I am looking at buying a 7STW built on a Mark X action. I recall reading on one of these forums(I can't find it in the archives) that the Mark X actions would develop problems with rounds such as the STW and 300 Weatherby. Can anyone tell me what the problems could be? If you can shoot a 375 H&H through it with no problems.....why would a 7stw be too much??? Thanks for any help.

Finley,

The magazine box on the Mark X "C" magnum action measures 3.400". The 7mm STW loads around 3.600 if I recall correctly.

Malm

I guess I should have added that it is built on a Mark X long action. It was a 375H&H before it the OAL should be fine? Thanks.

Finley,

Yes of course, if it will fit it will feed.

Malm

Is the Mark X action considered strong enough for the 7STW?

I wouldn't, but it's said to be safe......unless there is a little case lube left.....or an overly oily chamber, or thick neck, or wrong powder/charge.

That's the right lug trying to come out of the feed ramp. This is a 1953 FN but the Mark X long action is cut the same way.

No! Not safe. Read and heed Jack Belk's comments. Sure it has been done before, but that don't make it safe.

The 7mm STW is actually too long for most actions if a 160 grain bullet is used. To get the base of the bullet out of the powder space, you need about a 3.75" magazine length. And you need a 26 to 27 inch barrel to take advantage of that case capacity, my 7STW (Which I swapped away) had a 28 inch No. 5 Pac Nor.

This is a high pressure round, most handload data that gives those impressive velocities is around 60,000 to 65,000 psi. Way too much for a weak Mark X that has been lengthened to the Mystical 375 H&H length by reducing the bottom receiver lug strength.

The point is well-taken on the way the factory chooses to lengthen the magazine box on the Mausers (both the much-regaled FN and the more vulgar Mark X). Much of the metal behind the lower (right) lug is removed and reshaped into the feed ramp, leaving a marginal amount of action metal backing the locking lug. This is also the same way the original Winchester Model 70's were extended in factory form (knowledgeable gunsmiths move the box to the rear and leave the locking lug recess alone). If you buy a $1500 pre-64 Model 70 in .375 H & H or a $1200 Browning Safari in the same caliber (or .300 H & H as well), you're going to have a lower locking lug that doesn't lock on much.

That being said, the '53 model FN in Jack Belk's photo is the only one I have seen or heard of that appeared to be giving trouble. Whether that trouble is the cause of a poor heat treatment or an extremely excessive overload can only be determined by testing the metal and/or knowing the history.

Finley, you are correct that your .375 Mark X can be used to build a 7mm STW. The standard magazine minimum for that caliber is the same 3.60" (although others are correct that more is always better). It is irrelevant whether you overload a .375 H & H or a 7mm STW -- either will give you trouble if you push the envelope.

As for me, I'd prefer another action for long rounds.

Would it just be safer to have the barrel shortend and rechambered for 7mm Rem mag??? Thanks for your help guys.

Jarrett

No. The action has already been modified at the factory and will have the same strength (or weakness) no matter what cartridge it is chambered for. You are no more at risk with the STW version than the regular 7mm Magnum.

I think the Mark X action is a little under rated by "Mauser" afficianados. Back in 1985, I took 3 of these actions and converted them to shoot the 338/378 K.T., and within the past 3 years, I lengthened these to feed the super long Sierra 300 grain .800 BC Boattail.

You can't open a Mauser much more than this and expect it to hold any better with these pressures. To this day, these 3 rifles have been used sucessfully all over the world by some pretty serious folks and none to date have exhibited any weakness.

Stonecreek is right on the mark. If the action is properly lengthened "to the rear" by folks who know what they're doing, leaving the original lug mortise unaltered, then these actions should be plenty capable for the 7STW load.

Keep in mind one and all, ANY cartridge with excess case lube, wrong charge, or ANY barrel with an excessive oily chamber regardless of the caliber is potentially dangerous.

We build and make modifications to weapons for our customers knowing full well that we, the builders, have no control over how the weapon will be used or loaded. We custom assemble loads to test our work and we revisit every piece of the job to make sure that we have done everything possible to maintain safety. We turn these weapons over to our customers assuming they will follow safe practices when reloading or otherwise using these wepaons. That is as far as this train goes. People are going to do what they want anyway so all we can do is put forth an effort to properly caution and guide them.

If the rifle Finley is wanting to purchase has been properly "smithed", hasn't been in a fire or otherwise exposed to structural damage, then there is no reason that this rifle won't serve his needs. If he still has concerns about this, there are things that he can do to help aleviate these concerns. Posting on this forum is one way. Have an experienced gunsmith eyeball the weapon to see if the safety of the weapon has been structurally compromised is another. If none of this has eased his mind any, then he can simply pass on the weapon. Good luck Finley.

Malm

Thanks for the helpful insight. I will do as Malm has suggested and take it to have it looked at by a gunsmith. Thanks again.

Jarrett

G.Malmborg

Hello, what would be the proper way to open the magazine box to the rear? I just picked up a Coast to Coast 30-06 that looks to have been built on a surplus 98 action. I'm looking to turn it into a 30-378 within the next week or so. I had planned on cutting the back of the magazine out and fitting a new piece in that came almost to where the bolt face stops so as to allow a little room to pickup the next round out of the magazine. Then modify the stock to accept the new magazine dimensions. I did a 30-378 on a P-17 and built a whole new box for it, it seemed to work just fine and held 3 rounds.
Any thoughts for an Ametuer?

Lar45,

Without knowing exactly what you have to work with, I couldn't advise you one way or the other. I can say that if you need to pick up length in a Mauser action, you need to do so in a manner that doesn't alter in any way, the original integrity of the bolt locking recesses in the receive.

Your tag line is missing something. Try this:

"More Powder, Bigger Bullets, BIGGER EXPLOSION."

Happy holidays,

Malm