6-48 vs 8-40 base screws

[charlieb]

Looking for feedback on how many have actually had 6-48s break under recoil! Thanks guys!

 

[Buck51]

i have shot around 200 rounds thru my Dakota 76 Safari in 416 Rigby. It has the smaller 6-48 screws. No problems.

 

[Ray B]

I haven't had any break due to use. I've had more trouble with guys that claimed to be gunsmiths drilling in the wrong spot, etc.

 

[JRWcows]

I bet no one has had 6-48 fail.. I get the idea of using 8-40’s but unless using Chinese junk.. it would take close to a ton of force to make things go south..

 

[akrifleman]

The combination of light rifles, large brakes, and heavy recoil can be hard on all optics components.

 

[Ray B]

the advantage of 8/40 screws is not so much that the smaller ones may break, but that the larger screw has more bearing surface so that with blue loktight is more resistant to working loose.

 

[Jamie D Van Roekel]

I bet no one has had 6-48 fail.. I get the idea of using 8-40’s but unless using Chinese junk.. it would take close to a ton of force to make things go south..

I have a couple 8-40s. Put them in old rifles that had the 6-48s rusted or turned out.

 

[JRWcows]

Yes if you didn’t take care of your equipment just about anything can happen and it will happen No BS.. The problem these days if you don’t do things yourself you will find people cut just about every corner possible and then expect you to pay them top dollar!! Unfortunately form the screw manufacture to the base manufacturer to the gunsmiths if they aren’t doing their job you will be SOL!! Because it’s not going to fail at home[emoji6]

 

[sureshot375]

My buddy has a .416 rem that was built by a guy used to building deer rifles. I don’t know how much it weighs, but even with the muzzle break it doesn’t weigh enough. He had it for many years and probably never put a full box of shells though it.

Last year we got it out to shoot it because another friend was potentially going to borrow it for a elephant hunt. Ended up shearing the 4-48 screws in the course of shooting it to get ready for the hunt.

It can happen.

 

[akrifleman]

I have a couple 8-40s. Put them in old rifles that had the 6-48s rusted or turned out.

I wouldn't tap 6-48s unless something did break. You can always do an 8x40. If you already did that in anticpation of something that may never happen, you lose the ability to tap and upsize (and still fit many rings without further work to the ring).

You never know when your rust out or strip. I typically put black nail polish under the rings and in the rings as well. It does a shockingly good job of keeping the rings from moving around and putting all the load on the surface tension of the rings to receiver or rings to scope. Particularly on rifles when I don't expect to change the scope for many years. My comp rifles I change to much for doing the rings, but I still put it under the bases. You'd be amazed at how that stickness helps.

 

[GuttormG]

Looking for feedback on how many have actually had 6-48s break under recoil! Thanks guys!

Once, 1screw on a forward Leupold std base, rifle was a vz24 in 35Whelen.

 

[charlieb]

Thanks guys, If you didn’t already know me and Tim McWhorter build precision hunting rifles, I’m 33 years old and invested in building a modern shop with all the equipment to build rifles, my favorite builds are Dangerous Game Rifles and Alaskan Guide Rifles and I do some Extremely Lightweight Mountain rifles but I have in my personal collection 5 model 70 classic stainless 375 h&hs with the standard 6-48s, They don’t make them anymore! UNFORTUNATELY!! With that said I’m not into fixing something that’s not broken, yes I have a PM 949 tv milling machine and every tool possible to drill and tap the holes or end mill them out given there not centered from Winchester. So I appreciate everyone’s feedback on real world scenarios, imo properly torqued bases with quality screws should not shear given all the numbers I have run, I come here to ask you veteran big bore guys opinion! Thanks again!

 

[Inline6]

My buddy has a .416 rem that was built by a guy used to building deer rifles. I don’t know how much it weighs, but even with the muzzle break it doesn’t weigh enough. He had it for many years and probably never put a full box of shells though it.

Last year we got it out to shoot it because another friend was potentially going to borrow it for a elephant hunt. Ended up shearing the 4-48 screws in the course of shooting it to get ready for the hunt.

It can happen.

I'll bet you whatever you want the screws were already loose. That is what brakes things, if the smith would have bedded the bases with red lock tight this conversation could be different.

 

[sureshot375]

I'll bet you whatever you want the screws were already loose. That is what brakes things, if the smith would have bedded the bases with red lock tight this conversation could be different.

We had actually just installed a new vortex scope with illuminated reticle. It’s possible that the recoil loosened the screws, but they had been very recently and properly installed.

 

[Inline6]

We had actually just installed a new vortex scope with illuminated reticle. It’s possible that the recoil loosened the screws, but they had been very recently and properly installed.

Where the bases them self installed at the same time? What were the screws installed with? Meaning was a torque wrench used?

 

[C.W. Richter]

'have seen more than a few posts over the years when they mention 6-40 and 8-40 screws, when it's really 48 TPI per the above. that in itself has been the source of some problems. how the bases are designed can alleviate the force on the screws, but all heavy-recoiling, big bore rifles I have (.338 A-Sq to .458) all feature 8s. Gunsmith friends say that overtightening screws dramatically reduces strength, and lubricating screws reduces strength somewhat. I'd have to think that loc-tite would tend to increase the strength somewhat. Inherited an old lightweight 350 Rem Mag (worst recoiling rifle EVER!) Original owner broke a 6-48 and drilled out to 8-36. That was fun to sort out! When in doubt, have it checked out. Most custom bigger bore rifles come with 8s, for all good reasons. 8s impart greater clamping force, and with a larger area base, that force is spread out (reducing the force per unit area, reducing the tendency to snap off) which, if installed properly will rarely or never happen. There are even different strength screw compositions (diff. metals). You can get a 6 screw in stainless that's stronger than an 8 in carbon, but the receiver thread material is your limitation...

 

[sureshot375]

Where the bases them self installed at the same time? What were the screws installed with? Meaning was a torque wrench used?

Yes. New bases. Everything torqued properly and loctite by a good gunsmith.

Couldn’t get them out even heading them with a torch. He had to drill and tap.

 

[akrifleman]

Yes. New bases. Everything torqued properly and loctite by a good gunsmith.

Couldn’t get them out even heading them with a torch. He had to drill and tap.

He over torqued them. Loctite is a lubricant when wet, and your supposed to use 20% less lbs of force. This then created too much shear force when dry.

 

[Nevada Mike]

The bases in my DSB 404J Mauser 98 are the square bridges themselves. Nothing to break loose unless the whole action blows to pieces... not likely, tho'.

 

[fourfive8]

Four properly torqued #6s holding down two bases should be fine. Never had one break. But for everything 375HH and larger I have changed to #8s... just because. Nothing wrong with over engineering then never having to worry about it I do them myself and the biggest risk is breaking a tap which, by personal experience, is a real PITA! Some receivers are stickier and/or harder than others thus more risk for breaking a tap. Best way to do it is slowly, manually by hand using the tap chucked in a mill or large drill press then easing in-out by feel until correct depth is reached.