Help! 7 PRC DBM and AICS Mag Vertical Travel/Feed Issues

[Dunderhead]

I'm having issues with the amount of vertical play I'm getting with my AICS magazines. The mag feeds just fine if it's sitting anywhere in between the very bottom or very top positions of insertion. I've look around and it seems this much free travel up and down is normal but I just can't wrap my head around that.

- Action - Zermatt Origin LA - which comes with Remington style feed lips. Capable of accepting AICS Long, CIP, and CIP+ length bottom metal and magazines.
- Cartridge - 7PRC
- Bottom Metal - Grayboe M5 DBM 'Long' 3.715"
- Magazine - Accurate Mag 5rd 3.715" (300win mag length)
- Stock - McMillan Game Warden LR - Inlet for Rem 700 Long Action clones - Pillars installed

With a loaded magazine and the bolt open, there is approximately 0.25" of vertical travel between the magazine bottom position where it is stopped by the mag catch, and the top position where the top of the magazine makes contact with the bottom of the action/action feed lips. The amount of vertical play strikes me as excessive and seems like it would be temperamental with regards to feeding, and no surprise, it is.



With the magazine in the absolute downward position the bullet tips gets pressed into the vertical portion of the action just below the feed ramp and will feed no further. This might be fixed with some tweaking of the front portion of the magazine feed lips. All of the mag tuning videos I've seen are for short action mags and suggest a consistent gap of 0.4". My mag body has a noticeable taper front to back and I can't seem to find any recommended spacing for the 7PRC/long action AICS Mags.

With the magazine pressed all the way upward the bolt gets stopped by (I believe) the back of the magazine. It might be the back of the feed lips. I will try and verify. I've seen suggestions to shim the bottom of my bottom metal to limit the amount of mag insertion, but that will simply exacerbate the problem described above where the round feeds too low and is being driven straight into the vertical face of the action. I've also seen comments that the weight of a loaded mag will hold the mag low enough to keep from being over inserted, however what happens after I fire 4 rounds and now I have a mostly unloaded mag?



My next step is to reach out to MDT and see if their adjustable mag catch could be modified to fit into my Grayboe bottom metal. Any other suggestions appreciated!

Perhaps it's the engineer in me, but I just can't figure out the sloppiness and excessive vertical play that seems to be considered acceptable in this system. Having a rock bottom stopping point only on the bottom direction of travel with no purpose driven limit at the top seems like a system destined for failure.

Thanks to all for your time and insight!

 

[Evintos]

Most likely wrong stock inlet with wrong pillar height. The generic R700 LA inlet is not likely to work properly.

The inlet should've been McMillan Game Warden LR - Big Horn Origin (in Long action).

Zermatt purchased Big Horn Arms a while ago and company had a name change.

 

[Dunderhead]

I think you may be right about the pillar height. But If you browse McMillan's available stock, if you filter by action type and select Bighorn Origin, it will still give results that include "Universal Remington Clone". The Origin is a 700 clone, the bottom foot print is the same, so I don't know how that would have an effect on the seating depth of the action in to the stock.

 

[Evintos]

Stocks that have action and bottom metal specific inlets usually have proper stand off dimensions in the vertical (Z) axis and will have appropriate height pillars. The stock will be milled so that the DBM sits as flush as possible with the bottom of the stock and the action sits inline (neither too low or too high above the stock). From your vid and pics, your receiver looks like it sits low in the stock and there looks to be excess material (edge of ejection port below edge of stock by ejection port).

On the McMillan website, there is a Game Warden Universal stock option that has a straight cut on the receiver section to account for a variety of stuff like different R700 clone action ejection port lengths, which is not the same as the non-universal (specific to action) Game Warden LR that they occasionally have as ready to ship items, but is custom order majority of the times.

If you ordered the Game Warden Universal, you have been sent the wrong stock. However, if you did order a Game Warden LR for Remington 700LA, then you ordered the wrong stock. Hence my original thoughts on it being wrong inlet and correspondingly wrong pillar height.

Even if you solve for the magazine and Z height issue, I suspect that you'll end up having weird case ejection pattern/issues due to the excess material on the stock.