Clean / Dirty Bore


Clean Bore. Yuk.

Ever since I have started shooting – if I am working with a known load (not one I am working up) I will always shoot the first shot on a ‘Cold Bore’ Target I set up next to my main target. This shot is always the first out of the rifle for a day – a true ‘cold’ bore. After that, I will transition to my normal targets, but note where the difference (if any) may lie. Certainly, more than once, I have put the first shot in the middle of the target. Often, if it’s drifting, I am left with the impression that it’s as much to blame on the ‘cold shooter’ as it is the temperature of the barrel.

What did interest me, and something I hadn’t tested, was the effect of a clean bore versus one that had been shot through.

I was interested to test the difference. It was certainly a lot more than I thought.

I, generally, don’t clean the copper out of my barrels. This is a result of reading more than one article online, that simply suggested, that unless the accuracy of your rifle is diminishing, you don’t really need to worry about removing all the copper, in fact, in the Magpul Precision Rifle DVD, it’s suggested that the copper can provide a bit of a bearing surface and help smooth out the bore for you1 and help the rifle group.

I have put around 200 rounds through the Remington 700 build – and I was interested in testing the difference. It was certainly a lot more than I thought.


Dirty Bore. Much better.

So I started shooting on Sunday, and was really quite shocked at how far out my zero was. A couple of shots later, and I realised it wasn’t just my zero. The rounds were going all over the place! It’s rare for me to not be on the paper these days – but I had multiple shots not even close!

Like so many things in this area – it’s one thing to read about it, it’s another to test a theory and see how it relates to your specific firearm and situation.

While I expected a difference – I hadn’t expected this much. However, as more rounds went down range, the group progressively shrunk. Around twenty rounds later, it was back to something resembling respectable, around .83 MOA.

So. For my Rem 700, as it stands at the moment – I know know, that once the groups start to open up in the future (which could be in excess of 1000 rounds through it) I know it’s going to then need at least another 20 after a good clean to get it grouping again.


  1. This is more in relation to factory, cheaper barrels. High-end barrels should be smooth from the get-go.