We're all familiar with the issue of how clean or how dirty a particular barrel wants to be. Some seem to shoot well when very clean, others need 5-20 or more rounds before settling down.

I have a very accurate M70 375 H & H that I'll bee using for croc in Moz. in August. I know that with it's most accurate load (using a 300 gr. Hornady soft RN) it can be a little inconsistent. That is, it will shoot 3/4" groups, then open to 1.5", but I don't know exactly at which point in the cleaning cycle. Normally I don't hunt with this bullet, but use A Frames, which are almost as accurate and much better on game. Also, I don't worry about 3/4" vs 1" on game. However, in this case, where the best accuracy is desired, I want to determine just how many shots should go down to get the best accuracy. I will describe my planned test, and invite comments, especially from stuntpilot2, who is very good at this sort of thing.

1. Clean to bare steel using Wipe Out as needed, followed by J-B. (Wish I had a bore scope.)
2. Shoot five round groups using a known accurate load using standard bench method of front rest, rear bag, etc. Each group to be on a new bull, and allowing the barrel to cool between groups.
3. Here is the hard part. How do you set the standard to determine when groups are actually changing? The rifle will shoot 3/4" "good" groups, but that is the average. Some are 1/2, some are 1". The average of best groups is 3/4" Statistics being what they are, there is variance, which is why we have the concept of average, or mean, in the first place. I don't have enough data to calculate a reliable standard deviation for group size.

Of course, one could just go with the gut, but what the hell is the fun in that?

Brice, I think your test is fair enough. I would say that you ultimatley have to have a little gut in the mix, but a ruler will do in this example! In other words, as you measure your groups as you go along, at some point the average will mathematically change.

If you are in fact getting 1/2 to 1" for a bit, and then things open up to 1.25 to 1.75 for the 1.5 average, then your groups are opening up of course. I have had a few rifles that behaved similarly, and what I would see is that the 'good' group that was keeping the average groups down, would go away. This would get the average group into an unacceptable range for me, and then I would clean down to bare metal and start from there again. I found a range of shots where these rifles would produce accuracy that I was satisfied with, and I would hunt with them while I knew the shot count was in 'the zone', and always had high confidence in these rigs with that practice.

I will tell you, that all of these rigs improved with time and work, and got to where they could shoot a much larger quantity of shots where accuracy remained in my acceptable zone.

Good luck on the test and the croc!

If you are trying to replicate what you do when you hunt, then you should probaly shoot one shot from a cold clean barrel and then clean the barrel. Then shoot another shot that afternoon or the next day.

If they go to point of aim is probably more important than how they group. Maybe this doesn't sound logical but I have a .300 WinMag which, from a clean cold barrel, shoots to exactly the same point on the first shot. After that it groups like a herd of cats. But who cares, that first shot is spot on every time and my scope is wired to that point. And that is the shot that is most likely to be used on an animal at any distance, rather than the fifth shot from a dirty barrel.

Very good point Wink. One must not lose sight of what is truly needed. Fish, I think you're right. Just watching the mean move is probably sufficient.

I woke up at 1:00 am thinking that I missed something, i.e. that you should test the load you will hunt with. Why? Because different loads will foul differently. Ball powder will crap up faster than stick. Some bullets will copper foul more quickly than others.

While it is important to know where the first round will go, I've been on safaries where I fired up to 35 shots. There's meat for the camp or market, bait for chui, the occasional mercy put-down, checking zero after a bad fall, baboon opportunity, etc. So it's nice to know how long that nice tight zero will last.