Matrix 117g 6mm not stabilized in 1-7.5??

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Shumba

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Aug 14, 2008
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167
Location
Fort Worth, TX
I have a 243 Catbird (6mm-06 improved) The rifle is built on a Stolle Kodiak receiver with a Kreiger 1-7.5 twist 29" rem Sendero contour. This rifle shoots 107 SMK and 105 Berger Hybrid Tgts boringly into .2-.3 tenth 5 shot groups at 3480 FPS. I tried some matrix 117 in it and it literally sprayed a 12-15" 5 shot group at 400 yds (the 105 Bergers just shot a 1.3" group at the same distance) The load was retumbo (same powder I use for 105-107 bullets) seated to touch lands and a MV of 3300 fps. The bullets entered the target straight but all over. Is it possible the 1-7.5 at an elevation of 600ft and 3300 fps is not stabilizing these bullets? Any other ideas, I am baffled.
 
Shumba said:
I have a 243 Catbird (6mm-06 improved) The rifle is built on a Stolle Kodiak receiver with a Kreiger 1-7.5 twist 29" rem Sendero contour. This rifle shoots 107 SMK and 105 Berger Hybrid Tgts boringly into .2-.3 tenth 5 shot groups at 3480 FPS. I tried some matrix 117 in it and it literally sprayed a 12-15" 5 shot group at 400 yds (the 105 Bergers just shot a 1.3" group at the same distance) The load was retumbo (same powder I use for 105-107 bullets) seated to touch lands and a MV of 3300 fps. The bullets entered the target straight but all over. Is it possible the 1-7.5 at an elevation of 600ft and 3300 fps is not stabilizing these bullets? Any other ideas, I am baffled.
Click to expand...

You may have some thin jacket bullets? send me your address & I'll send you some thicker ones.
I've seen that exact thing from another 6-06, the thicker jackets will fix it.
or $ back:)

Marshal
 
I just opened up the calc program, and it indicates that the spin imparted onto said rounds at said twist and velocity is equal to 316,800rpm, which (I believe) should be far in excess of what is required to achieve full stabilization. So that definitely not the problem. Oxymoronically speaking, it may be due to your spin being TOO fast, at the velocity that you are spitting them out at, for the thin-jacket bullets to be able conform to. With too thin of jacket, too soft of lead, too fast of twist, the rifling lands can "skid" over the bullet, unable to stay within the grooves cut by the leading edges. This will "skuff" up, or even de-form the bullet, throwing the accuracy off, AND also could prevent it from achieving full rpm. Spinning something up from 0 to 316,800rpm in just a few milliseconds, while accelerating it from 0 to mach 3 within the same time frame, puts EXTREME (difficult to imagine) forces onto it. For your bullets to work, you would need to either send them at a lower velocity, or change to a SLOWER twist rate. Yeah I know, those wouldn't be acceptable options for me, either!
 
Guys could you point me in the direction of the documentation for over spinning bullets. I have always used a faster twist(several calibers) than rec. with great success. I have never been much for reading someone elses theories/experiences when I can develop my own at the range. I think I might have to have a look though to prevent any future mistakes.

Brent
 
Do you like math?? I believe this is known as the "greenhill" formula (I hope it formats correctly when I save the post - it may not):
Define the Variables: T = Twist rate in 1 turn per inches. L = Bullet length in inches. V = Muzzle Velocity D = Diameter of the bore grooves in inches. Constant = 3.5 Find the optimum twist rate from velocity, bore size and bullet length: T= ( 3.5 * SqRt( V ) * D² ) ÷ L Find the optimum bullet length from velocity, bore size and twist rate: L = ( 3.5 * SqRt( V ) * D² ) ÷ T Find the optimum muzzle velocity from bullet length, bore size and twist rate: V = ( L * T ÷ D² ÷ 3.5 )² Find a different constant to fit known optimim combinations. Constant = L * T ÷ D² ÷ SqRt( V )
 
Oh I forgot, there is also the "miller" formula. But no sense in getting out of hand with the math. But if you DO happen to be one of those individuals who actually enjoys doing math, I could feed you many more numbers, if you want. In THIS post however, I'm going to limit it to only 1. It may be plus or minus a little bit this way or that, if you are a hair-splitter (it's not really THAT critical though). But for starters, the number you should be "shooting" for is around 250,000. Somewhat higher than that should be fine, but I wouldn't suggest much lower than that.
 
Hmm, I don't get it. Why this is being brought up again and again??? All I said was that "his" thin-jacket rounds weren't handling his barrel's fast twist rate, at the stated velocity. But if there are folk who believe that something not right about that, I would appreciate it if they would quit beating around the bush, and just say what's on their mind. I sorry, but I just don't have the mental energy to spare on trying to correctly interpret cryptic messages!
 
Feenix you going to be in Missoula for the 1000yd. match in August? Can't wait to see what that 7.75 dasher will do in the mix.


Brent
 
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