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2Dogs
06-15-2009, 07:26 PM
As some of you know, Iv posted some questions here before. I am puzzled about these rate of twist on some of the rimfires. 16 twist has been the norm for rimfire but , there must be some advantage to 17 and 17 1/2. would somone please enlighten me on this?

tim
06-15-2009, 08:09 PM
The thinking is that they are less affected by wind.

2Dogs
06-16-2009, 05:01 PM
Thank You Tim. Now...I may be thinking wrong, but, wouldnt you have to shoot a little faster FPS with a 17 to 17 1/2 twist to insure bullet stability?

Bill B
06-16-2009, 05:54 PM
Here's the deal with the slow twists. If you live up in the North, avoid the slower twists, as the bullets tend to be unstable in the cold (yaw). If you live in the warmer South, they should perform very well for you. You shouldn't worry so much about the bullet speed, those numbers marked on the boxes don't mean much really. I've had rifles with 16" 16.5" 17" and 17.5" twists, I prefer the 16" or 16.5" twist, but I live up North.

Rich In Kansas
06-16-2009, 05:57 PM
No just have warmer temps. This is not true for all, always exceptions, but 16 twist shoots pretty good in all conditions with a variety of standard velocity ammo. 17 twist shoots better in the wind. But 17 sometimes has stability problems in colder weather (35 degrees for mine might as well throw rocks). I got 17 twist because here in Kansas we have lots of heat and wind. But our early matches in April I might as well not show up. Perhaps a 17 twist might shoot better in cold weather with higher velocity ammo such as biathlon. I don't think there are any concrete rules when it comes to rimfire though. Rich

tim
06-16-2009, 06:53 PM
Thank You Tim. Now...I may be thinking wrong, but, wouldnt you have to shoot a little faster FPS with a 17 to 17 1/2 twist to insure bullet stability?

No. It's not slow twists that have caused bullet instability as much as rifling configuration.

pacecil
06-16-2009, 08:40 PM
No. It's not slow twists that have caused bullet instability as much as rifling configuration.

Can you expand on this a little bit?

tim
06-16-2009, 08:59 PM
The short answer is that certain configurations have tended to have a few more out of round bores than others, and frankly a tenth or two out probably is more a culprit than twist rate.

Bill B
06-17-2009, 04:23 AM
Just wondering. If the culprit is an out of round bore, why would such a barrel shoot great on hot days and yaw like a crazy on the cool days? I would think an out of round bore would just plain shoot poorly all the time. I had a 17.5 twist barrel that shot great in the couple hot months that we have here and was unstable when the temps got below 50. I would think that if a barrel maker is making out of round barrels, it would be so for all the different twist rates that they make. My experience was (and I think it was the same for others), same barrel maker, faster twist, problem solved.

tim
06-17-2009, 09:58 PM
Different buttons, first of all. 17 1/2-18 twist is about the edge of stability to begin with. Why do YOU think the guys with the same twist in a 6-groover did'nt suffer much in the way of instability? Faster ammo reduces the effect somewhat.

Bill B
06-18-2009, 04:35 AM
>>>"17 1/2-18 twist is about the edge of stability to begin with".<<<

Sooo, you're saying it is the twist rate that caused the instabililty. We have reached agreement. I guess. :confused:

>>"Why do YOU think the guys with the same twist in a 6-groover did'nt suffer much in the was of instability? Faster ammo reduces the effect somewhat."<<

The 17.5" twist barrel that I had was the 6 groove so, no, I don't think that.

Bill B
06-18-2009, 10:10 AM
Ok, in the interest of accuracy, Tim, we are sorta both right and wrong. Thanks to posting here, I received a phone call and have learned "The rest of the story".

The deal with the bullet instability and twist rate, is that it was the combination of a real tight barrel choke and the slow twist that was the problem. It resulted in the bullet elongating such that a slow twist could not stabilize the bullet. There have been slow twist barrels that shot well in the cold north and could stabilze a bullet, but that weren't elongated by too much choke in a the end of the barrel. I hear that the problem has been corrected and if one wants a slower twist barrel, you should be OK. There are now some 17" twist barrels shooting very well up here in the cold.

See, sometimes this forum can be useful. :)

pacecil
06-18-2009, 10:26 AM
resulted in the bullet elongating

I take this to mean the decrease in diameter was added to the length. Most "chokes" might add about .0005 to bullet length. Is this roughly the number we should be looking at as having an effect on stability?

Bill B
06-18-2009, 02:33 PM
resulted in the bullet elongating

I take this to mean the decrease in diameter was added to the length. Most "chokes" might add about .0005 to bullet length. Is this roughly the number we should be looking at as having an effect on stability?

Yes, that's what I mean. I don't know the answer to your question, as I didn't get into those specifics in my conversation. My understanding is that the reason for the problem was discovered to be a combination of slow twist and a tight barrel/choke and the new slow twist barrels shouldn't have the same problem, as they are not as tight. The best bet, if one is considering buying a barrel, is to talk to the barrel maker and gunsmith and discuss the matter.

pickles
06-18-2009, 07:40 PM
O GREAT ONE I DONT BOW TO YOU!

And no, I will not shut up
?


Howard E. Newman Jr.

AKA pickles
Semper fi

tim
06-18-2009, 07:50 PM
O GREAT ONE I DONT BOW TO YOU!

And no, I will not shut up
?


Howard E. Newman Jr.

AKA pickles
Semper fi

The nice doctor give you some new pills there Howie? Was there a point there, English translation,clue?

--rock
06-18-2009, 08:10 PM
I have a 17 3/4 twist Benchmark 2 groove reverse taper barrel on my Anschutz 2013. When I shoot EPS ammo (Eley Match EPS, Club EPS or Biathalon--all EPS bullets) I get poor result until the temperature gets into the 70's. On the other hand when I shoot Eley SA (round nose), the gun shoots much better than when I shoot EPS--even in cold or moderate weather. A friend slugged the barrel, and its it extremely tight from the chamber to the muzzle--much tighter than Lilja or Anschutz barrels he has slugged. There is very little choke at the muzzle, but since the entire barrel is super tight, that probably doesn't make a difference. I also have a 16 twist Benchmark 2 goove reverse taper barrel for my Anschutz 2013. It also has a very tight bore with little choke and shoots great. But back to my main point, why would round nose bullets shoot better than EPS bullets in a slow twist barrel?

crappie
06-18-2009, 10:47 PM
I thought i saw somewhere where it was said that slight changes n twist like and inch or 2 can have as little effect as normal variation in bore diameter. Anyways, i have always wanted to try a 14 twist barrel. It would be an interesting test/article to chamber a few barrels with the same chamber but diff twists and then run them through the ringer.

Fred J
06-19-2009, 08:48 AM
Several years back, Remington was producing rifles with 14 twist. Weren't to accurate when it came to BR. Dead squirrels and rabbits couldn't tell the difference.