vertical string grouping

[jimbullet]

Trying to analyze my grouping. 180gr FMJ ammo from a STI DVC, 40S&W. 25 meters the grouping is a straight vertical line with 5 shot groups, about 1/2 inches apart for the 4 shots and the 5th shot was 2 inches higher. What is puzzling is that it was a straight line that I could put a ruler and draw a line for all the shots and they would be in a perfect line.

 

This was done on a slow fire to see the grouping.

 

Any ideas on what I need to look at or what is causing this? Any ideas would be welcome.

[jim vaughan]

The normal request is for the opposite - 1st shot different to the remainder.

Other ideas are loose sights, weak recoil spring, less than perfect barrel lockup, worn link and pin, worn slide stop, etc.

Also try a slightly stronger recoil spring and see if the group pattern changes.

Was your slow fire braced on sand bags? Try another shooter.  Jim

[jimbullet]

sights are sturdy, The link appears fine. The slide stop pin has peened where the lower barrel lugs contact which if I am not mistaken means a tight fit?

was shooting rested on a range bag. Will see about the recoil spring but I am not sure how a stronger recoil spring correlates to shot placement? I thought they were only to resolve feeding problems and how fast to return back to battery and ready to fire?

[N3WWN]

54 minutes ago, jimbullet said:

Will see about the recoil spring but I am not sure how a stronger recoil spring correlates to shot placement? I thought they were only to resolve feeding problems and how fast to return back to battery and ready to fire?

 

I have a Rock Island wide-body 1911 in 40 that I used to run a 10-11 lb recoil spring in.  I started to notice at matches that my 1st shot would often be at quite a different location on the target than what I called.  A couple of range sessions shooting groups confirmed that the 1st shot after chambering a round was in a different location.  

 

That gun ended up getting shelved in the safe for about 2 years for different reasons.

 

I recently pulled it out again and shot some groups and noticed that I couldn't shoot a group tighter than about 2-3" at 10 yards.  (My standard group at 10 yards is the size of 1 paster, or about 3/4", with my other competition pistols).  I replaced the recoil spring with a new 17 lb spring and the group tightened up and the first shot was longer a flyer.  This pistol is now just as accurate as the others.

 

While I'm not 100% sure, I think it had to do with how everything locked up.  The 1st shot placement was different because I manually chambered that round whereas the rest of the rounds from the magazine were chambered with the recoil cycle.  The larger group, AFAICT, was due to slight differences in how the gun locked up every time.

[jimbullet]

Thats interesting. I did have the first shot impacting highest than the rest. In saying that, Im not sure if the lock up would be any different to the rest of the rounds I fired as when I chambered a round, I often pulled the slide back and release it so it stripped the ammunition from the magazine. I dont guide the slide back though.

[jpl]

If it is stringing vertically as it warms up check for barrel springing.  Take the top end off the frame and remove the recoil system.  Press the barrel up into the slide lugs.  Does it stay there or "spring" back down?  If it is springing the front of the barrel is not fit correctly.