vertical stringing

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wboggs
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vertical stringing

Post by wboggs » Sat Feb 03, 2007 1:51 pm

I am new to back powder reloading and am having a problem with vertial stringing. Horizontal is less than minute angle but vertical opens to 2-4 minutes. Wonder what some of the basic causes could be?
Would appreciate any help. Thanks
beginner in black powder

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montana_charlie
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Re: vertical stringing

Post by montana_charlie » Sat Feb 03, 2007 3:40 pm

Wonder what some of the basic causes could be?
Basic causes?
- Variations in muzzle velocity - A lot of things can cause it, and 'consistency' in every loading step and every ammunition component is the cure.
A chronograph can help determine if you are suffering from this.

- Barrel bounce - Assuming you are shooting from a solid rest, placing the 'sweet spot' of the barrel on the front rest can reduce or eliminate it.

- Wind variations - Most noticeable at longer ranges, changing head and tail winds can seriously affect these big, slow-moving bullets...enough to make rather large changes in impact height.

- Barrel condition - Better lube, or enough lube may make the difference. Also, consistent blow tubing (or wiping between shots) might be the answer.

- Recoil control - It doesn't matter too much whether you choose to be a 'solid obstruction' that the butt pounds against, or a 'sponge' that gives when the rifle fires...just so long as you do it the same way each time.

- Sights (especially the front one) - How well does your choice of globe insert match the target you are using...over the range at which you are seeing it? If you are using a circular insert, one that is a bit large is better than one which is on the small side.

There are some 'basics' to consider. The possibilities extending out from them are endless...
CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

wboggs
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vertical stringing

Post by wboggs » Sun Feb 04, 2007 9:48 am

Montana Charlie:
Thanks for the very useful info on some of the basic causes. I am shooting the groups from a rest with the fore-end rested and not the barrel, same place each time. Butt rest is the same each time. I suspect velocity variation may be a major cause. The loaded rounds have varying resistance to chambering in spite of being loaded to the same overall length, which is 0.002" into the rifling. I suspect the powder is springing back from compression and varying the overall length by the time the bullets are fired. They are loaded in fired cases with no neck tension. I can seat with less powder and compression or with neck tension of 0.015". What do you advise? Will take the chronograph to the range next week and check velocity spread. Last time I checked it was about 16fps at about 1210 fps.
Thanks again. I'm sure all you experienced shooters have encountered and solved these problems.
Bill Boggs
beginner in black powder

Kurt
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Post by Kurt » Sun Feb 04, 2007 10:45 am

One more thing that MC did not list is excessive head space from case to case.
I check my case rim thickness with a V block and a dial indicator, or make a jig like you would use to check a .22 rim fire case.
I like using the V block because the dial can stay in place for consistency.

Kurt

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montana_charlie
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Re: vertical stringing

Post by montana_charlie » Sun Feb 04, 2007 1:37 pm

The loaded rounds have varying resistance to chambering in spite of being loaded to the same overall length, which is 0.002" into the rifling. I suspect the powder is springing back from compression and varying the overall length by the time the bullets are fired. They are loaded in fired cases with no neck tension. I can seat with less powder and compression or with neck tension of 0.015". What do you advise?
I also load into unsized cases without neck tension.
If your cartridges are 'growing longer' it should be discernable by eye.
Where the edge of a grease groove (for instance) sits, in relation to the case mouth, is a pretty easy-to-see gauge on my rounds. Also, if a bullet does look like it's out a bit, thumb pressure shoves it back down.

When it happens (I believe), it's the result of trapped air in the case...not the powder charge un-compressing.

If it's not caused by an air 'spring', your chambering resistance variation might be due to fouling in the leade. This is especially easy to have happen when the bore ride section of the bullet is very near to (or equals) bore diameter. Better (or more) blow tubing might cure it.
My advice would be to try this approach first.
(If the amount of fouling (or the hardness of the fouling) varies from shot to shot, that can cause velocity changes...and possibly vertical stringing...from an otherwise finely-tuned load and rifle.)

Alternatively, you can increase your powder compression a smidge to seat the bullet a few thousandths deeper in the case...but you shouldn't need to reduce the powder charge.

And, yeah...you could start using neck tension...but that (pretty much) means starting from scratch, and you will need to start an annealing program to keep the necks consistent.
CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

wboggs
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vertical stringing

Post by wboggs » Sun Feb 04, 2007 4:52 pm

Hi Kurt
Thanks for your input. What brand cases have the most uniform rims?
Bill Boggs
beginner in black powder

wboggs
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vertical stringing

Post by wboggs » Sun Feb 04, 2007 5:05 pm

Hi Montana Charlie
Will go with your suggestions and also seat a little further from the rifling.
I did think of chamber build- up and have thoroughly cleaned that area.
Have any idea what velocity variation will cause large differences in target impact point? I assume it is linear with increasing range.
Used to do a lot of Elk hunting north of Kalispel and into B.C. around Cranbrook and Fernie. JUst noticed you are from West of Great Falls.
Thanks
Bill Boggs
beginner in black powder

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montana_charlie
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Re: vertical stringing

Post by montana_charlie » Sun Feb 04, 2007 5:39 pm

Have any idea what velocity variation will cause large differences in target impact point?
When you started this, you mentioned 2 to 4 MOA as your vertical group size. 2 inches at 100 is kinda-not-too-bad, but 4 is stretching it up a bit.
But, I'm undecided if I would call that "large differences".

I can't correlate MV variations with changes in impact for you, because I just starting using my very first chronograph. I have much to learn before I could tell you anything meaningful.
I assume it is linear with increasing range.
I dunno about 'linear'. While it's true that 4 inches at 100 becomes 40 inches at 1000, a 25 fps variation at the muzzle might become something like 250 fps difference at long range.
Used to do a lot of Elk hunting north of Kalispel and into B.C. around Cranbrook and Fernie.
Didn't think there was anything north of Kalispell, 'cuz everybody who goes up there...never comes back.
CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

wboggs
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vertical stringing

Post by wboggs » Sun Feb 04, 2007 5:57 pm

To MC
The reason they do not come back is because the hunting is so good in Southern B.C. Have many stories to tell but that is another subject. My best Elk was a 375 B.C. out of Cranbrook. Saw him looking at me as I was bent over dressing a Mulie!
Bill Boggs
beginner in black powder

Kurt
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Post by Kurt » Sun Feb 04, 2007 7:04 pm

"Thanks for your input. What brand cases have the most uniform rims? "

Rocky Mountain Cartridge

Kurt

wboggs
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Post by wboggs » Fri Feb 09, 2007 10:38 am

To Montana Charlie

The chamber area was the major problem with fouling build up. Cleaned it well and had much less vertical. Some of the groups were triangular and pretty good.
Do you think a little longer brass or seating the bullet into the rifling would help any? Am using a blow tube and that leade area seems more prone to fouling build up.
Thanks again for your expertise.
Bill Boggs
beginner in black powder

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montana_charlie
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Post by montana_charlie » Fri Feb 09, 2007 1:02 pm

wboggs wroteCOLONThe chamber area was the major problem with fouling build up. Cleaned it well and had much less vertical. Some of the groups were triangular and pretty good.
Can I assume you are also certain there is no lead buildup in there?
Do you think a little longer brass...

If your cases are on the short side, that could aggravate a fouling problem. Have you ever made a chamber cast to find out how deep it really is?
...or seating the bullet into the rifling would help any?
In your second post you said you were seating .002" into the lands. Have you changed that?
Am using a blow tube and that leade area seems more prone to fouling build up.
The blow tube puts moisture into the powder fouling, which makes it soft.
Hopefully, that allows the bullet to 'squish' it's way into the leade when you chamber the round. If blow tubing doesn't soften the material...maybe it's lead, instead of burnt charcoal.
Thanks again for your expertise.
I have to smile at that comment.
I have a lot more 'book learning' than 'expertise', though I try to temper all acquired knowledge with some native logic.
If I start telling you something that doesn't compute, those with real expertise will correct me.
CM
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wboggs
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Post by wboggs » Fri Feb 09, 2007 2:49 pm

MC
I tried some bullets short of the rifling and some into it. I do not have a cast of length, only bore and chamber, which are .458 and .483 with only a short 1/16-1/8" 45 degree throat area. Will try to identify lead or fouling or both at next session. Brass is 2.098. I don't see much in Rem. or Win. that is greater than 2.1 that I could trim to 2.1. Seems as if I am making some progress with your help. Thanks
Bill Boggs
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Post by Ranch 13 » Fri Feb 09, 2007 11:21 pm

wboggs wroteCOLONTo Montana Charlie

The chamber area was the major problem with fouling build up. Bill Boggs
What are you using for powder?
If you're getting heavy fouling in the chamber, you're not running enough pressure. Try somemore powder , or maybe a bit more crimp.
Also your lube could be part of the fouling trouble.

wboggs
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Post by wboggs » Sat Feb 10, 2007 10:20 am

Ranch 13
I am using Swiss 11/2, 70gr. with a 528 gr. Postell, and SPG lube. Can't get much more powder in the Win. case, as it is already heavily compressed with an overall length of 2.935 to touch rifling. Am not using a crimp as I thought it would decrease accuracy. Have tried some fired cases with no neck tension and some neck-sized with 0.015" tension. Any recommendations?
Bill Boggs
beginner in black powder

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