243 Barrel Twist & Bullets [Archive] - Varmints Den

: 243 Barrel Twist & Bullets


Anthony
11-13-2010, 09:56 PM
I recently picked up a single shot 243. It has a 1-10 twist and I would like to get some decent accuracy. Any suggestions for starting points of bullet weights and types? I would like to shoot both deer and varmint (not necessarily with the same bullet, of course). Thanks...

George Foster
11-14-2010, 05:32 AM
75gr thru 105gr bullets should work fine for you.

Joe O
11-14-2010, 06:46 AM
Plenty of good game bullets available in the 80-100 gr range.Doubt the 1:10 twist will stabilize the 105s,however,it depends on length of bearing surface.I wouldn't bother to consider any bullet over 100gr with that twist,given the selection of great game bullets,like the Nosler 95gr partition,and others.All varmit weight bullets should work well.Have fun working up your loads.

pintopete
11-14-2010, 08:41 AM
I just happened to be reading Ken Waters' Pet Loads book. I was reading about the 6mm Rem (244 Rem). It makes many comparisons between the 6mm and the 243 Win and it is obvious that he liked the 243 Win. It also talks a great deal about the rate of twist and thength of bullets. Short flat base bullets, even in the same weight, seem to stabilize more easily than long pointy boat tail bullets. One example is the 100gr Round Nose bullets seeming to be stable in 1:12 twist. In the 244 with 1:12, I would stick with 90's myself which is the weight originally offered by Remington. For you, I can tell you for sure that the Hornady 95 SST's stabilize in a friends Rem 700 Sporter. According to Remington's current specs they have 9 1/8 twist. The same rifle also shoots the Hornady 100 round noses and Speer 75 gr HP's (huge hollow points) well. I used H4350 in both the .243 Win loads. My old .244 shoots the 60gr Sierra HP's extremely well with H4895. If you have access to Ken's book, you would enjoy the 243 Win and 244/6mm Rem articles. The tech stuff and twist rate information is universal. In your rifle, I don't think you will have any trouble with most bullets 105 or less. My suggestion would be to stay away from the long boat tails. Many say that flat base bullets are a bit easier to load and obtain good results from. Boat tails apparently only offer a benefit over 225+ yards. Good luck, Peter.

jonmdavis62
11-14-2010, 12:40 PM
One gun one load....38.5 gr. 4895 85 gr. Sierra H.P.B.T.

C Miller
11-14-2010, 01:37 PM
All barrels are different, having said that I have a Mauser built with a Douglas 1-10 barrel in 243. It won't shoot anything well over 95grs. I've tried every short 100gr bullet I can find and accuracy borders on bad to miserable and at distance I get an oval hole. Plenty of good deer bullets in the 87-95gr range though.

Anthony
11-14-2010, 02:36 PM
What is a realistic range far this cartage? 1000 yrds can be done with the .308. I'll be the first to say I'm not Carlos Hathcock. Most folks say 400 at most. Is 500 to 700 realistic? Or is it losing all lethal energy at the 5 and 7 range? And if I'm wanting to shoot this kind of distance don't I want to use a boat tail?

Thanks

Jim A
11-14-2010, 08:07 PM
500 to 700 might be reasonable from a benchrest setup but probably not for a hunting situation. I have shot 75 V-maxs out to 300 off of a bipod while hunting. Hold over is at best a guesstimate much beyond that with my gun/scope combo. If you check .243 ballistic charts you will see how much the different bullet weights drop off at your stated distances.
The .243 is a great varmint round and an good deer round. Enjoy. Jim

TinMan
11-14-2010, 08:41 PM
For Varmints, 70gr Sierra BlitzKing over IMR4895 is both very accurate and explosive terminal results.

Tennessee Slim
11-14-2010, 09:03 PM
First, understand it's not the bullet weight that matters, it's the bullet's length (relative to its diameter, but since we're talking all bullets of the same caliber, people don't usually mention the diameter bit). I shoot a .243 WSSM with a 1:10 barrel. It does a fine job of stabilizing a 100-gr Nosler Partition, which is a stubby, flat-base, round-nosed bullet but it won't shoot them long, skinny, streamlined 95-gr SMKs worth a dern.

In fact, the heaviest streamlined bullet I've found I can get away with is 85 grains, SGKs and TSXs, but my best long-range bullet is the 80-gr SBK. I've shot lots of them @500 yards with decent accuracy and my dope says they should stay supersonic to 800 yards. But by that point they're down to about 300 fpe so it's debatable what they'd be good for apart from punching holes in paper.

Deer where I live aren't likely to present themselves at more than a hundred yards so I gladly accept the aerodynamic penalty and go with the mass of the 100-gr Partition for my deer load. Coyotes are an altogether different story so for them I opt for a 70-gr A-Max and take the extra 500 fps.

DuaneinND
11-15-2010, 02:41 PM
I have used 10 twist barrels form Douglas, Shilen, K&P, Lothar/Walther, Llija, and Pac Nor. All have shot fton 55-100gr bullets with acceptable accuracy. Some have shot the 105-107 VLD bullets to the owners satisfaction. For distances up to 400 yards any bullet but a round nose will fly "flat" enough for field work. Beyond 400 the boat tail bullet will have less drop than a flat base bullet with the same o'give.
Pick a couple of bullets you think you might like, take the to the range and compare. Shoot at the same velocity, adjust to the same poi at 100 amd then shoot a target at 400. The paper won't lie if you compare on an IDENTICAL platform.

Anthony
11-15-2010, 08:58 PM
Is there a bullet length to width ratio to start with?

Tennessee Slim
11-17-2010, 02:40 PM
Is there a bullet length to width ratio to start with?
Anthony, I hope you'll excuse me if I presume to teach you how to bait a hook instead of just tossing you a fish.

IMHO, for reasons I'll address directly, your best option is JBM's online Miller stability formula (http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi) calculator. If all you're interested in is finding how heavy a bullet your barrel will support, feel free to skip the rest of this.

Yes, the Miller formula has an input for weight. Yes, I said weight doesn't matter. No, I didn't contradict myself.

Miller doesn't ask for weight so it can consider weight (or mass) per se, it uses weight to infer weight distribution, which is an altogether different matter.

The original stability formula was written by George Greenhill in about 1879. Greenhill's formula, very simply, was:

Minimally stable twist = 150 ÷ bullet length expressed in multiples of bullet diameter

If you prefer more concrete terms, this formula produces the same result:

Minimum twist = 150 x (bullet diameter^2 ÷ bullet length)

Greenhill is still widely used but it does have some shortcomings that weren't really his fault. He wrote it before the invention of smokeless powder, which means the only projectiles he knew were black powder bullets.

Black powder bullets usually had a gradual ogive and a flat base, pretty much like this:

http://img242.imageshack.us/img242/9175/285pxsecantogivesvg.png

Except for it lacking cannelure, this diagram is very similar in shape to the Minié ball used in the War Between the States.

Compare that to this recent very low drag bullet:

http://img688.imageshack.us/img688/7455/vldbullet.jpg

What's happened, of course, is that the bullet has been pretty drastically reshaped in the interest of improved aerodynamics and higher ballistic coefficient. That matters because the majority of the material removed to achieve that highly streamlined shape came off the front of the bullet, nearer the meplat. And that matters because the bullet will be more stable the closer the balance point (or center of gravity) is to the meplat. Or to put it another way, the closer to the base it is, the faster the bullet has to be spun to make it stable.

Beyond length vs. diameter, all other things being equal, a bullet with a larger diameter will stabilize at lower RPMs than one with a smaller diameter. This is because more of the mass is further away from the axis of rotation, which increases angular momentum. IOW, a bigger gyroscope is more stable than a smaller one that weighs the same. The blunter bullet has more of its weight nearer its perimeter, which also makes it more stable at a given RPMs for the same reason. OTOH, the spitzer bullet has more of its weight concentrated nearer the axis of rotation, so it has to be spun all the harder to make it stable. The Greenhill formula simply fails to consider these developments.

Here's another illustration:

http://img340.imageshack.us/img340/332/rsballistics0303c.jpg

Both these bullets weigh 300 grains (.375 caliber). The one on the left is highly streamlined and has a BC of .493. The one on the right is shorter and blunter and has a BC of just .250. The bullet on the left not only has it's center of gravity much closer to its base (as a percentage of its length), its mass is concentrated nearer its axis of rotation. Consequently, the long, skinny bullet has to be spun faster to achieve the same level of stability.

Provided two bullets have identical dimensions, what they're made from or what they weigh is irrelevant to how fast they have to be spun to make them stable. If a bullet made from lead is stable at a given RPMs, any identical bullet will have the same stability at those RPMs, regardless of whether it's made from balsa wood or depleted uranium.

But material is relevant if you're trying to trying to calculate weight distribution without having detailed information regarding the shape of the bullet. So that's why Miller asks for weight. Based on the weight you input and some default specific gravity (historically, 10.9 has been used as the SG of lead), it calculates the volume of your bullet. From its known dimensions of volume, diameter and overall length, it guesstimates what shape your bullet might have.

So that's why Greenhill falls short when dealing with high-velocity, spitzer-style bullets, and why bullet weight has no bearing on calculating RPMs needed for minimal stability but the Miller formula uses it anyway to pronounce your bullet stable or otherwise.

Anthony
11-19-2010, 09:47 PM
wow

thanks something to think about:eek:

Gary in NH
11-20-2010, 07:23 AM
Slim,
I have understood, barely, bullet stabilization but your explanation is the best and easiest to understand. Thanks for the re-education.