Home Forums Hunting & Shooting Hunting Optics Big heavy scopes, tiny base screws

I only have one scope that weighs about 24 ounces with best quality light weight Picitinny/Weaver scope rings. I only rarely use that rifle with that scope, but the bases on that rifle are attached with 6-48 screws. All of my scope bases are jig-aligned and are installed to the receiver with JB Weld (no release agent)and blue thread locker on the screw threads. None of my other scopes weigh more than 16.something ounces and most weigh from approximately 8 to 12 ounces (without rings).
I don't have a warm and fuzzy feeling of confidence that my one heavy (24 ounces with rings) scope will not snap the 6x48 base screws off, if I slip on the ice and the rifle hits scope first. I do feel a bit more confident with it's durability, since I remounted the bases with JB Weld.

I have an 11 ounce prism scope mounted to the rear scope base only, on one of my driven game rifles, I drilled and tapped the base holes out to 8-40 on that rifle to eliminate the "tiny screw" concern on that one.

What I am wondering is: For those of you that have heavy assed scopes that weigh a pound and a half to 2 pounds (and possibly more), don't you worry that those tiny little (6-48) screws, torqued 20 to 30 inch pounds, are going to break off during the rigors of hard hunting?

I know a few factory rifles are drilled and tapped for 8-40 base screws and some owners have their rifles upgraded to 8-40's, but the majority of hunters/shooters use the factory 6-48's. RJ

That's why I prefer Seekins or Nightforce picatinny bases, as they have a recoil lug that abuts to the front of the action, taking the shear forces off the screws.

Thinking the epoxy will back up the screws nicely. Especially if the surfaces that the epoxy adhere to were roughed or scored before gluing.

If you still feel insecure about the set up but don't wan't to disturb what you've already done, take the barreled action to a smith or machinist & have the bases dowel pinned.

FWIW, the only 2 rifles I've dropped in my life both had Nightforce scopes that weigh over 30 ounces & the bases were installed using #6 screws. All was well after the mishaps.



I personally feel that scopes are becoming just way to big & heavy, one thing will lead to another & they will require yet more weight in mounts & such to keep them in their place.. But, folks are buying the hell out of them. So what do I know?

I have been through the math, and both 6-48 and 8-40 screws are inadequate if there is oil between the scope bases and receiver.
I have been through the math, and both 6-48 and 8-40 screws are adequate if there is no oil between the scope bases and receiver.

Clark,

Interesting.

Know a custom riflemaker who mostly builds harder-kicking rifles for hunters who hunt "big stuff." He makes his own mounts, and uses 8-40 screws oiled and torqued a certain amount. Cannot remember the oil or torque, since we had a conversation about this around a decade ago--and he said none had ever come loose.

His rifles sell from around $15,000 to $30,000, and he keeps busy.

D’Arcy?

I’d never epoxy any screws. PITA to remove. You’d have to heat to around 600* to defeat the epoxy, May have to drill screw heads and still apply heat.

Torque the proper amt and they’ll be there.

I like 8-40 screws for any bigger gun. My Ed Brown Damara 300 WM came with 8-40’s.

When I built a 404J using a NH SS .300 RUM Classic M-70 donor, I had the smith drill and tap for 8-40’s.

DF

Doesn't the recoil force on the scope go forward? When a scope slips it usually moves forward and bullets slipping in the magazine move forward don't they? Learning here if I'm wrong.

Yes which is why the recoil lug on the base mates up to to front of the ejection port.

Actually, the recoil goes rearwards, but the scope and ammo is stationary, so they are "driven" forward during recoil.

Also, when mounting picatinny rings, you should slide them as far forward as possible in the slot. Same principle.

aalf, I meant to say as you posted the scope slides forward under recoil if it slips.

8\40, no jb weld, no lok tite. It's actually really easy. But then again, it seems I'm really lucky.

Yep, because that provides two "recoil lugs" for the rings.

Are you no longer pushing the rear ring rearward?

1/4-20 is the solution. I don't know why the industry hasn't gone to it

Dirt farmer, maybe someone else did, but I never said anything about using epoxy on screws. I don't. I use epoxy (JB Weld) between the bases and receiver. Here's how I do it:

I jig my 2 piece bases with a set of "as perfect as I can find" scope rings on a virgin lapping bar that was assembled on a known straight Pic rail.

Install headless base screws in the receiver that have been treated with a release agent.

Slip the 2 piece scope bases over the headless screws.

Take the scope ring/lapping bar assembly off of the pic rail and attach it to the scope bases, tightening the cross bolts to spec.

Slip the scope ring/lapping bar/scope base assembly off of the receiver.

Clean top pf receiver and bottom of scope bases thoroughly.

Apply JB Weld to the bottom of the scope bases.

Slip the scope ring/lapping bar/scope bases assembly over the headless screws onto the receiver and secure with surgical tubing or electrical tape.

Clean up any JB Weld that came out from under the bases.

After 24 hours, remove the scope ring/lapping bar assembly and headless screws from the receiver.

Clean the scope base holes with brake cleaner install scope base screws with blue thread locker and torque to spec.


As everyone probably already knows, the screw holes on scope bases are are drilled oversized to accommodate scope base receiver hole tolerances, When my bases are installed, the JB Weld is pushed up against the waxed, headless screws, in effect forming 4 recoil lugs on the 2 bases. If me and my rifle part company and the rifle hits a hard surface, it may lose zero because something moved in the scope or for some reason attributed to the scope rings, but, it will not be because the scope base moved in relation to the receiver. RJ

That should be a solid mount.

I just torque them down. Seems to work.

DF

IMO you are over obsessing a bit about the 6-48 screws failing. Just how many people or rifles do you know of that had an actual failure of the base screws? If you really believe that they are an issue then have your rifle and bases drilled and tapped for the 8-40's. The only base screw problem I have ever seen is one that was severely overtorqued and had the head twisted off - in that case the ham-handed installer would have likely twisted the head off a 1/4-28.

drover

Not over obsessing, I do not know anyone who has had base screw failure. I also don't personally know too many hunters that use really heavy scopes on their rifles. That is why I started this thread. With the popularity of large heavy scopes on many Fire members rifles, I figured I would ask their opinions/experiences. RJ

Suppose you had screws enough attaching the scope and mounts to survive the slip and fall that would have broken off the 6-48s. You have an attached scope that, along with the mounts, has just sustained a severe impact. What now?

8-40 is the way to go. That being said, the only failure I've had was with a T/C Contender pistol barrel....it was a 2-6x Bushnell scope mounted in a 3 ring Redfield base. I've never had any issues with rifles, even with some really heavy scopes, but these are on .308 class rifles.