Hey Mac you might do a site search on the topic. I think I remember that Jeff223 pulls his extension off when he's shooting for those little tiny groups he wins the matchs with. For a common boob like me , makes no difference.
I contacted NEF/HR by phone and talked to the manager regarding this issue. He was very pleasant and helpful. He said, as I understood him, that if the transfer bar is not all the way up when the hammer strikes it, then the bar will receive reduced impact from the hammer and so the firing pin will not receive the full whack either. This can cause a misfire but it apparently can also cause reduced primer performance that can in turn lead to lower muzzle velocity. Not pulling the trigger all the way back to keep the transfer bar up results in this. So anything that causes increased lock time can contribute to the problem, including a weak hammer spring and/or use of a hammer extension.
I think this is what I have been experiencing up until I removed the hammer extension today and shot less than an inch with Winchester White Box ammo.
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