I have been following this issue since MS first started allowing 35 caliber primitive weapons because of how many postings there were on the various forums in the state. Some have been corrected by stronger hammer springs. I guess the bottom line is that it is a "perfect storm" kind of problem.
I am in no way a gunsmith nor did I stay in a Holiday Inn Express last night but my interpretations of the various threads I have read on the issue are below:
First both the 35Whelen and 35Rem are rimless cartridges and they head space on the shoulder which is small in both rounds, a weak point.
Second is shoulder angle: Whelen 17.5 degrees Rem 23.25 degrees and shallow angle could lead to more "slip and slide" forward under the pressure of the firing pin strike which I believe would make the Whelen more likely of the two to suffer a FTF all other factors being the same.
Third is the chamber cutting tolerances of the gun makers. The SAAMI specifications for a given round most likely has a +/- 0.00xxx range for acceptable and mass produced barrels probably vary chamber to chamber within those tolerances. If true and you happen get a barrel that was cut on the minimum (tight) end of the specs then I believe you are much less likely to have a FTF whereas if your chamber is on the upper (loose) end of the specs I believe it increases the potential of the FTF issue.
Fourth is that the ammunition companies that must size factory brass to fit all potential chambers. If you are cursed with a loose chamber and shooting factory ammo then the potential for a FTF is higher than if you are blessed with a tight chamber.
The idea of chamber size came to light from posts about people not having FTF problems with Encore 35Whelen barrels made by aftermarket suppliers. The contention was that those suppliers tended to more carefully cut their chambers to the bare minimum side of the SAAMI range and did not seem to suffer the FTF problems. Believe I read on one page on the
Mike Bellm site that he cuts his chambers under the SAAMI minimum. He also touts Match Grade Machine for quality and precision of their TC barrels. To bad we can't get that kind of caring precision from the factory, it would make the Handi's truly worth what they are charging and might even be worth a modest price bump.
Like I said this is just my opinion, I am not a gun smith, nor a machinist, but I do believe the problem results from the sloppy "as long as it is within acceptable tolerances" attitude of many companies these days. Kind of a "take two aspirins and call me in the morning" approach.
