View Full Version : Horizontal Dispersion - Need Opinions
Gents, I am hoping that a few of you will weigh in on this.
I finished the build on this rifle about a year ago and have been working with it a lot, as it is a damn fine rifle.
https://www.m4carbine.net/showthread.php?135825-Not-my-first-build-but-likely-my-best
I have found that at 100 yards the gun really likes the following load:
77gr Nosler Custom Competition
22.0 gr H322
Wolf SRM Primers
Federal Brass (not a fan)
O.A.L 2.255
At 100 yards, the rifle and this load will repeatedly shoot under .25 minutes, and if I am doing my part, under 0.2 minutes.
As I move further out, the vertical dispersion of my group stays nearly the same, right around 0.2 - 0.25 minutes. The horizontal dispersion, however, keeps growing, at 200 yards it is roughly 0.5 minutes and at 300 yards the horizontal dispersion is approaching 1 minute, while the vertical dispersion is still staying around 0.2 - 0.25.
28171
Am i correct in thinking that this is a neck tension issue? I want to keep pushing the distance but I want to solve the problem with the horizontal dispersion before I do. Any insight at all will be greatly appreciated.
We get that from time to time as well. It's shooter induced... although I don't know exactly what causes it most of the time.
Are you getting a good straight back trigger break?
Thanks for the reply markm, was hoping to hear from you. Yes, I believe that I am, and I usually am good at calling my shots and fliers. If this is shooter induced, in regards to trigger manipulation, have you found a way to overcome the problem?
I do a lot of dry fire with my Glocks for ipsc, but not as much with any of my ARs/Geissele triggers. Also, in my 300 win mag, out to 600 (cant go much further around here) I do not see horizonal shifts like this unless I am completely neglecting to take into account the wind.
Do you wrap your thumb around the backside of the grip? If so, I bet you are pulling the rifle when squeezing the trigger. Try keeping your thumb on the same side of the grip as your fingers and see what kind of results you get.
Completely off topic, but did you see much of a difference with the adjustable GB on the rifle gas? I thought about getting one for my intermediate barrel, but I didn't think it would make much of a difference on the longer gas systems... it makes a world of difference on my carbine though.
I had two goals in mind when I decided to use an adjustable gas block, one to reduce the impulse from the BCG movement, and also to try and get the rifle to use just enough gas to cycle properly, and keep the rest of the gasses pushing the bullet. In both respects it seems to have worked well, the gun is very "soft" shooting, and I can squeeze a little extra velocity out of my loads.
That said, if I had to do it again, I do not think I would.
Load development was tedious while trying to make sure the rifle was using only the minimum amount of gas to cycle. Using a chronograph and ladder testing allowed me to get an idea of where the barrel liked to be velocity wise, but after adjusting the gas block, I would need to re-test loads to see how fast they were with the new gas setting, then adjust them again to get the velocity required.
All in all it was a lot of work (which I didn't mind) and a lot of material (which my wallet did mind) for what I feel is ultimately an underwhelming amount of gain.
TL/DR: Little gain for a lot of effort, likely would not do again.
Thanks for the reply markm, was hoping to hear from you. Yes, I believe that I am, and I usually am good at calling my shots and fliers. If this is shooter induced, in regards to trigger manipulation, have you found a way to overcome the problem?
Not really. Is this happening a lot/consistently? Do you have a nice, fast trigger, etc? I try not to over-react to occasional grouping issues.
There'll be days were it's a friggin fist fight to hold MOA. It just happens. There's guys that'd be thrilled to shoot the group you posted.... but with that vertical is so nice that it does beg to get the horizontal improved too.
StingerDan
08-27-14, 08:41
If reloading is your issue, horizontal dispersion is, as a general rule of thumb, caused by seating depth, as vertical is powder charge. Providing you have proper case prep, and are not overcrimping, or some other improper technique. Dan.
Vertical dispersion is generally a result of variations in pressure and velocity.
Horizontal is a result of wind.
Remove the human element (i.e., shoot from a secured machine rest) and you'll see rifle-ammo group trends.
In team rifle shooting (4 shooters) it is the responsibility of the shooters to hold for the tightest group they can. If rifles and ammo are consistent then all shooters should be able to hold a half to a minute of angle group height. The shooter is responsible for elevation.
It is on the coach and his wind reading abilities to keep the shooters' groups centered within a half to a minute of wind, keeping everyone synchronized and inside the 10 and X-ring.
Most folks will never experience this because they are shooting, loading, and proofing on their own and scratching their heads trying to figure out what is voodoo vice science.
Yeah... can you have a spotter watch each and every shot?
In other words... if you're back and fourth from left to right in an unchanged wind, you can get an idea where the issue is.
Thanks for all of the replys!
Markm, this does happen consistently with this load, but not with any other rifles. Trigger is a Geissele SD-E.
SingerDan, That would normally be my first thought as well, as I have found that to be the case many times loading for bolt guns. For this rifle I am loading for mag length, well out of the lands, which is what ultimately has me thinking it could be a neck tension issue.
Sinister, when this first started happening (any time I took the rifle past 100) I too thought it must be the wind. Nearly all of my shooting past 100 up to this point was done with heavy, long 6.5mm and .30 cal pills. So I initially took it as an opportunity to improve my ability to read the wind, quickly becoming frustrated as a result of making what seemed like no progress.
I have made a point of shooting in as close to zero wind conditions as possible, shooting the "let up". Ultimately, the horizontal dispersion remains.
I plan to do more work with this tonight and over the upcoming long weekend and will post any results I find. Thank you all again for your help.
I will have a spotter this weekend, a friend is bringing his new .260 over to work with some test loads he wants to try.
Excellent.
Try using as solid and consistent a rest as possible. A sand bag under the heel of the stock can help, as well as using a "Saddle bag" style system (kinda-sorta like this to minimize lateral spread):
http://img.photobucket.com/albums/v69/GuideGun/GunRestwRuger.jpg
Those Geissele triggers can make me nuts when trying to stack holes. Great triggers, but after coming of a bolt gun, I feel like I'm bouncing the friggin gun all over with the AR/Geissele combo.
Everything folks have said above is dead nuts on. My knee jerk was trigger (operator induced) and wind (mother nature - that b*tch) but as I read more and more - this seems more like an equipment issue.
Couple of things to look at.
1. Gas tube to key interface - if your gas block has shifted ever so slightly, (rotated or moved forward) the movement will be magnified at the key. This does goofy things to barrel harmonics - inducing horizontal stringing and vertical stringing.
2. Be very aware of bench technique - AR's can be finicky off the bench - also - not a fan of bipods on hard surfaces - ditch the bipod and shoot off of bags. Put the bags right in front of the mag well.
3. Probably the most unlikely, but worth a check if the issues above come up blank - check the scope. I see you are shooting NF - but hey, shit happens. Scopes - even the best can go wrong. Run a simple box test on the scope at 100 yds moving the reticle 2mins for each side - see where you come back to.
Good luck.
It could be trigger control or the effects of wind or it may not be. Have a friend shoot groups with the same loads and see if you get the same results.
It could be the load. I developed target loads for my 8mm and 30-06 rifles and observed horizontal stringing with lighter charge weights. I incrementally increased the charge weights until the groups were concentric. The charge weights vary depending on bullet weight and bearing surface length.
Vertical dispersion is generally a result of variations in pressure and velocity.
Horizontal is a result of wind.
Remove the human element (i.e., shoot from a secured machine rest) and you'll see rifle-ammo group trends.
In team rifle shooting (4 shooters) it is the responsibility of the shooters to hold for the tightest group they can. If rifles and ammo are consistent then all shooters should be able to hold a half to a minute of angle group height. The shooter is responsible for elevation.
It is on the coach and his wind reading abilities to keep the shooters' groups centered within a half to a minute of wind, keeping everyone synchronized and inside the 10 and X-ring.
Most folks will never experience this because they are shooting, loading, and proofing on their own and scratching their heads trying to figure out what is voodoo vice science.
Or as I like to call it shooting a weather report.
Are you using wind flags?
my guess from looking at your target is
if you are right handed, it's cant
if you are left handed, it's wind
markm had a good point though. pushing the trigger is a possible culprit, especially when it starts at the center and goes one direction. but the direction could be different with freehand vs bipod vs bags. basically, is the front of the gun fixed and your finger is pushing the backend? or is the backend fixed and your finger is pushing the front end?
Again, thank you all for the input. As of now I am planning to address as many of these points as possible during the holiday weekend. Some family members are IBS (International Benchrest Shooting) competitors and we are planning to get together at their home to try and figure this out once and for all. All shooting will be done from a solid concrete bench, bagged, with wind flags, spotter, etc. at 100, 200, and 300 yards. I plan to work up a number of rounds of this load, with slight variations to try and really pin this down. If you all are interested I will photograph and document our findings as we go.
my guess from looking at your target is
if you are right handed, it's cant
if you are left handed, it's wind
markm had a good point though. pushing the trigger is a possible culprit, especially when it starts at the center and goes one direction. but the direction could be different with freehand vs bipod vs bags. basically, is the front of the gun fixed and your finger is pushing the backend? or is the backend fixed and your finger is pushing the front end?
Cant will manifest itself with windage shots that are low - those groups do not show low or "corner" shots as they are referred. It very well could be a load tuning issue, but I'd make sure you rule out the mechanical issues before you start chasing load issues - that could make for some very frustrating bench time.
Cant will manifest itself with windage shots that are low - those groups do not show low or "corner" shots as they are referred. It very well could be a load tuning issue, but I'd make sure you rule out the mechanical issues before you start chasing load issues - that could make for some very frustrating bench time.
at distance, yes. at 200 yards, i wouldn't expect more than what's on his targets now
The load is NOT that hot. So I wouldn't discount some wind over a 200 yard shot.
I'm running .6 more grains with all else (component wise) equal... and that's still a .223 pressure load.
The load is NOT that hot. So I wouldn't discount some wind over a 200 yard shot.
I'm running .6 more grains with all else (component wise) equal... and that's still a .223 pressure load.
Max for 77gr bullets @ 223 pressure is 21.8gr H322. He's running 22.0gr. Going slightly above max hasn't shown any pressure signs in my rifle, so his load isn't that hot (as you said).
I haven't had the chance to run any of the hotter H322 loads over a chrono yet, but .6gr over his 22.0gr load seems like it would be pretty dang hot for such a fast powder.
Max for 77gr bullets @ 223 pressure is 21.8gr H322. He's running 22.0.
I haven't had the chance to running any of the hotter H322 loads over a chrono yet, but 22.6 seems like it would be pretty dang hot.
Oops... you're right... My mind was a full grain lower. He's a touch over max.... so he's running a tad hotter than I am.
Due to forecasted T-Storms this weekend I managed to get my work done with the rifle this evening...
First checked for anything wrong with the rifle itself and could find nothing.
Showed a few pics of my groups to my BR family members, and they all agreed that I was "shooting a weather report" as many of you suggested.
All three of us then shot the rifle, at 100, 200, and 300 w/ flags, spotter, all the good stuff. What did we find? Exactly what most all of you said, wind.
All of my precision shooting prior to this rifle had been done with either my 300 wm or a 30BR, and I thought that I was at least capable at reading the wind. Seeing the way these little 77gr projectiles get pushed around by even a mild breeze was a real eye opener for me. Truthfully I am glad this was simply an error on my part and not something in the rifle or load. Hopefully more shooting with this load will help me improve my ability to read the wind and compensate.
Thank you all again for your input, it is greatly appreciated.
Congrats on finding the problem. Wind is the great equalizer at a benchrest match.
Even with the best equipment if you can not read the wind you wont go home with a trophy.
And a AR is a hard gun to shoot off the bags.
And a AR is a hard gun to shoot off the bags.
Smooth tube and an A2 stocked fixed most of that
We'll since we've resurrected this 3-year-old thread...
Seeing the way these little 77gr projectiles get pushed around by even a mild breeze was a real eye opener for me...
I've been shooting a 17HMR a lot lately. You want to see bullets get pushed around by wind? The little 15.5gr crumbs don't stand a chance.
We'll since we've resurrected this 3-year-old thread...
Yeah, I was a little surprised to see this thread again as well.
I actually started competing in Benchrest a little over a year ago. I shot over 20 registered International Benchrest Shooting matches last year and I am still only scratching the surface of precision shooting.
It has been a real eye opener, and a real blast.
We'll since we've resurrected this 3-year-old thread...
Yeah sorry, no idea how I'd done that...
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