Ideas on vertical stringing?

Farlsincharge

Farlsincharge

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Why am I still getting vertical strings?

Semi - automatic rifle
weighing every charge
meticulously prepared brass
I have tried a Lee crimp die


In 10 shots I have up to 90fps variance.

Is 5 shots in 2 minutes enough to cause stringing?

Any other ideas?
 
Just how much vertical are you getting? Are you using a scope or iron sights? Is the rifle gas operated or blowback?

There are a couple of reasons for vertical stringing, that can be checked easily If it's a two piece stock, such as is found on a BAR, the fore end pressure between the action and the barrel may be causing the problem.

It you're using iron sights, it may boil down to changing the butt position on your shoulder. More than likely it's pressure from something, pushing the underside of the barrel up.
 
Is this a new problem or has it always been there? Also, does it walk in one direction, or deposit thse shots along the entire string randomly?

if the former, it is barrel heating more than likely

If the latter, anything from bedding to bipod...
 
It is a swiss arms black special target with a scope. I am shooting prone off of bags. Groups are about an inch wide (random not trailing in one direction) and 3 inches tall at 200 yards. I don't think it has anything to do with the rifle itself, unless a semi can be inconsistent enough to cause a 90fps difference in velocity?
I'm just frustrated as after all this work meticulously reloading I am getting such a wide spread on velocity.
 
What bullets? 90 fps SD seems like a lot if everything is weighed. Do you really need to crimp? If you think about it, 3 inch tall groups at 200 yards is still a 1.5 MOA.
 
The way the Black Special is made makes it very sensitive to differing amounts of forend pressure. You may as well be using the tip of the barrel for a rest. The zero off the bipod would be different than that from the bags, and that would be different from that of handheld positions. I had to get rid of mine, as these shifts made it useless for my application. With care as to a consistant hold the groups can be tiny, which made the shifts all the more obvious and aggravateing.
 
Have you ever read the article on load development by Jerry Teo aka mysticplayer. It is on longrangehunting.com If you haven't go there and read it. If you follow his system it will rule out the problem being your load.
 
Dogleg said:
The way the Black Special is made makes it very sensitive to differing amounts of forend pressure. You may as well be using the tip of the barrel for a rest. The zero off the bipod would be different than that from the bags, and that would be different from that of handheld positions. I had to get rid of mine, as these shifts made it useless for my application. With care as to a consistant hold the groups can be tiny, which made the shifts all the more obvious and aggravateing.
Click to expand...

It is not useless, though the lack of a floating forend is a limiter for the Sigs. It is a problem for all sigs, including the sniper model, but not something that the shooter can not work around.

If you use the mag as a rest, you will be much better off. Either put a 5rnder in it, and bag up, or put a 5/30 in, and put the base of the mag in the dirt. I have even seen a bipod that uses the front pin, though I would not recommend this.

This is 10rnds from a box stock sig at 500m shot slow using a mag as a rest. Shot prone in the dirt with RUAG factory ammo.
2009CSRAProvincials002.jpg

It is not my shooting, nor is it the best that I have seen, or the best I have seen from this competitor. This is just a pic that I snapped while scoring targets. The shooter lost one point in this target.
 
How are you weighing the charges? For me personally, I couldn't use a beam scale to save my life. My deviation came down with an electronic scale.

Everything else I've read, and the little I've done, on deviation shows that case uniformity is the key.

And when I shoot for testing I cool for 2 - 3 mins between shots.
 
Try weighing your empty deprimed cases and sort out a batch that are plus or minus 2 grains or better yet plus or minus 1 grain. Case weight is a measure of internal case volume and case volume effects chamber pressure and therefore burn rate. I had a .218 bee that strung about 3 inches vertically until I selected out a batch of cases by weight. Then in closed down to a 3/4 inch group or less

cheers mooncoon
 
carbonrod said:
It is not useless, though the lack of a floating forend is a limiter for the Sigs. It is a problem for all sigs, including the sniper model, but not something that the shooter can not work around.

If you use the mag as a rest, you will be much better off. Either put a 5rnder in it, and bag up, or put a 5/30 in, and put the base of the mag in the dirt. I have even seen a bipod that uses the front pin, though I would not recommend this.

This is 10rnds from a box stock sig at 500m shot slow using a mag as a rest. Shot prone in the dirt with RUAG factory ammo.
2009CSRAProvincials002.jpg

It is not my shooting, nor is it the best that I have seen, or the best I have seen from this competitor. This is just a pic that I snapped while scoring targets. The shooter lost one point in this target.
Click to expand...

If I could have gotten a floating forend I'd probably still have it. As it was, a shift of 2 or more MOA from position to position was more than I could manage. When I read about the OP was shooting a SIG, the first thing I thought of was his vertical stringing could be bench technique, and not loads.
 
Seeing as the barrel has some forend stock contact, I would either look at barrel heat causing vertical stringing, or else inconsistent forend pressure from shooting technique. You have a few different options:

1. Slow down your rate of fire! Make sure the barrel is never uncomfortably hot to the touch.

2. Center the rifle on the front sand bag so that the front action screw of the rifle is directly on top of the bag.

3. Free-float the barrel. Eliminate any barrel to forend contact and you will have less to worry about with regards to these listed sources of vertical stringing. The rifle's potential accuracy may even increase.
 
Jordan Smith said:
Seeing as the barrel has some forend stock contact, I would either look at barrel heat causing vertical stringing, or else inconsistent forend pressure from shooting technique. You have a few different options:

1. Slow down your rate of fire! Make sure the barrel is never uncomfortably hot to the touch.

2. Center the rifle on the front sand bag so that the front action screw of the rifle is directly on top of the bag.

3. Free-float the barrel. Eliminate any barrel to forend contact and you will have less to worry about with regards to these listed sources of vertical stringing. The rifle's potential accuracy may even increase.
Click to expand...

Farlsincharge said:
It is a swiss arms black special target with a scope.
Click to expand...
There is no front action screw, and unless there is something that I do not know about, free floating a sig is a prototype rich endeavor.

Many of the posts above are great advice for a bolt gun that is vertically stringing, but with a semi, there are other factors.
 
90 fps variation sounds like a lot.

Do you have a neck sizer or full length sizer you can take the decapping pin out of, so that the neck is sized small and not expanded by the button? This will greatly increase neck tension and often reduces velocity variation.

Another cause of pressure variation is too mild a load. You did not mention what your caliber/load is.

In a semi auto, variations in pressure/velocity cause even more problems thnan in a bolt gun.
 
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DISCLAIMER: My suggestions above are general principles for good accuracy. Since I am unfamiliar with the nuances and quirks of that particular rifle, and since it seems to be different from others, ignore anything I say that does not apply to this particular rifle :D
 
carbonrod said:
... free floating a sig is a prototype rich endeavor...
QUOTE]

The solution for this has already been mentioned - rest on the mag. The barrel is basically free floated if the shooter is not holding or resting the rifle by the forearm.

I had the same problem when I shot my AR15 off a bag, but when I rested the rifle on the mag, and gripped the magazine well, instead of the forearm, it returned to zero and the groups tightened up.

Variable cheek pressure (such as from a cheekrest being too high) will also result in vertical stringing.
Click to expand...
 
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