Advanced Marksmanship SHOT GROUP analysis help PLEASE!

[immelmann]

I am after a bit of help analysing my grouping if you wouldn't mind commenting please.

The rifle is a SAKO TRG 22 in .308WIN, only a couple hundred rounds old.
I use HBC BJD Dyer 155gr projectiles, Federal brass (POWER SHOK) and Federal 210M primers and 45.0 gr ADI AR2208 at around 2780ft/s.
It is the 26" barrel and scoped with a Nightforce NXS 8-32x56.
I shoot F-Class Standard.

I went to the range Saturday morning about 7am, confirmed my 50m windage zero in very stil conditions and shot some groups at 300m and 600m. There was less than 10 seconds between shots, chambered from the mag keeping my cheekweld consistent.
The shots were from a stable (Caldwell ROCK) front bag / tripod and rear hand squeeze bunny ear rear bag all on a shooting mat. The front bag leather gets caught up in the under forend accessory rail grooves and it is tapered down. I sit the rear point of the butt in the rear bag ears.
I am certain there was "no" wind, that is, I couln't feel any on my face and the leaves were sitting still.
I adjusted parallax so the crosshair hardly moved when moving my cheek on the stock and the picture was full and in line with the scope (no black movement on the edges).
The shots felt good (despite being attacked by ants).

The vertical element is not too bad suggesting the ammunition and vertical control isn't too bad.
However the horizontal control is a bit ordinary as seen by the shot strings.

300m

The first shot (coldbore yet fouled) was point of aim point of impact and same point of aim thereafter for subsequent shots. The figures are vernier lengths in inches.

600m

This shows exceptional vertical control and ammunition performance for the top 3 (and even other two) shots.

The horizontal issue is my concern - especially 'no wind' (less than 1 mile per hour from 1.30 pm if anything). The group is about 6 inches wide.

I was by myself and haven't been criticsized / coached on my technique but I think that may be part of the issue. If you want to see / think a pic of my position will help let me know and I'll put it up. I generally stay very behind the rifle and quite low.

Shooting the match (900m) later that afternoon and going back to the clubrooms I asked some advice from the other shooters.

One guy said I need to get a flat and wide under forend that is parallel to the bore and that will help prevent the frontend fouling on the bag. Also apparently I need to get the rear bag in the flat part of the under-butt.

Another guy said it was proabably wind. I ran Exbal with Kestrel data and even 1 mile/hr only pushes the proj 3.5 inches. That's still far off my 6 inch group.

I need to do some more dry fire at a vertical line and see what's going on.

Any ideas?
Thanks in advance.
Greg




Below is a link of a SAKO TRG if you are not familiar with them and will make my description easier to understand.

http://www.sako.fi/sakotrgmodels.php?trg22

 

[aron]

Re: SHOT GROUP analysis help PLEASE!

trigger control, make sure you're pulling straight back

 

[Augustus]

Re: SHOT GROUP analysis help PLEASE!

Just normal dispersion of a half min rifle and the effects of an intermittent 1 mph breeze could produce a target like the one at six hundred yds. Looks like the breeze was right to left.

The whole group is under a minute. Also the 300 yd group only shows around 1/2 minute of horizontal stringing. In totality the two groups indicate a half minute rifle and a little breeze. Shoot it at 100 yds, if you are holding consistent 1/2 min groups and the rifle shoots to the same POI day after day and your ammo is consistent, you should be able to hold similar groups at extended ranges unless you have intervening environmental conditions.

 

[rideHPD]

Re: SHOT GROUP analysis help PLEASE!

What leaves were you seeing that were still? If they were only low-lying shrubbery there may have been a slight bit of wind above the ground that you didn't see, as the apex of the trajectory is ______ far above the ground. Something to think about, maybe set up wind flags as well next time to see if you see anything change.

 

[immelmann]

Re: SHOT GROUP analysis help PLEASE!

The foliage (Australian eucalypt and natives) was about 15-20feet high and only about 10m off the side of the range.

Thanks for your comments.

 

[Barn Side]

Re: SHOT GROUP analysis help PLEASE!

Good to see another Aussie here!

Possibly trigger pull???

 

[stranded]

Re: SHOT GROUP analysis help PLEASE!

It seems to me I remember an article at 6mmbr(learning from texas warehouse) where speed/pressure cause vertical then horizontal stringing.The need to to find balance is essential. Or, if it was me shooting, I'd suspect flinch/trigger.(pushing with shoulder/palming with hand as squeesing)

 

[immelmann]

Re: SHOT GROUP analysis help PLEASE!

I will do some dry firing to try and 'see' some movement about a vertical line.
Thanks again.

 

[Texas Destroyer]

Re: SHOT GROUP analysis help PLEASE!

i assume you have checked all equipment? rings screws all tight check barrel when hot by using paper to see if touching stock after getting hot? normally that is all over target not stringed, stringing normally wind or trigger pull just my 2 cent worth. Oh and more practice!!

 

[immelmann]

Re: SHOT GROUP analysis help PLEASE!

I have been waiting on a 20MOA 1 piece base form ERA-TAC for over 6 months as there has been some delays with a third party and will get to the bottom of it once that arrives. It should have been here by now. With my 'cheap' 0 MOA base and crappy rings I struggle to get out to 900m. Some days I need to use the minute subtensions on the vertical by 1 MOA and others I'm about 1/8 MOA out.

I'll keep you posted once I have set the scope up again and done some dry firing with the new setup. I will probably need to make a new cheek piece again. In F-Class you really need to remove the bolt from the line before moving off the mound so I made a cheekpiece with cutout.

 

[rem700guy]

Re: SHOT GROUP analysis help PLEASE!

That would most likely be wind based on the vertical dispersion of the groups, even a very light wind of 1-2 mph will push deflect your bullets at 300 yards

 

[WeaselWalker]

Re: SHOT GROUP analysis help PLEASE!

A horizontal shooting group is either wind or a bad shooting position. If you're certain that there was minimal to no wind, then it's probably something with your position. When you're snapping in, take several shallow breaths and watch for any left to right movement of your reticle. Breathing should only cause an up and down affect when positioned behind the rifle. If this is the case then you'll have a better place to start diagnosing the problem.

 

[Rthur]

Re: SHOT GROUP analysis help PLEASE!

In the first picture(300), the first shot and remaining group looks like cold shooter. Some rifles have a cold bore variation then settle down.
The horizontal stringing is usually caused by poor trigger form. If you add in wind and a little trigger problem it could do this at 600. I saw a 1.0 mph wind listed on this target. More environmental details may help to the answer the low hits. It looks like you could add almost 1 moa or .2 of a mil(app.)in elevation.
I will also add that there was more wind between you and the target at 600 than was perceived.

 

[immelmann]

I have changed my trigger hand grip and will show results soon, as I'm about to go on holidays. I have confirmed my vertical crosshair is perfectly vertical and fitted a quality anti-cant level. I also need to test group size past 600m as I think the projectile is going transonic around 700m and opening up my groups. Apparently I need to be pushing the 155gr HBC BJD Projectile closer to around around 3000ft/s.

 

[immelmann]

I'm on holidays now so an update is in order.

The following isn't really and apples and apples comparison due to the following:
Now a new 20MOA one piece ring base.
Benchrest shooting now uses a flat forend (still not parallel with barrel however) compared to the accessory rail fouling on the benchrest leather.
Quality scope level and confirmed true vertical crosshair alignment to bore (with a plumb bob and other levels)

I shoot better with a factory Sako bipod compared to a benchrest. I think I load up the system better and it sits better in my shoulder. It feels right.

Rifle is about 600 rounds old.
Ammo is RCBS Chargemaster powder thrown.
Different handhold. I use the Accuracy First method where the thumb lies just above the trigger finger and gently on the side of the stock. My bottom 3 finger tips just touch the front of the handgrip. This reduces sympathetic hand movement on the trigger pull.

I dry fired two shots on dummy cartridges to test my position prior to firing each group live from the magazine.
Pictures below.

 

[immelmann]

Yesterday 300m off the benchrest prone

Yesterday 300m off the bipod prone

Today 600m off the benchrest prone

Today 600m off the bipod prone

 

[immelmann]

700m prone off benchrest.

700m prone off bipod. Fifth shot was off the page and a flyer. I didn't call this.

800m prone off bipod. Again 5th shot off the page / target frame and not called. I didn't bother with the benchrest as I prefer the bipod. It's much more comfortable and natural to me.

Light was good and I can see bullet holes at 700m at 32x, always the same point of aim. There was a gentle 3-4mph wind from 7 O'clock however the previous shots had a lighter wind.
At 800m the wind was starting to pick up a little more.
There is a short window to shoot 'windless' early in the morning where I shoot.

Afterward I Chrony F1'd 7 shots in good light for measure about 5 feet away.
1. 2778
2. 2777
3. 2760
4. 2754
5. 2777
6. 2793
7. 2778
for an average of 2773 feet per second. I don't know an error factor for my chrony or if this is even close. I haven't used a ballistic calculator with MOA or measured drop to proof this.

I JBM'd the load data and the speed of sound is 1147 ft/s, this is at about 975m. Mach 1.1-1.2 (approximately the start of transonic)is about 760-860m.

I'm guessing my projectile is getting transonically unstable and I need to load it hotter. A lot of the F-Class guys I shoot with run 30in barrels and around 3000ft/s.

Would you concur?

I need to see if MOA performance is affected by Copper fouling also.

 

[immelmann]

I now shoot a 47.4 grain load of AR2208 (similar to Varget I'm told) and get around 2940 ft/s. I'm pretty sure my projectile is still supersonic at 900m and the group stays tight.
I also shoot exclusively from the bipod and have done about another 600 shots with it. I'm very comfortable with the whole system. I find with my right hand thumb sitting alongside the stock it slides too much with a 1kg / 2.2lb trigger and is very off-putting. So now I shoot conventionally with a firm bipod load.
The Dyer HBC BJD 155 grain projectile is fantastic.
I shot a 'Presento' for David the manufactuer here locally and put it in a frame. He was chuffed.
Have a look below.

 

[AussieShooter]

Good to see another Aussie here!

Possibly trigger pull???

+1

 

[immelmann]

I've increased the second stage trigger weight to about 1.3kg as I can run the bolt very quickly and I don't lose the sear and don't get a very heavy trigger pull with quick bolt movement. This is a TRG specific problem.
So I shoot with a conventional grip and a heavier trigger wieght. And my scores / proficiency is increasing so am happy.

 

[immelmann]

With the 47.4 Gr AR2208 I have got 4/5 hits on at Type E torso target at 1100m during Gunslinger and have got hits on at 1236m on a IDPA gong just recently.

 

[Sterling Shooter]

OP,

Getting through the gobbledygook, there are two likely reasons for your horizontal stringing, wind and/or poor trigger control. Either you moved the rifle or the wind moved your bullet. In addition, there are seven other shooter errors related to an inconsistent/unstable position which could have produced horizontal grouping, but, rather than listing those possible causes, I would suggest you call your shots and plot both the call and shot in a data book. This will always reveal the cause of error, whether it is produced from rifle movement or for not having properly adjusted sights for wind and weather conditions.

One more thing, work on making your resistance to recoil consistent from shot to shot. This makes movement of the rifle while the bullet is still in the barrel more consistent from shot to shot. Unless you make recoil resistance perfectly consistent the bullet will not go in the hole produced by its predecessor. Although this sort of error is miniscule and linier, the effect at distance can be easily confused with wind not countered correctly.