.pdf
From the above........
• Good dimensional stability
• Excellent machinability
• Superior impact and creep resistance
• High fatigue endurance
• High strength and stiffness properties
•Chemical resistance to fuels and solvents
• Low moisture absorption - Delrin® can operate in wet environments with little effect onperformance or dimensions.
• Good wear and abrasion properties - with its low coefficient of friction and hard and resilient surface, Delrin® is
the material of choice in many wear applications.

What I received today. The stiff seems very solid when "clicking together" and I plan to cut some on my lathe this week or next.