6x48 vs. 8x40 base screws (2024)

Hello everyone,
I have a question, and I hope I have chosen the proper forum for some help. I am building myself a new long range rifle this summer. I am currently waiting for my reamer. I have been studying my options for scope bases and rings. I have noticed and read a lot of good ideas and opinions concerning 6x48 vs. 8x40 screws.

But, after searching I can't seem to find any tests or numbers saying how much more shear strength and clamp down force and 8x40 screw will add over a 6x48. Can anyone here help me? I'm very curious how much strength the larger screws will actually add to the mounting system.

Thanks for your help,
Steve

6.5Swede said:

Hello everyone,
I have a question, and I hope I have chosen the proper forum for some help. I am building myself a new long range rifle this summer. I am currently waiting for my reamer. I have been studying my options for scope bases and rings. I have noticed and read a lot of good ideas and opinions concerning 6x48 vs. 8x40 screws.

But, after searching I can't seem to find any tests or numbers saying how much more shear strength and clamp down force and 8x40 screw will add over a 6x48. Can anyone here help me? I'm very curious how much strength the larger screws will actually add to the mounting system.

Thanks for your help,
Steve

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Use a "Mechanics Handbook"....It will give you the info on any screw ever made

6.5Swede,

I hope this comes across the way I'm thinking it. It doesn't matter what the difference is, there are folks here who posted the 6X48 screws broke on their rifles. I noticed the other day when I bought some bases for a light weight Kimber they came with 8X40s.

Wildcater,
Yes, I understand what you are saying. I was just wondering if someone might know roughly how much stronger the 8x40's would be over the 6x48's. Even a percentage would be helpful.

But, your point is well taken. If the #6 screws aren't holding up, it don't matter. Maybe the #8's are needed. I hope I'm not overthinking this. I am just looking for some feedback and some friendly advice or suggestions.

Thanks again,
Steve

Steve,

Whichever you choose, I wish you the best with it.

I can't answer your question, but if we keep kicking it around someone will know.

I've had troubles with the smaller, and none with the bigger.

With scopes getting bigger, cartridges getting more intense, and muzzle brakes adding other forces to the equation, it stands to reason a bigger screw is going to be needed.

Some are adding screws (6) to the rings. Some are adding a 3rd ring.

HARPERC,
Excellent points. My build is going to be a 284 in about a 9 lb. rifle. I intend to use the rifle for some long range target shooting and hunting, but want it to remain portable. Most say that is not enough recoil to be an issue.

But, over the last 2 yrs I have noticed when I put heavy duty rings and mounts, along with heavier more reliable optics, a few of my rifles started shooting better. It really started me to thinking. The most striking change was in a 30-06 hunting weight rifle. A picatinny rail and a Super Sniper 10x scope was installed, a known load was tested, and the rifle started grouping 3 shots from a cold barrel under and inch easily.

My line of logic is if this change was helpful, why not just do the 8x40's for that little bit of extra insurance.

Now I'm starting to wonder about some of the rifles I traded away that I thought were not shooting good enough. Maybe it was junk scope mounts and scopes?

Thanks for your comments,
Steve

My line of logic is if this change was helpful, why not just do the 8x40's for that little bit of extra insurance.

Now I'm starting to wonder about some of the rifles I traded away that I thought were not shooting good enough. Maybe it was junk scope mounts and scopes?

Done right it's such a small cost, especially during a build.

I wonder how many rifles we've all cursed that just needed a better home to shine.

I have a Ruger #1 turned in groups with a new bullet that totally blew me away. Actually bought it for a donor action, went back to it just because I need it for a kid to hunt with this season.

HARPERC said:

My line of logic is if this change was helpful, why not just do the 8x40's for that little bit of extra insurance.

Number 6's will do you fine the majority of the time. BUT they have to be clean; torqued to the right amount; etc...etc. If you are just going to roughshod a scope on then 1/4-20's may not be good enough

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I actually had a veteran rifle builder tell me he had tapped and threaded 10x32's for customers who requested them. I asked him if drilling such large holes in a rifle receiver could be a problem. I know modern rifle actions are built with a lot of safety margin, but........

I have also learned through my own experience and research that base screws, no matter the size vary considerably in hardness and quality. This fact alone enters another variable into the question.

Thanks for the comments. They are much appreciated.

Steve

Number 6's will do you fine the majority of the time. BUT they have to be clean; torqued to the right amount; etc...etc. If you are just going to roughshod a scope on then 1/4-20's may not be good enough.

We ask a lot of our equipment. Monday I'll be transporting a 3 pound scope via ATV to shoot rocks, and I've transported via bush plane, horseback, boat, and taken tumbles I wince remembering. It all breaks eventually unfortunately.

Pinned may be a good option as well.

It seems like someone was making their actions with the rail as part of it? I could be wrong, about that.

I'm a menace with tools, the closer to unbreakable, the better.

While I have never had any of my #6 screws fail I have seen it 4 times and have been changing some of mine over, starting with the big guns while I have them apart. It is a very simple task and inexpensive. The threads are the same size which is fine, I have only seen shearing failures, never pulled out, but the screw diameter of the #8 has about 30% more surface area Area of circle = R squared x Pi
#6 = ~0.134" diameter = 0.014
#8 = ~0.153" diameter = 0.018 sq in or roughly 30% more material
(check my math)

If there were never failures I don't think there would be things like integral rails and pinned rails. Any rail should be bedded as well.
The ATACR I'm mounting on a 300 RUM is 19" long and the turrets are 3 1/3" wide so bumping the end of that thing can generate a lot of leverage. Odds are you will never have one break but unplanned things happen. I've never planned a fall or someone dumping a suitcase on top of my gun in the back of the car.

What's the weakest link in your system ?
Fix that first.

6.5Swede said:

........I have also learned through my own experience and research that base screws, no matter the size vary considerably in hardness and quality.......Steve

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My mind is going....trying to remember the details, but we had this experience a couple of years back.

Wedgy said:

While I have never had any of my #6 screws fail I have seen it 4 times and have been changing some of mine over, starting with the big guns while I have them apart. It is a very simple task and inexpensive. The threads are the same size which is fine, I have only seen shearing failures, never pulled out, but the screw diameter of the #8 has about 30% more surface area Area of circle = R squared x Pi
#6 = ~0.134" diameter = 0.014
#8 = ~0.153" diameter = 0.018 sq in or roughly 30% more material
(check my math)

If there were never failures I don't think there would be things like integral rails and pinned rails. Any rail should be bedded as well.
The ATACR I'm mounting on a 300 RUM is 19" long and the turrets are 3 1/3" wide so bumping the end of that thing can generate a lot of leverage. Odds are you will never have one break but unplanned things happen. I've never planned a fall or someone dumping a suitcase on top of my gun in the back of the car.

What's the weakest link in your system ?
Fix that first.

Gunsmith Thread Size Gauge Jig Can Hold Screws for Grinding to A Shorter Length | eBayGunsmith Thread Size Gauge Jig Can Hold Screws for Grinding to A Shorter Length | eBay8 40 Carbon Steel Bottom Tap Right Hand and 28 Drill | eBay

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Thanks!