ITS CRUNCH TIME....I am about to submit order for project rifle. It will be a 243 caliber, Krieger barrel in contour #4 or #5. It will "probably" be used 95% for varmints/coyotes and paper punching. I will be using factory loads(I dont reload at this time..i did) and probably be using bullets between 60 grains to 85 grains. My question is..what twist rate should I use? 1:12(good up to 85grains) or 1:10(good up to 100grains) I know 1:12 is good up to 85grains...but my gut is telling me 1:10. Decisions decisions?!?!? What do you guys think?? Thanks in advace.

I have always liked 1-10 for the 6mm's. Two new things are the long VLD bullets that require 1-8 and the 55 gr types.



One way of looking at twist is that if it's slow it won't work for sure with long bullets but if it's fast it might work with all bullets.

sounds like you have made the decision- the little bit of "potential" accuracy you might gain with a slower twist is not worth the lack of flexibility. I would go with a 10 for a working rifle.

O.G.,

I have my .243 Varminter shooting 55 & 58 grain bullets out of a Shilen barrel with a 1X14" twist. These are the only weights that I use.

Super accurate.

Good luck with the project.

Sam

60 gr...1:15"
80 gr...1:11"
100 gr..1:9"
120 gr..1:7"

These are minimum twist rates for the .243 bullet

Oldguns, perhaps the other 5% of usage will determine what you do with this, but I'd twist the barrel for most usage. Varmints are small, the range is long. If you have to shoot a deer with it perhaps it will stabilize an X bullet, Partition, or other premium lightweight. Out on a limb here but I believe that both are available in the 80 grain range though the Barnes would be quite long for weight.

My opinion on this is flavored by a Ruger#1 in .257 Bob that shoots deer weight bullets poorly, and varmint weights with extraordinary precision. It's all about twist and it works both ways. Yes, a quicker twist will allow you to shoot both, but it will not do as well with the shorter bullets, which is where you say you'll do 95% of your shooting. JMO

A fast twist will stabilize light bullets but a slow twist won't stabilize heavy bullets. There's no right answer so I say to error on the side of faster twists.....I'd go with 1:10 twist in this case.

oldguns -

May I cast a vote for 1:12?? It's been our experience that, yes, if one doesn't have enough "twist" then the heavier ones will not stabilize, but given our interest in small groups on paper, we've also noticed that with too much twist the lighter ones won't shoot well either. This is not to say that they shoot as badly as keyholing bullets, but 1 and 2" groups are not the same as .5" groups. A classic example of this for us is the 6.5 swede with a 1:7 or 1:8 barrel - yes it'll shoot 140, 150 and 160s like a tackdriver, but good luck on the 85gr'ers.

Additionally we might suggest that twist is overrated, ie, we're currently taking data for a 25-35 (yes, I know, not a bleeding edge cartridge), but we're doing so with a 1:16 barrel, and for 75, 85 and 87 bullets you'd think it was fitted with a $500 barrel (not a $60 marlin 25-20 barrel re-reamed to 25-35).

As such, if 95% of what you're going to be doing is varmints and paper, I'd go with the 1:12. [Besides, if in the future you need to go to heavier bullets - what better "excuse" for another addition to the gun safe??.]

do shoot straigth,
greg
www.gmdr.com

Savage99, DuaneinND, BIG SAM, Oddball, DigitalDan, Vapodog, gmushial...thanks for the replies....now to "tighten it up" even further...how much better/tighter(if any) would 70grain bullets shoot in a 1:12 twist than in a 1:10 twist.....thanks again

I would still go with the 1-10. When the barrel gets a little soft the accuracy will last longer with a faster twist. Sure enough you will want to shoot some long bullet to try out too.

Berger says 1-12 to 1-13 but that's just with the 70 gr range.

http://www.bergerbullets.com/catalog.htm

If it's bench rest accuracy your after then PM Knobmtn here for advice.

Berger always did like a slower twist rate than other source, and yet his bullets seem no shorter for their weight than other bullets.

Your getting twist rate confused with weight, when its length of the bullet you need to stablalize. The formula is T(twist)= (150Xd�)/length
the d is diameter, there is no weight in the formula. If you do a google search on the "Greenhill formula" you can put in the numbers and come out with the optimal twist. The bullet could have a long oglive and need a faster twist to stabilize for the weight.

Randy Ketchum, the gunmsith of Lynnwood Guns, contacted Sierra and asked how long one of their bullets was. He was told that was proprietary information.

OldGuns -



And that's the $64k question, and to which I suspect few have an exact answer, ie, this is why we're currently taking data with the 1:16 barrel (so we can compare it to our 1:10 barrel data). Our answer to the question would be to get one of each, shoot both, keep the one that works best, and try to get one's money out of the other via eBay.



W/re Greenhill formula - at the very best it's an approximation and over states what's needed to stabilize most bullets. If one does the stability calculation based on the actual physics one gets much lower twist rates. But as stated: the ogive length is the important variable - a rn with a short ogive to body length will require much less twist vs a VLD design where the ogive is more than half the bullet length. (The other important point is: stability is a function of rotational rate (which is a function of velocity), ie, the same bullet which might keyhole at 2500fps might shoot tight groups at 3500fps (from the same barrel), eg, a 50gr psp from a 1:14 barrel at 2000fps will keyhole hopelessly, at 2250fps will shoot 2-3" "groups", but above 2600fps will shoot well under 1".)



do shoot straight,

greg

www.gmdr.com