Home Forums Hunting & Shooting Gunsmithing Squared locking lugs

Has anyone taken a super accurate rifle and then purposly ground one locking lug so all the presure was on only one lug to see what the accuracy difference is?

The reason I ask is because I've hspent way to much driving lately and can't see how it makes much of a difference. Correct me if I'm wrong but the case fits prety snug in the chamber and when the round is fired the bullet travels down 20+" of barrel forcing the bullet to be true in a very snug barrel. How does a possible side movement of the case make any difference to the accuracy?

Never tried it as I can't afford the luxury of screwing up a good firearm.

i have seen some deadly accurate rifles, with only one lug touching. matter of fact 99 % of factory rifles have 1 lug touching. i had a guy come to me with a 788, got all freaked out because there was only 1 of the 9 rear locking lugs contacting. i asked how it shoots and he says 1/4 inch..243 if i remember. i eased his mind and sent him on his way.
ill bet if you ground one down you wouldnt see much diff.
altho when i build a rifle i always true and lap the lugs. i figure it cant hurt.. i believe bore/bolt alignment and everything square and a quality barrel are the key.

i too have given that same chamber thing way too much thought. i ride adventure motorcycle and on long trips my mind wonders and i give things like that way too much thought.

altho the case fits tight it has been sized (shunk down slightly)so it can chamber. when the firing pin strikes it drives the case forward aganst the shoulder using it as an anvel so the firing pin can dent the primer. when this happens their is a harmonics that travels down the barrel just ahead of the bullet . this harmonic viberation is impossible to duplicate and accuracy wont be as good. this is no secret as bench shooters and varment shooters have been neck sizing since dirt. so you have to neck size right???? here is one to think on... every ackley and improved chamber i own shoots better with form loads..i have seen many others report the same thing....

Send Bagabuck a PM, I bet he's done it.

reelman,

We had performed this test at USRAC (Winchester) about 15 years ago. The accuracy did not change. I still prefer both lugs to have some contact...just me.

In building a super accurate rifle from the ground up I would still lap the lugs in as well as trueing up everything leaving nothing to chance.

Have a great day,
Headache

The plunger spring in the bolt head has more effect on the case being pushed tight against one side of the chamber than the locking lugs do. I like even contact on the lugs to keep the bolt from flexing under pressure and 55 to 60 thousand PSI is a lot of pressure on the bolt lugs. So two lugs holding the backward thrush pressure from a fired round is always better than one, as far as accuracy i don't believe you could measure the difference

You know most rifles push the rear of the bolt upwards when cocking. You can machine all you want on the back of the bolt lugs and lug abutments,but if the bolt is loose by a few thousandths it will unload the upper lug and defeat all the work that you have done. Lapping lugs is a waste of time.

exactly,..most guys don't realize this...but then again, when the sear is dropped the bolt should fall before the pin hits the primer...

This is why some accuracy minded 'smiths will bush the rear of the bolt fairly tight to the receiver bore.

yes, you may be right , but it only takes me about 30 min to lap them and it just makes me feel better when i have both lugs having even contact , even tho it may be a waste of time

Here's a question that I've often wondered about.

How much deformation occurs when pressure builds and long does a lug that's ever so slightly out of contact stay that way?

There's a lot of dynamics at 50k psi and beyond. If an action and bolt are not surface hardened properly deformation occurs after repeated firings.

So ???

Some actions only have one lug locking the bolt and digest thousands of rounds with no problem. The Savage 340 is one action with only one locking lug.

A little off topic but what about bushing the firing pin? Anyone ever test this? I know gretan does an awesome job of it.

805,
Bushing a firing pin helps in keeping a rifle blanking primers. I don't think it does anything for accuracy. My BR rifles do have .062 firing pins. Most,not all, competition shooters press the edge of pressure in their reloading. If we blank a primer, the little piece of the primer goes down the firing pin hole in the bolt and can cause a miss fire. A smaller diameter firing pin tip fitted to a close fitting hole in the bolt face will handle a lot more pressure without blanking.

Little things that probably doesn't really help in accuracy, but sounds good and make the customer feel better and is a selling point for the Smith to make a little more money on his builds.

My favorite accurate hunting rifles:
Wby Mk V 9 lug bolt
Wby Mk V 6 lug bolt
Sako 85 3 lug bolt

That'd be way too much lapping for me. They are all accurate with no other work than shooting them.

small lugs are just a compromise for two larger lugs to give a short bolt lift and nothing else.

Yeah, you're right. They hold no inherent value over any other configuration. But, I surely like them.

How long might it take to lap 9 lugs?

if it built as it should be no longer than lapping a 2 lug version