When attaching scope-mount bases to the receiver, how much torque do you put on the screws for a rifle with moderate recoil (like a 270 Win., for example)? Also, do you routinely use blue Loctite on the screws? Note, I'm not talking about scope-ring screws, only the screws attaching the bases to the receiver.
Scope Mounting: Base-Screw Torque
- Thread starter South Pender
- Start date
- Location
- Western Manitoba
Every thing that I have read says that threaded fasteners have a "torque design" - so combination of thread engagement and fastener stretch. Torquing "tighter" does not make a "stronger" connection - is actually increasing the "stretch" on the fastener. Find the engineering design parameters for your screw size - use a torque wrench - be happy. It will NOT come loose. And, I do use the blue thread locker when I attach scope bases, after cleaning the hole and the screw with acetone and chasing the hole threads with a tap.
Right. I have a torque screwdriver, but am wondering what torque in in.-lbs. is recommended for the usual 6-48 screws found with most bases. Searching for the "engineering design parameters" for a 6-48 screw seems like a lengthy trip down the rabbit hole1
Good advice above.
I just installed a set of Talley bases and rings. Wouldn't you know it, the instructions gave a torque spec for the ring screws but not the base screws. Talley says check with the rifle manufacturer or give them a call.
I just installed a set of Talley bases and rings. Wouldn't you know it, the instructions gave a torque spec for the ring screws but not the base screws. Talley says check with the rifle manufacturer or give them a call.
Yeah. I can see why Talley would avoid giving a definitive answer to that question (although their ring-screw advice is first-rate). I too am installing Talley mounts and was curious about what tightness you all have used for base screws. In my case, the rifle is an older model, and contacting the manufacturer is not possible.
- Location
- Western Manitoba
Perhaps a curious observation? Why would Talley have any clue what tolerance or pitch an unknown receiver maker drilled and tapped those holes? Talley obviously controlled the drill and tap tolerance into their own "saddles" from the cap screws - why would they know what the unknown rifle maker did??
Butcherbill
CGN Ultra frequent flyer
- Location
- Blaster land, Okanagan BC
Iirc the last two rails I mounted to rifles were 20 inch pounds for the mounting screw torque specs, I’d check with the rifle or base/rail manufacturer to be sure. Yes I use blue loctite on rails/bases.
Same here. Torque value is what I use also.
- Location
- Western Manitoba
Maybe go here to Weaver Specs - torque numbers given on 4th column - appears to be listed for their various bases, rails and rings, aluminum and steel, both 6-48 screws and 8-40 screws, cross bolts, caps screws.
https://www.weaveroptics.com/weaveroptics-support/w-torque-specs.html
Warne brand suggests not more than 25 inch pounds on base or rail screws, and also specifically recommends to follow rifle manufacture specs:
https://warnescopemounts.com/elegant_tab/base-installation/
https://www.weaveroptics.com/weaveroptics-support/w-torque-specs.html
Warne brand suggests not more than 25 inch pounds on base or rail screws, and also specifically recommends to follow rifle manufacture specs:
https://warnescopemounts.com/elegant_tab/base-installation/
Right. I have a torque screwdriver, but am wondering what torque in in.-lbs. is recommended for the usual 6-48 screws found with most bases. Searching for the "engineering design parameters" for a 6-48 screw seems like a lengthy trip down the rabbit hole1
Weaver gives the following torque specs:
6-48 Screws: 15 in lbs
8-40 Screws: 18 in lbs
See h ttps://www.weaveroptics.com/weaveroptics-support/w-torque-specs.html
True. As you said, the fasteners themselves will have a clearly defined spec. The corresponding receiver SHOULD be the same if it's from the same era, but not enough certainty for Talley to guarantee anything.
- Location
- Western Manitoba
I have had a number of former military rifles - were likely drilled and tapped in someone's shop - in a few cases, I suspect that the correct pilot drill was not used - likely an oversized one from the standard "64th's" series of bits was used. So those threads will be even less engagement, than the design called for. Also have had examples where the screw that came out, was not to any "gunsmith" standard thread - was not 6-48 nor 8-40 - but was "made to work", and it apparently did. I believe now that the screws were BA sized, and "forced" into standard threaded holes. Mostly why I prefer to "chase" the threads in the holes with a correct tap - to know the threads are clean and are correct pitch / thread count for the screws that I intend to use.
I used to drill holes with drill press. If I ever could, I no longer am able to "free hand" the tap into that hole, "straight", so I used the drill press chuck to hold the tap in line with the hole. A year or two ago, I got a Forster jig - so I use those bushings now - I am pretty certain not much "wallowing" going on in the threads, now. Fresh taps also help - can buy them a dozen or more at a time, these days.
I used to drill holes with drill press. If I ever could, I no longer am able to "free hand" the tap into that hole, "straight", so I used the drill press chuck to hold the tap in line with the hole. A year or two ago, I got a Forster jig - so I use those bushings now - I am pretty certain not much "wallowing" going on in the threads, now. Fresh taps also help - can buy them a dozen or more at a time, these days.
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No telling what Bubba had going on in his shop / top of the deep freeze on the back porch...
I initially thought you were in overkill territory with chasing the threads in the receiver, but actually it makes a lot of sense with a used rifle. You never know if someone make a "close enough" fastener work at some point in the past (intentionally or not).
Thanks for those links, Potashminer. They give the specifics I was looking for.
Thanks, Glenn. This helps.
