Your TBM Kit will fit the SPR-A2/A4 with the DBM. As others have stated, it will drop right in (unless some other modifications have been made to the rifle after leaving FNH).
It will not drop right in to floorplate rifles such as the SPR-A3G or WSM models. All that is required for these is a re-inlet by a competent gunsmith. The receiver wouldn't have to be modified, just the stock inlet. Because of the design differences between the floorplate and the DBM, there was no way around this. Unfortunately, the current TBM magazines will not feed WSM cartridges, only .308 based cartridges. I use TBM to feed both .308 and .260. I know of others feeding 6.5 Creedmoor with no problems. No modification to the magazine or feed ramp was required for these .308 based cartridges.
TBM will fit, with very minor fitting, the PBR, PBR-XP and TSR-XP with the DBM magazine assembly. The fitting required is inside the stock inlet where the internal mag box sits in the rear of the stock's magazine well. The rear corners of the Hogue stock's magazine well need a slight amount of relief to allow for the TBM bottom metal to fit. Takes a 1/4"-1/2" dowel wrapped with course sand paper and a few minutes to accomplish.
TBM will also fit, with the same floorplate inletting, most Winchester Model 70 short actions. Because very few Winchesters ever shipped with the SA DBM magazine, most M-70s will need re-inlet. In the late 80's and early 90's, Winchester offered the M-70 with the first DBM magazines. The bottom metal material was anodyzed aluminum, where the SPRs are black oxided steel.
TBM was purposely designed to drop in, not only for customer ease of installation, but also from a manufacturing aspect: only one stock was needed to build both DBM and TBM rifles. No machining to the receiver meant these could be universal for assembly too, as well as easy on the customer for upgrade of their DBM. The magazine release was purposely designed to be snag resistent and mimick SCAR, FNAR and by extension, AR platforms. The magazines were intentionally kept as affordable as possible because FNH realized the proprietary nature of magazine was a hurdle when competing against a more ubiquitous AICS-style magazine. Availability was also an upfront concern and was addressed.
Originally, the concept was to simply lengthen the DBM magazine. Testing revealed that the longer magazines needed more support than the short magazine well and front latch of the DNM design could offer. The reliability was not there when pressure was applied to the exterior of the magazine, as one might experience when shooting in an unsupported position or resting the rifle against the magazine. Reliability and function are non-negotiable on these types of systems. The location of the release in front of the longer magazine did not appeal to users, either. TBM bottom metal needed to better support the magazine and incorporate a new release design. That's why is is not merely a longer DBM magazine.
The TBM Kit came along about five years too late, I'll agree. It competes against CDI's very popular aftermarket set-up. Each has its pros and cons. I believe the TBM kit to be the better of the two, but I am a bit biased. I am very pleased to read favorable comments from TBM kit owners. This is the best from of advertising a manufacturer could hope for. Let us know how it works out for you.
