best bullet weight for different calibers and twist rates

[bushwacker_hock]

I pickup my new f/tr 308 next week and will begin load development soon after. It's a blue printed Remington long action bolt (yes, it started its life as a 300 win mag) in 308 with a 1:10 twist throated for 168 gr (approx I guess). Reasonable freebore. The 168 gr is pushed at about 2600 pfs where the 155 Scenar gets to about 3000 fps. My question is since its throated for the 168 gr, how well do you think it will handle the 155 gr? Is that weigh worth the load development time and expense?

 

[Keith Glasscock]

I guess I better start with a question:

What range are you planning on shooting?

If you are planning on shooting the shortest F class range (300 yards) the 168 is everything you need. If you are going out to 600 yards, the 168 will work, but it isn't optimal. The 155 might be better, but don't be afraid to run heavier bullets. The 175 gr Matchking is a significantly better bullet than the 168 beyond 300 yards. Nice thing is, it has the same ogive so it will fit in the throat the same as the 168. I don't have any experience at 1000 yards, so I'll let the others that do chime in on that one.

With a 10 twist, you can literally shoot any bullet you can get the 308 to launch. I'd even look toward to 200+ class of bullets.

If you are looking to be competetive at F/TR, you will need to do load development in order to get your rifle consistently below 1/2 MOA at competition ranges. On the other hand, a good time can be had even with a load that only produces 1 MOA.

 

[bushwacker_hock]

I'll want to be 1/2 moa competitive at 600 yards assuming me and my rifle are capable of that. Under usual conditions in Alabama my ballastics says the hornaday match 168 gr has mv of 2700fps down to 1632 at 600 yds and 1135 at 1000 yds. the Sierra MK 175gr starts at 2528, 1738 at 600 and 1260 at 1000. The 75 gr looks as good as the lighter 155. My problem is just where to start my load development so I don't waste a bunch of time and money. Odd, but noticed the 168 gr has a faster mv than the 175 but is slower at the 600 yd point. Is the higher bullet wt keeping it from slowing as quickly. wouln't have thought that.

 

[Baddog0302]

"google" M118LR loads, several links to loads with 175 SMK

here is one http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1548904

 

[Keith Glasscock]

The long and short of bullet selection:

In F-class, the wind is your enemy. Anything you can do to minimize its effects, the better off you will be. Let’s look at the 168 versus the 175 Matchking.

We’ll launch the 168 at 2600 and the 175 at 2550. Using JBM’s calculator and Bryan Litz’s G7 BC, I get the following drift numbers at 600 yards for a 10 mph wind:

168 @ 2600 fps: 38.1 inches
175 @ 2550 fps: 34.2 inches

So what does that mean in terms of score? I like math – here goes. The 10 ring is 6 inches in diameter, so a miss over 3.154 inches (ring edge plus half the bullet diameter) is in the 9 ring.

With the 168 bullet @ 2600 fps, you will have to call the wind within 0.83 mph to keep it in the 10 ring.

With the 175 @ 2550 fps, you will have to call the wind within 0.92 mph to keep it in the 10 ring.

With a new barrel, there is no telling what it will like. If it is like mine, near max charges group well and give adequate vertical at 600 yards. Here are some numbers at (near) max loads (26” barrel):

168 @ 2780: 34.2 inches (This velocity is away from the node for me)
175 @ 2740: 30.5 inches (This velocity is right on a node for me)

Wind call accuracy required to hold the 10 ring:

168: 0.92 mph
175: 1.03 mph

Just for fun, the Berger 185 Long Range BT @ 2600 (not quite max) gives a drift of 27.0 inches and a required wind call of 1.17 mph. Of course, that performance comes at a steep price ($44 a box last I checked)

I would strongly suggest that you spend a little time playing with jbmballistics.com before you spend time and money at the range trying to develop a load. Also take a good look at the 308 Win page here, it is full of good advice (especially powder/primer selections).

If you are using Hodgdon powders and Winchester brass, data.hodgdon.com is a great source of load data.

Warning! Hodgdon’s data is good in large-capacity Winchester cases. Federal cases (and others) are significantly shorter in capacity and will be unsafe very quickly! Please always start at the starting charge! The little bit of powder used is far cheaper than a new rifle/face.

Good shooting!

 

[bushwacker_hock]

thanks for great info. My barrel is a 26in Douglas with the senderos coutour. I got got and am learning the RSI Shooting Labs software program and if I can figure it out provides extensive data on drop and path for varous loads and hopefully it will save me some powder.

 

[bugsplat]

Nothing really technical to add but I will say that the bullet weight to twist ratio I've found to be more of a suggested guideline than a science. Barrels can be just as picky with bullets as humans are with food. I've had some barrels that hated the bullet weight they were designed for yet loved either light weights or heavies but nothing in the middle. The simple truth is you never know until you try it. If you have the time, patience, and money try a little of everything. If you have another 308 that likes Load-XYZ start with that.

Probably not the answer you were looking for but if you reload, half the fun is finding that perfect load. I spend about 98% of this hobby behind a reloading bench. Shooting the rounds is just a test to see how well I made the rounds. I have more fun reloading than I do shooting.

 

[Redhighpower]

I had a Winchester Varmmit, 26in, one in twelve twist shot S 175's very well. Range at 1000yrs shot 98 and a 96. That barrel loved Varget and 175's