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How many groups from you is it? How many different bullet weights and twist rate combinations have you experimented with? |
Here's a three shot group (100M) from a hunting rifle shot about noon today. As much as I would like to attribute the result to "appropriate twist", I suspect it could be related to blind luck or perhaps a friendly gust of wind:)https://uploads.tapatalk-cdn.com/201...028f312450.jpg
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I had an interesting experience today with the same 22-250 mentioned earlier was testing some 62g varmagedon i wanted to see if i could get a load with cfe223. 2 loads on the upper end of my test had bullet failures out of 10 shots with the 2 groups i had 4 bullets come apart i thought i seen dirt fly when shooting about 40yds in front of me. Sure enough when i walked up to check groups i seen where parts of them hit the ground and missing 4 holes on paper for those groups.
Now im not saying this was my fast twist as it could just be a bad batch of bullets or their construction but none the less interesting i forgot my chronograph but estimated around 3400-3500 on the ones that failed. Disappointing as the groups were getting better the faster i pushed em Im gonna test them in my 1/9 223 as well see if i have better luck |
Sorry Chuck, I must have missed the point about the relationship between twist rate and group size because of the pic in your OP. And you must have missed my point that twisting a bullet with the least rotation required to stabilize it, might work even better? So, here is a pic of some consecutive groups I shot with a hunting contour barrel I used last year ... with the least twist required to stabilize the bullet ... which I think provides some support for the practice of not over rotating bullets. I don't think it is credible to suggest that a single/fast twist rate is a "fits all" solution.
https://uploads.tapatalk-cdn.com/201...d74165a613.jpg |
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here's the follow up question:
what the hell is the draw toward dink bullets with high powder capacity cases; for example 50 gr bullet in a 40 gr powder capacity 22-250. |
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http://bulletin.accurateshooter.com/...ity-litz-test/ |
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i shoot coyotes to 400 pretty routinely with a 222 running a 50 gr bullet at 3100. if your not shooting long, why burn twice the powder for another 6-700 fps with the same bullet? coyote tips over regardless....
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I have good success my way and you do your way. Have a good winter on the dogs |
I got a 1-9 twist .223. Better to stabilize 40-69 grain projectiles if I rely on what I read.
As I'm not extremely knowledgeable, I just use this as my baseline. I remember reading that 1-7 & 1-8 twists are to stabilize heavier/NEWER military rounds. :shark: |
I have a 8 twist Tikka. Never really saw a downside to having a higher twist rate than required.
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Some say that if you're shooting bigger bullets in bigger calibres you feel torque twist and can throw you off a bit, some claim quicker fouling in the quicker twist rate. I don't know, is slow twist cheaper to make?
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Maybe there is something to this match the weight to the twist thing. :sHa_sarcasticlol:
Another fluke perhaps? https://i.imgur.com/SGYMCAu.jpg |
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What exactly, are you trying to say? |
You’re guessing and I’m not? I don’t know.
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Nice to see that last group with the long Bergers that are appropriate for the 8 twist. As you have demonstated, they group much better than the “shorties” pictured in your OP which might group better with a slower twist.
IMO, the best way of testing consistency is to shoot some consecutive 5 shot groups. These are nice temperatures for longer strings. |
There are three other variables involved. Bullets, brass, and powder. Down here wind is the biggest weather issue for shooting groups.
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6MM br 1 in 8 ...105gr bullets bug holes, 87 gr v max 20 yards past muzzle they were mist......:thinking-006:....over stabilized....me thinks :scared:
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I have shot a boat load of 55gr 6mm BT’s in nine twist barrels at 4K to know better than the mist theory.
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The “greenhill formula” (and its fine tuned offspring) using the bullet diameter, length, specific gravity, and velocity ... provides the basis for calculating the optimum rotation required for stabilization. Although rotating a bullet faster than the “optimum” has no theoretical deleterious effect itself, bullet construction that is not “perfect” ... say in weight distribution, uniform jacket thickness, and a host of other factors... will amplify the imperfection and may result in poor performance. Consequently, the best advice is to choose bullet/characteristics that fit in the range of optimum stability provided by a given twist.
So, to address the issue posed in the OP, it is evident that maqnufacturers make slow twist barrels for specific (shorter) bullets, and faster twists for their longer cousins. Yes, we still need slow twist barrels because over rotating a bullet with deficiencies, is unlikely to give the best results. It is quite possible that a well constructed bullet may shoot “decent”, which does not rise to the standard of shooting “well”. If manufactures thought their barrels would shoot every length of bullet well with a fast twist ie: 1:7 ...they would just make them all that way and not bother with extra retooling costs. |
So shooting the same load in two rifles with different twist rates produced a difference in velocity of only 10fps? Has anyone actually measured the pressure produced in both barrels with the same load? If the fast twist barrel is producing more pressure , then you would need to change the load to produce equal pressure in both barrels to determine the true effect of twist rate on velocity. And even if the same pressure only produces 20fps more with a slow twist barrel, why not take advantage of that 20fps if the accuracy is the same? If I am only going to shoot a 55gr bullet , why use a twist that is optimum for 80gr, and give up 20fps that I can have for nothing?
I have owned six 7mmstw rifles, four with a 1 in 10" twist, and two with a 1 in 9" twist. All shot 140-150gr bullets well, but the 1 in 9" rifles did not shoot the 140gr bullets as well as they shot 150 gr bullets. The 1 in 10" rifles preferred the 140gr bullets. So is this simply coincidence, or is the twist rate a factor? And this is with only a 1" difference in the rate of twist. |
Fascinating post
The rub is of course, no matter how hard you try you can't keep all the variables constant while you manipulate rate of twist.
Some of the posts are very scientific and I really appreciate that. The Litz test (I think that is what it was) and Elk's last post may be showing that the small difference in MV moves the point of impact due to harmonics not bullet stabilization. I calculated the rpm of bullets exiting the barrel once and they were extremely high and it is hard to believe that a higher rpm makes them more stable. Maybe the different twists rates are just a marketing tool? As others have said, its how they shoot that counts. Good stuff. |
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