I was using Federal premium Accubonds and getting clover-leaf groups out of my 7mmMag...until a week ago. My groups have opened up to 1"-1.5", so I figured that something shot loose. I checked all of the screws, mounts,etc and also eliminated a scope problem. I also checked the bedding screws, which did not move.
I then realized that although I was using the same Federal Premium ammo, it was from a different lot. Could this be the problem? I didn't think that a different lot would change things so much....what are your thoughts on this, since I can't think of any other reason for it.
BTW, my barrel has about 700 rounds through it and still looks good with no signs of erosion.

You state POI changes then relate how groups opened up, with no other reference to POI?

However changing lots of factory ammo or reloading components can change your POI and groups.

Once had a hunter miss 3 antelope in a row, and on the way back to the house for lunch - he asks-> 'will zeroing in with one brand of ammo and hunting with another make a difference?' Seems he practiced/zeroed with cheap Wally World stuff, and hunted with the expensive Winchester Moly coated Premuim stuff!!!!!!!!!!!!

In short, you may have to live with it, or find another ammo that shoots as good as the "old" stuff. If the latter, you then buy all you can from the same lot.

Wolfgar, it can definitely be the difference. I got into a habit a while back of taking apart factory ammo to study what components it appeared that the factory's were using. To my surprise, I actually found with two boxes, purchased at the same time--but from different lots, actually had different powders! One had a coarse extruded powder, and the other box had a very fine ball powder. This was Fed premium ammo. I have heard of the same thing with other manufacturers as well, and even seen this with Winchester.

So long story short, it can sure impact your groups from lot to lot.

Good luck in getting back to those cloverleafs.

Regards--Don

Thanks fellas.
OldGuy, yes the POA changed AND the groups opened up.
I have ordered a test box from Superior Ammo, so I'll let you all know how that goes.

It can most definately be the difference in the lot.

I have been shooting Federal 168 gr factory Match ammo for over 23 years.
Thus, I have shot several different lots.
All of it has been very accurate. However some lots are truly more accurate than others. I have had some that were under 1 inch at 300 yards, others were 1 inch at 100. Also there is sometimes a zero change, usually around 1/2 inch at 100 yards, the biggest change was a 3 inch vertical change at 100 yards. Some times there was a 1/2" left or right zero change.

If you ever find a factory load that shoots really good go back to the store and buy ALL of that lot.
I save that for long range hunting. Then when hunting where I have under 200 yard shots I use a different lot, saving the good stuff.

You might try the Nosler Custom Ammunition that is loaded at the Bend, Oregon plant. They sell loaded ammo off the internet, and I am told that there is no "lot variance" I use the 160 Accubonds as well, the accuracy is astounding!

Glad you share my thoughts, makes me relax a bit!. I did order a test box (5 different loads using the same 160gr Accubond) from Superior. I'll find the best load for my rifle, then order 100 or so. Better yet, they keep your info on file so that when you order from them again, everything stays the same....any of you ever try a test box from Superior??

I have shot Superior Ammo in my 3 doubles. It was first class ammo.
If their load shoots good in your rifle I would order 500 rounds.

I'll second that. Ammunition factories test their lots to match prerequisite levels of pressure / velocity / accuracy and often with different powders. Accordingly, different batches may often be viewed as being different loads. When you happen upon a lot your rifle likes, you'd be well advised to stock up on that particular lot nr.

Wolfgar ----- If anything going down your rifle barrel changes, bullet lot-primer-powder, there may be changes in your POI, speed and accuracy. If you should happen to change something and see no difference, you are the simply very lucky in that respect. I once hunted with a reloader who had unlimited funds who bought his bullets an entire lot at the time, (120 boxs) from one of our worldwide bullet producers to insure consistency. When you are talking $45.00 per box think about that. He once got an entire lot that did not perform correctly and ordered another, thankfully it was OK. ------ As far as the manufacturers are concerned, one year production will certainly perform differently from anothers years production, and how do you know what you have when you buy it off the shelf that may contain several years production in Podunk USA. It all gets back to the same old thing, practice-practice-practice and have enough ammo loaded the same to do it extensively. Of course with factory ammo, that is quite expensive, just another reason to reload. Good shooting.

quote:

Once had a hunter miss 3 antelope in a row, and on the way back to the house for lunch - he asks-> 'will zeroing in with one brand of ammo and hunting with another make a difference?' Seems he practiced/zeroed with cheap Wally World stuff, and hunted with the expensive Winchester Moly coated Premuim stuff!!!!!!!!!!!!

I have met people just as clueless.

That's about the equivalent of a guy from Victoria, TX who bought a rifle, had it bore-sighted at the store and went hunting with it that way because he "ran out of time" to properly sight it in.

But it gets better. During a morning hunt, he missed a huge buck twice at relatively short range. Yet he took the VERY SAME rifle in the VERY SAME condition back out on the evening hunt.

Changing conditions from the moment you shoot a group to the next group can change the POI. For example, lets say that you shoot the first group from a cold and clean barrel, and then continue to shoot a second group. In this case, more than likely the POI will be different in the second group, since the barrel is not longer cold and clean.

Now, lets assume that the barrel shoots better after taking three fouling shots. In that case, before shooting a second group, and if you want to know exactly how accurate the new group will be when compared to the first group, then you would have to prepare the rifle so that it meets the exact conditions it was when you shot the first group.

Some rifles shoot well after a couple of fouling shots, and stay that way for awhile. But sooner or later copper and powder built-up on the barrel will affect accuracy or change POI.

Other things that may change the POI:
1. Rifle temperature
2. Copper/powder build-up
3. Lubricant/or not in the barrel
4. Differences in pressure from round to round
5. Ambient temperature
6. Altitude, and so on.

Now, the only big game rifle I have shoots the best group from a cold and clean barrel, so my rifle is always clean and cold each day I go out hunting. That first group is the only one I am interested on for hunting, not the second. However, if I am developing loads at the range, then I prepare for each group, not for a whole shooting session.

My cousin was sighting in his 7mm rem mag at my makeshift shooting range while I had my chronograph set up. He was shooting federal premium 140 gr partitions and when I was reviewing the velocities of the shotstring I noticed the first five shots averaged 200 fps lower than the later shots. When I pointed that out we figured out that the first five had been from one box of ammo, and the others from a newer box of a different lot number. The ammo was supposedly identical except for the different lot number, and it gave 200 fps difference in the velocities.

I figured that spending the extra money for Federal's premium line would eliminate these variables....what is the sense spending the extra money then? I will use the Superior handloads for now on, and cheap factory stuff for practice.

Wolfgar, I think that is an excellent strategy, and is basically what I do, except I load all my stuff, just cheaper bullets for practice the majority of the time, and the primo stuff for just before the hunt practice and hunting.

Good Shooting--Don

WOW, I cannot tell you how frustrating it was to see my groups go to hell. I even changed scopes! I'll let you all know about the test box.

Interesting, I always found Federal Ammo to be pretty consistant shot to shot box to box. Then again, I never got that tight on group size other than can I hit a grape fruit out to the distance I shoot from off the sand bags. It can be frustrating at times. Somethings its nothing more than just a bad day at the range.