Anyone have experience with this? I've seen at least one 338 Lap on a M70, and maybe a 338-378, but it surely isn't common. Is it considered unwise? How about rigging a "real" third lug, with the bolt handle, ala E Hubbels Enfield(s)?
I have an itch to try a short/fat 30-338 Lap.
Can someone remind me the formula for boltthrust?
I may be able to run this low-pressure enough to mitigate the larger case.
Thanks for any help.

Bwana-Win 70 has same barrel thread diameter as 77Ruger.And should handle cases that size, as the Ruger does...The model 70 could be rigged with extra bearing lug also.
That's what I would do for hairy cases in a Model 70 and they are nice looking action..Ed.

That's exactly what I wanted to hear.
Plan is to turn a 300 WSM (after shooting the b'jeezus out of it) into my latest wildcat, the 30 Something (30-338 LM Imp x 2 1/3). COL of 3.1" or thereabouts, using the factory 24" bbl. Should get just above 300 Weatherby velocities, with the shorter barrel offsetting the higher capacity. I'm thinking 200 @ 3k or so.
300 Wb = 91g?, 30 St = 104g? Something like that.
Should also give a nice muzzle flash to boot.
Actually, since the round is 1/2" shorter, we could compare it to a 24.5" Weatherby: marginally minimal.
If it all works out, maybe a 28" fluted and braked version next, with an A4 stock, tripod, big scope.

Barrelmaker Dan Lilja has the formula for bolt thrust and lug shear on his website. www.riflebarrels.com You may also wish to read his article on Rigby/Lapua cases on factory rifles that do NOT come in these chamberings.

The M70 was used by A Square for their 495 A Square. Also, Winchester has from time to time chambered custom shop guns in 416 Rigby. The M70 can easily accomondate up to a .625" case head (500 Jeffery or there abouts). The bigger problem is cartridge length. There you may find an issue.

That third lug you are talking about is only good for keeping that bolt from punching a hole in your forehead for one shot!

I would not use any mauser type action (Enfield, Mauser, M70 Winnie, Rem M700, Ruger M77, etc) with a cartridge using a 0.6" or larger case head and a chamber pressure greater than 55,000 psi. But then again, I am not suicidal either. I would use a BMG sized action for such endeavours, but perhaps shortened if COL was only 4" or so.

Scott

I appreciate the response, but you may be confusing threads Scott. The 30-cal BMG short-stuff is different.
This is a for-real longrange hunting caliber, on the Lapua case. The idea with the third lug is to change it from a "safety" lug into a real locking lug with a bearing surface on the action, to help counter boltthrust.
And as for length, the case is only 2 1/3" long, so I should be good there. Have to check the shank length on the factory barrel before I do a simple rechamber.
Getting ahead of myself, but I already see a 338 switch-barrel once I get the 28 incher on. Have to compromise on barrel contour so I can match the stock's channel.

Bwana-be,

The M70 can handle a 338 Lapua cartridge pretty much as is. Naturally, you will need to open the bolt face and do some feeding work. I would not recommend exceeding 62000 psi with your loads though.

I realize you like the wildcat game, but the 338 Ultra mag will do everything the 338 Lapua will do, and more efficiently. The advatage here is that the 300 Ultra mag is a factory offering of USRAC so all magazine parts are readily available from USRAC service. Also, since the Ultra mag is based upon the 404 Jeffery, you can readily get drop bottom magazines/bottom metal from Blackburn and increase you magazine capacity while you improve feeding potential at the same time. Just something esle to think about.

Scott

Scott, you're right, I am a bit wildcat crazy. And I'm sure the performance of this little squirt will nowhere near match the RUM, but it's going in a short action, and isn't meant to compete with the RUM. Maybe the Weatherby, which is pretty damn stout as is. So, yeah, there's cheaper ways to get a bullet to go faster, but I want a bullet to go this fast in a short action Mauser-style. This is about the best way I can figure. If I can handle the recoil (good pad!) then I will enjoy the package much more than simply ballistic data.
It is a sickness.
As for mag cap, that is a valid concern. I really like three down, and it'll probably take some creaticity to get there. Maybe make my own box. Doubt anyone will have a 3.1"xLapua mag anytime soon!

If the front lugs and the bolt handle/lug all engaged at the same time, as you would need if it were to be a true third lug, it still would not be a functional third lug. The front lugs would have to set back into the lug abutments several thou before you started to get viable support from the rear lug. I'm not an engineer but I read a lot about action designs. Consider how much bolt flex is found on the rear lug Remington 788.
I think this is covered in Stuart Otteson's books, "The Bolt Action".

Jay, I confess, I have no idea what you're saying.
Is it that the bolt handle flexes and fails to support the thrust? Don't hav S. O.'s nook; maybe you could elaborate.
Very interested.
We're assuming that all three lug are lapped to as close to 100% contact as is financially and physically possible. I don't see how the lugs in front would bear better or flex less than the bolt handle, if abutted at comparable distance from bolt center.

Bwana--All bolt lugs flex a couple thousands, but I know from experience if they are all lapped the same,that 3

lugs with a shear rating of 53,000 lbs is better than two lugs with a shear rating of 33 to 37,000lbs. In the cartridge size bases

that goes in that size of action(Enfield,Win), 30-06 base up to 505 Gibbs base, that thrust will range from 7500 lbs up to

14000 lbs with a 65,000 psi load.So you can see the margin of safety, either 2 or 3 lugs. And of course there is more margin of safety, if loads are down to 50-55,000 psi.Ed.

Right, I'm with you Ed.
If two is good, three is better.
Just confused by Jay's comment that the first two would have to flex before the third would bear weight. Doesn't make sense.
Ed, by what process do you build up the metal on the bolt handle?

Bwana-be,
It is not a good idea to open up the bolt face any larger than it already is for the standard belted magnums. The problem lies in extraction and ejection if you go larger. The extractor needs a surface opposite the extractor nose to hold the cartridge to the bolt face, this is called the 'pinch'. When you open up the bolt face, you eliminate most, if not all, of this surface and the extractor no longer has a surface to 'pinch' the cartridge against which holds it to the the bolt face until it is ejected.

Also, be very careful about using the bolt handle as a third locking lug. The middle section of the carbon steel M/70 receiver is not heat treated and may stretch very easily. They only heat treat the forward section of the receiver up to the ejection port and induction heat treat the primary extraction cam in the rear bridge.
Good luck,
Headache

Bwana--The front lugs flex a couple thousands with heavy loads anyway and with the support from the third they would all as a unit flex less.In my load testing for my wildcat
I had about 40 sticky loads,that I had to use a knockout rod to get them loose so as not to tear up rims. And it worked fine for me, as I didn't have to
reseat lugs and re-headspace.I built metal bearing spot on bolt handle base with a welder.Made an oval shape thicker
than needed, and other lugs were already seated perfect,
then I ground it back a little at a time till it was
close then used grinding compound till they seated
together by what what dye showed.In this process bolt is stripped, use barrel or barrel stub with a long headspace
button(homemade) to put presssure on bolt to get lugs seated.

Headache--That early 70 action still has more metal in the middle of the action connecting the front and rear bridges,
at least twice as much on right alone,
by far, than my Ruger 77 or the Enfields that I use.And I figure on those two it would take 80,000 lbs to pull them
apart if untreated, figuring cross-section.And 70 has more
metal there between front and back.As for case head size, the 70 bolt is like Ruger and Enfield and I got one set up
for 460 weatherby size case head and there is enough metal opposite the extractor to support it fine.Folks are putting
.640 diameter rims for Nyati and 600OK on .700 dia bolts
and making them work.I not a rabid 70 fan but it shouldn't
be dismissed as good action to use for bigbores. What ever
my Ruger can do the 70 can do.Up to 460WEA and 416 Rigby case size for high pressures.Ed.