mtngun
posted this
30 November 2016
You could start off your project by first building a good sturdy concrete shooting bench. I think you once said you do most shooting on a flimsy wood table from your shop.
Indeed! I hope to make improvements to my existing 100 yard bench (the wooden bench itself is sturdy enough but the shooting shack it sits in is the weak link, having only 2x4 pine floor joists :shock: ) and I plan to build a 200 yard range. The 200 yard range will definitely have a sturdy bench though I have not decided whether to build with concrete or wood. Depends on the exact location and whether I decide to make it portable (on a trailer). Anyway I had hoped to get those things done this year but it didn't happen. I'll try again next year.
In the meantime, my flimsy shooting shack is annoying, but I don't feel it is limiting my accuracy with free recoil style shooting. It's just that I have to sit still and not touch the bench while shooting. It sounds lame, but one adapts. :D
The majority of thoughs shooters use the Egan MX4 30 ARD bullet. It's a 1.25 long, 215 gr bullet. Most all of them use either a 11 or 12 twist barrel. The stability factors run ~2.0 at ~2000 fps. There RPM runs ~131,000 and all use Lino.
The prevailing philosophy in CBA competition seems to be that the key is bucking the wind at 200 yards and certainly the long heavy 30 caliber bullets are good at that. A 50 BMG would buck wind better still but recoil would impair the shooter. I'm guessing 30 caliber prevails due to a combination of tradition and human recoil limitations?
Even if you accept the long heavy wind bucking school of thought, a 14” twist will stabilize the Eagan bullet with a stability factor of 1.3 and should deliver better accuracy at a given velocity, or alternatively allow more velocity (and less wind drift) at a given accuracy, all other things being equal, though as with my lube shootout the differences in accuracy may be measured in hundredths. Yet improvement by hundredths is a necessary part of any benchrest game.
Has any CBA member done a side by side comparison test of different twists, using barrels from the same maker chambered with the same reamer and shot with the same load from the same rifle? If not, how do they arrive at the 11” and 12” twists? Greenhill? Following the crowd?
I notice that the prevailing philosophy in jacketed benchrest (out to 300 yards) is that aggs and low recoil are more important than wind drift, that you can compensate for wind (if you are Tony Boyer), but you can't compensate for agg, so they shoot slow twists (requiring light bullets) to optimize aggs.
Who is right? Or are they both right, given the peculiar limitations of cast bullets?
 that 2300 fps and 118,000 RPM can yield competitive accuracy. Because a 180 gr. spitzer at 2294 would have competitive wind drift at 200 yards.</p>
<p>Summary: I can't fault the choice of the 30BR. I can't fault the choice of 118,000 rpm -- yes, my experiments often operate at faster RPM's but I'm not agging sub-MOA at those faster RPM's. I do wonder about lino because it will get blown around more than a denser alloy. I do wonder about the 12.3” average twist because it's leaving a wee bit of accuracy on the table compared to a 14” twist.</p>
<p>That's just theory, and obviously the barrel will have the final say in which load it wants to shoot. </p>
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