What's the deal with these?

They are larger then 6-48s, more area.

Is this an issue? How much does it cost to have this done? Is there a recoil thresh hold that is used as a bar for the necessity of these screws or does 8-40 just sound cooler?

There are alot of people who would argue that you HAVE to have them, but its doubtful most have even had 6-48s break on them. 6-48s have worked for a LOOOOOOOOOOOOONG time, even on heavey recoil'rs, but like so many other things in life, they are thier for those who want them...........
Yeah about 12 years ago... when 8-40s really started to pick up, rifles were throwing scopes off their backs right and left, I donno it just suddenly started happening one year, never happend before!!
I should poke to much fun... I have a few that have 8-40s.

[ 01-15-2003, 12:25: Message edited by: smallfry ]

Nebraska---

6-48 screws have been a standard for gun sights for decades.

Scope mounts *were* made with a recoil shoulder that prevented shear stress from being put on the screws.

When scope mount makers (Redfield first) cheapened their mounts and started straddle milling instead of end milling the mating surfaces, the stress of recoil transferred to the screws......which sometimes broke.

Then scope makers started making scopes with large objectives which meant they have to be mounted higher above the bore....THEN they made them more complicated which made the scopes heavier and suddenly 6-48 screws weren't strong enough to take the approximately 70% increase in stress.

8-40 screws, being about .025 larger in diameter, have increased shear strength but the problem of loosening is still there.

Heavy kickers using a recoil stop mount with 6-48 and a sensible scope will stay in one piece for a lifetime with no problems, no locktite and no changes.

The bigger the scope or bigger the rifle the more resistance to stress needs to designed into the mount.

If the scope is too big, too high and mounts ill-fitted they'll loosen and loose zero no matter what size screw you put in them.

Some try to straighten crooked mounting holes by re-drilling the 6-48 holes to 8-40....It DOESN'T work!! You'll just have a bigger off-center hole unless the hole is *bored* straight....you CAN'T drill it straight, it's impossible and against the laws of nature.

I like using the 8-40s because alot of the rifle I build have very large scopes on them, and some are good recoilers.

I also align the base holes to the barrel center line, but I do not "drill them" I mill them or "bore" them. This methode certainly works and helps a great deal when building 1000+ yard rifles.

FWIW
Celt

Gentlemen, on heavy recoilers I have used red lock-tite and a dab of ACRA GLAS under the base. Holds like a woman onto your billfold. To remove I use a very little bit of heat and it lets go. Never had one fail yet. 375 WBY on a 8 LB rifle with a heavy scope is the biggest I've used it on, but it never let go. Keeps it tighter than a frogs ass(that's water tite).

Haven't had any 6-48 break but just last week had some bend. These were in the rings on a Brno 602 in 375 H&H. They were Hilver rings ( I think the same as now being sold as Lynx)and they have a integral recoil stop in the rear section only. There was enough flexing in the tiny gap between the top and bottom ring halves to cause a significant dent in my expensive european scope. Don't I wish they made them in 8-40.

[ 01-16-2003, 14:22: Message edited by: OzzieDoc ]

ozzie doc---

It seems you have a totally different problem than the one discussed. There's VERY little tension or shear on ring screws and there should never be a dent in a scope if the mounts and rings are aligned right.

I think you have another problem that should be examined before an expensive scope gets screwed up. It sounds like the rings are of different heights.

In 21yrs. I've seen a total of 2 rifles with sheared off screws. 8-40 screws don't hurt, but are somewhat of a solution to to a barely existing problem,

JBelk
What seems to have happened is as follows.
The steel rings are fairly narrow and only the rear ring incorporates a recoil stop which engages in a matching slot on the rifle. The Brno has integral parallel dovetails and the scope when mounted appeared to be in perfect alignment. After shooting about 40 rounds I noted that the scope had moved forward on the dovetails and it appears that the front ring slid forward while holding the scope itself tightly because the lower part of the rear ring had tilted forward a little against the recoil slot. The bending of the 6-48 screws in the small gap between the top and bottom halves of the rear ring allowed this to happen and it was the imposed angle between the top and bottom ring halves that dented the scope. It would have been much better if the scope had simply slid within the rings. Perhaps an 8 -40 would have prevented this by not allowing the ring halves to tilt in relation to each other. (but perhaps not)
Hope this makes sense.

Ozzie Doc

Paint those horrible Hilver mounts green and throw them into the long grass! Then buy some Talleys.

GG

Ozzie Doc---

I agree with painting green and throwing in the long grass........or paint brown and throw 'em in the barn yard!!

The rear ring dovetail failed if the ring tilted on the action. I've never seen that happen but figure the rings must be incredibly poorly made out of inferior materials for that to happen.

Get a set of Talley's post haste. You're suffering from "bad gear" and it's nearly cost you a scope. I wouldn't keep those rings in sight any longer than it took to undo the screws.

GG375 and JBelk
Already done. Trying to decide on new mounts. Talley, Warne are clearly under consideration. I read that Leupold is bringing out CZ mounts in the next couple of months. Might wait and see.

Two rifles with sheared off screws would be enough for me. Spend the $40 and go with the 8-40's. Talley sells bases to accomodate 8-40 screws.

chuck

Regarding the necessity of boring (to 8-40) to correct ever-so-slightly misaligned holes --

Is it something any gunsmith should be able to do? What is a reasonable price to bore 2, and simply drill out the other two which ARE properly aligned?

I really don't know the difference between boring and drilling either, perhaps you could explain that too.

Thanks,
Todd

Just another guy with sheered 6-48's. I had a 13.5# 338/416 Rigby with a Nightforce scope atop it for awhile. If you're not familiar with Nightforce scopes I'll mention that they approach 2# in weight.

After an estimated 30-40 rounds I had the scope start to sheer off. I noticed it fairly quickly and prevented any further damage to the scope.

The rifle was retapped for the 8-40's and I did the double fix by mounting a Premiere Reticles scope on the rifle such that my scope weight went from about 2# to 1# and the front objective went from 56mm to 40mm...problem solved.

This base screw size does have it's place, but it's generally atop a fierce recoiling rifle of relatively light weight with relatively heavy and high mounted scopes.

Reed

Todd--

Prices vary but straightning holes *requires* a milling machine or jig borer to do. Drill presses don't work.

The difference between *bore* and *drill* is that a boring bar has one cutting edge and a drill has two. With a drill the point centers into the hole and then both flutes cut equally. A boring bar has one flute which allows it to cut one side of the hole and not the other. The secret is in how solidly mounted the work and the tool is and the resistance to side deflection of the tool and machine.

It seems weird but it takes a machine weighing several thousand pounds to correct a crooked hole not even an eighth inch in diameter.

I charge $20 a hole and $20 set-up.

If you can find the old Redfield, Leupold, or Bueller mounts with the built in recoil shoulder you wont need bigger screws. The screws can't shear because there's NO shear stress on them.

An alternate is to do like is done on quarter ribs--- an eighth inch dowel pin can take approx. 4000 lbs of shear before failure. Two of them makes it as strong as an intergral part of the receiver like a Ruger mounting system.

JBelk,
Do you align them with the barrel centerline or with the first screw hole?.
Just curious how others are doing it.
Thanks,
Celt

I would not argue that JBelk does not have a better way, but I don't have the gear.

I deal with misaligned sight screw holes by soldering a 6x48 into the hole, cutting it off, filing to contour, and drilling and tapping to 8x40 using a Forster jig.

Works for me, but I ain't doing high buck rifles.

Chuk - when you have worked on well over 10,000 rifles in 21 years, two case of sheared off screws is nothing statitically, especially when both situations were similar to what Reed mentioned. I strongly suspect that the 6-48 screws on these rifles weren't tight. I'm not saying that it is always a waste of time, just that most people don't need it. When you get to a situation like Reed's you definitely need them and I strongly suspect even they might not be big enough. You have to match what you are doing to the individual situation. It probably is a waste of time to put them on a 9 lb. 300 Win with a 3.5-10x40 Leupold. If the scope mounts are installed PROPERLY, that sope isn't going anywhere.

Celt---

I NEVER index on what somebody else did. It's best to always determine where the proper place for a hole is and put it just there.

It's absolutely amazing how far off many factory rifles are....not only in where the scope mount holes are but other important things too.

Leftoverdj--

I repair a LOT of rifles done as you describe.....usually by TIG welding the holes up and redrilling. Thanks for the work.

Good on you, JBelk.

But you don't get none of mine.

My customers, back when I was smithing, were a bunch of rednecks with $75 rifles they were trying to get sighted in the month before hunting season.

Cheap, fast, solid, and close enough for the scope adjustments to take care of the slop was what they wanted and that's what they got. Never did one that wouldn't sight in and never had one come back for screws pulling loose.

There's a place for your way, and I'll freely grant it is a better way. I'd send one of my good rifles to you before I'd tackle it myself for such work.

But as long as there are rednecks with rifles not worth your time and effort and hunting season coming close on them, there's a place for my way, too.