I shouldn't have looked....borescope shock

B

Boyd Allen

Active member
A while back I picked up an old benchrest rifle that is based on a DGA action and a Six thumb hole stock. I have shot groups in the low twos with it, but after spending some time getting more blue patches out of it during the first very thorough cleaning since I got it, I stuck a bore scope down the barrel and looked at the throat. Agggh! The rifle was built before gunsmiths commonly had scopes, and this one got by with a chambering error that I had not seen before. At the end of the case neck part of the chamber, there is a ridge that sticks up all the way around, right where the freebore starts. It even casts a shadow. Well, I guess that that means that I will be cleaning a lot for copper, and that I should be glad it shoots in the twos, and not worry about trying to get into the ones. Have any of you run into this? It seems to me that a dull reamer, pushed too hard, may have been the culprit.
Boyd
 
since you have a borescope///would a throater catch it before actually throating ??
mike in co
 
Boyd Allen said:
A. At the end of the case neck part of the chamber, there is a ridge that sticks up all the way around, right where the freebore starts. It even casts a shadow. Well, I guess that that means that I will be cleaning a lot for copper, and that I should be glad it shoots in the twos, and not worry about trying to get into the ones. Have any of you run into this? It seems to me that a dull reamer, pushed too hard, may have been the culprit.
Boyd
Click to expand...
Boyd, there IS a ridge at the end of the case neck where the case neck diameter ends and the freebore starts, actually I would call that a shoulder if you are seeing what I think you are seeing. For example in a 6PPC with a 0.262 neck there is a ridge (shoulder) as the hole transitions to the freebore, usually about 0.2435" diameter. On most reamer prints that shoulder would be drawn as a 45 degree slope, in actuality that shoulder would be whatever the grinding wheel was dressed at when the freebore diameter was ground.
 
Jerry,
Thanks for the interest. I have looked at all of my other barrels with a bore scope, and so I have a pretty good idea of what I am looking at. Giving a little more thought to how this could have happened, it would seem that a reamer with or without the throat built in could not let this happen. The end of the neck part of the chamber is not shaped normally, it is more abrupt than they are usually cut. Giving it some more thought, it looks like someone used one of those Sinclair gizmos to check chamber length without cutting the neck of the case back far enough to make room for the neck diameter part to back up without hitting the end of the neck. If the guy that used the tool was just a little off, he would have felt some resistence right at the end of bolt close, and possibly attributed that to neck tension, lacking a bore scope, he would have not known what he did. The barrel is well along in its life. I think that since it does not seem to foul out rapidly and start throwing shots, and will do twos, that I will use it for letting friends try out that type of rifle, and practice holding off in in difficult wind, where my mistakes will probably hide the lack of potential. Heck, I might switch to a variable scope and use it for some squirrel work. The last time that I was at the range (with my other PPC) a friend had some 55 gr. ballistic tips that I tried on top of all the 133 that I could fit in the case. They shot well and were ripping right along, something like thirty seven and change out of that short barrel was impressive. (The pressure seemed OK.)
Boyd
 
Boyd - You'd best fix that chamber or that rifle will never shoot twos again. I had a barrel once, that was a consistent twos shooter. One day a friend insisted that I use his bore scope to take a look inside it, which I did. It looked like the inside of a sewer pipe. Aaaarrrggghhh. I lost all confidence in that barrel and could never shoot it without mentally picturing that hole. Bore scopes are evil!

JMHO

Ray
 
And if that barrel looked perfect through the scope, you would keep shooting, looking for that load that shoots in the .1'S and zero's to no avail, and probably never get better than the .2's

Your doomed either way. Blame it on the junky bore scope;)
 
If the rest of the barrel is pretty good you could set it back a thread or two - - - . I have some friends who have had great results setting barrels back and lapping them a bit. They tell me they don't last a long time but then they didn't cost much.
 
Last edited:
I managed to get the barrel off without incident, and was able to take a look at the whole bore. It must be an ancient cut barrel, form a time when bore scopes were not common. There are built in "features" that are so different that it is almost humorous that it shoots at all, much less, in the twos. The little ridge that I mentioned is an irregular knife edge most or all of which does not touch a chambered bullet that is seated into the lands. The trick is that as the loaded round slides into place, the bullet is scratched in one area. A friend has a 6mm throating reamer. The next step is to insert it and give it a light twirl. I can hear you all cringing, but if it even makes contact, it will be cutting almost nothing, sort of like a stainless version of lightly deburring a case mouth. Wish me luck. After I use the reamer, I will bore scope again, and then check loaded rounds that have been chambered (at the range) for marks. If all goes well, I will post my best results, along with a picture of the resultant blue patches. I sure am glad that I came across a full tub of JB. It can only make it better.
 
I knew a really good billiards player a long time ago that was on a real hot streak, couldn't miss a ball. Between matches one evening he and another player were leaned against the pool table, well, the other player lightly rolled both his and my friends cue across the table...my friends cue showed to have just the slightest bit of warp (this was at the time about a $6000.00 cue) My friend couldn't win another game thinking all the time his cue was warped.
I think I'll order a borescope!
 
Going to look at your barrels, or show the competition theirs? A long time back, I brought a concentricity gauge to a match that I was shooting, rolling and straightening all my rounds as I loaded them. After a while some of the other shooters came over each with a few rounds to be checked, which I did, with a studied look as concern, and the needle fluctuated. I guess I will never know how much doubt I planted, especially when I told them that mine were straightened to .00075 or so. If you can't sing well, you better know how to dance ;-)
 
Borescope= Worry Data

Boyd
A borescope is spending a lot of money to determine "Worry Data" . "Worry Data" is information you didn't know before to worry about, and you can't do anything about. :)
 
The best feature of owning a bore scope, In my opinion, is to see how well ones barrel has been cleaned. I suppose another may be to use to inspect the barrel of a rifle one is considering buying.

A couple of the best shooting barrels I have owned made me cringe when I looked at them with my borescope.
 
Boyd, Have you considered taking a cast of the chamber, to get it out in the daylight, where you can get a good look at it? An information overload!
Regards,
Bob
 
Bore scopes are good tools if used properly. When I get a custom blank, the first thing I do is clean it and examine it thoroughly with a borescope. Once it is chambered I repeat the above so I have a good baseline to compare future erosion with. It helps to see how effective your cleaning regimen is as well as carbon build up in the thrat area. It is invaluable when buying a used rifle as it puts the BS to bed.
 
If that ridge is sticking out into the throat, a throating reamer should take it out. Hoping that your throating reamer is as tight as the one that did the chamber to begin with. I guess, if you gently fed it in, and just skimmed the ridge out, without going to the leade, it should work anyway. A friend bought a used a 6mm Rem with a factory varmint wt barrel, that shoots 1/4" groups, and I borescoped it. Looks like a blacktop driveway. Told him to keep shooting, until it shoots1/2" groups, then I'll put a new barrel on it.
 
You must log in or register to reply here.
Back
Top