HELP please vertical stringing

[df06]

I have  G2 with a 14 "  stainless MGM 357 Max bull barrel. I am shooting 21.5 Lil Gun and 180 Hornadt XTP bullets. At 100 yards I am getting 4-6" vertical stringing. The forend is a decelerator rabber type, as is the grip. I am shooting off a short harris bipod attached to the stud that is on the decelerator forend, and with a sand bag under the grip.
Horizontally I am holding about 1" spread.
What should i do to correct this vertical stringing?

Thanks

[skarke]

Check the gap between the barrel and frame when locked up.  It shouldn't be 0.  Occasionally, you'll see this.  Even if you get good lockup, 0 gap will cause vertical stringing.

Also (and I'm sure that you have already done this), make sure that you don't have a short chamber, or long cases.

One last thing, I'll bet that sandbag is your culprit. any pistol MUST have consistent movement of the grip upon firing. Try using a piece of leather nailed to a board with baby powder or graphite on it for your grip to slide on, with a slight angle up and away for elevation adjustment where the grip rests(move the gun forward to lower your shot).  Easy to make, and works like a champ.

 

[securitysix]

I've never had a problem with vertical stringing from using a sandbag under the grip.  I also don't shoot off of a bipod.  Rather, I shoot with a sandbag under the fore end as well.

Something else that could be the cause of your vertical stringing is velocity variation in your ammo.  I've had vertical stringing problems with a couple of .223 handloads, switch to different handloads with the same rest setup and suddenly my groups are just fine.

Lil' Gun likes a good crimp.  If your ammo isn't crimped, or is crimped too lightly, you could get inconsistent pressure build leading to velocity variations.

[Ken ONeill]

1. Variation in crimp or too light crimp
2. Variation in your grip- either tension or position of hand.
3. Variation in the way the grip contacts / doesn't contact the sandbag. I'd lose the sandbag.
4. It's unlikely that an innacurate load would result in only vertical stringing, rather than larger group dispersion, unless crimp is the problem. in my opinion.

[df06]

I appreciate all the suggesrions.
I do have a pretty light crimp.
So, will try a harder crimp, a different powder, lose the bag, & try with out a bi pod.
Thanks again

[Tommyt]

Wow talk about going 360% with that said if your new method(s) fail
I'm looking for a Max 

good Luck with it hope it works out
Tommyt

welcome to GBO

I appreciate all the suggesrions.
I do have a pretty light crimp.
So, will try a harder crimp, a different powder, lose the bag, & try with out a bi pod.
Thanks again

[skarke]

Ok, if you are looking for bench performance, or varment performance, there is nothing better than this:

http://bowersp.com/rests.aspx

If you are looking for good field performance, imho, get yourself a good elbow rest like this

 http://www.midwayusa.com/viewProduct/?productNumber=166806

and rest it on a strong branch, limb, stump, rock, or other such thing while nesting the forend solidly in the bag.

And like Ken said under the grip........

3. Variation in the way the grip contacts / doesn't contact the sandbag. I'd lose the sandbag.

If these shooting technique things don't fix it, then get thyself some feeler gauges and a good dial caliper and see where you're at.