What Causes Horizontal Groups?

W

Wildman

Guest
I recently went to the range to test fire some new loads out of my .325 WSM. I shot a 3-shot group at 100 yards using the new Reloder 17. The first shot was at 6 o'clock, the second shot was 1 1/4" to the right, and the third shot was also to the right opening up the group to 2 3/8". The temp was 88°F and high humidity. The wind was 0-5 mph. The three shots didn't vary 1/8" vertically. I then decided to try a different powder, H4831sc. The three shot group was nearly identical to the group fired with Reloder 17. Then I switched powder to H4350. This proved to be a much better choice. The first two rounds were approx. 3/4" apart horizontally and the final shot dropped and opened up the group to 1 1/4". Still not to my liking but I think I can work with this powder and bullet seating depth to improve upon. Why did my 3-shot groups go horizontal using the first two powders?
 
Wind and bench technique are my guesses. It has nothing to do with the load. At this point all your loads are equal.

al
 
Is there another explaination?

The wind was so light I don't see how a bullet could possibly drift that far at 100 yards. I have shot benchrest for a number of years and am capable of shooting groups under .200 at a hundred yards with my bench rifle. The one thing that puzzles me that with each shot fired the bullet kept drifting farther and farther to the right. The temperature was 88°F, and after just three shots the barrel was pretty hot. I allowed the barrel to cool off in between each three shot group fired. Isn't H4350 known for its resistance to temperature change? Any other thoughts or comments?
 
hmmmmm, well that certainly resets my perspective! :) If you shoot BR then hmmmm

Although these WSM's do whack one about some......

I'm at a loss. I've done some temperature testing of late, specifically with WSM's and more specifically focusing on H4350, VARget, RL17 and some assorted ball powders and am currently of the opinion that the whole concept of certain powders being "less temperature sensitive" is overblown advertising hype.

As are claims of increased velocities for certain powders, like RL 17.

But I digress:

I still do not think it's got anything to do with the loads, nor do I think the barrel is walking.

I do know one thing, for MYSELF shooting something this brutal for real accuracy requires a lot of setup and technique changes from the automatic bugholes of a PPC..... lucky for me I'd just gone through several years of hysteria trying (and finally succeeding) to tame my new 6X47L tight twisters... HEAVY rear bag and weight in the butt did wonders for me. They twist and bounce and hare of in sidewards directions for me....

I'm currently putting together a 325.... Bartlein barrel, Manners stock, Borden action, designed around 200-220gr bullets should make a killer walkaround elk slayer IMO. Now if Barnes would just step up to make a real bullet........

Keep us posted on the horizontal..... hope somebody else can help. :)

al
 
Thank you for your input. I think I am going to retry these same loads again and see if it repeats. But this time it will be on a day when the temp is at or below 70°F. I expected that all three of these loads would have produced groups under .75" at 100 yards. I am still perplexed by the HUGE groups I got. The scope I have mounted is a Leupold Var-X III variable with 3-10x. The rifle is a Winchester Model 70 with a stainless steel 24" barrel and a 1:10 twist. The load I was shooting in it was an IMR-4350 that produced 1/2" groups pretty consistantly. I like to experiment with different loads and thats all this was about. I thought if I could learn something from this that would be great.
 
I have had the same thing happen.
At the last match some of the guys looked at the groups and between large horizontal stringing and a couple of groups looking like they were shot from a 410 shotgun they decided it was the scope.
This scope had work done to it in the form of having the plastic screws one in bottom and one in left side. We backed the screws all the way out and it seemed to settle down. I will be going back to the range for a little practice and hopefully borrow a scope this weekend and we will find out for sure.
 
I have not ruled out my scope as a possibility. If I get similar results during my next outing at the range I will replace the scope and see if that takes care of it. Thanks for your response.
 
Two more ideas on the scope.

Parallax and/or play in base.

If the scope doesn't have adjustable parallax it's probably unshootable at 100yds..... I recently went through this with several Leupolds.

And bases..... Harold Vaughn illustrated a test where he tapped the bases right and left with a small hammer and fired two separate groups. I tried it and was quickly convinced.

I now bed my bases and screws and assemble everything with powdered rosin on the base surface, oil on the screw threads. And of course Kokopelli's all the way.

al
 
al,
I think you touched on it. I assume this is a hunting rifle with the usual pencil thin barrel. If so, then the barrel is probably walking due to heat build up.

Wildman,
You didn't say but how long did you wait between firing the loads with different powders? I would bet the bore in not concentric with the outside diameter of the barrel. I had a 30-06 once that did exactly the same thing. It would walk the bullets across the targets to the right. If I kept shooting it would eventully settle down more or less. This was with a barrel that had been recontoured so I am pretty sure the bore was not centered somewhere about half way down the barrel. I never did get rid of all of it, but by using a lot of fore end pressure I was able to lessen it to a degree that it was useful for hunting purposes. The WSM will put a lot of heat in a barrel in a very short time period.


Donald
 
Al,

The scope I have does not have a parallax adjustment on it. So I suppose it could possibly be my problem.

Don,

You brought up an interesting point...something I hadn't thought of. This is a hunting rifle with a standard Winchester barrel. I did fire each three shot group within approx. 1 -1 1/2 minutes of time. The barrel was quite hot. I then waited for approx. 10 minutes before I shot my next three shot group. Long enough that the barrel was nearly normal temperature. That would explain why the first shot was always at 6 o'clock and then each shot after would go further to the right. The last group fired with H4350, which had the tightest group, I remember taking extra time in between shots for it to cool because i felt that heat was a factor in my previous two three shot groups. This will be something I will look for the next time I go to the range.

Thank you all for your input.
 
Last edited by a moderator:
If you want to avoid parallax with a non adjustable scope, find a cap that fits over your eye piece (some of those juice bottle tops go close) & punch a ¼" or smaller hole in the centre of it.

Stops you moving your head far enough for parallax to become an issue, though it can be a bugger acquiring the target.
 
The last time I had a set you drinkin' case of horizontal grouping, it turned out to be a bedding issue, cant remember what it was but I beleive it was a tiny discrepancy , like a spec of overflow in the poured bedding. Groups varied from 2" to 4" horizontal and about 1/4" vertical @ 100 yd. A careful exam of the bedding with a magnifying glass might be fruitful.
 
Horizontal

Something we have realized since messing with tuners is barrels will sometimes deliver horizontal groups. I have seen this in a tunnel where there was no wind so I know it isn't always a "weather Report". horizontal can be tuned out as well as vertical and diagonal vertical. Lots of everything gets blamed for what the barrel is giving us.

Something I have noticed over the years I have been testing for the best load for BR rifles is sometimes certain loads at certain seating depths will give horizontal but it goes away with a different seating depth. There is a lot more to tuning than the platform and barrel.
 
Last edited:
As mentioned earlier, I have been shooting IMR-4350 and have been able to get 1/2" groups pretty consistantly under good weather conditions. I currently have my bullet seated .005 off the lands which seems to work best for this rifle. After carefully reading each of your comments and suggestions I would have to say the most likely cause for this phenominon is either scope related, heat related, or bedding. I am hoping to get out to the range this weekend to repeat my test firing of these same powders (RL-17, H4831sc, and H4350). I will keep you informed on how I make out. Thanks for all you help.
 
POI moving

I had this happen to me last Friday with my Rem 700 308 and a 10x40 scope.

After firing about 20 rounds, the POI started moving right about 3 inches each shot. After 3 rounds I stopped and started looking. I saw that my bore was pointing about 3 inches right off the target frame with the cross hairs centered on the bull. Something ain't right in Denmark here.

I found that the windage went south. The scope will be replaced next week by the mfg.

For what it's worth.

Roy
 
Don,

"You brought up an interesting point...something I hadn't thought of. This is a hunting rifle with a standard Winchester barrel. I did fire each three shot group within approx. 1 -1 1/2 minutes of time. The barrel was quite hot. I then waited for approx. 10 minutes before I shot my next three shot group. Long enough that the barrel was nearly normal temperature. That would explain why the first shot was always at 6 o'clock and then each shot after would go further to the right. The last group fired with H4350, which had the tightest group, I remember taking extra time in between shots for it to cool because i felt that heat was a factor in my previous two three shot groups. This will be something I will look for the next time I go to the range."

Wildman,
Please re read the part I highlighted. Does this not answer your question. This is exactly what my '06 was doing. I am so used to looking at BR barrels now that I forget how thin some of these hunting barrels are. I still have that old barrel and recently took a look at it. Can't believe how thin it looks. It would walk the bullets across the target to the right for about 3+ inches the longer you shot it. It would finally settle down at about 3.5 inches right of center. Then when the barrel was cool it would return to point of aim. I finally put enough side pressure on the right side of the barrel at the forend to lessen the walking but never eliminated it. I finally got it down to about 2 inches of horizontal at 100 yds. I took several deer with that rifle afterwards, but never with more than 1-3 shots, and never at more than about 50-150 yds. Hope you get the problem solved.

Donald
 
Check and eliminate one thing at a time.

Parallax as others have touched on is the first thing to eliminate. Leupold turrets will give you backlash. In 1000yd prone I never forget when you turn the knob clockwise you're OK this will "tighten" if I back off then go at least a minute or two past where I want to be then go back it will take up the backlash.
As others have said "technique" is one of the things you have to develop on your end if you want repeatable results. If you are a Stool Shooter or a High Power shooter or Prone, F-Class you have to get yourself a routine that "WORKS" and do the same thing every time.
Your barrel should not have any pressure points (sure you know this) but check. Be sure your bedding is tight and I use hex bolts on my action bolts torqued. Someone else said check your scope bases, scope mounts. Back to the barrel if it is a "skinny" hunting deal then 1 moa for 3 shots is great on a stock tube. The last thing take a look at the crown it won't hurt to check.
Like "Slingblade" always thinks of the simple things first!;) "I reckon." At 100 yds you should be getting reasonable results. A rifle is a "tuning fork", it has a frequency where it will stabilize, and the group should tighten up. I have a PSS in .308 that at 300yds would never go under a moa (3") I shot that barrel out and a friend who was a USMC 2112 had a take off barrel that they didn't like the way it shot M-118 SB. He cut off about a .5", we screwed it on, he finished on the short chamber, recut the crown. Now she will group 1", YES 1" at 300 for 10 shots is the best, if I do my part she has never shot over .5 moa even out to 600yd. I hope I helped.
 
You must log in or register to reply here.
Back
Top