henry d Posted February 8, 2007 Report Share Posted February 8, 2007 Okey dokey, simple words for simple peoplewhat are the most important factors in deciding the correct weight(shape/speed/etc.) for the rifles twist rate? Reason I ask is Axe is about to go into cranium meltdown and is taking me with him, we`ve tried the usual suspects and it seems to get harder and harder to find an easy, or indeed a coherent answer. Cheers one and all Quote Link to comment Share on other sites More sharing options...
Poacher Posted February 8, 2007 Report Share Posted February 8, 2007 I'n no pro on this subject and i don't pretend to be however i've found this which maybe of use "One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emanuel College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to: Twist = 150 X D2/L Where: D = bullet diameter in inches L= bullet length in inches 150 = a constant This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula. The twist formulas used in the Load From a Disk program, featured at this web site, uses a modified Greenhill formula in which the "150" constant is replaced by a series of equations that allow corrections for muzzle velocity from 1,100 to 4,000 ft/s (300 to 1200 m). The Greenhill formula is simple and easy to apply and gives a useful approximation to the desired twist. The Greenhill formula was based on a bullet with a specific gravity of 10.9, which is about right for the jacketed lead core bullet. Notice that bullet weight does not directly enter into the equation. For a given caliber, the heavier the bullet the longer the bullet will be. So bullet weight affects bullet length and bullet length is used in the formula. To measure the twist of a barrel, use a cleaning rod and a tight patch. Start the patch down the barrel and mark the rod at the muzzle. Push in the rod slowly until it has made one revolution, and then make a second mark on the rod at the muzzle. The distance between marks is the twist of your barrel. To see how this works out, assume you bought a .222 Remington rifle and you measured the twist rate as described above. The twist was 1 in 14. You have two .224 bullets you want to use, the 70-grain Speer SPS and the 50-grain Hornady SX. The Speer bullet measures .812 inches in length and the Hornady measures .520 inches. Using the formula above we calculate the following twist rate: Speer 70-grain: 1 in 9, Hornady 50-grain: 1 in 14 These calculations show that the 50-grain bullet will be stabilized, but the 70-grain won’t. Sure enough, when you try these bullets out, the 50-grain shoots ¾ MOA while the 70-grain won’t group on the paper at 50 yards. Twist is important!" its taken from http://en.wikipedia.org/wiki/Twist_rate hence i cannot guarantee its accuracy (mind the pun) Quote Link to comment Share on other sites More sharing options...
Dunkield Posted February 8, 2007 Report Share Posted February 8, 2007 What calibre? In simple terms, slow twist like 1 in 12" on a .223, you stick to 55grns or so as a max bullet weight. Anything much heavier and it may tumble as there is unsufficient twist to stabilse the bullet. If you have 1 in 8 or 7 twist you can use bullets of 69 grn and higher as the twist will still stabalise them. Quote Link to comment Share on other sites More sharing options...
JohnGalway Posted February 8, 2007 Report Share Posted February 8, 2007 Edited by poster as the eejit was removed thankfully Quote Link to comment Share on other sites More sharing options...
henry d Posted February 8, 2007 Author Report Share Posted February 8, 2007 He`s been forcibly ejected Quote Link to comment Share on other sites More sharing options...
Dunkield Posted February 8, 2007 Report Share Posted February 8, 2007 Damn I missed that bit. Does that answer your questions H, or do you need more detail?? Quote Link to comment Share on other sites More sharing options...
henry d Posted February 8, 2007 Author Report Share Posted February 8, 2007 It will be of no use to Axe any more, as he was thinking of the .223(T3 1 in 8")but is now looking at a CZ and then swithered, so is now thinking about .17 rem/.243/22-250/30-06/7.62/6.5x57/6mmBR Now what does that equate to with the 6.5x55 ?? and how does boattail/ogive curve/weight affect it ?? Quote Link to comment Share on other sites More sharing options...
Graham M Posted February 8, 2007 Report Share Posted February 8, 2007 http://members.shaw.ca/cronhelm/CaliberTwist.html G.M. Quote Link to comment Share on other sites More sharing options...
Dunkield Posted February 8, 2007 Report Share Posted February 8, 2007 Now what does that equate to with the 6.5x55 ?? and how does boattail/ogive curve/weight affect it ?? The 6.5 seems unafected by all this nonsense, it just keeps on plugging away regardless! The 1 in 8 T3 .223 would be fine with almost all bullet weights, unless someone wants to contradict that? Quote Link to comment Share on other sites More sharing options...
sussex lad Posted February 8, 2007 Report Share Posted February 8, 2007 Now what does that equate to with the 6.5x55 ?? and how does boattail/ogive curve/weight affect it ?? The 6.5 seems unafected by all this nonsense, it just keeps on plugging away regardless! The 1 in 8 T3 .223 would be fine with almost all bullet weights, unless someone wants to contradict that? My AR is a 1 in 8 and wouldnt shoot any factory 55g under an inch at 100 yards The only factory ammo it has shot well was some Remington Tactical Urban 64g soft points Now i only feed it 69g HPBT home loads which it loves Quote Link to comment Share on other sites More sharing options...
JohnGalway Posted February 9, 2007 Report Share Posted February 9, 2007 Now what does that equate to with the 6.5x55 ?? and how does boattail/ogive curve/weight affect it ?? The 6.5 seems unafected by all this nonsense, it just keeps on plugging away regardless! The 1 in 8 T3 .223 would be fine with almost all bullet weights, unless someone wants to contradict that? *Raises Hand* My T3 Varmint has shot 50gr UMC JHP's to 5/8th of an inch and AE 50gns in same rifle shot by Conor got a touching 3 shot group, both at 100 yards. Then the AE's shot around 2 -2.5 inch group last time Yet she doesn't like or has inconsistant results with 45gr, 55gr, 62gr, 64gr & 75gr. Hope to get to the range again on Sunday. Quick question on bullet length, without disassembling the cartridge (which I think may be illegal here anyway) where would you find out what length the bullet is that's in a shop bought cartridge? No reloading over here as yet. Quote Link to comment Share on other sites More sharing options...
TikkaT3 Posted February 20, 2007 Report Share Posted February 20, 2007 Now what does that equate to with the 6.5x55 ?? and how does boattail/ogive curve/weight affect it ?? The 1 in 8 T3 .223 would be fine with almost all bullet weights, unless someone wants to contradict that? I have not tried anything under 55gr (brilliant weight in T3 1-8" twist). However I can confirm that 75gr A-MAX are spectacularly good. On Saturday I had groups of 0.572" at 100m and 0.368" at 150m during the testing of a new load. I would love to get them down to a range to have a go at longer distances. To use them though the magazine did need a bit of modification. Quote Link to comment Share on other sites More sharing options...
Dunkield Posted February 21, 2007 Report Share Posted February 21, 2007 As a slight update to this, my friendly, very knowledgeable gun shop man says if you drive 40grn heads too quickly out of a 1 in 8 barrel they explode not long after leaving the gun. So there is a lower limit for quick twists just as there is an upper limit for slow twists. Quote Link to comment Share on other sites More sharing options...
stirky Posted February 22, 2007 Report Share Posted February 22, 2007 My cooper .223 has a 1/9 twist barrel and shoots anything from a 50grn bullet upto 75grn very well. Quote Link to comment Share on other sites More sharing options...
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