Big Uncle

Last week a friend brought me his Montana to see if I could do anything to improve it's accuracy. I took it to the range and it did shoot poorly. It did not take long to find that the action was high centered on the magazine box. The Montana has a blind magazine and the problem was fairly obvious from the markings on the stock. The bottom of the magazine box made a trip to the bench grinder and got a touch up with cold blue. The fix took maybe 30 minutes. Now it is shooting much better. In fact it is the best shooting Montana that I have seen. My friend won the "Kimber lottery".

Nomercy448

If I’m understanding the issue correctly, Ruger M77’s have the same common issue with pressure points created by the mag box, and benefit from the same solution of free-floating/pressure relieving the magazine box.

It’s always remarkable to me how much difference something so little can and does make. Definitely something folks should be checking in their rifles when and if they have issues with load development or factory ammo selection.

Bocajnala

It sounds like something the factory should be correcting if this is an ongoing issue.

Especially a rifle in that price point.

-Jake

Big Uncle

Yep, it is the same as the Ruger issue. Guys usually just get it fixed on a Ruger (if they notice the problem) and do not say much about it. It is normal to get a good Ruger 77 and I think most of us tinkerers know about the magazine box on them. There does not seem to be much of a "normal" with the Kimber rifles. Some guys get a good one, and some guys get a lemon, I briefly had a lemon Montana with the same magazine box issue that proper bedding did not fix. I shortened the box, rebedded the action, etc. If I had kept it it would have had a new barrel, but some other fellow wanted it badly (even with a warning) just because it was a Kimber and he was very impressed with their advertising. in this case I was happy that my friend was lucky and just one simple fix did the trick.

Nomercy448

Ya’ know, it may have a bit to do with who is doing the buying of Rugers versus Kimbers. Most guys buying Rugers aren’t going to be afraid of turning a screwdriver and running a bastard file, while I expect most Kimber buyers will be looking for a more turn-key product, not interested in popping the hood. Kind of the same difference between a guy who buys a Camaro and a guy who buys a Corvette.

Luckily for both, the fix is pretty simple.

Bocajnala

Maybe I'm not understanding something.

There shouldn't be a need for a "fix".

Especially if it's as common as it sounds like. Why has ruger and kimber not corrected the problem.

-Jake

Nomercy448

It’s a matter of several factors:

1) Manufacturing variability in part dimensions means some of the magboxes - which are meant to be relatively pinched between the action and bottom metal - are pinched harder than others.

2) Stock inlets are especially variable

3) Paying someone to hand fit the mag boxes of every rifle would mean a price increase to the end product.

Effectively the same reason manufacturers use full contact barrel channels or pressure pads in their stocks instead of free floating, or the same reason manufacturers don’t pillar block and bed actions... Added labor = added production cost...

bronko22000

Let's see if I'm understanding this also. What you guys are saying is that the magazine box may be too long (high) and is being pinched between the stock and the receiver. This "pinching" then causes the action not to be properly seated in the stock which affects accuracy? Removing some of the material from the bottom of the magazine box allows the action to "seat" correctly into the bedded stock and thus improving accuracy. Is this what you're referring to?

Nomercy448

Yes, but not just a matter of not seating properly, but rather also creating pressure points against the action, and effectively, a flexing moment against the action. As the action heats, this tension varies, as it resonates in firing, it can vary, or be inconsistently dampened. Removing this pressure point or fulcrum allows consistent bedding and repeatable pressures against the action from one shot to the next.

bronko22000

That's pretty much what I was thinking when I stated correctly seated in the bedded action. Thanks NoMercy.