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7mm Berger 180 Hybrid twist rate help

 
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  #8  
Old 01-28-2011, 07:13 PM
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Location: Windsor, CO. USA
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Re: 7mm Berger 180 Hybrid twist rate help

This is not a rant on Berger. Great bullets! What I talk about here may be specific to my rifle, but I don't think so.

First of all, don't bother. The simple fact is that your bbl is not twisted tight enough to stabilize those bullets. I've been pretty vocal here about the tribulations I had trying to get these to shoot in my 7 RUM, with a factory 26" bbl and a twist rate of 9.5. I essentially destroyed the bbl in about 400 rounds (a guess). I tried every concievable configruation with seating depth, I tried H1000, 50BMG, US869 (I think that's the name of it, on Kirby's recommendation) Retumbo and something else I can't remember now. I did ladder test after ladder test, to no avail. I emailed Berger and the knowledgeable guy I talked to said that 9.5 was the marginal, and that 1 in 8 would be best.

Second of all, I went the "push it faster and the twist doesn't matter so much" route as well. I was getting about 3200fps with the 869, maybe a touch more, before I got pressure signs. That was as fast as it would go. Now, keep in mind that my dad has a factory .300 RUM that he has no problem pushing 220gr SMKs at 2950 - 3000 fps in 26" bbl, and it shoots clover leaves.


I bet I spent 300 dollars trying to get those bullets to shoot. I got pissed and pulled the bbl. I'm going to make an Edge or something like it on the action. If I were to try a 7mm again and I wanted to shoot THOSE particular bullets, I would get a custom bbl, 30" finished, and twisted precisely to the Berger's specifications. In fact, and in hind sight, I could have bought a blank from a custom bbl maker for what I put into bullets and powder trying to get the Bergers to shoot.

Just my opinion.

Hicks
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  #9  
Old 01-28-2011, 09:53 PM
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Join Date: Jul 2010
Posts: 89
Re: 7mm Berger 180 Hybrid twist rate help

Quote:
Originally Posted by Hicks View Post
This is not a rant on Berger. Great bullets! What I talk about here may be specific to my rifle, but I don't think so.

First of all, don't bother. The simple fact is that your bbl is not twisted tight enough to stabilize those bullets. I've been pretty vocal here about the tribulations I had trying to get these to shoot in my 7 RUM, with a factory 26" bbl and a twist rate of 9.5. I essentially destroyed the bbl in about 400 rounds (a guess). I tried every concievable configruation with seating depth, I tried H1000, 50BMG, US869 (I think that's the name of it, on Kirby's recommendation) Retumbo and something else I can't remember now. I did ladder test after ladder test, to no avail. I emailed Berger and the knowledgeable guy I talked to said that 9.5 was the marginal, and that 1 in 8 would be best.

Second of all, I went the "push it faster and the twist doesn't matter so much" route as well. I was getting about 3200fps with the 869, maybe a touch more, before I got pressure signs. That was as fast as it would go. Now, keep in mind that my dad has a factory .300 RUM that he has no problem pushing 220gr SMKs at 2950 - 3000 fps in 26" bbl, and it shoots clover leaves.


I bet I spent 300 dollars trying to get those bullets to shoot. I got pissed and pulled the bbl. I'm going to make an Edge or something like it on the action. If I were to try a 7mm again and I wanted to shoot THOSE particular bullets, I would get a custom bbl, 30" finished, and twisted precisely to the Berger's specifications. In fact, and in hind sight, I could have bought a blank from a custom bbl maker for what I put into bullets and powder trying to get the Bergers to shoot.

Just my opinion.

Hicks

Groper,
I've ran the calculator many times, the number is almost always above one with an average of around 1.2. The only way I can get it below 1 is to really put in extremes in all the categories.

Hicks,
Thanks for the post, but I gotta admit thats not what I was hoping to read! Hopefully I'll have a little better luck with them then you did, but I'm not holding my breath.
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  #10  
Old 01-29-2011, 07:34 AM
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Join Date: Dec 2005
Location: Tucson Az
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Re: 7mm Berger 180 Hybrid twist rate help

I managed to get the 7mm hunting 180 VLDs to shoot with extremes in twist:

Made a 1 in 7 twist 7 rem mag that shot bugholes till the 3 groove throat got rough and it began to destroy bullets.

Last year I found a like new early edition LSS 7 RUM that I couldn't pass by on the used rack. I knew the twist was a bit too slow or so I thought. For grins I tried the 180 VLDs and they shot very well at approx 3150 fps. A friend saw that rifle and talked me out of it. I have no idea the exact twist of that Rem but I had heard they used 1 in 9.25 at that time.

All you can do is try them and see.


Kiwi Nate: the news that the 300 gr .338 bullet may not be a hunting bullet is not good news. A friend talked to Walt Berger at the Shot show. He said they are still working on the issues of the 300 due to some guys shooting it from monster magnums. I think they are going to have to make two versions with max velocity limitations on one.

My friend asked Walt about the upcoming 250 VLD/hybrid. They won't issue it till they work out the problems with the 300s. Now I wonder what that 250 will be like. I'd love to shoot it in a standard magnum for hunting. Now you have me wondering if it will be useable.
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  #11  
Old 01-29-2011, 04:02 PM
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Posts: 89
Re: 7mm Berger 180 Hybrid twist rate help

I shot some Hybrids today, they managed a 1moa group at 300 yards with no signs of instability. Running it through the calculator it comes out to a stability factor of 1.3.

I believe I'm gonna stick with them for a little while and see what I can do with them. The only thing I'm worried about with them is getting a good load developed with these nice high temps we have coming up only to have the bullets tumble and fall on their face next winter.
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  #12  
Old 02-03-2011, 11:55 PM
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Posts: 327
Re: 7mm Berger 180 Hybrid twist rate help

Thats when you can use this tool to make sure your ok for next winter --> http://accurateshooter.net/Blog/millerformula.xls

Remember required twist rates vary according to the conditions, and contrary to popular belief, increasing velocity only increases stability SLIGHTLY. By far the biggest factors are AIR DENSITY, and bullet length (which is always the same if your using same the same bullet of course).

The above spreadsheet will help you find an ideal twist rate if you dont mind restricting yourself to a temperature and altitude range, you can get away with significantly slower twist rates than what manufacturers recommend.
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  #13  
Old 02-04-2011, 04:46 AM
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Join Date: May 2007
Location: Taranaki New Zealand
Posts: 182
Re: 7mm Berger 180 Hybrid twist rate help

Hi Hicks and Groper, The twist rate factors and related issues you have described are true and well founded. That said, there is a factor that is not considered in these equations, the problem of bullet jump and bullet to bore alignment.

A 7mm RUM for example, has 400 thou jump with the VLD. After ignition, the bullet leaves the case and enters the slightly oversize freebore, travels through this void, then finally engages the rifling. In some instances, the projectile does not engage the rifling in a square, or atleast uniform manner, resulting in a degree of bullet deformation, as well as yaw. In such instances, the more twist rate is increased, the worse the yaw. I believe this is why Weatherby used a 1:10 twist for their 7mm cartridge for so many years.

In the example of the 7mm RUM given, increasing velocity will not increase stability, it will increase yaw. But increasing twist rate will also induce further yaw. What Remington engineers hope, when using the slow twist in the RUM, is that all the factors will work together to produce desirable accuracy. So, we arrive at a point where in this case, we should be atleast entertaining the idea that there was another flaw in the particular rifle in question.

The 7mm Remington Magnum is different again. The cartridge is designed with minimum freebore (unless it is custom throated) while most rifles have a generous magazine box, allowing the user to seat bullets close to the lands. Nevertheless, in high velocity cartridge loadings, any imperfections in the concentricity of the hand load (such as case neck uniformity), will potentially cause yaw. Increases in twist rate magnify the problem.

My original point was, which looking back, I believe I did a bad job of explaining and it was poorly qualified, is that in the 7mm remington magnum and similar or higher power cartridges, increases in twist rate do not always produce desirable outcomes and are not nearly as forgiving as say the 7mm08.

All too often, we blame poor accuracy on the wrong variable. Again using the 1:9 1/4 twist 7mm Rem Mag as an example, these rifles are pretty much bread and butter for my wife and I, we accurize these for clients regularly. Across the board, the 180gr VLD shoots well in these rifles, often around .3" sometimes around .5" which is excellent. Ok so lets say that I receive a Sendero rifle one day that shoots .75" with the VLD after tricking it up. Can I blame twist rate when all of the other rifles shot .3 to .5"? Ofcourse not.

The bottom line, atleast to me, is that as long as we don't understand some of these more subtle problems and instead (in this instance), adopt increased twist rates, we are only adding pressure to companies like Berger who ultimately, will have to continue to toughen up their bullets to counter problems we are creating.

Ok, I hope I have explained things in a useful way, perhaps help people see this particular issue from a different angle (or is it- oh crap, yet another variable! )

AZShooter, I would anticiapate that the new .338 VLD's will work well on game weighing 200lb and above. On lighter game, results may be dependent on whether the bullet strikes major muscles and bones. On rear lung shots, the results may be inconsistent and sometimes disappointing. Time will tell. I need to keep up with the play so I will do some testing in due course. A lot of people consider the .338 to be a large game only caliber and for these guys, a tougher jacket will be acceptable. If the bullets are tough, it will be a problem for the guys who simply enjoy the .338 and want to use it on everything.

Last edited by Kiwi Nate; 02-04-2011 at 05:36 AM. Reason: typos
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  #14  
Old 02-04-2011, 05:05 PM
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Join Date: Sep 2008
Posts: 327
Re: 7mm Berger 180 Hybrid twist rate help

indeed you are correct nate, increasing twist rates beyond what is minimal is seldom a good idea... I was referring to the exact opposite, running the bullets out of a slower twist than reccommended by the bullet manufacturer... The calculator i posted can help you work out if you will have enough twist to be stable depending on the conditions you plan on shooting them in - which was the OP`s original question....

Going to faster twists was what we were talking about in a different thread recently, and the argument for faster twists was strictly with regard to being able to design bullets with a significantly higher BC, never said they would be more accurate
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