Accuracy Question

[j_unzicker]

I am hoping you guys can help me with this. I shot a 4 shot 1" group today out of my 7RM with 62 grains of IMR4831 pushing a Berger VLD 168gr. bullet. So I pushed it out to 500 yards and shot very erradic like about 12" group.
Theoretically, if a gun shoots MOA at 100 shouldn't you expect that (barring shooter's error) that gunn with the same load would shot 1 MOA at all distances? Or can a bullet loose it's accuracy as the distance increases?
Also, with this same set up I had shot a 5.5" group at 700 yards right after I first bought this gun used. Someone told me I should clean it good, so I used Birchwood Casey's Foaming Bore Scrubber. I haven't been able to get it to shoot tight groups since. Before I was shooting 1/2" groups at 100 yards.
Any suggestions? Should I just chalk it up to shooter's error and keep practicing (I was using a bench rest), or should I try to modify something in my load, bullet selection, COAL?

 

[elkaholic]

I am hoping you guys can help me with this. I shot a 4 shot 1" group today out of my 7RM with 62 grains of IMR4831 pushing a Berger VLD 168gr. bullet. So I pushed it out to 500 yards and shot very erradic like about 12" group.
Theoretically, if a gun shoots MOA at 100 shouldn't you expect that (barring shooter's error) that gunn with the same load would shot 1 MOA at all distances? Or can a bullet loose it's accuracy as the distance increases?
Also, with this same set up I had shot a 5.5" group at 700 yards right after I first bought this gun used. Someone told me I should clean it good, so I used Birchwood Casey's Foaming Bore Scrubber. I haven't been able to get it to shoot tight groups since. Before I was shooting 1/2" groups at 100 yards.
Any suggestions? Should I just chalk it up to shooter's error and keep practicing (I was using a bench rest), or should I try to modify something in my load, bullet selection, COAL?

There are a whole lot of variables mentioned here! The 1" moa to approx. 2 1/2" moa at 500 was probably shooter error (quite possibly wind). As far as loosing accuracy after cleaning goes, if that really is the case, it wouldn't be unusual. This is especially true if the rifle was on its down hill run accuracy wise. Sometimes a dirty shot out barrel will group a lot better than a clean one. How many rounds have been fired through it? Another possibility is damage from the cleaning process itself, especially if it involved the muzzle (crown) I'm not saying you did that, but it happens....Hope you get it figured out....Rich

 

[j_unzicker]

Thanks, Rich. I am concerned that I may have damaged the rifle during my cleaning process. I don't know hold old the rifle is, but it is in very good condition as far as how it looks both outside and also inside the barrel. How does someone damage their crown? what things can go wrong in the cleaning process?
My cleaning process involved using the bore scrubber and letting it sit for an hour and then scrubbing with a wire brush. and then using a patch until the patches came out clean.
Also, when I shot at 500 yards there was a slight wind, about five mph, but it was nearly head on.

 

[screech]

Did you check to see if youre bullets are "key holeing"? If so youre twist isnt fast enough for those bullets. I would be surprised if they werent stabilizing but just checking.

 

[j_unzicker]

I did notice that occasionally some of my hole tears in the paper were not perfectly round. Is that what you mean by keyholing? I shoot a factory Rem 700, but don't know exactly what the twist rate is.

 

[CRNA]

I did notice that occasionally some of my hole tears in the paper were not perfectly round. Is that what you mean by keyholing? I shoot a factory Rem 700, but don't know exactly what the twist rate is.

I really don't think that twist rate would be a problem for 168g. Now, if you were shooting 180g, then I would say that you might be a little slow (twist wise) from a factory tube. When I ordered my McGowan barrel I was asked what weight bullet I was going to be shooting through my 7MMRM and I told them 168-180s and they said a 1:9 twist would be fine. Having said all that, I don't know what gun you have, but I am pretty sure that you wouldn't have a twist problem stabilizing 168s.

 

[CRNA]

I did notice that occasionally some of my hole tears in the paper were not perfectly round. Is that what you mean by keyholing? I shoot a factory Rem 700, but don't know exactly what the twist rate is.

I really don't think that twist rate would be a problem for 168g. Now, if you were shooting 180g, then I would say that you might be a little slow (twist wise) from a factory tube.

 

[roninflag]

what rifle? sporter/heavy barrel? what scope? is the trigger adjusted? how far off the lands? i shoot at 100 and 200 then 500. the 200 yard groups are a better indicator. roninflag

 

[j_unzicker]

I did a test with my rod to check the twist. It appears that my Rem 700 has about a 1:9...Berger said that 1:10 or faster with the 168's would be fine. So I think I am good there.
Some other suggestions that have come back are that I may have damaged the crown. I inspected it with flashlight (but not a microscope) and some some small scratches or wear marks on one of the riflings right at the end. I clean this gun once from the muzzle with a wire brush and a multi-piece aluminum rod (I know now that that was a mistake). So I am concerned that I have permenantly damaged my barrel. What should I be looking for in a damaged crown?

 

[elkaholic]

I did a test with my rod to check the twist. It appears that my Rem 700 has about a 1:9...Berger said that 1:10 or faster with the 168's would be fine. So I think I am good there.
Some other suggestions that have come back are that I may have damaged the crown. I inspected it with flashlight (but not a microscope) and some some small scratches or wear marks on one of the riflings right at the end. I clean this gun once from the muzzle with a wire brush and a multi-piece aluminum rod (I know now that that was a mistake). So I am concerned that I have permenantly damaged my barrel. What should I be looking for in a damaged crown?

If you can actually see marks at the crown, chances are, that is the problem. Your factory twist should be plenty for that bullet. When you clean, get a quality one piece rod (like a carbon fiber tipton) use a bore guide, always clean from the receiver end, do not drag the patch back through the muzzle. In general, be "very careful with the muzzle end". At this point since you think you can see damage and your groups apparently opened up after cleaning, I would take it to a gunsmith and have him inspect it. If it is damaged near the end of the muzzle, he can trim the barrel back and re-crown. You would be surprised how many people damage their rifles in the cleaning process. Don't feel bad! Just learn from it. Good luck and let us know what you find......Rich

 

[j_unzicker]

Thanks...I'll take it to our gunsmith and see what he says.

 

[j_unzicker]

I called the local gunsmith. He said that I could take it in and he could look at it and work on it if needed. He also suggested that I could try Tubb Final Finish Bore Lapping Bullets. Any thoughts on that? He suggested that if I use it to start with the 3's instead of the 1's since my gun isn't new. He said that will prevent the compound from taking too much metal and too much life out of the barrel.

 

[elkaholic]

I have not used the bore lappers myself, but have heard both good and bad. I think it is a little unusual to try them on a damaged barrel, but then I'm not a gunsmith. Personally, I think I would take it to the gunsmith FIRST. I guess I have a little personal bias about firing gritty stuff down my barrel! Others may have a different idea.....Rich

 

[DanMan]

If you have already covered this in your post - I overlooked it.
Anytime I have a proven shooter that goes south I start looking for something loose like action screws, stock, rings, bases et. The last time that I had a problem I found that my sling stud on the forend was too long and was actually touching the barrel. I backed it out and put in a spacer and the accuracy returned.