I have a 1x13" in my Palma gun as well, mostly the result of following the herd mentality. But having played with faster twists and "overstabilizing" bullets, it has since ceased being of any concern to me. Stable is good. More stable isn't a problem, and has some potential advantages . . . not an issue.
11" twist and the 308 Win
- Thread starter cowboybart
- Start date
I have a 1x13" in my Palma gun as well, mostly the result of following the herd mentality. But having played with faster twists and "overstabilizing" bullets, it has since ceased being of any concern to me. Stable is good. More stable isn't a problem, and has some potential advantages . . . not an issue.
It is actually not so much about bullet weight but bullet length. A 200 grain cup and core round nose can stabilize in a slower twist rate than a 180 grain solid copper of VLD design
One thing to keep in mind is the discipline you are shooting/competing when it comes to barrel twist. F-class at LR 1000 yd competition the faster twist rates will add to your spin drift and also have an impact to your aero-dynamic jump. This can come into play on precision, X count, or even holding the 10 ring. Not as big a factor at mid range. It's all relative as aero-dynamic jump increases with distance, wind speed and deflection, so if the shooter isn't a good wind reader it's all a mute point anyway. I would assume the same would apply to 1000 yd benchers which also need the utmost precision. I shoot F-class TR and personally try and match the twist rate to the optimal bullet weight to squeeze out all I can from all variables impacting accuracy. I am somewhat anal and OCD when it comes to such things though 
Shilen twist rate .308
- 7" * for heavy VLD bullets and/or subsonic ammo.
- 8" for bullets heavier than 220 gr.
- 8" Ratchet rifled 4 groove
- 10" for bullets up to 220 gr.
- 10" * Ratchet rifled 4 groove
- 12" for bullets up to 170 gr.
- 13" * Ratchet rifled 4 groove
- 14" * for bullets up to 168gr.
- 15" * for bullets up to 150 gr.
- 17" * for bullets up to 125 gr.
Interesting posts from folks that have been there and done that. My .30 caliber rifles have 1-10 but for my .308's I would like the 1-12's more. I like to play around with stubby 125's and 130's shooting them at rodents and steel targets at 300 yards where a high degree of ballistic finesse does not matter much and I can get over 3,000 fps.
I measure the length of all my bullets and run the Miller twist program and now I am beginning to play around with the Hornady 4 deg. freedom ballistic program that shows stuff like spin drift. The longest .30 bullet I have in my collection is the 180 grain Barnes triple shock HPBT and 208 H Amax less plastic tip and the shortest the 125 grain Speer TNT HPFB. Considering my limited expectations the 125 TNT's work well, shot from .308's and .30-06 with 1-10 twists up to 300 yards.
I measure the length of all my bullets and run the Miller twist program and now I am beginning to play around with the Hornady 4 deg. freedom ballistic program that shows stuff like spin drift. The longest .30 bullet I have in my collection is the 180 grain Barnes triple shock HPBT and 208 H Amax less plastic tip and the shortest the 125 grain Speer TNT HPFB. Considering my limited expectations the 125 TNT's work well, shot from .308's and .30-06 with 1-10 twists up to 300 yards.
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One thing to keep in mind is the discipline you are shooting/competing when it comes to barrel twist. F-class at LR 1000 yd competition the faster twist rates will add to your spin drift and also have an impact to your aero-dynamic jump. This can come into play on precision, X count, or even holding the 10 ring. Not as big a factor at mid range. It's all relative as aero-dynamic jump increases with distance, wind speed and deflection, so if the shooter isn't a good wind reader it's all a mute point anyway. I would assume the same would apply to 1000 yd benchers which also need the utmost precision. I shoot F-class TR and personally try and match the twist rate to the optimal bullet weight to squeeze out all I can from all variables impacting accuracy. I am somewhat anal and OCD when it comes to such things though
Spindrift is a non-issue..... shooting 1000 yards it is always exactly the same every time no matter what direction you shoot..... from the first shot to the last. The only thing will change Spindrift is if you chang barrels or bullets during your string of Fire
I believe you are taking my point out of context a bit or maybe I wasn't clear enough with my point so I'll try again. I get that the spin drift is the same from shot to shot at 1K from the same barrel. If you shoot the same weight projectile from a 13 twist and a 10 twist at 1K, the 10 twist will have more drift! Why I finished my post with "I shoot F-class TR and personally try and match the twist rate to the optimal bullet weight to squeeze out all I can from all variables impacting accuracy"
Gyroscopic Drift Formula from Bryan Litz - Applied Ballistics For Long Range Shooting - 2009 -
(Drift = 1.25 (Sg + 1.2) x (TOF^1.83)
So it's mostly affected by bullet sectional density, twist rate, and air density. As for the aerodynamic jump, a faster spinning projectile will have a more exaggerated impact from the same wind value than a slower spinning projectile at 1K. Hopefully that clears up my point. Maybe we're saying similar things different ways
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My point is what difference does it make weather your drift is 2 inches or 2 feet. You get your dope from the first shot the BBL ever shoots at 1K and it NEVER CHANGES till that bbl dies. THAT is your 1000 yard base zero, and all you ever need to adjust for is environmental changes and coriolis. And, truthfully, I have NEVER met a shooter yet who has his "coriolis dope" for a 1000 yard match.
Tod
22 inches
Agreed
Neither have I. I never mentioned coriolis.....I mentioned aerodynamic jump! Please read my post carefully before you try to discredit my comments! I tried to give you an out and not highjack the thread but you continue to push. I understand your point but you're obviously missing mine. Let's agree to disagree
22 inches
Agreed
I never mentioned coriolis.....I mentioned aerodynamic jump!
True, but you FIRST mentioned spin drift....and then added Brian's spin drift formula.
Simple fact...spin drift is a non issue in a 1 k BR/F-class match.
Tod
OK......I'll do now what I should have initially when you misinterpreted my FIRST post: I'll break down that FIRST post and the intent.
Now let's take my last comment from my FIRST post:
There are many variables that impact accuracy. Matching the optimum twist rate to the intended bullet is one. There are several bullet stability calculators we have at our disposal to do so. I shoot F-Class. We have 30 minutes to shoot 2 sighters and 20 rounds for record at 1000 yds. The top shooters often use almost every minute of that time as we must wait for the target to get pulled, scored, and raised. This impacts the number of shots we can get off in the same condition often times only 1 or 2. If the shooter dose not understand aerodynamic jump he/she will have vertical problems at distance and will not be competing at the top on windy days. This separates the "spotter chasers" from the wind readers. I do not shoot Benchrest but understand it is common place to shoot sighters in different conditions and then shoot record shots at a very fast pace in the same condition? I get the sense you understand all the above so maybe it's the semantics twist, spin drift, AJ etc....and the combination in which I used them that caused the discourse. Where I agree with you is once the barrel twist is chosen it's a constant with spin drift but making that choice has a definite impact on target when including aerodynamic jump (which again was the intent to my FIRST post) So technically if you choose a faster twist rate than the projectile needs to stabilize and faster spinning bullets have MORE spin drift and faster spinning bullets have a more pronounced effect from aerodynamic jump.....spin drift does matter in certain competitive disciplines if you want to be at the top. Every near or breaking the line matters on target!
I will work harder on my command of scripting the english language for future post. Hopefully at least someone can learn something from our back and forth which is what this forum is for. Sorry to "all" for highjacking the thread.
The OP wanted to know if the heavies will shoot in a 11 twist. My actual FIRST post in this thread I told him they would as I did it last year with a 11.25 twist in F class.
Please read this in it's entirety which includes aerodynamic jump! To address one with out the other is a misinterpretation of my intended comment. (This is where our indifference start) Your comment has been that spin drift is a non issue. Standing on its own I agree as it's easy to dial for, however when you add the factor of Aerodynamic Jump from wind at distance it does matter and is a significant variable in LR F class when selecting a barrel twist if you want to compete at the top!!! A 13 twist barrel will have less spin drift than a 10 twist......FACT! I did not have that in my first post but I did in my second attempting to explain your misunderstanding of my first. A faster spinning projectile will have a more dramatic impact from the same wind value at distance......FACT!!! This is where aerodynamic jump comes in. Now for aerodynamic jump. Here is an explanation for you....(not mine but you can find something similar in any book on ballistics) "Wind also causes aerodynamic jump which is the vertical component of cross wind deflection caused by lateral (wind) impulses activated during free flight of a projectile or at or very near the muzzle leading to dynamic imbalance.[54] The amount of aerodynamic jump is dependent on cross wind speed and the gyroscopic stability of the bullet" OK so another way of putting "gyroscopic stability" of the projectile is matching the optimum twist rate for the barrel to the bullet choice! Again I attempted to explain on my second post and added Brian's spin drift formula.
Now let's take my last comment from my FIRST post:
I shoot F-class TR and personally try and match the twist rate to the optimal bullet weight to squeeze out all I can from all variables impacting accuracy. I am somewhat anal and OCD when it comes to such things though
There are many variables that impact accuracy. Matching the optimum twist rate to the intended bullet is one. There are several bullet stability calculators we have at our disposal to do so. I shoot F-Class. We have 30 minutes to shoot 2 sighters and 20 rounds for record at 1000 yds. The top shooters often use almost every minute of that time as we must wait for the target to get pulled, scored, and raised. This impacts the number of shots we can get off in the same condition often times only 1 or 2. If the shooter dose not understand aerodynamic jump he/she will have vertical problems at distance and will not be competing at the top on windy days. This separates the "spotter chasers" from the wind readers. I do not shoot Benchrest but understand it is common place to shoot sighters in different conditions and then shoot record shots at a very fast pace in the same condition? I get the sense you understand all the above so maybe it's the semantics twist, spin drift, AJ etc....and the combination in which I used them that caused the discourse. Where I agree with you is once the barrel twist is chosen it's a constant with spin drift but making that choice has a definite impact on target when including aerodynamic jump (which again was the intent to my FIRST post) So technically if you choose a faster twist rate than the projectile needs to stabilize and faster spinning bullets have MORE spin drift and faster spinning bullets have a more pronounced effect from aerodynamic jump.....spin drift does matter in certain competitive disciplines if you want to be at the top. Every near or breaking the line matters on target!
I will work harder on my command of scripting the english language for future post. Hopefully at least someone can learn something from our back and forth which is what this forum is for. Sorry to "all" for highjacking the thread.
The OP wanted to know if the heavies will shoot in a 11 twist. My actual FIRST post in this thread I told him they would as I did it last year with a 11.25 twist in F class.
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No kidding with 1/12, I have a 1/12 in a Shilen and they suggest and show only going to a 170gr
Ned Ludd
Silver $$ Contributor
A 10-twist will handle bullets up to the ~215 gr range just fine. How much heavier do you wish to go? Berger's twist rate calculator will provide you with the appropriate twist rate info if you know the dimensions of the bullet(s) of interest: https://bergerbullets.com/twist-rate-calculator/
After that, all you really need to do is obtain an appropriate barrel blank, decide how you want it chambered (i.e. buy a reamer with the appropriate freebore, or load some dummy rounds with the bullet of interest for the smith to work with) and find a competent gunsmith to do the work. If you don't want to be bothered with finding the barrel yourself, the smith will usually take care of that for you.
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