Why I Hate Bore Scopes - by Eben Brown
- Every now and then a well meaning customer will call or email us saying he's got a bore scope and he's seeing something disturbing in the new barrel we made for him. It's usually just a tool mark, burr, or discoloration. But for liability reasons, we have to take the customer seriously. We don't know if the customer knows what he's looking at... It could be a barrel obstruction. We can't give any assurances over the phone or email so he has to send it in. We check it and sure enough its just a tool mark, burr, or discoloration. And even though we do the $65/hour re-inspection for free, the customer is never happy when he is expected to pay the shipping charges. The bottom line is that we made the customer a great barrel but he is unhappy because of a Bore Scope.  I hate when that happens!
- I'd like to start by explaining: Our barrels are not mass production items where maybe 1 out of 10 or 1 out of 100 gets inspected. Each and every one of our barrels is inspected, checked, and measured throughout our production process. Our bores are deep hole drilled on machinery that turns the barrel and keeps the drill stationary. This is the only way to assure the straightest hole... Which is especially critical for long lengths as in rifle barrels. After this, our bores are then reamed to within .0002" of exact bore dimension. That's not thousandths. It's Ten Thousandths. 2/10,000ths is the spec. This reaming removes all but the deepest drilling tool marks but leaves the shallow reamer tool marks. Our barrels are then button rifled, which swages the rifling into the bore as it burnishes the remaining toolmarks. At this point the barrels are referred to as "blanks". They are about 1.25" in diameter and 29 inches long.
- The blanks are cut to length before turning. This assures that the bore is centered at both ends when we do the actual contour turning. The next step is to clamp the barrels between centers and turn the contour. We have invested heavily in machinery that is custom built to our specifications. Massive tailstock and tailstock bearings to dampen vibration. Programmable steadyrests keep the center from flexing as the cutter moves down the length of the barrel. The result is the straightest possible barrel with the straightest possible bore.
- From here, the barrel gets chambered with reamers that have fitted, free rotating pilots. They're mounted in a floating reamer fixture that follows the bore. There is no play or chatter and our chambers get reamed perfectly straight and perfectly centered, and perfectly aligned with the bore. We do a similar process at the other end to assure that the crown gets the same amount of perfection.
- We intentionally do NOT lap our bores. First of all they do not need it because they are dimensionally consistent within .0002". Second of all we do not wish to introduce a potential fault into our process... Hand lapping can cause hourglass shaped bores. Third, lapping for cosmetics diminishes your precision to the depth of your deepest tool mark.
- I have never had much use for borescopes because they have no precision and are only good for magnifying tool marks and blemishes. Our precision is checked and proven throughout the process by sophisticated instruments and gauges. To be sure, if the customer didn't have a bore scope, he would have just gone out and shot the barrel and would most likely have been thrilled with the accuracy it delivers.
- But since he has this borescope... And since he has seen something in the barrel that bothers him... And since we have no way of knowing what he's looking at... We can't just tell him its probably a minor burr or cosmetic flaw and he should forget it and go shoot the barrel. What we have to say is: "If you feel there is something wrong, go ahead and send the barrel back and we'll check it out."