Concern about twist rate for Berger 105 Hybrids

[Bugs]

Joe. . . I set the Reade Range group record last year with Hybrids and a Brux 8.2 twist but am starting to think that Jim O'Hara may be on to something. I've never shot barrels (many assorted 6 x 47 barrels, all cut rifled) faster than 8 twist but am going to order a 7.8 or so to see how it works.

Mike Bonchack

 

[LRPV]

Does anybody get 105 hybrids that are actually as long as Berger has them listed at? I have been through different lots of them myself and the ones i get are around .025-.015" shorter than stated on Berger's spec sheet. If you put your actual numbers in their twist calculator you might find out that you are fine with the old 8 twist.

 

[spclark]

Does anybody get 105 hybrids that are actually as long as Berger has them listed at?

Good question, worth pulling out the calipers when you get a fresh batch.

When I started with them I didn't bother measuring OAL or BTO between batches, they seemed to shoot just fine anyway.

With 155 Hybrids I noticed a difference of about 0.030" between the first batch I used and later ones from 2013. This year some I'd received in May were back to the shorter end of the range. They've all shot fine for me at the same 0.020" jump.

6mm's may be more sensitive to speed + twist....

 

[normmatzen]

My 6BRX lives at near sea level and does real well with a Bartlein 1 in 8 barrel. All it has ever shot was Berger 105 Hybrids. I'm running 3005 fps in a set forward 28" barrel.

 

[JDMock]

After reading these posts, I began to wonder if an 8-twist was optimal for the 105 Berger Hybrid in my 6mm Dasher. My newest barrel is a cut-rifled 4-groove at 28 inches.

At the last match, I had shots that seemed to be lost for no apparent reason. After consideration of the extra length of the Hybrids, I put an older Bartlein barrel on my old BAT. It is a "gain twist" barrel (8.25 - 7.75). This 2009 vintage barrel has quite a number of rounds, but I thought that I would give it a try at our monthly 600 yard match. (Prince Memorial Range, Goodwill, LA).

I loaded two loads for the match..... 32.0 gr. of Varget with the Hybrids jumping ~ 0.020; and 32.5 gr. of Varget with the same seating depth. The 32.5 gr. load seemed a little warm in our 92 degree heat w/ high humidity, therefore, I used the milder load.

I was very surprised by how the rifle shot and it did not have a single "flyer" in the 20-shot match. I ended the match with a personal best 194/6X score.

In the future I will use my newer 8-twist barrel with shorter bullets than the 105 gr. Hybrid. Good shooting...James

 

[marwitz89]

Thanks for the information James. I ordered a Broughton 7.3 twist and a Bartlein 7.5 twist for my BRX that I plan on using strictly for my hybrid bullets. The 8 twist barrels I have would probably work but I figure this will ease my mind.

Joe

 

[normmatzen]

Come on guys,

You want me to believe that 7.8 twist is markedly different than 8 twist?

That is a difference of 2.5% so I would expect the rotational speed to change 2.5% as well.

Lets see, I weigh powder to 0.6% and segregate bullets to 0.6% weight groups and seat bullets to 20% seating force and cases weigh, and cases volume is etc etc. And you expect the ballistics to be within 2.5% and the stability to be better than 2.5%. Only way that argument is valid is if we are next to a cliff that is stone stable and a shear drop.

7.5 I would accept.

But, I would like to see some lab testing to say I'm wrong! And, no anecdotal evidence!!

 

[johara1]

Does anybody get 105 hybrids that are actually as long as Berger has them listed at? I have been through different lots of them myself and the ones i get are around .025-.015" shorter than stated on Berger's spec sheet. If you put your actual numbers in their twist calculator you might find out that you are fine with the old 8 twist.

Most all i checked were a lot shorter than the advertised length but when i set the record with them they were very close to that length but to be honest i think is was a little bit different than the ones you see today……… jim

 

[1shot]

I just screwed a 32" light Palma 1-7.75" on and hopefully will be doing some load development today. This is chambered in 243 AI with a .269 neck so I may have some data by tonight. The bbl. has been broken in and so far seems to act right for a new bbl. We will see how it behaves when I start pouring the coal to it.
Lloyd

 

[johara1]

Come on guys,

You want me to believe that 7.8 twist is markedly different than 8 twist?

That is a difference of 2.5% so I would expect the rotational speed to change 2.5% as well.

Lets see, I weigh powder to 0.6% and segregate bullets to 0.6% weight groups and seat bullets to 20% seating force and cases weigh, and cases volume is etc etc. And you expect the ballistics to be within 2.5% and the stability to be better than 2.5%. Only way that argument is valid is if we are next to a cliff that is stone stable and a shear drop.

7.5 I would accept.

But, I would like to see some lab testing to say I'm wrong! And, no anecdotal evidence!!

Where are you going to find a 1000 yd. lab, it is kind of amazing that 4 -7.83 barrels shoot better than twice as many 8 twist barrels from 100 to a 1000 yds, Always the same chamber seating depth same loads and the 7.8 will shoot smaller…….. Not only with 105 Hybrids but 103 Spencers, 104 BiB's and 115 DTAC's with the same powder and primers ……..and over 6000 rds………….. jim

 

[normmatzen]

Jim,
I shoot at a 1000yd "Lab" every week!

And, I abhor anecdotal evidence. Too many years in electronics engineering and audiology!

 

[normmatzen]

I would not, however, consider any input on this subject from Brian Litz as anecdotal evidence!

 

[TonyR]

Interesting topic. Berger has a new twist rate calculator (invented by Bryan Litz I believe) that addresses this issue:
http://www.bergerbullets.com/twist-rate-calculator/
According to this thing, a 7.75 twist will have a 3% BC advantage over an 8 twist with a 105 Hybrid going 3000 fps under standard conditions. A 7.5 would have a 5% BC advantage, the maximum possible improvement from a faster twist. I would think that a 3% BC advantage would be noticeable on a 1000 yard BR target over the course of a season's or big match agg.
The science behind this calculator is over my head but I trust things Bryan Litz develops.

 

[noload]

I just checked the length of my 105 HYBs =1.257" is my avg lgth. 105 VLDs are 1.227" avg. lgth. Both New Lots of 500 each.

 

[michaelnel]

I just received 800 of these (lot #6043). Measured 10, and they ranged from 1.241 to 1.250" long.

Their bullet specs in their Quick Reference Sheets (http://www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf) show 1.292" for OAL.

Wonder why such a discrepancy?

I also wonder why they advertise them as being good for 1:8 twist, and then come out and say you really need faster than that. I have about 700 of these and a 1:8 twist barrel, and my first session (an OCW test) with these bullets was pretty terrible. I hope I am not stuck with a bunch of expensive bullets I am not going to be able to use.

 

[normmatzen]

I'll gladly accept Brian's data on improvement in BC with faster twists. The BC chances about the same amount as the twist changes.
But, we were talking stability here, not BC.
And, I do not believe a skilled shooter will care about a 5% change in BC!

 

[big bad bill]

After considerable frustration trying to shoot Berger 105 hybrids in my 6BR Kreiger 8 twist (30.0g Varget), I have discovered that with 60F ambient and a cold barrel, my groups were just under .5 inches with few holes touching. When the ambient was 80F or/and a barrel temperature of 110F or higher, I get .2 inch or better groups. It seems my barrel/load/ambient conditions were on the edge of stability for the bullet. My solution is to have a 7.5 twist barrel built.
Bill

 

[dkhunt14]

Too many guys on here are having trouble getting the 105 Hybrid to shoot. I believe the 8 twist is at the edge of stability and depending upon the velocity, altitude and temperature it seems to me that it might be borderline. I know my Dasher at 1000 yards will shoot 10 shots in the 4 to 5 inch range and won't shoot the Hybrids at all. I don't need an engineer to tell me why, I just know it doesn't. I believe a 2 to 3 percent increase in twist would put a @#%$ of a lot more RPM's on a bullet. Might make the difference if you are on the edge. Matt

 

[johara1]

Jim,
I shoot at a 1000yd "Lab" every week!

And, I abhor anecdotal evidence. Too many years in electronics engineering and audiology!

I guess i deal with what the targets tells me…… small group aggs. and records as evidence…… I never did rely on what other people tell me, You have to do it yourself……. jim

 

[JDMock]

I'm with Jim on this. I didn't switch to the 7.75 twist because of some formula that told me that the hybrid was "marginally stable", but because I was experiencing some unexplained flyers with the 8 twist. Let the target tell you when it is time to change. Good shooting...James