300 Norma twist?

Broz

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I don't know, I'd guess the common assumption is that it may hurt velocity.

The velocity loss in faster twist barrels is so small I am not sure it is detectable if it even exists. There is a lot of data for Cheytac improved velocities out there and with the transition to tighter twists a lot of this data from trusted sources at different twist rates with same weight bullets. My new 375 ELR sends 400 gr bullets at 3150 fps with a load just under max pressure. That is among the highest velocities I can find data for. And it is a 7 twist. My 300 win mag same length barrel as my 30 Nosler. 300 win is a 10 twist, 30 N is a 9 twist. Both rifles, side by side hit exactly the same velocity with exactly the same powder charge of N-570. Again zero evidence of velocity loss. I use to think this made sense too, because I heard it some where. But today's actual data pretty much proves it is more myth than not.

The barrel availability issue is real. But it is changing. It will change faster if we do not "settle" for barrels that are not offering us top performance from our bullets.

Jeff
 
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Two questions, within reason, and knowing this is a long range forum, and assuming optimizing long range means high BC bullets, how can the faster twist hurt? And two, Why are people afraid to twist their new long range barrel using what we know today about what it does for BC's?

Jeff

CameraZOOM-20180419151701114_zpsrsn0f92k.jpg

That's a great question, and I sure don't have the answer for it, but have some thoughts based on my own experience.

I've used both 9" and 9.5" twist 30 caliber barrels extensively for 300 winmag builds (as well as a 30 Nosler, and a few 300 Normas, the winmag is ever popular though). Full disclosure; the 9" twist barrels were mainly rock creek blanks, while the 9.5" twist are from benchmark. I believe the benchmarks to be a better shooting barrel in general, but per their recommendation when I started using them, they suggested 9.5" twist for up to 230's in the magnums as they tend to be less finicky on load development. I haven't quantified the data, but I do know the 9.5" twists have been more consistent for me in load development. Is it because they're a better barrel, or a twist rate difference? Not sure... I'd wager it's because they're a better barrel, but they're input I also put value in.

I've also ran 8" twist .284 caliber barrels in a 280 ackley with a 140 VLD that had zero issues shooting in the low .3's on average. Most would think that'd be overtwisted for a 140, but it shot great and was shot to 1400 yards a few times with success.

One other area of concern might be bullet jacket integrity with high velocity/fast twist barrels. Berger has documented their 338 cal 300 grain Elite hunter bullets coming apart above 3000 fps. Would that be exacerbated with a faster twist barrel or no? Again I don't know... I know for those velocities they recommend their tactical bullet line. Sierras I believe have a thicker jacket as well? You're using lathe turned solids in that 408 aren't you? Be interested to see how production bullets do with that velocity and twist.

You do much more ELR stuff than either I or most of my customers, so I'm curious, how much higher BC are you seeing for a faster twist barrel? Or is the BC not so much the improvement, but the high RPM still happening as bullets go transonic-subsonic keeping the bullet more stable? Obviously BC is changing with difference velocities, I wasn't aware of the BC value actually changing with twist rate as opposed to it remaining more stable at subsonic velocities.

Mike
 
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Totoro

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With faster twist and higher MV, can we expect cup/core bullet jackets to withstand that much friction and not deform vs a solid?

For banging solid targets I see no issue, but on soft tissue targets I wonder if the bullet can hold together enough for a quick kill.

Or does it not matter?

BTW, Mike you're killing me with all those pills!

As far as the SMK, their jackets seem thicker to me by the way they behave on game.

Back in the day I shot 168 SMK in BHA 308 match ammo at coastal blacktails, smallish deer. SMK would pencil right through the vitals and leave a trickle of blood trail. So I reverted to head and neck shots.

Enter Berger 168 VLD in 308 HSM ammo, hit the vitals and it is bang/flop every time. The vitals would be mush, frags everywhere.

Maybe thats changed with the new SMK, I havent read or shot enough bigger muley or elk to give the SMK my vote.
 
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Broz

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I too have been at this a while. Over the years I have seen bullets come apart and never make it to 200 yard targets. My first instance was with 50gr bullets from a 220 swift. Gray vapor trails and no hole in the target. I also seen it happen with 7twist in big cased 7mm's with lighter projectiles over 3300 fps. And some 6mm's. Many of these were 3 grove barrels that do inscribe the jackets more. Most of the stories out there about bullets coming apart are from very high velocities and small calibers with 3 groves. I personally have pushed 300 Bergers to over 3200 fps with great results. None have came apart for me, but they were all above 8 twist.

The picture I posted of the Sierra's I am testing was posted so all could see the twist recommendations on the box, since we seem to be under the impression a 9 twist is optimum for 230's. If so then why would Sierra recommend these 230's for " 8 twist or faster" (Copy from their site in RED "This bullet requires a barrel twist rate of 1x8” or faster".) To me that means 8 twist is a minimum. They advertise these bullets at .8 G1 BC down to 1880 fps. That's awesome if true and that's why I have them. But I have the feeling from my own experience that they may not see this from 10 or 9 twist even if they stabilize and from my experience for sure not down to 1880 fps. I believe if tested in slower twist they may not get these great BC's. Heck, they may not in an 8 either. Time will tell. 8 twist or faster recommendation hints at a 7 twist would ok too? Does it not? Look how many 6.5's, 6mm's and even 223's are using 7 and 8 twists today with all bullet weights. Many comp rifles too. Why?

When I ordered my 375 barrels I had the same concerns about jacketed bullets. The only info I found came from a trusted source and said they have shot some jacketed 375 pills from a 7 twist and they shot great and held together. When I test the new Big Berger's we will find out first hand. But that is a ways down the road.

There is nothing wrong with being cautious and staying in a comfort zone. Nothing at all. If it is working, don't fix it. The only cost for this comfort zone is, following from behind only has one view. I have obtained some great data with results using cup core bullets in some test 30 Norma's with 8 twists. They were easy to load for, they held on to their BC and they shot very very accurately.

Please do not get the idea I am saying faster twists make higher BC's. What it does is extend the higher BC node. You MV and twist rate will dictate how far that is.

I am in the barrel waiting period of my next 30 cal build. Barrels are 8 twist and I assure you the velocities will be over 3200 and hopefully 3300. I may be foolish but I am confident from my own testing and some trusted sources. I have nothing to gain by offering what I have here. It is up to all of you what you choose. But judging from all recent data and those boxes of Sierra 230's, faster twists are here today.

Thank for the conversation. I will return to my corner and comfort zone now. ;-)

Jeff
 
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I am in the barrel waiting period of my next 30 cal build. Barrels are 8 twist and I assure you the velocities will be over 3200 and hopefully 3300. I may be foolish but I am confident from my own testing and some trusted sources. I have nothing to gain by offering what I have here. It is up to all of you what you choose. But judging from all recent data and those boxes of Sierra 230's, faster twists are here today.

Thank for the conversation. I will return to my corner and comfort zone now. ;-)

Jeff

I'm not debating your opinions or data on the matter, just merely forwarding the conversation/dialogue with questions of my own. Don't go to your corner just yet! :)

One thing that's interesting is recommended bullet twist rates per are not the same for a given projectile weight. Berger lists their 230's as a 9" twist "Optimal", Hammer bullets lists their 227 grain Hammer Hunter as "1:8" or FASTER", Sierra lists their 230 as 8" or FASTER. Why is this? Don't know but I'm sure each manufacturer has their reasons.

I do know from Berger they only recommend whole numbers for twist rates, and they ALWAYS round down to the nearest whole number for a twist rate. A 9.8" twist may be all that's needed, but they'll round down to 9"...

I think why faster twist rates may be working nowadays, is how we're actually chambering our barrels. The old methods of chambering off steady rests and with various techniques of "dialing" a barrel in are in many ways obsolete, and while they certainly produced accurate rifles, those methods very much depended on a barrel bore being as straight as possible. With certain methods nowadays, we ensure that a bullet is entering the lead of the throat/lands as square as possible, and I think that can affect how a bullet handles a relatively fast twist rate. If a bullet conversely enters the lands off course and has to self correct throughout the path of the barrel, a fast twist rate may be too much for a bullet to overcome that. It's just a theory of mine...

Mike
 

Broz

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Mike, I think everything is better today. From bullets to barrels to machining. Consider this , how much has the rifling methods on barrels improved over the years? There is little doubt in my mind earlier rifling techniques left some to be desired. I can remember checking twist rates and if they were with in 1/2" of the twist you ordered it was good. I also remember a barrel that checked a little different twist rate at both ends. Now if it starts out at 10 and finishes at 9 1/2 it is fine. But if it starts at 9 1/2 and finishes at 10 not so good. At some point in that barrel that bullet has to load to the opposite side of the rifling and what does this do to a jacket? For this reason I like a very slight gain twist in barrels. It keeps the bullet loaded to the same side of the rifling all the way through.

You mentioned earlier the differences between lathe turned solids and lead core bullets as far as twist. The solids always want more twist if they are the same weight. Now the question is why not twist them tight so you can shoot them all? Have we ever seen a bullet "Over Stabilized"? The thought that faster twist rates are slower is pretty much proven a myth today. That is why I posted about my 375 and the great velocity from a finish 7 twist. As for Berger, we all know the majority of the data there is based off of testing done at the Applied Ballistics lab. Is that why we seen a lot of the Berger boxes go to faster recommended twist rates for the same bullet? Like the 215 30 cals, they were rated for a 1 in 10, now 1 in 9, same exact bullet. I think we just learned tighter twist bring something to the table with little negative effects. From my observations when we see a new bullet with a higher BC it has a new longer nose. After we tested the 155 gr Berger 6.5 bullets, Berger has decided to go after more BC. I cant say for sure, but I will bet a dollar to your donut the new 156 will have a longer nose. 1 gr longer. A good indication of what a slightly longer nose does for BC. When comparing the 230 Sierra to the Berger 230 target the first thing we see is the Sierra is a tad bit longer. Then we notice it appears the nose is sleeker. ( all of this is just observation) I think Sierra is catching on and jumping on the BC wagon and I will assume they did their homework on what the tighter twist has to offer. I know Ryan Avery has tested the 230 Sierra out to 3 or 400 yards from either a 9 or 10 twist. Point is not an 8 and they stayed stable at his altitude. If I get my barrels in time it will be very interesting to test retained BC's from my 8 twist compared to a 9 or 10.

So Mike, when you see those 30" .308 / 8 Twists come across the table, find it in your heart to push them through for me and we will have some actual results before fall hunting season. :D :cool:

Thanks
Jeff
 

WRO

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There is nothing wrong with being cautious and staying in a comfort zone. Nothing at all. If it is working, don't fix it. The only cost for this comfort zone is, following from behind only has one view. I have obtained some great data with results using cup core bullets in some test 30 Norma's with 8 twists. They were easy to load for, they held on to their BC and they shot very very accurately.

Please do not get the idea I am saying faster twists make higher BC's. What it does is extend the higher BC node. You MV and twist rate will dictate how far that is.

Ballistic Coefficient - Hornady Manufacturing, Inc

Hornady did testing with different twist rates on a few bullets for BC, in their test it showed a higher BC with a faster twist with certain bullets.

I don't think they have any reason to lie..
 

Broz

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Thanks WRO, I hadn't read that before. I had suspected this to be true, as I hinted at it in above posts, but didn't want state it based on speculation until I have tested myself in a good comparison. For that I need the 8 twist barrel. Now I am even more motivated to test for myself and even more confident as to why Sierra recommends 8 twist or faster for their new (Higher BC) 230's.

The other interesting point is it offers some comfort to concerns of jacket damage from tight twists and they tested the 225 / 30 cals in a 7 twist. Cool!!

Jeff
 

WRO

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Thanks WRO, I hadn't read that before. I had suspected this to be true, as I hinted at it in above posts, but didn't want state it based on speculation until I have tested myself in a good comparison. For that I need the 8 twist barrel. Now I am even more motivated to test for myself and even more confident as to why Sierra recommends 8 twist or faster for their new (Higher BC) 230's.

The other interesting point is it offers some comfort to concerns of jacket damage from tight twists and they tested the 225 / 30 cals in a 7 twist. Cool!!

Jeff

Its a 6% average upgrade in BC on the 212's that's pretty significant. It seems there are much higher benefits at lower speeds too..
 

Broz

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Its a 6% average upgrade in BC on the 212's that's pretty significant. It seems there are much higher benefits at lower speeds too..

Agreed. So talking with the guys at AB today I asked for their data and research. They agree faster twists do increase a given bullets BC over the entire velocity range. The info I got also includes that it is due to the higher bullet RPM produces a lower limit cycle yaw ( spinning more closely to perfect axis). I was also told that it is less gain after a 1.5 SG, but there is still an obvious gain.

Spin em up boys!! :cool:

Jeff
 
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So Mike, when you see those 30" .308 / 8 Twists come across the table, find it in your heart to push them through for me and we will have some actual results before fall hunting season. :D :cool:

Thanks
Jeff

Ha! I'll see what I can do, haven't seen any blanks show up yet... 30" finished lengths will be special one offs as well.


Mike
 
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Great discussion fellas!

My thinking with Berger relabeling the recommend twist is very much the same as they updated the BC on some of their bullets.

On the other end, I do believe there is a marketing aspect as well.

Suffice to say, those savvy enough and willing to test theory and boundries, I wholeheatedly applaud thee for your efforts.

Thats how we can learn and move the sport forward.

Lets add another twist (pardon the pun) to the discussion; how about a gain twist barrel? Yes, I have heard and read cut barrels have a nominal amount of gain from breech to muzzle. But how about spec'ing out a honest gain twist?

Is it even possible?

I took a read from Frank Green @ Bartlein and it makes sense, so how can we use this technique to our advantage?
 
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Great discussion fellas!

My thinking with Berger relabeling the recommend twist is very much the same as they updated the BC on some of their bullets.

On the other end, I do believe there is a marketing aspect as well.

Suffice to say, those savvy enough and willing to test theory and boundries, I wholeheatedly applaud thee for your efforts.

Thats how we can learn and move the sport forward.

Lets add another twist (pardon the pun) to the discussion; how about a gain twist barrel? Yes, I have heard and read cut barrels have a nominal amount of gain from breech to muzzle. But how about spec'ing out a honest gain twist?

Is it even possible?

I took a read from Frank Green @ Bartlein and it makes sense, so how can we use this technique to our advantage?

Actually spec’d out gain twists have been around for a long, long time. The new computer controlled cut rifling machines can do whatever gain twist you want or desire. Can start at 15” and end at 7” if you wanted to.

With that said, it’s been a “general consensus” that gain twist barrels don’t add much benefit... but then again I haven’t seen any hard data proving it either way.

Many thought that by using a gain twist you’ll have a more gentle pressure curve and may be able to gain more velocity that way. Well we’re obviously not seeing pressure with twist rates that historically are considered “too fast”. That’s clearly not the case here though.

There are other methods to smooth out that pressure curve. Mainly dealing with freebore and chamber throat designs.

I’ve got some other ideas that’ll maybe one day come to fruition but right now they’re just unproven ideas.

I’m racking out, just boxed up 5 Barrels headed to Australia! Got the pickup loaded and headed to Riggins tomorrow to see if we can’t find a bear, have enjoyed the discussion. I’ll check back here Sunday!

Mike


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Thx for the insite fellas, its tantalizing these days to play with all these options with the only limitation being the depth of our individual pocketbooks.
 
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