168 Stability With 1-10 Twist

[agr516]

I barreled a 7mm Dakota to shoot the 168's with a 1-10" twist based on the recommendation of Berger's website as well as my gunsmith. I am wishing now that I had gone wih a 1-9" as I have never been able to get these bullets to shoot at all. I have tried velocities from 3100-3300fps. The 140's shoot fantastic but are not what I had in mind for this rifle. Is anyone shooting 168 Bergers through a 1-10 twist and havng any luck? If so, what is your chambering and velocity?

Thanks

 

[expiper]

Dear agr.....dont feel all alone....your not the only one.....most 9 1/4" factory bbls wont shoot em either.....I have an 8" twist that makes em shine ....they are a gr8 bullet,you just gota hav enuff twist to make em work....I highly reccommend MORE twist than most advocate....esp in cold weather or low elv.....Roger

 

[agr516]

Oh I am definately in low levation at around 250'

 

[KevinThomas]

agr516,

Another point to consider here when dealing with a particular twist in a given barrel is how it was made. If you're talking about a cut barrel, it should measure very (very) close to whatever is specified in the stated twist. Not so with buttoned barrels, which can vary by a half inch or better +/- from what is speced. Nature of the beast, as the pitch of the button is what controls the rate at which it turns during its passage through the drilled blank. Hard or soft spots (we're speaking in relative terms here, of course) will cause that button to turn fater or slower, slightly altering the twist rate for some distance within the barrel. Not a knock against buttoned barrels, I have many of them and most are fine shooters. But it is something to be aware of when you consider a twist rate.

Roger has given you good advice here, especially when thinking about a buttoned twist; go with more than what you think you'll need. Rarely causes any problem with some extra spin, whie not enough will create headaches every time.

 

[flatlander]

I recently built an AR10 in 7-08 AR30 on DPMS-style receivers from J-D Machine, chambering a 1-10tw. Krieger contoured blank that finished at 25" for this rifle. It handles the shorter Sierra 168s very well, giving very good accuracy at 600yds. But since Berger & JLK 168s are too long for magazine fed ammo, I haven't tried any of them through it.

Also have three 1-9tw bbls. (two 30" & one 28") chambered for a straight 284, which all handle bullets up to & including Berger & JLK 180 VLDs, so I may yet try the 168 VLDs in single load mode, just to see how they'll shoot in the 1-10 bbl. Elevation here is 2660'MSL.

edited to add: Kevin's point is a very valid one - I waited several months longer than anticipated for a 1-14tw 6mm blank from Tim North at Broughton a couple of years ago. When I called to ask about the delay, Tim related that the button he'd been using to make 1-14tw bbls. had suddenly started making 1-15tw with a new batch of SS blank material. The incident does speak well of Broughton's QC - they caught it before shipping slower twist bbls.

 

[RDavies]

My last hummer barrel was a 7mm which was supposed to be 9" twist but ended up around 9 3/4". This was a button rifled barrel as well.
This one wouldnt consistantly shoot 180gn pills but it loved the 168s at 2820 fps out of a 284 with 28" barrel.

 

[fullersson]

arg516,

Your post doesn't make me feel so good right now. My buddy and I just ordered two 30 cal barrels a 16 twist and a 19 twist. The 16 is going to be a .308win and the 19 is going to be a 30br. I figured the twist for the .308win and came up with a 14, but according to Berger and Bryan Litz the 16 is what we needed. We decided to go with the recommendations of the professionals and so we shall see. Between your post and Mr. Henry Rivers I'm still having my doubts about the slower twist rates. I don't know if you are familiar with Henry Rivers but he is a world class short range benchrest shooter. I took some classes at my local technical college and he was one of my instructors. When I told I had ordered a 19 twist for a 30br build he said "well that should be interesting". That didn't instill a lot of confidence either. Good shooting, Brian.

 

[newhornet]

I just had a .280 built, Krieger barreled in 9 twist on Berger's recomendation that it would stabilize a 180, so the 168's should have done fine.... Couldn't even stabilize a 168, so NO need to try the 180's. I went with Hornady A-max's in 162 and they seem to do fine at 500,.....that is as far as I have tried them thus far.

 

[jsimonh]

I shot the 168s out of a 9.5 twist in 7RM, they stabilized fine but I couldn't get them to shoot worth a darn. I moved to the 180 hybrids and had much better luck. The 7RM is gone now and a 284 9 twist is being built for the hybrids.

 

[RGRobinett]

arg516,

Your post doesn't make me feel so good right now. My buddy and I just ordered two 30 cal barrels a 16 twist and a 19 twist. The 16 is going to be a .308win and the 19 is going to be a 30br. I figured the twist for the .308win and came up with a 14, but according to Berger and Bryan Litz the 16 is what we needed. We decided to go with the recommendations of the professionals and so we shall see. Between your post and Mr. Henry Rivers I'm still having my doubts about the slower twist rates. I don't know if you are familiar with Henry Rivers but he is a world class short range benchrest shooter. I took some classes at my local technical college and he was one of my instructors. When I told I had ordered a 19 twist for a 30br build he said "well that should be interesting". That didn't instill a lot of confidence either. Good shooting, Brian.

With 30 cal. FB bullets measuring up to .950" long, your 19" twist will prove a very sound choice - it won't do well with longer projectiles. The 16" twist should perform very well with either BT,or, FB bullets of up to 1.10" long: FB bullets of this length perform quite well via 1:17" twist barrels. RG

 

[agr516]

RGRobinett,

Are you using a program to determine that Fullersson's bullets should stabilize in hs 19 twist? If so, what does it say about a 10 twist .284 stabilizing 168gr VLD's at 3150-3200fps at 250' altitude?

Thank You,

Agr516

 

[customshooter]

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Start there....

 

[Squid284]

I have two rifles with the factory 9.25 twist barrels (when they wear out I will upgrade) and I've shot 168 and 180 Bergers without any issues or keyholeing. If your velocity is 3300FPS you should have a stabilty factor of 1.36 which is still on the high end of the marginal stabilty range I wouldn't necessarily blame the 1:10 twist, maybe something else is going on? I'd try playing with your bullet jump or do a OCW test. Higher velocity/altitude will help stabilize better. It took me a long time to find the best seating depth for the 168's. Good luck.

 

[RGRobinett]

RGRobinett,

Are you using a program to determine that Fullersson's bullets should stabilize in hs 19 twist? If so, what does it say about a 10 twist .284 stabilizing 168gr VLD's at 3150-3200fps at 250' altitude?

Thank You,

Agr516

"

Confirming calculations, both myself, and others have, in combination with bullets based upon the .925" long J4 jacket, successfully used 1:20" twist barrels (Sg + 1.4) to consistently win/place/show in registered BR events. Depending upon the point-up die, and jacket LOT,FB bullets on the 'short jacket' usually measure .930" to .950" in length. For these bullets, a 19" twist is a "no-brainer", producing 1.5 Sg.

The Drag/Twist calculator, found on the 'calculators' page, at JBM Ballistics, is a very accurate tool. These calculations correlate very closely to the Tioga Engineering (Bill Davis) bullet design [program] calculations.

Not to disparage the "new guy", but, the twist calculator at the bottom of the JBM home page does not correlate at all with either the JBM, or, the Tioga programs, both of which, have proven very reliable - right down to, "the edge of the cliff."

As pointed out by Kevin Thomas, above, button rifled barrels may vary quite a bit from the nominal twist rate - confirm what you have - with buttoned barrels, "hanging ten" may prove disappointing. RG

 

[agr516]

Thank you guys for the help. I will check the true twist of my bore and see if I indeed have a difference in the twist over what was spec'd. If I should be stabilizing these bullets with the velocities that I have tested in, then I may just have a rifle that doesn't like them. When I say 3300, that is on the very top end of my pressure tolerance and is hotter than what I would like to be. I did most of my testing at 3150-3250 and tested seating depths from a .010 jam out to a .030 jump. I may do another seating depth test to see if an even further jump would make a difference. When working with the 140's, I found that a .010 difference in seating depth with the vld's can mean the difference between .75 MOA and a ragged hole. I think I should also step back in the distance of my load testing. I have only been testing at 100yds to find a load that looked good before stepping back to 300-500 to really see what it was doing. I just never found a load that could consistently group better than .75" so I never did any longer range tests.