Help with poor grouping

[Ruskin]

Hi all,
I'm trying to sight in a 7mm mag for a buddy. Having a difficult time and looking for some advice. I did my rifle in 30-06 Rem 700 in the same way and it's dialed in 5" groups at 700 yards. These two rifles are for an elk hunt in OCT. Not sure what's the deal, but here's the set up for my buddy's the 7mm mag:

It's a browning x-bolt 7mm mag. I installed a rail as a base (used blue loctite and torque to spec). Scope is vortex hst 4x16x44. Mounted to rail w vortex precision scope rings. All torqued to spec and rechecked after first box. Shooting Hornady 162 SST

This picture is our third shooting session, first 5 shots of the day at 100 yards. 10-15 minutes between shots. Outside temp of 75'. We had professional instruction in session 1 and feel our shooting form is reasonably good.

This group seem very poor. Prior to this new scope my buddy was shooting Hornady SST 139gr producing 1.5in groupings.

Any suggestions / advice? Could this be the ammo? Or the scope? Or just my buddies shooting form?

We have hopes of shooting long distances, but can get a decent group at 100!

In advance, thanks.

 

[Broz]

Appears it is bouncing between groups. Check all scope mounting first. If its an EGW rail check it double close and make sure the crappy screws and screw holes are not egging out or shifting.

Jeff

 

[Cahunter805]

I'd buy a few boxes of different ammo and test them. Try some Nosler accubonds and some Barnes. Let the rifle tell you what factory ammo it likes.

 

[JG358]

Appears it is bouncing between groups. Check all scope mounting first. If its an EGW rail check it double close and make sure the crappy screws and screw holes are not egging out or shifting.

Jeff

I agree, First thing I'd be checking is the scope screws. Check to make sure the gaurd screws are tight too.

 

[rayporter]

with any ol scope that is not completely T U no one is that bad a shooter.

unless you use a 2x4 for a rest and let the butt sit on the bench there is a problem with equipment.

i do see a possible wind problem. if you dont use wind flags get some. if nothing else hang ribbons on stakes at 25 yd and 50 yd. you can get the 50 yd in your scope to watch the ribbon. have your bud watch the flags when you shoot. he will know if you are not getting shots off in the same conditions.

if the hornady sst 139 gr ammo is still available it is easy to check to see if it is the ammo. one group and you will know a lot more than you do now.

 

[jdmdavey]

i second the ammo. Shoot a few different brands and weights to see what she likes to eat. always been my experience.

 

[Ruskin]

Guys I went back through my shooting data. Below is a pick of the first couple of rounds on Tuesday. I was the shooter that day (different shooter than today). Shots made a big group that day also. Between tues and the group today I did re torque the top ring and the ring to the rail. (Yes the rail is EGW. No I can not get to those screws without removing the scope. But the x-bolt has 8 screws for the rail and I loctited them all)



Grouping was similarly poor as today. If a rifle doesn't like ammo. Can it be this bad?

 

[Shrek]

Very possibly a scope problem. If you have a second scope you can try I'd do it.

 

[jlmoeller]

Here is what I would do:
1. check all the obvious stuff, loose scope base-rings, action screws, action shifting in stock, ect.
2. clean the barrel to bare metal - shoot when clean and shoot when dirty some guns shoot better dirty
3. shoot a known accurate rifle to check your bench technique
4. replace the scope with one you KNOW is good
5. check barrel crown
6. float the barrel if needed and bed the action

Start simple and work to the more complicated things. Don't breeze by #2, clean the barrel until no copper traces are found. If it doesn't group better after 15-20 rounds through the barrel move on to the next step. I have seen guns go from 3 moa to 1/2 moa after a through cleaning. I have also seen guns that just would not group unless they had 10+ rounds through the barrel. Some guns like to be dirty.

I hope this helps - don't be afraid to ask more questions.

Jason Moeller

 

[Jeff Martin]

i would focus on the scope. Easy change just to test.

 

[Cahunter805]

As stated earlier just start eliminating possible problems. First and easiest would be shoot some of the 139gr loads that shot good before.
Next switch scopes. Then try different ammo after that.

 

[PathFinder]

It's all just application of the scientific method. Keep changing one thing at a time until you get it right. The X-Bolt is floated and bedded from the factory, the free float can be checked by running a dollar bill between the stock and barrel all the way down to the action.
Then:
1. Try diff. ammo. Lots if necessary. This sucks if you don't reload but you only have to do it once. Try Barnes and Nosler for sure.
2. Clean to ABSOLUTE bare metal, then test your most accurate load again if desired results haven't been achieved. My A-Bolt does well dirty or clean but I got it copper fouled badly once and it went from .6 MOA to 2.5 MOA. Cleaning brought it back.
3. If that doesn't work, take the scope off and remount.
Or whatever order you prefer.

 

[Broz]

I still see two groups in each test. No one can be sure, and all have offered good advice. But my best guess is that the mounting system is failing and allowing the scope to move (had 6 bad EGW bases come across my bench, so I may be a little hasty, but it is experienced hast) OR, the scope is failing causing it to move internally and double group. Scope fail of this nature, even the best of scopes, can be caused by the top of the rail, after bolted to the action, is not true and rings not in alignment. Did you check it with a straight edge? Center points? Bad ring alignment will induce stress through the rings into the scope tube and can cause a problem like this. Thus the reason we bed all rails especially less expensive rails on factory actions. Like I said, cant be sure but this is where I would start looking if I was going to fix it.

Jeff

 

[volsfan252]

Thanks for all the feedback guys, I checked the scope and it is sturdy and tightened to spec so I took the advice of seeing what type of ammo she likes. I picked up some Federal Vital Shok, 150 grain and HSM 168 grain. For whatever reason, my xbolt just doesn't seem to like the heavier grain in the HSM or the Hornady's. I was able to get a tight grouping today with the Federal's and while I was hesitant to take out the 150's for a SW Colorado Elk hunt, in those conditions my fps on impact out to 700 yards is still above 1500fps. Really appreciate the feedback, this forum has been tremendously helpful over the last year prepping for my first Elk hunt

-Jason

 

[Cahunter805]

Jason
I would be sure to retest a few more times and also verify drop out to whatever distance you want to shoot and then 200 yards further. Remember shooting off a bench and relaxed is much easier than with bull fever. Good luck!

 

[djsmith46]

Glad to hear you seemed to have figured it out. BUT I second re-testing your groups. I had POI problems just like you with my Tikka T3 7mm mag this year. Everyone kept telling me to check the float of the barrel, scope, rings, rail etc which was all sound advice. It turned out to be the gun wasn't bedded properly even though the "dollar bill" would run down the barrel to the action. The stock was hydrodipped around the edges of the gun and effected how it was seated. So I sanded and scraped all the ink out and now its tacking nails. The weirdest thing was the gun every once in a while would shoot an amazing group which lead me to believe it was me. The only conclusion I have is that for some reason as the barrel heated up it found a spot in the bedding it "liked to be" and it would shoot straight. I literally missed two black bear this year as a result of this problem, thinking my gun was shooting straight (because of the decent groupings while the barrel was warm). Good luck.