Had an 18" SPR for 2 years and sold it.
POSITIVE:- Very Accurate (sub MOA - .75 best group)
- Great fit-n-finish
- Well executed early piston design
NEGATIVE:- Heavy (the Noveske N4 Recce that replaced it is nearly 2 lbs lighter: swapped PRS for a UBR)
- Piston op-rod rides too high above the barrel (in my layman's opinion)
- Proprietary parts (although I never had a need to replace them)
- Had trouble with Timney trigger (POF replaced it Free of Charge)
- One (only) Customer Service experience - just had a very hard time getting a hold of anybody via Email or Phone (took several weeks)
- Wish they could use standard rails from DD, Troy or LaRue - or do a better job of lightening them up as they are bulky & heavy
All in all, it is a great rifle.
SUMMARY (my opinion):
Do you need a piston: NO
Are there better values & options for your money in the market today: YES
What drew me to stray: weight, bulk and proprietary parts
What to consider instead (as I did): Noveske Switchblock or LaRue Stealth or OBR 18"
...I went with Noveske SwitchBlock route as I shoot suppressed, the Stealth is a relatively heavy upper and the OBR was not available at the time. I now own 2 Complete Noveske's (16" Recce, 10.5" LoPro), BCM 12.5" and LMT M4 and love them all. I
currently covet a Knights SR15 and OBR, but hell, this is always changing.