A week ago I developed a load for my 300WM with just under 1 MOA result (2 rounds of four shots) to which I am satisfied. After I got home I gave the barrel a good scrub using a brass brush (I seldom use brass brush) and noticed a lot of black powder residue coming out.

To confirm my results last week I shot with the same load yesterday. The group size open up to 2.5 MOA. I know it is not the load or my shooting, as I was very careful with every shot. The group size dropped down to around 1.5 after 16 rounds. Needlessly saying I was disappointed. The only variable that I can account for is the extra scrub down with the brush.

My routine cleaning includes just wet patches of Butch's Bore Shine follow by dry patches. I scrub down the barrel only once in a blue moon. My question is simple, how can I control cleaning and achieve accurate results? Any suggestions?

Danny Boy

Two things: First off, two good groups isn't really enough to verify that you really had a load that was sub moa. It could have been coincidense, so you may have really had a 1.5 moa load. Second, it is not uncommon for a rifle to shoot better after the barrel is fouled a bit, but, 16 fouling rounds is an awful lot, certainly a good bit beyond the norm.

That seems pretty normal for my a-bolt in 300 win mag. I do not scrub the bore until performance suffers from fouling. I oil the bore after each shooting session, run a couple of dry patches down the bore before I shoot it again and then fire a "fouling" shot before I start shooting groups. It shoots 1/2" to 5/8" groups with 180 gr. Barnes XFB.

When I do scrub the barrel, it takes me 3 - 4 shoots to get it fouled and shooting right. Sixteen sounds like a lot.

Here are some other variables. A stock that moves from moisture, heat or cold. A barrel that moves as it warms. A scope that changes POI when the power or other adjustments are made. A screw that you tightened or is coming loose. A bad case that caused a flier. A bad bullet. A bad primer. The wind.

In general most of the shots we fire are from a barrel with both powder and metal fouling in it.

My last test of fouling showed that a 260 Rem with an imperfect but free floated factory barrel and a pillar bedded action fired 92 shots without cleaning. All of the bullets went into about 3/4 MOA or better. Finally a flier happened. Why I don't know but I threw the case out and cleaned the barrel. It's going for 100 shots now.

I have a custom 300WM with a shilen select match 1-10" barrel built on a win70 action and pillar bedded synthetic stock. My barrel likes 1 sometimes 2 foul shots after scrubbing, but that is it. Arts is absolutely right on the money. One day of 1 load does not prove it is a good load. I had several loads that on some days went .5 moa 5 shots, other days as large as 1.5 moa. I then used H4831SC with 200 grain SMKs and now I shoot no larger than .5 moa 5 shots when I do my part. The best thing you can do is take the brass you fired your shots with and redo the load with those brass and see if you can duplicate it. If you can't duplicate the results it is not your load (or a loading variable has changed). Anymore I try to duplicate the load and group twice before I set on that load. I then change seating depth till I tighten the groups as much as possible. Did you make sure your seating depth hadn't changed (checking with a bullet comparator)?

I went to the range and tried the same load again. I got 1 MOA. I know I rush the shots a bit as I had a golf game to attend to in the afternoon. The barrel was very hot after 10 shots that I had to quit.

Next time I will save the same brass to validate the load. A great suggestion.

My rifle is A-Bolt Composite Stalker shooting 150 gr. Interbond with 77.4 gr of H4381SC. H4381SC is a lot better than the H4895 that I tried before. I don't have a comparator, however, I measure the OAL for every round and that is consistent @3.36".

Regards...

Danny Boy