Vertical Shot String????

SHulion · 03-23-2009, 05:35 AM

What causes this? I went to the range yesterday and got some really nice groups with my Endeavor, 110 gr. of BH209 and a 265 gr. FTX with the Harvester green sabot. Then I decided to try 120gr. of powder and got a vertical shot string. The holes were within a half inch of each other horizontally but were strung out about 3 or 3 1/2 inches vertically. Does this meen that its no longer burning all of the powder in the barrel or am I doing something wrong?

UncleNorby · 03-23-2009, 05:39 AM

Do you know whether they impacted higher sequentially? A vertical string may mean nothing at all, but if each shot impacts higher than the last, that could mean something.

lemoyne · 03-23-2009, 05:59 AM

A vertical string some times means that the powder load is to much or to little, it can also come from a mounting screw or butt stock or forearm screw loosing up. If you put the sand bag to far forward on some guns it can cause it but usually not that bad. Lee

hunting junkie · 03-23-2009, 06:06 AM

Sounds like the gun was getting dirty.

spaniel · 03-23-2009, 06:22 AM

If you were shooting Pyrodex or 777 I'd say your barrel was getting dirty, thereby increasing pressure and therefore velocity, resulting in the vertical stringing. But BH209 is not SUPPOSED to do that, right?

The other possibility is this -- how hot was it out, and how much time were you taking between shots? If your barrel is getting too hot, even if properly bedded, you can get vertical stringing. Upping the powder charge on an already-warmed barrel could have been enough to reach the point where you needed to take longer between shots to maintain groups.

In temps over 60F, I let 5min pass before reloading a ML if I really want the best groups. While my Omega is a tackdriver and is fully bedded, it will do that if I shoot/reload/shoot/reload on a warm day.

SHulion · 03-23-2009, 06:28 AM

I forgot to mention that I went back to the 110gr. load and the group shrank back to around 1 - 1 1/2 inches.

sabotloader · 03-23-2009, 06:52 AM

SHulion

All things being equal usually verticle stringing is an indication that the barrel is heating and expanding - pushing it way off the stock... then as Lee indicated as you move up the powder chain you are also changing the Harmonics (vibrations) set up in the barrel each time you shoot. These Harmonics could cause the POI to walk - especially in a gun with a separate fore arm and add to the that a forearm resting in a support such as it would be when shooting from a bench.

Lee has solved that problem in his Triumph - hoping to get it done in mine as soon as I get a chance... got to get these darn PRB guns to shoot right first.

Grouse45 · 03-23-2009, 07:38 AM

I alway's increase the powder (speed of bullet)and it goes away. If 110grns of BH209 is good, i would try and see if you can get 115grns to work. If not go back to your proven 110grns. 120 you already know you have a problem.