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Is pinning the rail to receiver a good idea?

270guy

Hi All,
I have a Rem 700 SA, that I'm putting a high end scope on (Zeiss V8). Want to have in QD rings, and rail. I don't want to have the rail detach, and have $$$ and tears all over the ground. My question is, would it be a good idea to have the rail pinned to the top of the receiver, so the pin(s) take any recoil loads, and the rail screws only have to keep the rail secured to the receiver? I would think a rail with a built in recoil step (that is gets pushed up against the top front of the ejection port), would do a similar job to pining? The rifle is used at the range and hunting on foot, chambered in 6.5 x 47L, so no magnum.
Or am I just being a little paranoid, and the normal screws and some epoxy will work just fine? Maybe I just answered my own question.

Any input welcome. Cheers
 
When putting heavy barrels on Long action repeaters, I often pin the rail to the receiver with 4 interference fit .125" pins to use the rail to stiffen the action. Otherwise, not required. --Jerry
 
If you are really worried have it drilled and tapped for #8 screws. 6.5s don't make enough recoil to worry about in my opinion. Harold Vaughn's book talked about using screws that are countersunk rather than counter bored, this makes way more sense to me.
 
The action above was drilled/tapped for 8-40 screws. I charge less for 4 pins than I charge to change the screw size since pinning is very straightforward, I don't need expensive carbide end mills to place the holes exactly, and there is no risk of breaking a tap off.

--Jerry
 
I agree that it is just not a bad thing to do, albeit unnecessary in most cases. And yes Jerry, I agree with your logic. I don't care much for tapping those little holes. It's an easy job...until it isn't.:eek:
 
If the fit of the rail to the receiver has 100% contact then the torque of the mounting screws creates a friction hold that can easily exceed the shear strength of a couple dowel pins and all of the mounting screws. The key is how much torque can be applied to those screws to achieve enough clamp load to do the job. Consider the flywheel to crankshaft connection on pretty much any engine except an ACVW. There may be a dowel there to orient the two to each other, but the transfer of the engine's power from the crank to the flywheel is strictly by this same friction hold. And add in that the power pulse spikes that the flywheel damps out greatly exceed the rated engine power to hopefully get an idea of just how powerful of a hold this can be.

Next consider that the shear strength of ferrous metals is roughly 57% of their tensile strength.

I'd up-size the mounting screws for more clamp load and lap the rail to the receiver before I'd install a dowel pin in shear.
 
Screws are for clamping. Pins for shear forces. I usually do both, pin and 8-40. I have had rails come loose with taper head screws. With the aggressive brakes and heavy scopes theres a lot of shear forces. I had an issue with one in particular, 8-40 and a 1/8" pin, ended up beating the pin hole out! Went to 5/32 and added a second pin. I think the more effective muzzle brakes are the biggest problem. They have gotten so effective it must be like hitting a wall when the bullet exits. Never had a problem with a light scope or radial brake.
 
ntsqd said:
If the fit of the rail to the receiver has 100% contact then the torque of the mounting screws creates a friction hold that can easily exceed the shear strength of a couple dowel pins and all of the mounting screws. The key is how much torque can be applied to those screws to achieve enough clamp load to do the job. Consider the flywheel to crankshaft connection on pretty much any engine except an ACVW. There may be a dowel there to orient the two to each other, but the transfer of the engine's power from the crank to the flywheel is strictly by this same friction hold. And add in that the power pulse spikes that the flywheel damps out greatly exceed the rated engine power to hopefully get an idea of just how powerful of a hold this can be.

Next consider that the shear strength of ferrous metals is roughly 57% of their tensile strength.

I'd up-size the mounting screws for more clamp load and lap the rail to the receiver before I'd install a dowel pin in shear.
Click to expand...
I agree. Many bed the bases to the action. This does much of what you are saying. That said, I see no harm in pinning them. Simple, easy and effective. Some actions, particularly the Anodized Stillers, had problems with scope rings slipping on the rail under recoil. Same rings, weight, caliber, scope etc, held fine on a Panda. That hard coat anodized finish is just hard to grip, vs the Panda. Nothing really wrong, just mostly inconvenient to need a heavier set of double screw rings to do the job. And fwiw, you(or I) will never see this on a 6ppc. A 30 with a NF BR and you will, very likely.

Anyway, I concocted another fix but wanted to pin the rail to keep the rings from walking forward. The only reason I didn't is the perception of the action being modified hurting resale value. IMO, it shouldn't. It should add to it. Lol!
 
Alex Wheeler said:
Screws are for clamping. Pins for shear forces. I usually do both, pin and 8-40. I have had rails come loose with taper head screws. With the aggressive brakes and heavy scopes theres a lot of shear forces. I had an issue with one in particular, 8-40 and a 1/8" pin, ended up beating the pin hole out! Went to 5/32 and added a second pin. I think the more effective muzzle brakes are the biggest problem. They have gotten so effective it must be like hitting a wall when the bullet exits. Never had a problem with a light scope or radial brake.
Click to expand...
Hmmm. Unless the scope was falling off backward, I doubt it has anything to do with the brake. As you probably know, it's normal for the recoil force and the gun moving rearward that put the force in place that try to pull the scope off forward.

I use to like big guns but as I get older, my guns get smaller or have brakes. I just can't get back into the big boomers. Brakes are awesome but I don't think physics will support any gun having a negative recoil.
 
Not too familiar with the dovetailed CF actions, but given my long ago experience with a rimfire scope that wouldn't stay put (cheap AL rings & student budget) I can see the problem. I don't have any rules to contend with, so the weight of a pictinney rail & rings is OK.

Interesting comment about brakes causing problems. It may not be that the brake can truly reverse the recoil. It could be that the impulse from a brake is sharp enough that it exceeds the impulse of firing w/o having the same amplitude. I don't know enough to venture a guess, only to propose the idea. It would be interesting to see a test done with some high speed D/A equipment and a 3 axis accelerometer (because the impulse vector direction may not be exactly along the bore CL).
 
gunsandgunsmithing said:
Hmmm. Unless the scope was falling off backward, I doubt it has anything to do with the brake. As you probably know, it's normal for the recoil force and the gun moving rearward that put the force in place that try to pull the scope off forward.

I use to like big guns but as I get older, my guns get smaller or have brakes. I just can't get back into the big boomers. Brakes are awesome but I don't think physics will support any gun having a negative recoil.
Click to expand...
Ya a guy would think the brake should help. I think that they have gotten so good that they are stopping recoil more abruptly than your shoulder alone would do, thus increasing that shear force. So your getting nasty shear in both directions. Just my observations. I have only had issues with heavy scopes like the NF NXS and aggressive brakes. These have all been bigger cases 80 grains of powder plus.
 
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shear strength of the 4 pins installed in my rail is about 6000 lbs. Now I didn't install them for that, they are installed to stiffen the action. --Jerry
 
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