6.5x284 Norma Build Barrel Twist?!

[Wedgy]

I do think the Berger calculator pretty accurate.

When I built my 300NM, the internet said 1:8 and a few people thinking 1:7.5 to handle the 230's. I felt this thinking likely BS so I called Berger to get their thoughts. They told me to run a 1:10 like I had planned.

My rifle with a 26'' 1:10 Bartlien shoots the 230's sub .5moa as well as 210's sub .5moa

Just because a bullet flies straight and punches a round hole in paper does not mean it will have the stability to perform(expand and keep going straight) when it hits meat. Many bullet "failure" can be attributed to this, often the bullet is found bent like a banana and made a sharp turn after hitting the animal.

 

[Lobber]

Interesting point, Wedgy. I suppose a lot may depend on the bullet design as well.. What you are describing may not be as much of an issue for a Berger hunting bullet, which tends to be fairly explosive upon impact; compared to say a Barnes, which needs to stay on course into the animal to perform as designed. Ask 5 different bullet manufacturers this same question about stabilization for their specific hunting bullet, you may get 5 different answers based on materials, jacket design/thickness, and overall bullet design.

 

[Wedgy]

Interesting point, Wedgy. I suppose a lot may depend on the bullet design as well.. What you are describing may not be as much of an issue for a Berger hunting bullet, which tends to be fairly explosive upon impact; compared to say a Barnes, which needs to stay on course into the animal to perform as designed. Ask 5 different bullet manufacturers this same question about stabilization for their specific hunting bullet, you may get 5 different answers based on materials, jacket design/thickness, and overall bullet design.

Funny you mention Berger, the 195 got a bad rap at the start for poor performance but I suspect it was under stabilized. Guys were shooting it from 9 & 8.5 twist barrels and probably had enough stability to fly straight but not enough to perform correctly.

 

[tim_w]

Its really simple. If you care about the bullet max BC and stability in ALL conditions and elevations then use the twist the bullet manf recommends. If you not then you have choices to make. Also there is no way one inch in length of twist angle is going to have a real noticeable effect on barrel life. Long shooting strings and pushing max pressure with double based powders has the most effect after bore surface area to powder weight used.

If you are that worried about the initial bullet engraving angles effects peak chamber pressure and heat etc then get a barrel with a 1 inch gain twist.i.e. 1:8 - 1:7 twist. Bartlien does this frequently.

 

[tim_w]

Funny you mention Berger, the 195 got a bad rap at the start for poor performance but I suspect it was under stabilized. Guys were shooting it from 9 & 8.5 twist barrels and probably had enough stability to fly straight but not enough to perform correctly.

The same thing is happening with the new line of SMKs. People are complaining about bad groups when on the ragged edge and at a little better vertical stringing. All using twist rates that do not fully maximize stability. But those using the actual full recommended twist that gets you around 2.0 seem to be doing just fine to include a fair number of F class shooters. I swear its like people can not read. A company recommends a twist rate and shooters immediately try a barrel with a twist rate 2" angle slower and give a bad review. Its one thing to try it for an experiment or because you know you are @ 5k ASL or pushing them way faster and have done the stability calculations.

Think about it why would a bullet manf purposely reduce its bullet sales and audience by recommended a faster twist than needed especially when its a twist rate that is not commonly used for that caliber or any production guns?

 

[Wedgy]

Its really simple. If you care about the bullet max BC and stability in ALL conditions and elevations then use the twist the bullet manf recommends.

Note that these have changed even long after a bullet has been released. Berger has been good on on updates but still changes AFTER release. As innovation occurs Hammer Bullets has been on top of SG/twist/performance as they are pushing the limits of twist, materials, and innovation(testing on meat). Again, if you haven't been playing the mono game for a decade or more you should update on SG & penetration. Look in to Cutting Edge Bullets as well , they seem to dominate the ELR.

 

[Greyfox]

You didn't state what your purpose is for the rifle. For hunting to 1000 Yards, I would tend to agree with stwcattle that the benefit of the heavies in the 6.5x284 are not material enough, and the current offerings in the 140 weight class well proven. IMO, they will probably prove to be more effective in the larger capacity variants of the 6.5. I will be very interested in seeing the 150-155gr performance on game, as there are few reports out ay this early stage to draw firm conclusions. I personally choose the "minimum" twist rate neccessary to "fully" stabilize(1.5) my choice in bullet, preferring not to comprimize accuracy and throat erosion, a well proven effect of excess twist observed by bench rest shooters for many years.

 

[jpfrog]

You didn't state what your purpose is for the rifle. For hunting to 1000 Yards, I would tend to agree with stwcattle that the benefit of the heavies in the 6.5x284 are not material enough, and the current offerings in the 140 weight class well proven. IMO, they will probably prove to be more effective in the larger capacity variants of the 6.5. I will be very interested in seeing the 150-155gr performance on game, as there are few reports out ay this early stage to draw firm conclusions. I personally choose the "minimum" twist rate neccessary to "fully" stabilize(1.5) my choice in bullet, preferring not to comprimize accuracy and throat erosion, a well proven effect of excess twist observed by bench rest shooters for many years.

@Greyfox you have me second guessing my choice in a 26" 7.5 twist for the remage barrel I should be receiving in the next couple of weeks from NSS. I have 147 ELDM for it so far, and have some of Steve's 124 Hammer Hunters. Will I be over doing it in the 6.5-284? Should I try a heavier Hammer offering such as the 130 Sledge or the 137 Hunter??

 

[Hatrick]

JP, It has been my assumption that there is nobody more knowlageable than Steve on the hammers. When it comes to his bullets you should just trust him. He has 20 packs of bullets to try and if they don't work he said he would buy them back.

 

[jpfrog]

I definitely trust Steve- he sent me some 124gr 6.5 and 181gr .30 cal bullets that I think are fantastic. I will keep using the 124 in my 6.5x47 if they don't work in the 6.5-284. I may just order some of the 137 anyway, since I need to also place an order for some .277 hunters. I'm running low in time and have a lot of handloads to get ready for the fall!

 

[Edd]

The difference in the engraving angle between a 7" twist and an 8" twist is a whopping .83°.

 

[Greyfox]

@Greyfox you have me second guessing my choice in a 26" 7.5 twist for the remage barrel I should be receiving in the next couple of weeks from NSS. I have 147 ELDM for it so far, and have some of Steve's 124 Hammer Hunters. Will I be over doing it in the 6.5-284? Should I try a heavier Hammer offering such as the 130 Sledge or the 137 Hunter??

I think that a 7.5 twist would be fine for the 147 ELDM's and the Hammer bullets. It's about as fast a twist as I would probably choose it I also wanted to shoot 140's while trying the heavier/longer bullets. I wouldn't be worried about your build. IMO.