View previous topic :: View next topic |
Author |
Message |
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Sun Feb 28, 2010 7:12 pm Post subject: Theories why bullets sting vertically or horizontally? |
|
I shot these groups this weekend at 250 yards. I got pondering why a string would be almost pure verticle or horizontal. I've had this happen once before with a different rifle. I think it shows that a barrel's harmonics can be in the verticle or horizontal direction. Any other theories why this occurs?
250 yards, .270 Win, 130 GMX, 55 grs IMR4350, COAL 3.325", CCI Primers, Remington Brass.
250 yards, .270 Win, 130 GMX, 55,5 grs IMR4350, COAL 3.325", CCI Primers, Remington Brass.
|
|
Back to top |
|
|
Vince Site Admin
Joined: May 25, 2005 Posts: 15718 Location: Brisbane AUSTRALIA
|
|
Back to top |
|
|
Gil Martin Super Member
Joined: Jan 28, 2005 Posts: 1837 Location: Schnecksville, PA
|
Posted: Sun Feb 28, 2010 7:51 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
It depends. What rifle were your shooting? I have not encountered stringing to the degree on the above targets. Is the barrel channel floated or glassed? My preference is to free float barrel channels starting about two inches in front of the receiver ring. All the best...
Gil
_________________ Gil |
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Sun Feb 28, 2010 7:58 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Gil Martin wrote: |
What rifle were your shooting? |
Its a Tikka T3 Lite. It has shot very well with all loads 1 MOA or better with consistent POI. My 150 Berger VLDs shoot vertically also, but tigher at 1/2 MOA. The only difference between these two groups was 0.5 grains of powder.
Last edited by slimjim on Mon Mar 01, 2010 8:15 am; edited 1 time in total |
|
Back to top |
|
|
woods Member
Joined: Oct 15, 2005 Posts: 89
|
Posted: Sun Feb 28, 2010 9:19 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Horizontal stringing at 250 yards? Most probable causes are wind or cant.
Vertical stringing? Most probable cause is velocity variation.
Do you have an anti-cant device and do you chronograph your loads?
_________________ Guns only have 2 enemies, rust and politicians |
|
Back to top |
|
|
DallanC Site Admin
Joined: Jan 18, 2005 Posts: 3572 Location: Utah
|
Posted: Sun Feb 28, 2010 9:32 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
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.
|
|
Back to top |
|
|
PaulS Super Member
Joined: Feb 18, 2006 Posts: 4330 Location: South-Eastern Washington - the State
|
Posted: Mon Mar 01, 2010 12:54 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
With a light barrel you might be getting barrel hamonics whipping the barrel in both directions with a change in powder charges. You might be able to tune your loads to exit during the static points of the whip and get nice tight groups without the stringing.
_________________ Paul
__________________
Speer, Lyman, Hodgdon, Sierra, and Hornady = reliable loading data
So and So's pages on the internet = NOT reliable loading data
Always check data against manuals
NEVER exceed maximum listed loads |
|
Back to top |
|
|
chambered221 Super Member
Joined: Aug 17, 2007 Posts: 3455 Location: Lost for good !!!
|
Posted: Mon Mar 01, 2010 7:02 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Horizontal is usually wind induced but can also be caused by a gun recoiling at an angle instead of straight back.
Canting the gun should show some drop in POI and does not affect the accuracy of the group unless different amounts of cant is employed.
Most common causes of vertical are harmonics, bedding, inconsistent velocity, barrel heating, or a hard front rest. (gun bounces)
I see you've stated that the gun usually shoots a MOA or better.
That vertical group is better than a MOA !!! (MOA @ 250 yards is 2 1/2")
It also sounds as if the gun shoots some vertical with whatever you shoot in it.
I would caution you as to making any conclusions based upon two 3 shot groups.
My advise is to step back and restart your development with the OCW method to see how good the gun can shoot and go from there.
_________________ Ask as many people needed, sooner or later your question will be answered the way you want it answered !!!
A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government.
~George Washington |
|
Back to top |
|
|
SingleShotLover Super Member
Joined: Dec 26, 2007 Posts: 1005 Location: Illinois
|
Posted: Mon Mar 01, 2010 7:19 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Pretty much anytime I have had a previously accurate rifle start stringing it has been due to changes in barrel contact (as DallanC mentioned) or action screw tightness. Horizontal stringing generally indicates pressure on the side of the barrel opposite the direction of the stringing and vertical usually ends up being pressure from under the barrel. Action screws that loosen can cause stringing in any direction. Barrel contact is common in wood stocks that were previously floated if the barrel channel wasn't sealed properly. Wood grain swells from moisture to the point of barrel contact and should be dressed back down and sealed with a good oil, polyurethane or "spar" varnish finish.
_________________ If you can't hit it with one, you probably can't with two either!
The biggest problem with a closed mind is that it never seems to come with a closed mouth.
SSL |
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Mon Mar 01, 2010 8:20 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
woods wrote: |
Do you have an anti-cant device and do you chronograph your loads? |
In this particualr shooting situation, my anti-cant device is ensuring the crosshairs line up with the vertical and horizontal bands that highlight the X,Y axis of the target. I hope to have access to a chronograph in the near future. To date, I've dervied velocity once I'm satisfied that I have the load correct by compariing bullet impacts at 100 yards with bullet drop at 250 or greater and using a ballistic calculator.
|
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Mon Mar 01, 2010 8:24 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
PaulS wrote: |
With a light barrel you might be getting barrel hamonics whipping the barrel in both directions with a change in powder charges. You might be able to tune your loads to exit during the static points of the whip and get nice tight groups without the stringing. |
How much charge change would you recommend? 55 grains gave a horizontal string and 55.5 gave the vertical string. Should I try 55.3 or 55.4?
|
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Mon Mar 01, 2010 8:52 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Had double sandbags for a rest configuration. I shoot 2 shots then let the barrel cool. I don't wait a specified time because, depending on the air temp for that day, the cool down time will vary. I wait until its cool to the touch. Wind was very light. Same set-up for both groups.
chambered221 wrote: |
I would caution you as to making any conclusions based upon two 3 shot groups. |
The mentor that got me started on reloading had me setting up 5-shot strings every 0.5 grains across the range of min-max powder. I found very quickly that this ate up my supply of bullets and, more importantly, it only took two shots to determine if a load was bad. Yes it takes 5 or more to tell if its the right load to stick with, but a load with no potential can be exposed in only two shots. Thus I came up with my own process for developing a load. I shoot 3-shot groups in 1-grain increments skipping the min and max recommended powder weights. This gives me a quick look at the performance of the bullet-powder combination in 12 to 15 shots. I then look for the sweetspot, and would load five rounds where I think the sweet spot is, then 0.5 above and 0.5 below and fire for affect. I ususally can tune a load in 25 to 30 rounds and still have 20 bullets left to load from the orginal purchase. In this situation, I already have a good load/recipe for a 130gr copper bullet that shoots 0.5MOA, so I did a quick look with this new copper bullet by loading 6 rounds with a powder charge that was 1 and 0.5 grains lower in powder charge. I felt that was a safe approach because the other 130gr bullet, Barnes TSX, had more bands thus less bearing surface so I was anticipating a slightly higher internal pressure with this GMX bullet.
Last edited by slimjim on Mon Mar 01, 2010 11:22 am; edited 2 times in total |
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Mon Mar 01, 2010 8:56 am Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
Thanks for all the good comments. I found the OCW method chambered221 refered to. Time to do some more studying.
Optimal Charge Weight (OCW)
|
|
Back to top |
|
|
chambered221 Super Member
Joined: Aug 17, 2007 Posts: 3455 Location: Lost for good !!!
|
Posted: Mon Mar 01, 2010 1:42 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
I should have mentioned that the OCW method can be found in the articles section of Hunting Nut......sorry !!!
I do link the link you provided though.......it has some info there that I haven't seen.
OCW can help limit (time and components) initial load development all while eliminating a lot of the variables.
_________________ Ask as many people needed, sooner or later your question will be answered the way you want it answered !!!
A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government.
~George Washington |
|
Back to top |
|
|
slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
|
Posted: Wed Mar 03, 2010 8:53 pm Post subject: Re: Theories why bullets sting vertically or horizontally? |
|
I spent time digesting the OCW article. Sound like a good way to find the sweetspot. The process I had developed is similar but not as thorough - a coarser look compared to the 0.3gr powder increments OCW uses. I'll try OCW the next time I do load development. In this particualar situation, I don't have enough GMX bullets remaining to do my experiment and also start over with the OCW process. I could buy more but I'm not sure I'm interested in this bullet long-term. This GMX bullet is one of the longest .277 bullets out there but is 20gr less in weight resulting in a very low stability factor for the standard 1:10 twist. I will test and shoot what bullets I have but I ultimately want more stability margin.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
|
Back to top |
|
|
|