by wildcatter » Sun Jul 10, 2011 12:37 pm
FYI..It seems this might be a good post area, to further the State-of-the Art, so to speak.. This is not intended to load you down with tons of data, but only to summarize the results, which could be helpful in your further load developments..
So, this week, we shot allot of factory ammo, "WITH" the factory crimp and the same factory loads "WITH" my LeGendre Side Crimp. All from the same lot, to compare the SC to the factory Taper Crimp. The results, though not conclusive, tend to point out some trends, that can have profound effects on our work.
The weapon is an AR-shop gun, in the 20" barreled variety. Also, keep in mind, my personal SC is quite narrow (about .015-.020" from top to bottom) and much deeper than anything I've seen from other Loaders here. I do this by taking the LEE crimping collet and use a Dremel Fiber wheel to open the four slits wider than LEE has them, thus giving me a much deeper crimp.
"WITH" the SC the averages for speed and pressures, were as follows:
speed = 2179fps
SD = 20fps
ES = 49fps
Pressure = 35993psi
SD = 1177 psi
ES = 4084psi
The group size averaged 1.5MOA at 200yds
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"WITHOUT" the SC the averages for speed and pressures, were as follows:
speed = 2169fps
SD = 16fps
ES = 49fps
Pressure = 34288psi
SD = 421psi
ES = 865psi
The group size averaged 1.0MOA at 200yds
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As you can see there are some differences. If Bench Rest Accuracy is the goal, then a slight Taper Crimp is the choice. If moderate pressure increases can be tolerated, then the SC comes into play.
In all of our experiments, so far, the Side Crimp dramatically increases bullet-pull and thus gets the powder cooking before bullet release, which makes for better thermal dynamic possibilities or in other words, better powder-burn efficiency.
This efficiency allows us to use much slower powders, thus lowering pressures. When those pressures go down, we can then bring them back up to normal, with a result of dramatic bullet speed increases and their possible benefits.
However, with those speed increases comes degraded accuracy. "BUT", the accuracy at 300yds was the difference of a 3" group vs a 4.5" group. I maintain that, for my needs anyway, that is exceptable, especially with the huge increase in Knock-down capability it gives me. Of course, only I would think that factory speeds weren't enough, which is totally wrong. We kill, using factory recommendations, with deadly aplomb, again-when using factory speeds/pressures/bullets. It's just that I keep planning for the return of the Dinosaur Era. Which, BTW, have you seen any dinosaurs in your AO's, lately? Then, I must be doing a good job, right? So, with the Hoot's, ringing out all the accuracy he can and with me and some others, applying all the speed we can, you dear reader can make your own judgements and assessing your own risks, for as Smokey says.."Only YOU can Prevent a Barrel Rupture" (which can and does happen with high or even low pressures). Keep yourself and your loads safe and reap the rewards or Dangers..
..t
Last edited by
wildcatter on Sun Jul 10, 2011 4:28 pm, edited 3 times in total.
Safety First..t
