Loss of zero after 20 shots... any ideas?

I went to the range this afternoon with my Browning BAR 7 mm rem mag. My first 20 or so shots went perfectly. Every one punching within a couple inches of the bullseye at 100 yards.
I switched ammuntion after the first 20 shots, to a bullet with a plastic ballistic tip and then my shots started flying off all directions. Even the remington soft points I had originally had accuracy with. I checked my scope, rings and base and everything felt secure.
The only thing I can think is that the barrel may have gotten too hot and started causing accuracy problems, but I don't think that would have thrown off my shots by 10+ inches at 100 yards but maybe I'm wrong.
Anyone have any ideas or experiences like this?

Just how hot did you get it? Have you checked for copper build up? Fill the barrel with "Wipe Out" foam and let it sit for a few hours and then clean it following the directions. Then go blast it some. But remember that when you're out in the woods the first or maybe the second shot are the important ones. They're from a cold barrel.

Husb0023,

Mike has stated it right. During the actual hunt routine the first 2 or 3 shots matter , & at the range you tend to shoot groups which heats up the barrel, & moreover you are using a Browning BAR a semi auto which reloads a new shell in the chamber as the bullet leaves the muzzle , in bolt actions little time is precise for reloading and the heat tends to dissipate . I believe , this may be the explanation to the rifle shooting haywire after 20 odd shots , I have had a BAR in 270 Winchester but never did experience any such flaw full scenario at a target shoot , and 10+ inches is way too far off the target at 100 yards , surprising !!!!!! I hope someone form the forum might be more accurate in deciphering in for such a occurrence....

Monish





Monish

Originally Posted by husb0023

I went to the range this afternoon with my Browning BAR 7 mm rem mag. My first 20 or so shots went perfectly. Every one punching within a couple inches of the bullseye at 100 yards.
I switched ammuntion after the first 20 shots, to a bullet with a plastic ballistic tip and then my shots started flying off all directions. Even the remington soft points I had originally had accuracy with. I checked my scope, rings and base and everything felt secure.
The only thing I can think is that the barrel may have gotten too hot and started causing accuracy problems, but I don't think that would have thrown off my shots by 10+ inches at 100 yards but maybe I'm wrong.
Anyone have any ideas or experiences like this?

Did you give it any time to cool down? I like to give my rifles 5 minutes after every few shots. If you shot those 20+ rounds in short succession then that is what happened, you WAY overheated your barrel. I used to have a Remington model 721 30-06 that after 3 shots it would start "walking" upward. You had to give that rifle 5 minutes after every 2-3 shot's.

I echo everyone else---sounds like it got hot to me. BAR's are bad about shot stringing.

Ed

i would like to have you check to see if the barrel is free-floating or if there is an obstruction. all that would be necessary is a bubble of finish to move the accuracy after the barrel warmed up... a simple test is to see if a dollar bill will slide up and down between the barrel and stock when the barrel is hot...

is the action glass bedded?
and all screws or bolts snug?

However the above that other offered and were covered is what i would have to go with...

My first thought is that it is really easy to heat up a BAR. Shooting hunting ammo through a semi auto just feels good, especially when you fill that magazine. If you feel that you didn't over heat the barrel then possibly you have a bedding/free floating issue. If your rifle is stringing shots as it heats up you might very well have a contact point between the barrel and the stock. It is entirely possible that the barrel makes contact only after heating up. Usually a "string" of shots moving out of zero indicate this type of problem.

I had the same problem with a .416. Turns out the "crown" of the barrel had been damaged, probably on one of the trips to the range. I had to have the rifle re-crowned. Look at the end and see if there is a ding or dent in the crown where the bullet comes out. I also agree with some of the advice above as to heating up but your post seems to suggest that the first few shots with a cold barrel are also off.

If after considering all of the above posts you are still off, you might give consideration to the scope. As I was preparing for my safari this past summer with lots of trips to the range, I ran into a sudden loss of grouping somewhat similar to what you experienced. The rifle had been shooting well, in fact very tight groups. Suddenly the shots started walking all over the target. After checking screws, rings/bases, cleaning, praying to the shooting gods and much distress, I finally came to the conclusion that the scope must be the issue.

So I took a scope off of another rifle and put it on my Africa rifle. Voila, the groupings immediately returned. No doubt about it, it was the scope. The crosshairs were not holding.

Here's the kicker, the scope was my Zeiss Conquest 4.5-14. No matter how good your glass may be, don't count it out. Humans make these things and therefore things will break. To the credit of Zeiss, I got a brand new scope back a few weeks after I sent the broke one in.

It's kind of a pain, but again if all else fails from the posts above, replace the scope with another one and see what happens.

Originally Posted by PHOENIX PHIL

If after considering all of the above posts you are still off, you might give consideration to the scope. As I was preparing for my safari this past summer with lots of trips to the range, I ran into a sudden loss of grouping somewhat similar to what you experienced. The rifle had been shooting well, in fact very tight groups. Suddenly the shots started walking all over the target. After checking screws, rings/bases, cleaning, praying to the shooting gods and much distress, I finally came to the conclusion that the scope must be the issue.

So I took a scope off of another rifle and put it on my Africa rifle. Voila, the groupings immediately returned. No doubt about it, it was the scope. The crosshairs were not holding.

Here's the kicker, the scope was my Zeiss Conquest 4.5-14. No matter how good your glass may be, don't count it out. Humans make these things and therefore things will break. To the credit of Zeiss, I got a brand new scope back a few weeks after I sent the broke one in.

It's kind of a pain, but again if all else fails from the posts above, replace the scope with another one and see what happens.

Good advice. I was thinking also that he should check his scope. I once had a Bushnell scope that held its zero on a Winchester .270, but I then put that scope on a Remington .30-06 and suddenly it was shooting patterns. Well, it didn't take long to figure out it was the scope. So I bought a new scope and had no issues after that.