Rifle Bolts: 2 lug vs. 7?


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PMDW
November 15, 2004, 05:45 PM
Does one have an advantage over the other? Easier to clean? More reliable? Or did someone just decide to be different one day?

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steveno
November 15, 2004, 06:30 PM
due to tolerance stackups I have always been skeptical as to whether or not all 7 lugs were ever touching. if the load is safe 2 lugs are enough and if the load isn't safe I doubt that the extra 5 lugs are going to do you any good

artherd
November 15, 2004, 08:03 PM
3 seems a nice number. Tripod being inherently balanced and sharing of the load.

rbernie
November 15, 2004, 08:04 PM
Experience has shown that two large lugs are at least the equal of bunches of smaller ones - just look at all of the MilSurp Mausers that are still ticking, split left lug notwithstanding.

And, of course, as Steveno pointed out, the odds that all of the bolt's lugs will be appropriate load-bearing diminishes with each lug added, due to production tolerance issues.

Vern Humphrey
November 15, 2004, 08:08 PM
An interesting experiment is to take an out-of-the box multi lug action, coat the bearing surfaces with an appropriate tell-tale (Dykem blue, magic marker, lipstick or simply smoke them) and work the action. That will tell you right away which lugs are in contact with their locking surfaces.

Delmar
November 15, 2004, 08:10 PM
The advantage would be a lower bolt lift. Weatherby has touted their 54 degree bolt lift for decades on the MK V action. Once you get used to it, it feels kinda clumsy to get back to a two lug action.

Fumbler
November 15, 2004, 10:58 PM
My Tikka T3 has two lugs and the lift is only 70° (most 2 lugged guns are around 90 degrees). The lugs are slightly narrower than other 2 lug designs, but if they chamber the gun in .338Winmag then I think it will handle a .308 just fine.

As long as all the lugs make equal contact I don't think it matter which is better as far as performance goes. Many semiautos have multiple locking lugs just so the bolts dont have to turn so far.

Badger Arms
November 15, 2004, 11:33 PM
The more lugs, the less rotation a bolt has to go through to unlock but also the more force that must be exerted over that shorter throw on tight spent cases. This is why the AR-15 has a problem with steel cases.

The trick with multi-lug designs is that the lugs must bear SYMETRICALLY around the centerline of thrust. The AR-15 design has 6 lugs bearing symetrically and another lug doing virtually nothing. In fact, this lug causes the two lugs adjacent to the extractor to bear a greater percentage of the load than the other lugs. You can grind this lug off (or relieve the bearing surface about 1/16" and you ADD to the strength of the lockup by causing all of the lugs to bear evenly. Mark Westrom over at Armalite patented the idea. Anybody looked closely at the 7th lug on their AR-10? In this case, 6 is better than 7!

shoobe01
November 15, 2004, 11:43 PM
Yup, its for automatic simplicity and lightness. You can get -- if everything is adjusted right -- the same bearing surface with much less lug. So, theoretically not as huge a barrel trunnion, etc.

In practice, this seems to never pan out really. It would seem some middle ground, like some triangular "three lug" systems I recall seeing might be it. The AR's 22.5° system seems to have its following though, so its mostly that or garand/ak style two lugs over what, 60°?


For bolt rifles, I can hardly see how the overall design really matters. Even things totally shocking to us today, like the rear lugged Enfield, worked just fine for decade upon decade. Quality of build and fit seems more critical than any specific system.


In a related vein, I have always thought it would be cool to have a straight-pull-type of camming action where the firer lifts the bolt handle thru something trivial like 15° but the bolt head rotates more like 60°. Presumably rotation and unlocking could continue thru some lateral movement, to alleviate primary extraction issues...

Fumbler
November 16, 2004, 12:51 AM
Blaser makes a straight pull bolt action.

Badger Arms
November 16, 2004, 12:53 AM
In a related vein, I have always thought it would be cool to have a straight-pull-type of camming action where the firer lifts the bolt handle thru something trivial like 15° but the bolt head rotates more like 60°. Presumably rotation and unlocking could continue thru some lateral movement, to alleviate primary extraction issues...Take a look at the Browning BLR Lever Rifle. The 90 degree (or so) rotation of the lever unlocks and retracts the bolt. It's a clean and smooth design.

TK73
November 16, 2004, 01:32 AM
In my personal opinion, there's still nothing better than Mauser's M98 action with the two locking lugs on the front of its bolt, long claw extractor and controlled round feed. Winchester's M70 pre-'64, current Super Grade (CRF), similar Dakota 76 or Ruger's M77 Magnum Express action are equally as good. I can't imagine myself purchasing a bolt-action rifle featuring another action. But then I am highly opinionated. :cool:

Badger Arms
November 16, 2004, 03:29 AM
Ahhhh, you haven't worked a Sako 75 action lately, have you? Me, I like tripple-lugs. Why make a 2-legged stool?

TK73
November 16, 2004, 06:31 AM
...believe me, I know and have handled virtually every model variation of Sako's M75 (model Hunter, Synthetic Stainless, Hunter Stainless, Finnlight, Deluxe, Battue). Actually, I agree with you, the M75's action is butter smooth and these Finnish rifles are very well made, but these characteristics alone hardly qualifies to make the M75 superior. Actually, I've liked the older Sako L61R Finnbear/L579 Forester/L461 Vixen or M691/M591/S491 actions from the '90s much better than the new M75. The older SAKO bolt-actions featured two locking lugs. One feature on the latest M75s I particularly don't care for is the stupid key lock system. Each shooter has its own ideas and requirements, so if the M75 appeals to you, don't hesitate to choose one. ;)

The comparison of a two legged versus three legged chair is ill-suited. I don't want to sit on one with three legs either. :D

Kind Regards!

Badger Arms
November 16, 2004, 11:15 AM
Don't get me wrong, I'm not bi-lug-phobic. I do think a three-lugged system is superior for all of the reasons commonly stated: Shorter lift, shorter lugs, more even lug seating, smaller ring required, smaller diameter receiver, the ability for smoother raceways, larger scope clearance (or lower mounts), etc. Had Mauser designed three lugs, we'd all be arguing about how bad 2-lugged designs were. The facts are that two-lugged guns came first and stuck. Them lawyer gadgets do not a worse rifle make as most can be simply left in the 'off' position. But then again, my Browning A-Bolt doesn't have one.

greg531mi
November 16, 2004, 11:06 PM
I have never owned a Weatherby Mark 5, but heard from guides, that it is the most proned to lock up in the cold and dirt. If you get one drop of freezing moisture in that action, it might take a hammer to open it in the field.
That's what I heard....anybody has problems with their Weatherby's???

TK73
November 17, 2004, 05:25 AM
...actually the Mauser 98 action is a three-locking lug construction. The third locking lug is located on the rear of the bolt in addition to the two on the front. :neener:

rbernie
November 17, 2004, 07:49 AM
.actually the Mauser 98 action is a three-locking lug construction. The third locking lug is located on the rear of the bolt in addition to the two on the front. Actually, it's not. The third lug is non-load-bearing in normal use (spaced 50 thou from the receiver, IIRC) and only comes into play as a safety lug in case the two primary lugs fail.

And, as a side note, the early small-ring Mauser designs ('88-'95) didn't have this safety lug, which is one of the reasons that the '98 actions are considered safer.

Delmar
November 17, 2004, 03:16 PM
Take a look at the Browning BLR Lever Rifle.

Take another look-its a 45 degree stroke. Cams do wonders!

Badger Arms
November 17, 2004, 05:10 PM
Bah... Back of the safe. Now I'm going to have to dig it out later. Evil infomation that I could have done without.

Kestrel
November 17, 2004, 11:15 PM
Early this year or maybe it was late last year, Beretta told me they were discontinuing the key-lock in the Sako rifles. The gentleman told me it would only be available as an option.

I haven't seen one in a long time - does anyone know if this has happened, yet? (Remington was also to discontinue their lock-out silliness, but I don't know if they have or not.)

Steve

Badger Arms
November 18, 2004, 12:20 AM
Okay, it's MUCH shorter than I thought, but it feels just the same as last time. I'm sure nobody stole it, changed the engineering, and put it back in my safe. Wow, that's short. And... it extracts just fine. Why aren't all guns like this? Who needs a bolt gun?

hubel458
November 18, 2004, 01:52 AM
Most 6-7-8-9 lug setups don't all bear evenly, so they won't be as
strong as 2 or 3 lug designs that are bearing evenly, 3 lugs being
strongest. Figuring shear strength of lugs a Wea will have about 33,000 lbs
of shear if all lugs are bearing. Ruger, Mauser, Savage,
Enfield- 33-36000, other two lug designs, 28-33000. These levels
allow for a multiple safety margin, example a 3006 has about 7100 lbs
bolt thrust. On a 50 cal McBros the lug shear rating is about 75,000 lbs,
and average 50 cal load is about 25,000 lbs thrust...Ed.

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