Twist Ratios

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logunmk1
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Twist Ratios

#1 Post by logunmk1 »

Hi guys

Wanting to move up from pistol rounds to rifle. Can anyone explain the twist ratios which appear to be available when purchasing .223 as I am not sure which would suit my application best.

Thanks

Garry
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Ovenpaa
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Re: Twist Ratios

#2 Post by Ovenpaa »

It is all down to the weight and length of bullet you wish to shoot and at what distance. A slow twist such as one revolution in 14 inches (1:14) is suitable for bullets of around 50 grains whereas a fast twist is suitable for heavier longer bullets so use a 1:7 to stabilise say an 80 grain bullet. I would not say heavier bullets are exclusively used for longer distances as there are many factors to consider beyond just weight and twist.
/d

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Re: Twist Ratios

#3 Post by Maggot »

Ovenpaa wrote:It is all down to the weight and length of bullet you wish to shoot and at what distance. A slow twist such as one revolution in 14 inches (1:14) is suitable for bullets of around 50 grains whereas a fast twist is suitable for heavier longer bullets so use a 1:7 to stabilise say an 80 grain bullet. I would not say heavier bullets are exclusively used for longer distances as there are many factors to consider beyond just weight and twist.
As David days, a lot of us pretendy AR types will use a 1:8 barrel and 74/69/77gr match bullets to give us a match consitant bullet at the longer ranges...they still get blown about a lot wallhead

I will use 75gr PPU HPBT at 100/200 because hand loaded they are still cheaper than a surplus or cheap factory load with (as far as I can tell) very similar performance to the 77 SMKs.
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Re: Twist Ratios

#4 Post by Ovenpaa »

Also you can over rotate a bullet, typically a fast twist rifle such as a 1:7 on a warm day with a 50 grain bullet can lead to the jacket separating from the core, you may see a p**f of something a bit out from the firing point as it explodes, the good news is the core invariably keeps heading towards the target.
/d

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logunmk1
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Re: Twist Ratios

#5 Post by logunmk1 »

Thanks for your help guys, the information is priceless and much appreciated
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Re: Twist Ratios

#6 Post by Mattnall »

Ovenpaa wrote:Also you can over rotate a bullet, typically a fast twist rifle such as a 1:7 on a warm day with a 50 grain bullet can lead to the jacket separating from the core, you may see a p**f of something a bit out from the firing point as it explodes, the good news is the core invariably keeps heading towards the target.
Dave, have you ever seen this on a .223 in the UK?

I have a 1:7" barrelled .223 and shoot long bullets in it mostly but often I use it for pests and put 52SGKs through it and these go mighty quick. Never had a problem on paper or fox.

I've seen it in the past with 357Mag and 44Mag with some of the copper washed/TLFMJ bullets but even that seems to have stopped now. In these instances the jacket split and peeled back but didn't separate, the holes in the paper had small sections cut out radially.
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Laurie
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Re: Twist Ratios

#7 Post by Laurie »

Mattnall wrote:
Ovenpaa wrote:Also you can over rotate a bullet, typically a fast twist rifle such as a 1:7 on a warm day with a 50 grain bullet can lead to the jacket separating from the core, you may see a p**f of something a bit out from the firing point as it explodes, the good news is the core invariably keeps heading towards the target.
Dave, have you ever seen this on a .223 in the UK?
I induced it one hot summer's afternoon in an 8-twist 223 with 52gn Hornady AMaxes. The first few shots grouped well, then severe vertical stringing appeared, then four out of five bullets disintegrated at around the 80-90 yards point as the barrel heated and fouled. Years ago, Hornady had some thin-jacket 224 varmint models called 'SX' (super explosive) designed really for the 222 Rem with its 1:14 twist, but which could also be used in the standard SAAMI 1:12 223 under most conditions. Hornady warned that 1:10 or faster twists risked bullet failure in flight and that they shouldn't be loaded for such rifles.

Bullet blow-up is a very complex matter and has proven to be very difficult to induce from a standing start. It is it seems a mixture of bullet jacket strength / integrity; the rotation rate; barrel and ambient temperatures; pressure level on the bullet base; chamber freebore lengths and throat condition. All one can say is that a worn, badly fouled and very hot barrel is as much a part of the mix as twist rate and pressure. Berger Bullets went into this in some depth in the early days of F-Class when the 6.5-284 was the most widely used cartridge in F/O. There was a string of reported bullet blow-ups of Berger 140gn VLDs in the USA. (Hotter conditions than we see and American Effers 'string-shoot' so barrels become very hot too.) The company sought as much information as possible about conditions from witnesses / victims and tried to induce failures on its test range, but failed completely. Nevertheless, it redesigned its entire match bullet range across all calibres. The original VLDs with thinner J4 jackets became the company's 'Hunting VLDs' in the orange boxes; new more robust jacketed models became 'Target VLDs' (or BTs, or whatever) in the yellow boxes. Before these naming / packaging changes were introduced, early modified models were labelled with the word 'Thick' in parenthesis after the bullet weight and type. I still have examples of 140gn 6.5mm Berger BTs of both types still packaged in yellow boxes but with the single word difference in nomenclature. Ironically, under the post Dunblane law changes, all such were legal for target shooting, but as soon as Berger reclassified the thin-jacket version as a 'Hunting' model, you needed the special permission to buy and hold them as so-called Section 5 bullets. (Thank goodness that particular piece of nonsense was abolished last year!) In the USA, some long-range precision shooters use the 'Hunting' models by choice as they find they get better results from the thin jacket models.

My own 223 experience aside I saw bullet blow-up again in a 600 yard benchrest comp a couple of years ago. 6.5-284 and Hornady AMaxes again. The bullets mostly didn't break up in a grey p**f here, rather could be seen as grey streaks in flight from around 200 yards from the muzzle and failed to reach the target. Temperature wasn't a factor in this case as it was cool, or maybe even cold.
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Re: Twist Ratios

#8 Post by Ovenpaa »

Matt, I have seen them blow a few times in .223's, to mitigate the failure it is fair to say they quick rounds on a hot day with a very high round count through both rifles. The rifle that routinely blows .224 bullets on a hot day is the Vikings 22-6,5x47 so an 80 grain SMK at 3,275fps
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Re: Twist Ratios

#9 Post by Mattnall »

OK, thanks Dave and Laurie. It looks like you managed it but had to get extreme conditions to do so.
It's just I've never seen it and I have shot plenty of light fast bullets out of a 1:7" (in shall we say 'normal shooting', not trying to induce a failure) but hear many many people who report actually experience it, most I'm guessing are just repeating what they heard on the internet or evidence from many years ago when availability of fast twist .22 barrels out paced the quality of .22 bullets, or they were somewhere hot and cooked their ammunition in the sun first.
Plenty of other calibres get quoted but most of these I've little or no experience with so I cannot comment on that.
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Gazza
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Re: Twist Ratios

#10 Post by Gazza »

I found this below. Could any of you bullet boffins say as to whether the diagram is accurate?

https://i.imgur.com/jsCknnj.jpg

According to the Venn diagram if I'm shooting a 55gn bullet then this will be good in all twist rates listed ?
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