I'm ready to buy one now.I think i'm going to get the 50 from MSTN.Can i install the 50 without taking flash,gas block,and delta ring off?

All you need to do to install the #50 is remove your handguards.  It mounts to your A3 receiver rails.  

One of my favorite quotes from this site:

"A monkey can install a SIR M; a retarded monkey could install the SIR C."

It's really that easy.

girard,

You won't be dissapointed with the SIR 50! [:D]

Just remove the hand guards and there will be 3 cross bolts on the receiver section and 4 screws fot the yoke which goes around the barrel nut.

Just put the receiver cross bolts in and lightly tighten them so that the SIR can still move.  

Pull back the delta ring drop in the yoke and tighten the 4 screws down.  

With the yoke tightend down now you can finsh tightening the cross bolts across the receiver.

Tightening down the the receiver section first might make it harder to get the screws in the barrel nut yoke.

Don't forget to use the loctite that comes with it.

Good luck!

Sounds good thanks,butyou raised a question.Does the model 50 also come in M and C models?

Girard the 50 only comes in the C model, at least for now.  The C and M models both attach the same way with the barrel nut yoke so they both mount to the receiver just a good.

If anything I feel the C gives you more options because you can leave the delta ring on and switch to the hand guards,RIS, RAS,RAS2, etc...