Originally Posted by
geargnasher
I just went and checked my M70 Classic .30-'06 chamber dimensions with an impact slug and I found my cases have about .005" combined clearance (.0025" radius) even with the oversized (.310") boolits I have been using. Pulled boolits still @ .310". This gun shoots an honest 2" at 100 yards at ~2700 fps, often much smaller but I won't claim "average", I figure a gun is only as accurate as the largest group it shoots with a given load.
I want to narrow down, for my own testing and the testing of others, what the particular obstacles are with shooting cast in a Military Swedish Mauser accurately and fast. It has been said that it is possible to shoot ~130 Gr. boolits at at least 2300 fps into an inch at 100 yards. I think that is pretty good for ANY caliber with cast, but I don't see what in particular is the holdup with the Swede. I KNOW there is an obstacle, I can't even come close to that yet, most of my "patterns" have been just that, sprinkle the 8-1/2"X11" target with holes. WHY is this one so different?
Based upon past reading, here are a few, not all I'm sure, mentioned obstacles:
>>Military Swedish Mausers usually have oversized chamber necks and extremely long throats, necessitating the use of specially formed cases and carefully fit, often custom-designed, boolits. Why is the chamber neck so critical? Not so much with other calibers, why does a few thousandths make accuracy go from minute of backstop to minute of angle? It doesn't in other guns, it only makes an inch or two difference at most. There must be more to it than that.
>> State of anneal. I know case neck tension and consistency of that tension is an accuracy key. Again, in my experience it has only meant a difference of an inch or two at most in group size, not whether you hit the target paper or not. There MUST be more to it than that.
>>Twist rate. The Military Swedes have a fast twist and deep rifling. So what. If I can get to 2700 accurately with no real special loading techniques or especially well-fitting brass and a 1:10 why can't I get that with a Swede at, say 2150? There is obviously more going on than the twist rate or RPM threshold.
>>Powder burn rate. People have been experimenting for years with this in great detail. Most of us can assume that what works for one gun won't work for another exactly the same way, so that will probably remain a variable unique unto each particular gun, but we should be in at least a certain ballpark for certain velocities with particular alloys and particular velocity ranges. I can tell one thing from what others have posted and my own experimentation, there is no best powder for the Swede.
>>Fillers. Now that changes everything, especially powder selection and pressures. Why does it affect accuracy so much? We've seen consistent ignition and low ES with some of Larry's first test results, and accuracy was still terrible. So it stands to reason that the filler really is doing more with "cushion" and "protection" as well as aiding clean, straight muzzle exit. I think we can safely say that fillers are doing more than "bridging the neck" to get good, even ignition and consistent pressure build. If that were the case, any filler would do.
>>Crimp. I've found with other calibers crimp won't substitute for neck tension much. Most of the time I delete crimping entirely for this reason. I don't know for sure what works best here with the Swede, but I can see using tight, hard case necks and a bridging filler may give good consistency at launch with minimal or no crimp. I've seen at least one reference to .0015" interference fit or "neck tension" and many references to "standard benchrest loading practices" which fall pretty close to that. Again, I don't see that it matters 12" or better in group size no matter what crimp you use.
>>Lube. I have pushed some lubes to the point of failure. Very few good lubes I know of will fail to perform at 2000-2500 fps, which I believe is the realistic window here. I don't believe that lube alone will get groups from a foot to an inch.
>>Alloy. Seems to be straightforward. Use a tough, springy but not too hard alloy. This can be achieved by using a fairly low-Sb alloy and heat treating or "water dropping" it to get hardness with a tough, springy and resilient nature. Fairly generous leeway here.
>>Gas checks. No one here can convince me easily that material, style, or brand will make that much difference.
>>Chamber dimensions. I think Felix explained that quite well above, and I agree with him.
So what are we REALLY up against here? Is it just a matter of "tolerance stacking" with each variable being mysteriously magnified? WHAT ELSE AM I MISSING?
It just doesn't compute.
Larry, I'm sure you have your own stepladder algorithm to working this out, I'm wondering if you have comment or anything to add to the above.
Gear