I switched from a B&C stock which shot consistently well. I changed to the Hunter 700 for the ergonomics (definitely better) and the DBM set up. While the Magpul stock has produced the best 5-shot group to date - .312" at 100 yards -
it has also produced some slightly larger groups than the B&C. Compared to the B&C, the level of precision has not been as consistent, which I found disconcerting.
With the B&C stock, groups were consistently in the .5 to .65 MOA range, the best (ever) being .462 MOA. Here are two "best" 5-shot groups with the Hunter 700 stock from a single range session, during which I also had a few close to 1.0 MOA;
At that point I was disappointed with the lack of consistency. Not quite ready to give up on this stock, I took some time to try to figure out why the loss in consistency and I believe I've found the culprit;
I noticed that as I torqued down the action screws and contact was made between the trigger guard assembly and the bedding block, I did not get that immediate hard resistance that I had with the B&C stock. The screws would only
slowly tighten, requiring more screw rotation to reach the torque setting. Upon examination, I found that Magpul uses steel inserts in the plastic trigger guard assembly for the action screws to pass through. In my case, the steel inserts were not quite flush with the top of the assembly where it comes into contact with the bedding block, resulting in the need to compress plastic. I'm not certain that at even 60 inch-pounds that the metal inserts ever made contact with the bedding block. Additionally, it was difficult to seat a loaded magazine against a closed bolt, and even an empty magazine contacted the bolt hard enough to cause drag. I'm pretty certain that neither of those conditions are beneficial for consistent precision.
My fix was to take down the plastic on the top of the trigger guard assembly (where it contacts the bedding block) to the top of the steel inserts, carefully and slowly using a file. With that done and the steel inserts in direct contact with the bottom of the bedding block, the action screws torqued down as expected. However, this also caused the magazine to sit even higher further aggravating the interference between the closed bolt and the top of the magazine.
The fix for this was simple - I placed a thin brass washer on top of the trigger guard assembly, one for each screw, which pulled the magazine down but now too far away from the bolt. I needed to thin the brass washers using a file until I achieved 100% reliable feeding from the magazine. With this done, there is now zero contact between the top of the magazine and the closed bolt. In fact, the operation of the DBM assembly now seems perfect, the bolt closes smoothly and the action screws tighten down as they should with metal-on-metal contact between the trigger guard assembly and the bedding block. At least in my case (sample of one), the Magpul DBM assembly works well but is not quite perfect without some work.
I spent considerable time working this out last winter but have yet to fire the rifle again. This thread has motivated me to hit the range tomorrow to see if there is any improvement (I'm betting there will be) and I'll post the results here.
Remington 700 SPS Tac in .308
Timney set to 3 lbs.
SWFA 10X42 HD in Seekins rings on Leupold 15 MOA steel base (bedded to receiver)
Hunter 700 with Arca-Swiss QD plate (and modified trigger guard assembly)
VG6 Precision Gama 7.62 brake (added after this photo was taken)
