Advice needed. I hope I didn't ruin a new barrell. - Page 2 - RimfireCentral.com Forums

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  #16  
Old 03-30-2006, 11:29 PM
Gut bomb

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There's not much you can tell by looking down the bore but the crown is another story. The crown is the finished cut of the end of the barrel. This is very importent for rifle accuracy because this is the last contact the bullet has with the rifleing. If there is a small nick on one of the rifling lands this will leave a gouge on one side of the bullet causing it to fly untrue. Also if this area is not cut perfectly square to the axsis of the bore it will effect accuracy. You can do a visual inspection of the crown with a magnifing glass
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  #17  
Old 03-31-2006, 06:39 AM
Oldeyes
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.17 caliber bore issues

The .17 caliber bore diameter can be pretty much of a 'special case' when it comes to being a bit finicky about its cleanliness. There also seems to me to be a fairly wide variance in the smoothness and intrinsic trueness of the lands and grooves surfaces between various .17 caliber rimfire manufacturers. This intrinsic bore smoothness and trueness also seems to impacted by the production methodology by which the rifling was achieved and also by where the particular rifling tooling just happened to be in its manufacturing production life cycle. Let's face it, in the world of relatively inexpensive, non custom barreled rimfire rifles, some bores have to be manufactured at the effective end of the life cycle of the production tooling. However, in that you were able to eventually achieve some subsequent pretty decent for the shooting conditions groups, we will assume for the moment that you have a good and well manufactured bore.

The tiny bullet out the .17 HMR cartridge is designed to experience a rather narrow range of coefficient of bore frictions as it travels down the barrel. When you have a situation where the rather tiny internal bore surfaces are effectively 'obstructed' with the manufacturing grit and debris, heavy oil, protective coatings, etc. associated with the rifling creation and firearm shipping process, that bore related coeffiecient of friction can be rather artificially high for a few shots. And yes, the associated chamber pressures also probably go to places that they should not, but you seemed to not have a problem in that arena. However, the net effect of such bore constricting 'obstructions' is that the bullet is slowed in the bore.

Given what I have witnessed in other situations with rimfire bullets being shot out of otherwise constricted bores (as in very severely leaded), it is entirely conceivable to me that enough bullet energy was absorbed in the .17 caliber bore to allow the bullet to subsequently be stopped by a layer or two of cardboard. That really does not surprise me at all. I have seen rimfire bullets fired out of greatly constricted bores that are severely elongated and quite firmly lodged out at the very end of the barrel. The bullets that were actually able to exit such a constricted bore actually cut holes in the targets that appeared as if someone had shot the target with a bunch of nickles on edge. Thus, the 'keyholing' bullet destabilization that you observed (often accompanied by a very pronounced 'whizzing' sound from the bullet actually spinning on its longitudinal axis in flight) is a normal consequence seen in situations where the original rimfire bullet ballistics and the resulting bullet spin stabilization have been somehow greatly impaired during the bullet's travel down the bore.

So, that's a rather brief review of the potential technical aspects of what could have occured in your situation. Your experience with your first couple of shots again makes a good point for at least a minimal bore cleaning before your first shooting, but I know that you already figured that one out for yourself. As to any permanent bore damage having been done in your situation, I doubt it. At this point I would do a good wet patch cleaning with Kroil or your favorite bore solvent and then a couple of passes with a good quality brass .17 caliber rimfire brush. Then finish off your cleaning process with a dry patch or two. The grouping accuracy will probably drop for a few shots after such a cleaning, but then you can continue with your barrel 'firing to break in' process. The barrel accuracy characteristics will probably set back in and stabilize with use, hopefully resulting in greatly improved shot to shot accuracy. Good shooting, sir.
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  #18  
Old 03-31-2006, 08:03 AM
BobforBass

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Oldeyes,

Thank you so much. That is the kind of info I was looking for. Thank you too Gut Bomb. I am feeling pretty comfortable that all is ok w/ the Contender. I'm no expert but I sure knew something wasn't right that first day out w/ the gun.

When I get a calm day and a good rest I'll post pics of what I can do w/ this gun.

Again, thank you all for your posts.

God bless,

Bob
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