Theories why bullets sting vertically or horizontally?

slimjim

I found that these GMX bullets varied in weight from 129.4 gr to 130.8 so I reloaded three rounds with bullets at 130.0 and shot them at 500 yards. More shots are needed but this indicates to me that it is possible for small variations in bullet weight to cause small variation in velocity and vertical dispersion. The vertical spread is 0.25 MOA.

chambered221

IMHO......I really don't think a grain to grain in a half of bullet weight is going to matter at all to 300 yards. Out to 600 yards I'll consider it. Past 600 most definitely sort them.

I'm glad to see your finally getting a chronograph, the type of experimenting your doing will prove it's worth.
Don't just use it to check consistency and averages. Be sure to set it up and use it in conjunction with your long range target testing. I think your gonna be surprised at some of the things you learn.

And always remember.............they don't lie !!! Even though you'll swear that they do !!!

slimjim

chambered221 wrote:

IMHO......I really don't think a grain to grain in a half of bullet weight is going to matter at all to 300 yards.

Ok, I'll test it. I have loaded 2 bullets that weight 129.4gr and two that weight 130.8gr with 55.5gr IMR 4350. I can shoot them at 250 yards to 500 yards. The first two pictures were at 250 and the last one I shot yesterday was at 500 yards. What range would you suggest I shot them at? It may take a couple of weeks before I get back to the range.

chambered221

As I've stated before......I don't put a whole lot a faith in a couple of shots here and there.

As an example; My Model7 has shot 3 shot groups @ 100 that measures just a tad over .250, it has also given me targets well under the .500 mark with 5 shots.
The fact of the matter though is it's very consistent gun between +.500 to -.750 with an occasional above that.(3 shot) When someone ask I generally reply that it is a sub 1 inch gun and leave it at that.

This is a correlation of many groups over a period of time.......the only way to honestly judge the performance of said gun/load !!!

kbis

So there is no real way to tell if vertical or horiz. stringing is a result of load develoment?

slimjim

chambered221 wrote:

As I've stated before......I don't put a whole lot a faith in a couple of shots here and there.

I don't disagree and like to see consistency over time. However, if bullet weight is the only thing I change and, when I change to all bullets the same weight and the group shrinks, and when I change to bullets that weight different and the group expands, then I would say indications are that the underlying assumption has merit. I'll be tracking this as I shoot further so we can monitor how this turns out.

slimjim

kbis wrote:

So there is no real way to tell if vertical or horiz. stringing is a result of load develoment?

If by load development you mean changes in the load then what chambered is advocating is that it takes multiple sessions to confirm a pattern. I've had both horizontal stringing and vertical stringing occur during load development and testing on every rifle I have. My theory is the barrel can have a harmonic that is horizontal as well as vertical (common belief). If an individual rifle is consistently giving horizontal strings during load development, then its time to check for other causes like a stock bedding issue.

Elvis

I had a old 303 that used to be a real cow at verticle stringing. I took ages to work out why. we were bombing up goats on day and the shots kept getting higher and higher till the scope FELL OFF the mounts were loose and kept moving with recoil. thus if I get verticle stringing the mounts are double checked. yeah I know Im a plonker and this is a little off thread.my .270 will group different loads into a rough group the size of a playing card the hotter/faster loads to the top of the group I have tested this on a benchrest and used about 6 different loads from 160grn round nose down to 110 hollow points 150grn 140grn and 130grn.so maybe weight does have some bearing. maybe velocity does too. keep shooting and let us know your findings.

Aloysius

Slimjim, I'm certainly not an expert on the distances you mention. Here it's difficult to find a shooting range for 3 or 400 m and shooting game at these distances is normally not done.
But just to make you think: when you have different bulletweights, do they have different sizes? And the same weight the same size? Maybe this one is little longer and thinner alltough it's having the same weight? And I would expect that different bulletweights or shapes could have different optimum loads, so the worst groupe at the used load might be the best groupe with halve a grain less or more...
so when testing you should also check the influence on load development for each size and weight...
and still just thinking: a bullet produced on a CNC-lathe should have the same size (when cutting equipment was still sharp and OK), so they can only differ in weight.
But: because I don't see machine-markings on a Barnes-bullet, I have the feeling that they are not made on a CNC-lathe but pressure-shaped (don't know the best english word for it). Or is there a difference between different production lines? Huntingbullets with the square hole made on a press and competitionbullets on the CNC-lathe?
(I would expect that a lathe produces more accurate bullets than a press)

slimjim · Last edited by slimjim on Sun Mar 07, 2010 10:24 pm; edited 2 times in total

Aloysius wrote:

just to make you think: when you have different bulletweights, do they have different sizes? And the same weight the same size?

Aloysius, I checked bullet length compared to weight. You are right, I found a correlation. I checked 6 bullets. The 3 bullets at 129.5 grains weight had a length of 1.376". The 3 at 130.5 had a length of 1.382". This is a 0.006" difference. All the bullets within the weight range were within 0.001".

BTW, the only bullets I know that Barnes CNC-machines are their banded solids. Their length and weight are very tight in tolerance, within 0.2 grains. The molded bullets like the Barnes TSX or Hornady's GMX can vary by as much as 1.0 to 1.5 grains within a box of 50.

chambered221

Use a bullet comparator and I'll bet you'll find differences in ogive readings up to as much as .008 !!!

slimjim

chambered221 wrote:

IMHO......I really don't think a grain to grain in a half of bullet weight is going to matter at all to 300 yards.

slimjim wrote:

Ok, I'll test it. I have loaded 2 bullets that weight 129.4gr and two that weight 130.8gr with 55.5gr IMR 4350. I can shoot them at 250 yards to 500 yards.

chambered, you were right. Got to shoot these 4 bullets today at 250 yards. Though the velocity was slightly higher by a few feet per second for the lighter bullets, you couldn't tell by the impacts. The two bullets at 129.4 gr have the line between them. The 130.8gr bullets shot the same hole. These bullets are really shooting nice. They clocked at 3000 fps with a std dev of 9 fps.

fnuser

DallanC wrote:

IMO horizonal strings are due to contact with the stock and barrel. M700's are notorious for this as remington puts a contact bump to put pressure against the barrel at the end of the stock.

This is my experience also The most notable example I had was a Ruger #1 in 7STW that strung vertically till I "accurizated" the hangar under the forearm.

slimjim

fnuser wrote:

I had was a Ruger #1 in 7STW that strung vertically till I "accurizated" the hangar under the forearm.

I did this (pad under the barrel near the front of the forearm) with a .243 I had the groups really shrink. It had a solid walnut stock. Over time I noticed that it grouped great every time I shot it. However, the POI changed every time shifted from day to day. I figure it was the affects of the weather changes on the wood stock. Maybe this technique works better on composite stocks. I see quite a few manufactures using this technique.

slimjim

While researching the web on I found this information regarding accuracy and what aspect of the bullet makes the most difference. It supports what chambered221 said as weight is down on the list.

From the GS Custom Bullet Website.

When examining bullets for the qualities that will afford one the best chance of selecting a product with which good groups will be highly probable, one must look for uniformity of the following, in order of importance:
a) Bullet base
b) Bullet meplat, ogive and shaft form
c) Bullet diameter
d) Bullet weight
e) Bullet length.