The Midwest URR prevents the upper from rotating. All of the other fixtures usually work fine under normal torque values.
I’m not very familiar with the bev block, but it looks like there is only a small part that interfaces with the charging handle path in the upper to prevent the upper from rotating.
the MWI URR (and a few others) have a sail that engages the charging handle journal, yes, this prevents rotation. the BEV block has a similar "nub" that isn't as substantial that also prevents rotation
as well as the entire "block" portion that sits vertically in the BCG path. if you want, you can remove the bolt and install the BCG as well as the BEV block and it will not rotate.
i think you are overplaying how much rotatable moment is going on here as well as not understanding that when you engage with the barrel extension, you are transmitting force from the wrench, through the barrel nut, through the upper, which is free to rotate slightly but kept from doing so by a sail or nub as the case may be. the
clamping force exerted by the nut is immediately relieved during removal, and when installing, that clamping force is not intended to be significant. 35-80 ft-lb about arm's strength. this is not the shear failure or plastic deformation point of 7075 aluminum, it is well below it.
if you are applying enough torque to go well beyond this, that is a problem of the person using the breaker bar or whatever trying to goon the nut on the upper (which you should not do), and during removal if there is excessive force needed to remove, there are methods that can make it easier such as penetrating oil, heat, cut off wheels, et c. i can dig around for a junk upper and see what exactly it would take to actually break it through ineffective rotation stopping power. i guarantee you it will be far in excess of any human's arm strength.
you do you though, if you sleep easier with using an MWI URR and then i think you're all the better for it vs bubba using a piece of carpet, some cardboard, and a couple whacks on the vise's arm.
i might be retarded. the MFI rail i got for my MP5 is
listed for an MP5K but on
the MFI website they're saying i can do whatever. there isn't a real difference, is there? i could have just slapped the rail on the whole time? i haven't opened the packaging up since i've found out how anal HKparts is with returns
the optic rail is the same between the MP5K, MP5-PDW, SP89, HK94, SP5, MP5 and it's variations. the few that are different you likely will never see in the wild like the SMG, MLI, or MP5KA1. the mounting point differ between
receivers typically, so a G3, HK33, and MP5 might have some difference with the claw mount or low profile mounts, although the "high" NATO claw mount should work on all of them.
