7mm 10 twist with 168's?

[AckleyImproved]

Hi

I have the opportunity to purchase a 280Rem but it has a 1:10 barrel. I am uncertain if the 10 twist will stabilise the 168 weight projectiles. Anyone know for certain if it can? I see Berger lists that the 168 needs a 10 twist, but researching people say a 9 twist, but maybe they say 9 twist so you are not limited to only up to 168's? It seems I cant find a definite answer on this one!

Thanks

 

[JRS]

The 10 twist recommended by Berger is the MINIMUM twist required for the 168.

 

[AckleyImproved]

The 10 twist recommended by Berger is the MINIMUM twist required for the 168.

Yes I understand that, but I have read that it is very borderline. Another way to put I, will a smaller capacity case like a 7mm-08 with a 10 twist stabilise a 168VLD??

Cheers

 

[JRS]

The 10 twist will not be borderline, with the 168. If, however, you use heavier bullets, your best choice would be a 9 twist barrel.

 

[3Ackleys]

I have a 10 twist 280 Ackley. It will shoot the Berger 168's .7 to 1" 3 shots at 100. It will shoot the 140 Bergers .4 to .7

 

[AckleyImproved]

Excellent news indeed. 10 twist will stabilise the 168 weight match bullets no problem well then the decision is made! I would of hated to get caught out with stabilisation issues!

 

[FeMan]

I have a 1:10 twist in my 7mmSTW. I live at sea level and the Berger 168's stabilize fine. The 175 Nosler LRAB's stabilized 75% of the time If you are shooting at altitude, you might get away shooting above the 168s with a 1:10.

 

[Laurie]

Berger has added a menu driven twist rate stability calculator to its online ballistics suite with a link to a database containing the company's bullets.

http://www.bergerbullets.com/twist-rate-calculator/

The answer to your question depends upon what you want to use the 280 for. If an L-R match rifle, 1-10" is a bit slow for bullets the length of its 168gn VLD getting the result of 1.28 SG, 'marginally stable' at 2,800 fps; 1.31 SG, (same comment) at 3,000 fps MV.


If you have a look at this calculator and Bryan Litz's current thinking on this issue, the desirable minimum Sg value has now risen to 1.5 based on the Miller formula. This takes Michael Courtney's recent work on board which shows that while a bullet may be stable at marginal Sg values and will shoot tight short-range groups, BC is apparently adversely affected (seriously so) below a certain key Sg value. For 0.224-inch dia match bullets in the 52/53gn weight range, the key value was found to be ~1.3 in real life range tests. This isn't a great issue for short-range benchrest competitors, but could be for 1,000 yard F-Class as a diminished 'real BC' will produce greater wind drift and the risk of dropping into transonic speeds.

 

[expiper]

just a lil' note from a backwoods shooter,,,,over the years I have fiddled with many 7mm Rem Mag "deer" rifles,,,mostly Rem 700's,,,with 9 1/8 or 9 1/4 twist,,,,measured a few with the trusty cleaning rod method,,,nothing "precision",,,and found most of em didnt shoot the Berger 168 VLD's well (they are a great bullet ,,,but gota have the twist to work),,,they will shoot Sierra 168's fine,,,,(im shur the experts will tell us the Sierra is shorter and thus shuld work,,,we know that) ,,,,sooo if your goana hunt game/meat with this rifle and not planning on going to the super shoot,,,then I would shoot lots of various 150's (hunting or target styles) and maby try 160 class hunting bullets which I have found to work very well,,,,,,I dont hav the gyroscopic stability data on em but just shareing what I hav found blastin away here in the back woods,,,,Roger