Mauser 93 to Grendel - dealing with Lug Setback

[calshipbuilder]

I've got an old spanish 93 mauser made by DWM, it was poorly sporterized, but left in 7x57. I want to turn it into a 6.5 grendel - its been in the family a while.

I got the barrel off and noticed there was a lip on the internal lugs. I measured across the lugs from the receiver face and it looks like there is .004 of lug setback on both the top and bottom lugs.

I'm not sure if this setback is fatal to the action, especially when switching to a low pressure cartridge like the Grendel, which has lower pressure and less bolt thrust than the original 7x57.

My plan is to leave the lugs exactly where they are - I don't want to risk lapping and removing what hardening remains - spin on a grendel barrel and use the numrich 7.62x39 feed kit (maybe a new extractor too).

What do you guys think, should I move forward, or does the condition of the action make it too risky?

Thanks.

[dpr]

It needs to be machined and sent in for heat treat. That's a lot to lapp and have come out smooth and flat. Small ring Mausers tend to be soft. Even if you decide to build one on another small ring action with no set back I would recommend sending it in for re heat treat. I've seen set back too many times on small rings.

[SMarquez]

Isn't lug setback measured with head space gauges?

[calshipbuilder]

using a headspace gauge might be more accurate, but I don't have one, and since the barrel is off and I can actually see set back, I can use the depth gauge on my dial calipers to get a rough estimate.

any recommendations on where to send the action for a heat treat? Some net searching says Blanchard Metals Processing..

Thanks

[buffybuster]

These old Mausers were casehardened, probably a low carbon steel and unsuitable for heat treatment hardening. A possible alternative after remachining the lug abutments is Meloniting the action, a form of casehardening.

[TRAP55]

Gas carbonizing heat treatment and quenching, Blanchard does it all the time on small rings. Anyone can heat treat metal, very few have the expertise to treat a Mauser action, Blanchard specializes in it. Get all your machine work done first, lug face resurface, D&T for scope mounts, charger hump re-profile, etc., before you have it heat treated. PM me if you need gunsmith sources that specialize in that work.
Blanchard Metals Processing CO
1115 Pioneer Rd
Salt Lake City, UT 84104-3716

Phone: (801) 972-5590

[calshipbuilder]

Great info Trap55, thanks. Since you seem to have a good idea on this, after proper heat treatment and hardness testing comes back fine, would it be possible to chamber in .260 remington (and shoot commercial ammo safely), or should I stick with 6.5 grendel.

[TRAP55]

Even after heat treating, you need to keep the operating pressure to the original working pressure of 42 to 45,000. With a good barrel, the 6.5 Grendel would be an interesting conversion.

[MongooseV8]

You could also build a 260 Ackley Improved and stick with normal 260 loads. Your pressure levels will be lower that way.

[MongooseV8]

But for all the cost and effort you should really build a stronger 98 large ring if possible.

[calshipbuilder]

already scrapped one of those, excessive lug setback and small bolt lug cracks in a vz24 chambered in 6.5x284. It was my first stab a reloading, but I did not put the rifle together either.

I'll stick with Grendel, its a fun cartridge and I already load for it

[Toxic Shock]

To repair bolt lug setback on a small ring Mauser, there are several things to consider. First, the depressions on the receiver abutments should be ground flat rather than machined. If you try to reface them with a boring bar on a metal lathe, both the interrupted cut, and the change in hardness between the compressed metal and the "normal" sections of the bolt lug seats will induce chatter. You can use a tool similar to the one used resurface the "C" ring face on a '98 Mauser to do this. Keep in mind that the diameter of the abutments are larger than the barrel shank threads on this receiver, so that the disc that you use to do the grinding will need to be inserted through the raceways, and then attached to the rest of the tool.
After removing the bolt lug setback depressions, which usually requires .004" to .005" of metal removal, the receiver will require case hardening. This is where cost versus reward comes into play. You will need to determine for yourself if this particular receiver is worth the expense, as apposed to using a replacement. Myself, I would prefer the re-casehardening, as then I would have confidence in that receiver's hardness.
Third, whenever you remove material from the face of the bolt lug abutments, you will be increasing the gap between the bolt handle and the extraction camming surface. .005" of change shouldn't make very much difference, but if enough material did need to be removed that it did, then some metal would need to be welded to the front of the bolt handle root to compensate for it.
Lastly - small ring Mauser's are are excellent receivers, but were designed during a time when cartridge pressures were lower than today. If you respect the limitations of these receivers, and only use them for cartridges or pressures that they were designed for, they will make really good and handy rifles. The 6.5 Grendel is one of many rounds that would work really well in this type of action.

[SMarquez]

Or you could go with this Mauser action to start out.

http://www.e-sarcoinc.com/dumoulin-mauser-action.aspx

[calshipbuilder]

Thanks for the recommendations. I would not be using a 93 mauser as a base for a custom rifle did it not have sentimental value.