Cratered primers are a problem with many commercial rifles. The firing pin hole is enough larger than the pin that cratering easily occurs. They're made this way for ease of manufacture but the cratering you've experiences is why precision rifle-smiths offer firing pin hole bushing as a service.
In a stock 700 I would look for primer flattening as a pressure sign rather than cratering. Flattening is, of course, the reduction of the radius on the external edge of the primer cup. At extreme pressures the primer not only flattens completely but flows to fill the radius on the case. At this extreme, the spent primer is larger in diameter at the closed end than the large end.
An even better method of gauging pressure is measuring the growth in diameter of the case head, just in front of the extractor cut. An increase of more than a few "tenths" (.0001"s) indicates case life reducing pressures.
Another thing; when shooting off the bench, lay your thumb up along the stock to the trigger hand side of the action - enough to stabilize the trigger finger but not so much as to affect recoil or put the recoil into your hand, that's what that meat socket, the shoulder, is for. (This advice is useless if the rifle rises too high in recoil - so maybe I'm yakking out of my butt here.)
I found 43.0 gr Varget worked quite well with the 175SMKs in my rifle, so that is where I've settled for now with that bullet. No pressure signs. It is a 700SPS Varmint in .308, and at the moment my challenge is no longer finding a suitable load, it is learning to shoot to the capability of the rifle and the ammo. Then I'll be able to go to Boomershoot next year ;-)
Or one that you have shot and cleaned many times before. I have two that are worthy, so I'm thinkin' 'bout it. There's no going back, hence my reluctance to be a guinea pig.
In your case, DJ, I'd follow the included preparatory cleaning instructions to the letter, but other than the initial cost, I don't see a downside. It either works, or it doesn't, but it does not affect accuracy either way.
So far, I've not see anyone claim that it makes cleaning more difficult, and it doesn't appear to have made yours inaccurate. One of mine is three seasons old with a stainless barrel, the other is 32 seasons old with a blue steel barrel. Both are capable of 1 MOA or better groups, when I do my part.
I 'spect I'll give it a try.
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JS-Kit/Echo comments for article at http://smallestminority.blogspot.com/2008/05/range-report.html (9 comments)
Tentative mapping of comments to original article, corrections solicited.
Thanks for the report Kevin; I'm becoming inspired to dig out my 700VSSF (.308 also) and give it a workout.
Cratered primers are a problem with many commercial rifles. The firing pin hole is enough larger than the pin that cratering easily occurs. They're made this way for ease of manufacture but the cratering you've experiences is why precision rifle-smiths offer firing pin hole bushing as a service.
In a stock 700 I would look for primer flattening as a pressure sign rather than cratering. Flattening is, of course, the reduction of the radius on the external edge of the primer cup. At extreme pressures the primer not only flattens completely but flows to fill the radius on the case. At this extreme, the spent primer is larger in diameter at the closed end than the large end.
An even better method of gauging pressure is measuring the growth in diameter of the case head, just in front of the extractor cut. An increase of more than a few "tenths" (.0001"s) indicates case life reducing pressures.
But you probably knew all this.
Another thing; when shooting off the bench, lay your thumb up along the stock to the trigger hand side of the action - enough to stabilize the trigger finger but not so much as to affect recoil or put the recoil into your hand, that's what that meat socket, the shoulder, is for. (This advice is useless if the rifle rises too high in recoil - so maybe I'm yakking out of my butt here.)
I found 43.0 gr Varget worked quite well with the 175SMKs in my rifle, so that is where I've settled for now with that bullet. No pressure signs. It is a 700SPS Varmint in .308, and at the moment my challenge is no longer finding a suitable load, it is learning to shoot to the capability of the rifle and the ammo. Then I'll be able to go to Boomershoot next year ;-)
So, it appears that Ultra Bore Coat works. What's your verdict?
Well, I'd say that it does not adversely affect accuracy, and the barrel does seem to clean easily, so I'm pleased.
In order to be sure, I think you'd have to have two identical rifles side-by-side and compare.
Or one that you have shot and cleaned many times before. I have two that are worthy, so I'm thinkin' 'bout it. There's no going back, hence my reluctance to be a guinea pig.
In your case, DJ, I'd follow the included preparatory cleaning instructions to the letter, but other than the initial cost, I don't see a downside. It either works, or it doesn't, but it does not affect accuracy either way.
So far, I've not see anyone claim that it makes cleaning more difficult, and it doesn't appear to have made yours inaccurate. One of mine is three seasons old with a stainless barrel, the other is 32 seasons old with a blue steel barrel. Both are capable of 1 MOA or better groups, when I do my part.
I 'spect I'll give it a try.
Note: All avatars and any images or other media embedded in comments were hosted on the JS-Kit website and have been lost; references to haloscan comments have been partially automatically remapped, but accuracy is not guaranteed and corrections are solicited.
If you notice any problems with this page or wish to have your home page link updated, please contact John Hardin <jhardin@impsec.org>