IMO the culprit is lock time vs barrel time.
The tester was me, the testing protocol involved same-day same-target alternating-methods on each successive bull for a minimum of 4 bulls per method (set vs unset), groups of 5 shots measured c-to-c. IOW each rifle had a minimum of 8 groups fired, 4 set and 4 unset, all on the same target with proven loads. Some rifles actually had many dozens of groups fired, using different bag techniques. Rifles included RFs and CFs, bolt actions and single shots; trigger types included the simplest crudest over-center type SSTs, the better sear-equipped SSTs, the CCDSTs and the wide-spaced double-lever DSTs. Sorry no 3-lever or 4-lever types were tested. Set pulls ranged from 2 oz to 8 oz, unset pulls ranged from 2.5 lbs to 6.5 lbs. It's been many years since I began this testing and it continues to this day on a sporadic basis. So far I've tested maybe 25-30 rifles, about equally split between bolt actions and single shots, RFs and CFs, sporters and match rifles. This was shooting at ranges from 50 yds to 200 yds, mostly on a wind-shielded private range but some testing was also done on a non-shielded public range. Front tripod with U-bag, rear rabbit-ear bag, smooth leather on both. Some experiments with stacked front bags instead of the tripod. Several thousand rounds fired including my next-to-last hoarded Eley RF and my very last Federal RF. Scopes ranged from 4x to 24x, Weaver to Unertl.
In no case, not one single case, did the rifle, any of the rifles, make smaller groups with the set feature than when using it unset.
Think about that. Dozens & dozens & dozens of targets, each with 4 set groups and 4 unset groups fired alternatingly and successively at the same time by the same person, and not one of the targets showed better accuracy when using the set feature. Difference ranged from 8% to 16% with no pattern or trend apparent to me.
Also please remember that many of the early post-WW2 Benchresters at the Pine Trails range and others began by using set triggers but soon, very soon, they had all abandoned the set triggers for light-pull non-set ones. The set feature is a big help to me when my hold is less than steady such as offhand or field shooting, but apparently the increased set lock time becomes more noticeable as the steadiness of the rest improves. JMOFWIW and I know some will disagree with it, but it's mighty hard to argue with the testing and the Benchresters.
Regards, Joe
