Hello,
I have been looking for good flip up caps for my Viper PST w/ 50mm Objective lens.  Just received the Butler Creek Tactical One Piece flip up covers size 43-44.  They feel quite loose and I am sure that they will come off with recoil.  The next size down is 39-40, I am afraid those will be too small.  Has anyone found a good fit?  Perhaps the Multiflex models or original BC model?  Or the Vortex product (although i read on here they did not fit well either)?  

In case anyone is wondering I have the Butler Creek Multiflex (yellow button) size 14 on the eyepiece and they fit very well.  

Thanks

http://www.aadmount.com/Caps/Caps.html

My lgs didn't have a BC that would fit tight on my Viper HS 50mm.  But he did have a Vortex flip up that did fit well, don't remember the size but you could check Vortex website under accessories for help.  Fit is nice and tight and folds flat on top the lens.  I use a BC on my eyepiece and vortex on the front.

Great thanks!  I will reconsider the Vortex if they work for you.  Those AADMOUNT look really nice but $99 is a bit steep, especially since the BC eyepiece works well.

The BC caps are shit. They will work well for a little while, them one day you'll flip em up and they will snap.

I finally went with the night force bikini covers, and they are working out well

I have two sets of the BC's and they been around for 4-5 years now with no problems so far.  First thing I do is toss the bikini covers if a scope comes with them.  The only one I did keep and use is on my aimpoint comp4s.  For the leupolds, I have their aluminum flip ups which I really like.

I received the Vortex flip cap for the Obj Lens.  It fits very well, nice and snug.  The "collar" looks nice and appears to be well made, better than BC in my opinion.  The hinge is a little flimsy, much like BC's, and I predict will eventually fail after a few years.  For the price that's OK with me.  I would recommend.  

In summery for Vortex Viper 50mm Obj best caps are:
BC Multi-flex size 14 for the Eye
Vortex size 7 for the Obj