Different POI with 'regular' vs. set trigger pull?

[MZ5]

I was shooting my 527 (223 Rem) recently in my quest to get it to shoot outstandingly well rather than pretty decent.  For this purpose, I was shooting off a bipod up front and a rice bag under the buttstock.  For whatever reason, the first couple shots in a particular string I didn't 'set' the trigger first; I just used it as a 'regular' or 'normal' trigger.  I realized what I had done and pushed the trigger forward to 'set' it for the third shot.  Through the scope I noticed that this bullet hole was low and left of the previous two.  I fired another using the set trigger, and the 5th shot I used the 'regular' trigger action.

I retrieved the target to verify what I thought I saw through the scope and found that indeed the 3 shots fired using the 'regular' trigger action were all right on top of one another, and the 2 I fired 'set' were also right on top of one another, but low and left of the other three shots.

Has anyone experienced this before?  The only explanation I could come up with was that the difference in trigger pull was causing me to pull the rifle slightly right and up when using the 'regular' trigger action vs. the 'set' trigger action.  I swear I didn't, but that's all I could think of.

How else could firing regular vs. set change POI?

[Skunk]

The only explanation I could come up with was that the difference in trigger pull was causing me to pull the rifle slightly right and up when using the 'regular' trigger action vs. the 'set' trigger action.  I swear I didn't, but that's all I could think of.

That's what I was thinking while reading your post, but you never know. Next time I get the 550 out to the range, I'll do a comparison. Can't really comment on the difference in POI between the two on mine because I like the set trigger pull so much that the regular pull option seldom gets used. Now you got me wondering.

[skarke]

Set triggers are out of favor from accuracy shooters because of this very type of issue.  basically, a set trigger uses a tiny "hammer" of sorts to knock loose the main sear, releasing the striker.  It is a click, then another click.  No matter how fast this occurs, lock time is very important, and set triggers by design have slower lock times than, say, a Jewell.

That said, set triggers are VERY cool, and there are some fine, accurate examples still manufactured.

[skarke]

Here is a diagram of what I'm talking about.  Though antiquated examples, single sets and double sets generally work under the same technology in existence for more than a century.

http://members.aye.net/~bspen/triggerterm.html

[hotrunner]

Yep, I've noticed the P.O.I. changes when I use the set trigger on my 527 (.221 Fireball.) In fact the rifle shoots so well without it, I no longer use it. If you zero with the set trigger, you have to shoot every time with it afterward for accurate shots, and who among old geezers like me will always remember?

[MZ5]

and who among old geezers like me will always remember?

LOL!  That's how I came to notice it in the first place!  I was shooting a couple or three rifles that afternoon, and I just forgot to set the trigger!

Today's load work was without the set trigger, and I like the set trigger better, but even the standard trigger is pretty darn good.

Thanks folks for the responses, especially you hotrunner since you've had it happen to you before.  I was intrigued to hear that lock time is actually longer when the trigger is set.  I'd never heard that before.