First, the offending rifle. It's a Remington 700 Sendero SF, chambered in 7mm Rem Mag. The sighting is done through a Simmons 3.8-12x44mm Aetec mounted in Redfield style rings and bases. I tuned the factory trigger down to a crisp and consistent 3.5 lbs.
Second, the possibly faulty handloads. They are 139gr Hornady SST's over 66.5 grns of RL22 in Winchester cases, lit up by Federal GM215M primers. The bullets are seated very close to the lands. I am very careful about weighing powder charges. The dies I am using are Redding Competition, the ones with the Titanium bushings. I don't, however, have a concentricity gauge to check runout with. I also don't have a chronograph to check velocity deviation.
The problem is this. When I fire a group, I often get two rounds very close, say .4 or less, but the other round is sometimes up to an inch and a half away, but usually closer to an inch. There is no set order in which the rounds impact. Sometimes, the first round is the flier, others, its the second round, and just as often, the third.
But, just to cause me grief, sometimes I'll fire a group without even a hint of a flier, just a tight little cloverleaf of about .5.
Now, I realize that it could be crooked ammo, wide velocity spreads, faulty scope, or a bad bore. The bore looks pretty good though, very minor looking tool marks. The crown looks OK as well. The reason that I'm posting this long, drawn out question, is that I thought that maybe some of you fellas had seen a rifle do something similar and could enlighten me.
Does this scope have parallax adjustment and if so are you setting it carefully?
Have you fired these rounds only at 100 yards? If so, you may want to try them at 200 or further.
Do factory rounds exibit the same pattern?
Have you had other good shooters try the rifle and if so do they get the same results?
If the runout is very significant you should be able to see it with the naked eyeball. Slowly roll the loaded rounds across a clean & flat surface observing the very tip of the bullet, if it wobbles it's got it bad.
Are you shooting over a rest on a bench or from a bipod in the prone position? If from a bench be careful that the front swivel stud isn't contacting the rest on recoil.
Yes, the Aetec has an AO, and I do my best to eliminate all apparent parallax. I have fired groups at 200 and 300 yards, and they all show the same tendency to throw one round away from the others.
The factory rounds that I have tried (Hornady) group about 1.5 inches, and make pretty round groups, with about equal spacing between rounds. The throat in my barrel is slightly long, and I figure that factory rounds just can't make the leap accurately.
I rolled my handloads like you suggested, and I didn't see any wobble, but it could be so slight that I just can't see it. I really need an RCBS Casemaster.
Unfortunately, no one else that I shoot with has any ambition to shoot precisely, and most of them flinch when firing a .308 Winchester. Their idea of sighting in a rifle is to lean over the hood of a truck at fifty yards, and adjust the scope after every shot. So I'm afraid that letting any of them fire the rifle would simply be a waste of my powder. Sigh.
I shoot off of a bench, over sandbags. I place the front bag a few inches in front of the action, so the sling swivel isn't contacting during recoil. However, the rear swivel does contact the rear bag. Could the rear swivel be part of the problem?
I'll pay more attention to the way I pull into my shoulder next time I go to the range, and I see if that helps.
Thanks for the help so far, maybe between smarter heads than mine, this problem will get squashed.
The fact that the factory rounds group in a consistent pattern is a good indicator that it may be your rounds. Also the fact that the rounds exibit the same flier tendancy at longer ranges point to something.
If the rear rest were the problem it should show up in the factory round (if you were shooting them over the same setup).
Having many non-precise shooters around is a standard condition, you're in the same boat as many of us but somewhere near you is a precision shooter and maybe we'll find him here for you.
Have you played with the seating depth?
Can you find a box of Federal Gold Medal Match ammo (I don't even know if they make it for the 7mm Rem mag.) to try?
Are all you cases from the same LOT?
Are you careful to get back into the same position after every shot? Same shoulder pressure has been mentioned, how about cheek weld, grip tightness? Do you hold the rifle's fore end with your "off" hand?
The factory rounds were fired the same way as the handloads, over the same bags on the same bench, so I guess the rear swivel isn't the culprit.
I have experimented some with seating depth, but if the bullet is seated any deeper, overall accuracy suffers. I even seated them down to the cannelure and crimped the bullet in the case, but groups were 2.5 inches with that set-up, since the cannelure on SST's is very high on the bullet.
As far as I know, Gold Medal ammo only comes in .223, .308, .30-06, and .300 Winchester. (Darn Federal, ignoring the .284 bore.)
The brass I'm using is Winchester W-W Super, bought in a 50 piece, bulk bag from Midway USA, so I assume it's from the same lot, but who knows if Winchester is careful about keeping brass lots together.
Just like pull tension, I really didn't think about getting the same cheek weld, but my grip is fairly consistent, as I try to put my finger on the trigger the same way every time. I'll make sure my cheek goes to the same place every time from now on. My off hand goes back under the stock to hold the rear bag.
You have a point about the evidence pointing to my handloads, and I have been thinking the same thing for a while. I just thought that I would check to see if maybe some of you serious shooters had seen a similar problem in another Sendero.
This may, however, be a case of me trying to put the blame on the rifle, when it is really the ammo's fault.
I wouldn't write off the rifle yet- a buddy of mine at school brought in his sendero in .22-250 for a good cleaning. Upon inspection he noticed the rifling did not come all the way out to the crown on one side of his barrel. After recrowning and a bedding job we took the rifle to the range. He was getting the exact same situation as you- with Winchester Supreme ammo (50gr Ballistic Tips) Two shots would be almost touching or touching and the other would be off. The rifle was still shooting 1/2 to 3/4 moa but could have been tighter except for the flyer- this was the same for 100, 200 and 300 yards. After several tries, he asked me to shoot to make sure it wasn't him- I fired three 3 shot groups with the exact same results. We tried everything- nothing would help. If I was to make a scientific wild ass guess it would be the barrel has a stress point in the steel- I believe Remington barrels are hammer forged- I would suggest having the action and barrel cryo-ed to stress relieve it. Couldn't hurt and at best it might help.
Just another angle to consider...