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ns66
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Posted: 3/5/2012 8:47:52 PM
[Last Edit: 3/5/2012 8:49:49 PM by ns66]
Hi my rifle has carbon-15 upper, the aluminum rail sits on top of the carbon receiver and held by dove tail and 1 screw, as you can see from the picture below found on the net. i find the CH end of the rail is not very secure since there's no screw. my scope is big and heavy (6-24x40), i worry the CH end of the rail will become loose after heavy recoil. i wonder if there's some kind of clamp that will tighten the rail (the half circle shape part at CH end) to the upper receiver below?

OlCrow
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Posted: 3/6/2012 7:19:27 AM
[Last Edit: 3/6/2012 7:24:47 AM by OlCrow]
Who made that upper? Bushmaster?

Personally I wouldn't use something like that. Buy a real upper and your problems are solved.

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ns66
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Posted: 3/6/2012 12:16:44 PM
yeah it's bushmaster, well i asked them if i can swap the carbon upper to aluminum after finding this rail problem, i was told it may not fit the carbon lower
chibajoe
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Posted: 3/6/2012 12:49:44 PM
[Last Edit: 3/6/2012 12:53:29 PM by chibajoe]
If it's a Bushmaster Carbon-15, the lowers are standard and will accept any AR-15 upper. If it is a Pro Ordnance (or very early BM) Carbon-15, the lowers will not accept a standard AR upper.

Not sure what you mean by "not very secure." Unless there is something wrong with your upper, the rail should be 100% solid on the reciever, even without the retaining screw. If there is any movement in the rail then you should probably send it back to Bushmaster.
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ns66
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Posted: 3/6/2012 4:48:12 PM
[Last Edit: 3/6/2012 5:04:26 PM by ns66]
Originally Posted By chibajoe:
If it's a Bushmaster Carbon-15, the lowers are standard and will accept any AR-15 upper. If it is a Pro Ordnance (or very early BM) Carbon-15, the lowers will not accept a standard AR upper.

Not sure what you mean by "not very secure." Unless there is something wrong with your upper, the rail should be 100% solid on the reciever, even without the retaining screw. If there is any movement in the rail then you should probably send it back to Bushmaster.


it's the new bushmaster superlight, it's the bushmaster representative who told me their aluminum upper may not be perfect fit to their carbon lower

the fit between rail and upper is not perfect so there are some play, in fact when i got my bushmaster brand new i can literally lift the end of the rail up by about 1mm by hand, it's sent back to bushmaster and they replaced the upper, the new one seems to be tight (no movement by hand), but will it hold under heavy recoil i don't know

actually the bigger problem is not the "lift force" but the "push force", since rail and upper are held by dovetail (the rail slides onto the upper), there's no force to hold them together along the horizonal direction (barrel direction) except that single screw. but the recoil force is primarily along the horizonal direction (the scope will be pushed forward on the rail after fire), all the high g kick will be on that single screw, it's really dumb to design it this way

this guy has the same problem
ns66
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Posted: 3/6/2012 5:33:35 PM
i think this is in the wrong forum sorry, can mod move this to optics/mounts forum? thanks

right now the only thing i can think of to fix this problem is add a scope ring sit on the hardguard, that will help move some recoil force to the forearm, not just on that single screw, but how does it get to the right height?