Besides the obvious width differences between the standard size SIR like the the ARMS #45 vs the slimmer #46, are there any advantages of one over the other?  More rail space, mounting options, better cooling?  To anyone who owns or has used both, is there a significant diffence in feel between the .25 inch size diffence? Thinking about putting one together but don't really have a way of getting my hands on them prior to purchase to see which feels better to me.

I did a small SIR round up at the start of this thread... it may be helpful.

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Thanks new-arguy for the response. This is exactly the type of useful info that I was looking for. I sent you an email requesting additional info regarding weight of SIR to an M4 type carbine.