Rate of twist vs. bullet wt

[spruilldog]

I bought myself a remington 700 sps varmit in 243 for Christmas. Merry Christmas to me:)! I finally shot it today with 100Grain core-loct express. Did pretty well but did not group as well as I hoped. 1.6-1.7 inches. I know I need to try some other ammo but I was wondering, since it is the "varmit" model is the barrel twist, 9 1/8", set up for the smaller grain bullets? How does twist rate relate to opitimal bullet grain generally speaking and why? I plan to use it on coyotes, bobcats, and whatever else I think might need a bullet, but would like to use it as my bean field deer gun as well. If I have to go down the 80-90 grain bullet is it still adequate for deer out to 300yds? I know bullet construction must be appropriate.

[Brian Pfleuger]

Look here for some mighty fine info on this (and many other things):

http://www.chuckhawks.com/rifle_barrel.htm

[Swampy1]

dog,

Most factory .243 Win barrels have a 1-10" twist. This is good for any non-VLD bullet up to about 100 to 105 grains.

Any 105 VLD will most likely need a 1-9" twist... available on some factory barrels I've heard.

The 115 VLD's will need a 1-8" twist. Custom barrels only here I think.

Best,
Swampy

Garands forever

[LateNightFlight]

Spruilldog; I book marked a page recently that might help. http://www.ammoland.com/archives/455-Best-Bullet-Weight-For-Your-Gun.html

They didn't specifically get up to a 1:9 twist, but it's reasonable to extrapolate a slightly higher bullet weight in the progression.

.243 / 6mm
1:15 up to 70 grains
1:14 70 - 75 grains
1:13 75 – 85 grains
1:12 85 – 100 grains
1:10 100 grains or more

Suffice to say, I think Swampy's got the matter in hand. :)

I'm a little surprised Remington went with a faster twist rate/heavier bullet for a varmint model. My SPS Varmint in .223 has a slow twist for the lightish bullets. None-the-less, the heavier bullets out of your .243 will put coyotes down fair and square and you're all set for deer. I'm thinking you have all the practical versatility anyone could ask for.

The trick is finding factory .243 ammo at an in-between weight of the 100 & 115 grain loads. (Out of curiosity, and because I have a .243 as well, I just looked around at Midway and couldn't find anything.) But off hand, I'd venture a guess there's a 100 grain load out there that will work for you, and another guess that Remington had 100 grains in mind for that rifle, even if it doesn't match up perfectly with a chart in front of us.

That gun should shoot at least 3/4" groups out of the box, and I think you'll get there when you find the right ammo. And these days I'll say, "Start cheap." I was recently surprised by the great groups I got from a 7mm with Winchester Super-X Ammo, when I only intended to get a new scope on paper and headed towards zero.

Pretty nice present. Merry Christmas, indeed! :D

[MTMilitiaman]

It doesn't really surprise me Remington went with the faster twist rate. I wouldn't expect them to get bit in the butt twice by the same mistake. When they came out with their 6mm Remington, they made the mistake of offering it with a slower twist rate to accommodate lighter varmint bullets, and as a result, the 6mm never achieved the popularity of its chief competitor, the .243 Winchester.

Don't give up on the rifle after one range outing with a single type of ammunition. Let the barrel get broken in before you make any judgment calls, and for sure try it with a few different ammunition types. Different ammunition, even with the same bullet weight, can shoot radically different from the same rifle.

Faster twist rates are necessary for heavier bullets because heavier bullets in the same caliber are usually longer, and longer bullets have to spin faster to be stable.

[Scorch]

Rifling twist needed to stabilize a given bullet depends on the bullet's length, not its weight. Sounds like a minor distinction, but it really can make a difference.

[Swampy1]

Rifling twist needed to stabilize a given bullet depends on the bullet's length, not its weight. Sounds like a minor distinction, but it really can make a difference.


True.... which is why I make distinctions above between VLD and non-VLD styles bullets...... the secant ogive VLD's are longer than conventional short, tangeant ogive designs.

Best to all,
Swampy

Garands forever

[darkgael]

Here's another link. It's to an online calculator that uses the Greenhill Formula for calculating proper twist rate for a particular bullet.
http://www.z-hat.com/twistrate.htm
Pete

[spruilldog]

I am far from giving up, just need to find the right bullet. I might try the Fusions next because I have had good luck with them in the past in my other guns. I think they are in 95 grains. I was hoping this gun would like to eat cheaper bullets but the fusions are at least cheaper than some. Mainly thinking about it just got me curious about how twist rate and bullet wt(or length) are related. I do find it interesting that Remington appears to have had heavier bullets in mind in a "varmint" gun but I have read about the fate of the 6mm in the past. My groups could also have been better possibly with a better set up. I was itching to put it on paper so went out during lunch from work. Target was proped up on a sand pile leaning back some and I was shooting off of sandbags that I set on top of the cab of my truck while I sat on my toolbox. Not the best but got me started anyway. I'll report back after I get to a real bench and maybe try some new ammo. If I have to handload I'll start doing that. My goal is to have a shooter for under $1,100. This x-mark trigger really breaks clean for a factory trigger. Pulls about 6-7 lbs but I plan to remeday that soon as well.

[spruilldog]

What is a VLD bullet? :D

[Swampy1]

What is a VLD bullet?

Very
Low
Drag

VLD's are typified by a long secant ogive and are most usually heavy for the caliber giving a high BC projectile.

Mostly used for long range work where the fastest muzzle to impact time is king...... i.e. resistance to wind and acheiving small groups and high X-count.

Very common usages are 600-1k BR, LR Highpower (800-900-1k), US Palma (1k), F-Class (600-1k), and the 600 yard stage of the NM Course.

See my tagline for more....

Best regards,
Swampy

Garands forever

2007 NRA Missouri State 600 yard Service Rifle Champion
Score 774-29X.... with an M1 Garand