1/5 Twist and Supers

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2sBlind
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1/5 Twist and Supers

Post by 2sBlind »

Hi All,

For my next build, I'm looking to build a ~7 inch, mostly super/occasional sub suppressed build. I know this isn't quite the norm, but it's what I'm interested in hah.

I've been looking at the Q HB 1/5 barrel, which I know will be good for stabilizing subs, but I can't seem to find an answer to the question of "is a 1/5 just as good as a 1/7 for supers, with the added benefit of being better for subs or would I be sacrificing performance of my primary use case (supers) by choosing that fast of a twist rate (idk, does a faster twist rate = lower muzzle velocity, for instance?)?”

I've read a whole range of answers, from 1/5 is fine for supers (you can't over stabilize a bullet), to you'll have a lower velocity (if so, how much?), to things like some supers will spin themselves apart if they rotate to fast.

Would I be better off with a 7” - 1/7 for my needs?

Hoping some of you experts and bright minds can teach me something new! Much appreciated!
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dellet
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Re: 1/5 Twist and Supers

Post by dellet »

2sBlind wrote: Fri Oct 30, 2020 12:27 am Hi All,

For my next build, I'm looking to build a ~7 inch, mostly super/occasional sub suppressed build. I know this isn't quite the norm, but it's what I'm interested in hah.

I've been looking at the Q HB 1/5 barrel, which I know will be good for stabilizing subs, but I can't seem to find an answer to the question of "is a 1/5 just as good as a 1/7 for supers, with the added benefit of being better for subs or would I be sacrificing performance of my primary use case (supers) by choosing that fast of a twist rate (idk, does a faster twist rate = lower muzzle velocity, for instance?)?”

I've read a whole range of answers, from 1/5 is fine for supers (you can't over stabilize a bullet), to you'll have a lower velocity (if so, how much?), to things like some supers will spin themselves apart if they rotate to fast.

Would I be better off with a 7” - 1/7 for my needs?

Hoping some of you experts and bright minds can teach me something new! Much appreciated!
Every question you asked has both yes and no answers.

What exact bullet are you asking about?
What speed will you be shooting it?
What powder will you be using?
What will be your rate of fire?

Faster twist rates lowering velocity is a true, lie. The bullet travels measurably farther and traveling at the same velocity will take longer to exit the muzzle. To prove this you will need loads with an ES of about .00005 fps, and a chronograph that will measure inches per Mili-second. I look forward to the video.

For the most part a 7" barrel will limit the velocity enough that most bullets will work. You will still be capable of 2000 fps hand loads and that will spin a bullet over 280,000 rpms. for some bullets that is too much, others are good to over 300,000. 2200 fps is over 315,000 rpm.

With faster powders, starting speed and pressure combined with a fast twist, can cause bullets to be damaged to the point of coming apart or starting to in the barrel and fracturing as they exit the muzzle. I have done that in a 1/5 twist as well as a 1/10, but it is certainly easier with a faster twist.

Bullets that survive a slow rate of fire, may not hold together at a fast rate of fire due to heat in the barrel.

With factory ammo it will be trial and error based on velocity and bullet choice. With hand loads you can tailor velocity to the bullet.

If you shoot solids like CNC turned copper or brass almost all those problems go away, but I have blown a few of those up also.
300 Blackout, not just for sub-sonics.
cdl
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Re: 1/5 Twist and Supers

Post by cdl »

The Sig MCX's are 1:5 and mine shoots great.

RPM = Velocity (fps) x 720 / twist
Example: 2000 x 720 / 5 = 288,000

Some say Hornady says keep it under 290,000 RPM. I don't say that, but I keep an eye on the fast ones. Cast lead is probably less than half that.
Mas Casa
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Re: 1/5 Twist and Supers

Post by Mas Casa »

To echo what cdl said, I had a Sig MCX Virtus pistol with a 1:5" twist for a brief period of time in early 2019. I contacted Sig before shooting it to see what grain bullets would stabilize. The rep said 150s to 208s. For supers, I tried Winchester 150gr Power Points (with the dark grey tips). I sighted in at 50 yards and then shot a three shot group with all the impacts touching. Sorry I no longer have the target to provide a photo.
ReadyAimDuck
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Re: 1/5 Twist and Supers

Post by ReadyAimDuck »

If you go with the 1:5 twist, It sounds as though some very popular loads for this cartridge may be excluded from what you can/should be using based on what others said. What comes to mind are the very popular for hunting and defense 110 grain bullets. If I am doing the math right, these would be spun up over 330,000 RPM.

I have no knowledge on this subject, however. I am simply taking what has been mentioned above and doing the math on 110 grain bullets at 2300 fps. This may be worth considering if in fact these bullets cannot handle that spin, and you have interest in shooting bullets at that weight.
pj-schmidt
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Re: 1/5 Twist and Supers

Post by pj-schmidt »

ReadyAimDuck wrote: Fri Jan 01, 2021 5:06 pm If you go with the 1:5 twist, It sounds as though some very popular loads for this cartridge may be excluded from what you can/should be using based on what others said. What comes to mind are the very popular for hunting and defense 110 grain bullets. If I am doing the math right, these would be spun up over 330,000 RPM.

I have no knowledge on this subject, however. I am simply taking what has been mentioned above and doing the math on 110 grain bullets at 2300 fps. This may be worth considering if in fact these bullets cannot handle that spin, and you have interest in shooting bullets at that weight.
I'm not aware of any popular loads for 110gr bullets that will get to 2300fps in a 7" barrel. Although caution is always warranted, it is very unlikely standard bullets on top of standard loads (or factory ammo) with have issues in a short barrels even at a 1:5 twist.

Now a 16" barrel with a 1:5 twist would cause me some worry.
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dellet
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Re: 1/5 Twist and Supers

Post by dellet »

8" 1/5 twist, Nosler 110 Varmageddon, 2150 fps. Roughly 310,000 rpm on the bullet.

Hot barrel, near the end of the first magazine on a walk through carbine course. My wife was shooting and I could see rounds basically flying everywhere, By the time I got her stopped the can was toast.

Image

When I called Nosler, they would not give me an upper limit for RPM. I then explained the above and the answers was "that's probably too fast, too hot or both.
300 Blackout, not just for sub-sonics.
cdl
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Re: 1/5 Twist and Supers

Post by cdl »

You remind me of my mortality. With a deep breath, I feel for your loss and sincerely wish you the best. 

Reminds me of a story. I was in a client's home that had just been destroyed by a tornado. There was a 2x4 completely penetrating the mattress of his bed. Luckily no one was hurt, but he looked at me with a straight face and said; "Good thing it was my wife's side..."
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dellet
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Re: 1/5 Twist and Supers

Post by dellet »

cdl wrote: Fri Jan 01, 2021 9:10 pm You remind me of my mortality. With a deep breath, I feel for your loss and sincerely wish you the best. 

Reminds me of a story. I was in a client's home that had just been destroyed by a tornado. There was a 2x4 completely penetrating the mattress of his bed. Luckily no one was hurt, but he looked at me with a straight face and said; "Good thing it was my wife's side..."
Hey, someone has to be the bad example. It’s sobering to make mistakes like that.

That was probably 2-3 years ago and all my wife’s fault :mrgreen:

I probably have somewhere around 5-700 rounds of the same load shot with no problems. The difference that day was my wife was shooting a course. So instead of 30-40 rounds over a couple hours, she probably shot almost a full magazine slow fire, then Within 15-20 minutes started on the course.

To get the same spin in a 1/6 you need 2600 fps.
300 Blackout, not just for sub-sonics.
ReadyAimDuck
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Re: 1/5 Twist and Supers

Post by ReadyAimDuck »

pj-schmidt wrote: Fri Jan 01, 2021 7:38 pm I'm not aware of any popular loads for 110gr bullets that will get to 2300fps in a 7" barrel.
I totally overlooked the fact that this is with regard to a 7" barrel, and gave you a number based on a 16" barrel. You are correct. My mistake.
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