Vertical Strings.

[stilkikin]

Ok, here's the deal. I have vertical stringing I didn't have before. The gun is a Crosman G1 that has a Titan .22 barrel on it. I just put a new Tarantula spring in it and I now have bad stringing. At 37 feet I'm getting a 3" pattern. I've put close to 500 rounds through it now and it's not getting any better. The barrel bolt is tight, its not stringing left to right. I know I have a couple nicks in the new Apex seal, it was shooting fine with those before the spring change though. The scope is not moving either, not enough for me to notice on the reference marks anyways. Can someone throw some ideas my way to give me a little help. This gun was shooting 1/2" groups before. I'm going to change the seal tonight and report back tomorrow.

[Calmark]

Hi Stilkikin,

I'd look at your breech seal.  If its bad, that could be a source of inconsistency.  Also, recheck your barrel pivot bolt.  I've had vertical stringing when mine was just a tad loose.  Once I got it tight enough to not drop under its own weight after cocking, that solved my problem.  You might consider loctite on the bolt to hold it in place too.  Good luck!

[thekid]

Change the breach block to receiver bushings from plastic to brass.
You can make them yourself or buy them from gene I believe he makes them.
This will help keep things tight.
Rob

[Fisherdude]

You didnt say which pellets you use.  A batch of pellets with undersize pellets could be the pproblem.   A bad seal could cause verticle stringing.    If you have a muzzle break make sure it is good and tight. Brass pivot screw washers are a must.

[DardanosPorter]

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[DardanosPorter]

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[stilkikin]

I get the strings no matter what pellets I use, Barracudas, Beeman FTS, RWS Meisterkugeln, CPHP's, all of them. I was shooting ragged hole groups at 10 yards. I took the gun apart, found a burr I missed where the trigger goes into the receiver tube and filed it down and installed a new Macarri seal. I took the barrel bolt out, checked the washers for wear, lubed, locktited and installed with a hand driven impact wrech. It can't get any tighter. I'd still like to get brass washers though. I need to do the breech seal too. I'm thinking that is a contributing factor cause I have real bad barrel droop so I know there is an angle where the seal meets the face of the receiver. I's a little better now but not much.

[thekid]

This a common issue..
Check the live jam to make sure it is still strong, that is what holds the barrel closed.
a new spring having not set yet will hit harder and if the live jam spring is week it could knock your accuracy off... with up/down vertical stringing.
Rob

[stilkikin]

I thought that one through, I'm thinking of shimming the spring to exert more pressure. I get good lockup though. I think at least...

[AirScopes]

Which direction are the strings going (up, down)? Are you changing any of the turret positions? I assume the string is not continuously moving up or down... as it would not stop at 3 inches?

What kind of scope and mount are you using?

it doesn't take much to string. movement of scope on the railscope in the rings, turrets, focusing rings... a fraction of a fraction of an inch at the focus... 37 feet with a 3 inch range is about 1/3 of a degree... a total change on a 12 inch scope of about .007 inches tilt... or raising the front of the scope by less than 1/10th the width of an average  human hair. it will be tough to see.

Travel in the mount is only one potential cause. if you have a vertical bracket (only wavering between the highest and lowest in that range, but randomly), it could be quite a few things, breaking down to varying velocity, movement of the sight, or difference in the rifle between shots (barrel seating?).

when I start to think about the numbers, it is amazing that we can hit anything...

Richard

[SAADE]

Richard makes good points... a few thousandths of an inch as measured at the scope or at the muzzle is amplified HUGE at the point of impact out at 30 yards or even more.

[stilkikin]

I fixed it. I took the live jam out and shimmed it 2mm. Then I took out the breach seal and put three layers of masking tape on the back side and cut around the seal. Everything works fine now. Thanks for you guys input, glad I'm not alone out here.