6.5 twist rate for 139-142gr projos

[benwitt11]

I recently bought a used .264 Win Mag with a Hart 1x9" twist 26" barrel. With this be able stabilize a 140ish gr pill at yardage? Or am I limited to 120 and under? Sierra lists a 1 x 9" twist for this caliber, buy currently in vogue 6.5 cal guns are listed frequently with a 1 x 8". The round count is quite low on the barrel, I rather not incure the expense to change it, but the ballistic are quite a bit better on the larger pills.

Thank you in advance. I appreciate the advice.

 

[montyb]

Re: 6.5 twist rate for 139-142gr projos

my 1-9" Sendero would not stabilize the 142 SMK, but shot the 140s fine.

so, 140s are a go, but the long 142 may or may not work for you.

 

[BOLTRIPPER]

Re: 6.5 twist rate for 139-142gr projos

my thinking is that the overbore stuff like the 6,5x284 and long case magnums need a slower twist....

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Thanks for the info. Now to read up on SMK's vs Berger's. Cheers.

 

[wadebrown]

Re: 6.5 twist rate for 139-142gr projos

I shoot a 1-8" twist with those weights and it is no problem to stabilize them.

 

[dmgreene]

Re: 6.5 twist rate for 139-142gr projos

There's been a lot of talk about the button rifled barrels not being the exact twist that they are supposed to be. If it is a true 9 twist you will be on the border line with the 142's but it should stabilize the 140's. You won't know till you try.

 

[TEAMSENDIT]

Re: 6.5 twist rate for 139-142gr projos

most 6.5x284 shooters use a 8.5twist for the 140 class bullets, and the 264 mag is even a tad hotter than the 284 so it will be close. if you are concerned try the berger 130vld's they will for sure stabilize in your rifle and they will be smokin out of the 264 mag.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

The 130 Bergers look to be the place to start. If the published bc is close to accurate, I'm sure it will out shoot me pretty easily. Thanks for the suggestions.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Just got back from a somewhat disappointing day at the range. The rifle will not stabilize 140's. They key hole even at 100. I'll work up some of 130 Bergers when they arrive, but I have a feeling I'll have to go down to the 123 Scenars. Kind of sucks.

 

[HotIce]

Re: 6.5 twist rate for 139-142gr projos

I use 1:8" in my 260Rem with 139gr Scenar. Works great!
I will use 1:8" even in my new 6.5mm CM, since I'm planning to use the same bullets.
Get 1:8", it leaves you more possibilities open.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

I will definately go 1-8 when I rebarrel, but would like to run the one I have for a while as it's only got 200 or so rounds down it. It is a 1-9 though, and therein lies the problem.

The gun is a .264 Win Mag, so it is unfortunate not to be able to take advantage f the heavier bullets in this caliber. When rebarreled I'll be switching calibers to 6.5x55 Swede with a 1-8 twist.

 

[Rich Emmons]

Re: 6.5 twist rate for 139-142gr projos

I've had a 1-9 savage barrel shoot excellent with 142's. I think 1-9 should work especially with magnum velocities.

Questions:
Have you tried to measure actual rifle twist yourself?
Have you chrono'd your load?

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

No, and yes.

The gun was sold to me as a 1-9 by a guy I've know for many years and trust. I will measure it for my own sanity.

Loads were factory Winchester and Remington of which I know are not the best, but surprised me with their performance. 140 Spitzers at 3050-3090 over 25 rounds with both brands. Remarkably consistent I thought. These came with the gun, so I've been shooting those until my reloading components arrive.

Maybe using a more modern BT design makes the difference. The Berger 130's should be here today and I hope to have some loads ready by the weekend. Cases are all prepped and powder is waiting.

 

[BLAWTON]

Re: 6.5 twist rate for 139-142gr projos

There should not be a need for anything faster then 8.5 unless you are using a really slow case. The 264 should push the 140 or 142's with a 1:9 but its something you will have to try. Its just to close to tell.

 

[999yards]

Re: 6.5 twist rate for 139-142gr projos

It will be fine especially with a 264Win Mag case.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Bear with me, newbie question then. If 260's and 6.5x47L rifles are commonly running 2700-2800 fps in 1-8, why would this round be alright at 3000-3100 fps with a 1-9? Does is come down to bearing surface of longer ogive bullets vs the higher fps?

 

[BLAWTON]

Re: 6.5 twist rate for 139-142gr projos

Ok speed has a effect on stability. It doesnt mean as much as twist but for example a whisper is going to take alot more twist cause the bullets is going so slow. A extra 200-300 fps is going to equal about a .5" of extra twist but it might not stay stabile when it gets close to trans-sonic.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Thanks for that. Is there any good reading that you can suggest about bullet weight and speed and relation to twist rates? I'm really just trying to develop an understanding on how this works, and searching for something that complex is a nightmare. I'm not asking you to spell it out, but is there a book or two that can help me learn about this? Reloading manuals are just that, and delving deeper into mechanics of shooting beyond load recipes is something I clearly need to learn more about.

Thank you for the advice, I sincerely appreciate it. There are few people in this area that shoot like this, or perhaps I just have not found them yet. My friend who is guiding me through this is capable of teaching me how to reload, but there is a lot other than just reloading mechanics to learn. This is one of the only sites I've found online that I trust for accurate information.

 

[BLAWTON]

Re: 6.5 twist rate for 139-142gr projos

Buy Mr. litz's book


http://www.appliedballisticsllc.com/

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Done. Thanks.

 

[benwitt11]

Re: 6.5 twist rate for 139-142gr projos

Even after a bit of light reading of the articles on his site, it's very clear why the bullets did not stabilize. Thanks for heading me in the right direction. I can't wait to get the book.

 

[BLAWTON]

Re: 6.5 twist rate for 139-142gr projos

No problem.