Gunsmithing AICS mag seats too deep

[PinesAndProjectiles]

I've got an ARC Nucleus in a Gen 4 KRG Whiskey 3.

The mags will fit and feed just fine, until there is any type of force pushing on the bottom of the magazine.

This pushes the mag too deep into the mag well and will not allow the bolt to close.

Any ideas on how to fix this?

All I've been able to find is info on tuning mag feed lips and I dont think that's my problem.

 

[tnichols]

Sounds like the problem may be in the bottom metal itself? I’m curious what others have to offer.

 

[diverdon]

I just tried it on my MDT with MDT mags and with the weight of the rifle resting on the bottom of the mag the bolt hung up the first time I tried it. The next 20 times I tried it with the entire weight of the rifle on the mag it did not hang up though I felt a little extra drag a few times.

My first thought is that it is a bad practice to rest the rifle on the mag. Second thought is to wonder if it could be addressed by grinding a few thou off the back of the mag in the center. I'm not going to try that as I don't see that I am going to have a problem in operation.

I have the .223 bolt.

 

[diverdon]

As I continued to try it I discovered in my rifle that the binding happens when in addition to resting the weight on the mag (1) a rearward torque is applied to the mag or (2) the entire weight of the rifle is put on the rear bottom corner of the mag.

 

[PinesAndProjectiles]

The problem rests between the feed lips and the bolt.

The bolt will clear the mag just fine, but the weight causes it to snag up on the feed lips.

It's as though the mag doesnt have a hard stop in it to keep it from going in too far.

Normally it's not an issue, but it caused an issue this past weekend when shooting off props.

If I could "bed" the mag per se, it would eliminate future issues.

 

[diverdon]

How far forward (as a fraction of bolt travel) are you when it happens?

 

[PinesAndProjectiles]

The bolt hits right at the rear of the feed lips.

 

[parshal]

My experience is it's the feed lips as already mentioned. Close the bolt, then push the mag up and slide the bolt back. You may find it's hitting along the entire length. The height with a detachable mag has to be just right. The real "fix" is to bed the action a bit higher but you may find it sits too proud of the stock. You're sort of dealing with stacked tolerances with the stock and bottom metal. The stock needs a bit more height. Looking for the quickest fix I go the shim route.

I'm sure a professional will come along and tell us the best way to do it. I'm betting this is a very common problem that most builders find.

 

[PinesAndProjectiles]

My experience is it's the feed lips as already mentioned. Close the bolt, then push the mag up and slide the bolt back. You may find it's hitting along the entire length. The height with a detachable mag has to be just right. The real "fix" is to bed the action a bit higher but you may find it sits too proud of the stock. You're sort of dealing with stacked tolerances with the stock and bottom metal. The stock needs a bit more height. Looking for the quickest fix I go the shim route.

I'm sure a professional will come along and tell us the best way to do it. I'm betting this is a very common problem that most builders find.

Thanks @parshal . I was starting to think the same thing, but I really dont want to shim my action in the chassis.

 

[parshal]

I completely missed that it was a chassis! I'm curious to see what you find as a solution.

 

[MarkLeupold]

Glad I'm not the only one experiencing this. If you have a DBM (I know the OP doesn't, but for reference) I've found increasing the depth into the stock at the front action screw and decreasing the depth (ie. shimming) at the rear action screw by about 20 thou each worked for me. I don't really like that fix, so I've been working on a DBM design that gives mags a hard stop once they lock in.

For chassis, you're really kind of stuck with what they give you. If there's some way to increase tension on the mag (maybe decrease front to back length of the magwell, I know some chassis offer this), that would help with your tilting problem.