N150 in 308

[nigdnn]

Hi new member here long time rifle shooter and reloader, but I have decided for many reasons to only use Lapua scenar 155 in my and my wife's 308( wife's 308 is a 1/13 twist at 30") mine is a 1/11  32 inch.

Im looking for suggested loads with N150 for 1000 yards or am I better to go with N550 I want to keep around the 3000 fps range

I know all about RS52 but the availability of it in my neck of the woods is scarce, and I have plenty of N550 and N150

Thanks 

Nigdnn

[The Gun Pimp]

N140 is usually the 'go to' load with 155s.

 

[Richiew]

N150 from web site is 39-46 grain s . Also taking that my load for a 175 grain bullet is 44.5 g of n150 so your lighter bullets can take a bit more and there’s more space in the case ?? . Start about 43 and work up in 0.5s to get something in the high 2800 fps with good accuracy. N550 quotes max 50.2 g for top end 2900-3000 fps , depending on how much wil fit in the case . As before start a bit lower and work up . 
cheers

 

[Laurie]

A 13 twist as on your wife's rifle is decidedly 'slow' for the 155gn Scenar which is an exceptionally long bullet for its weight. At a tad over 1.290" bullet OAL, it is the longest 308 bullet in its weight class by quite a margin. The Berger stability calculator gives it an Sg of 1.19 at 3,000 fps MV in standard ballistic conditions (1.5 optimal). Yes, I know people have long used 155 Scenars in 308 TR / Fullbore / Palma rifles with this twist rate, but performance can deteriorate markedly beyond 800 yards with this degree of spin. The 13 rate is ideal for the much shorter original 155gn SMK (#2155) which is one reason (and a very good reason too) why the NRA specified this bullet in its contract ammo. Your rifle's 11 twist rate is ideal for this bullet.

I used to use N150 a lot with 155s in 308, as the combination often gives superb precision, but it's difficult to get enough of it into a Lapua case for 3,000 fps level MVs. I never tried N550 with this bullet weight, but suspect that (despite what Viht says in its powder descriptions) it is considerably slower burning than the single-based 150, and therefore won't develop full working pressures with the bullet weight. When talking single-shot competition rifles, top loads are often very heavily influenced by the chamber throat length the gunsmith gives it. TR and similar rifles are normally chambered with very short 'freebores' which reduce maximum charges, if nothing else because of the effect on physical powder capacity in the case. Always worth trying it though!

[nigdnn]

Laurie the rifle is a dolphin ftr and is throated for 155 gun bullets ,my wife's HPS I dont know how that is throated .

Another thing is I have around a 1000 Lapua scenars 155 grain on my shelf, and maybe 400 2155 SMK

so to sum up then do you think i would be better in the HPS to go with the SMK 155 ?

I will do velocities with both powders and bullets in both rifles

 

[nigdnn]

Gunpimp/ Richiew thanks for you comments

[Laurie]

45 minutes ago, nigdnn said:

so to sum up then do you think i would be better in the HPS to go with the SMK 155 ?

 

Good question! In your shoes, I'd try both in this rifle (the HPS) and see how they shoot. You'll likely find the HPS rifle very short-throated, the chamber having been cut with one of the TR/Fullbore reamers such as the old 'Bisley 150' chamber or whatever its more modern equivalent is. In your rifle, I know having had Dolphin do several rebarrelings for me in various cartridges, Mik usually uses a minimum-freebore reamer, then 'throats' it as a second operation to suit the customer's intended bullet, so you'll likely find somewhat greater freebore. But again, you'll have to see.

Returning to the pros & cons of the various bullets, the old 155 SMK is relatively low BC (0.214 average G7), but its great 'pro' is that it is an exceptionally stable design as speed drops into the trans, then subsonic speeds. That is another reason why it has been adopted by the NRA for its ammo given that many TR rifles in use will struggle to keep their bullets supersonic at 1,000 yards especially in colder weather conditions.

The Scenar is higher BC, but interestingly, Bryan Litz gives two BCs for the design (Ballistic Performance of Rifle Bullets 3rd edition). The 'cooking' Scenar gets 0.236 average; the Scenar-L 0.221, not a great deal better than the antediluvian SMK. This puzzled me as I'd thought the 'L' was identical to the ordinary Scenar, except for a guaranteed improvement in production quality / consistency. However, according to Litz's bullet measurements / drawings, Lapua made some shape changes here, to nose and tail sections. IIRC, Lapua dropped the older 155gn plain-Scenar version some years ago, and they've all been the 'L' variety in this weight in recent times, so it depends what you actually have. (If both, don't mix them in an ammo lot 😀 !)

Run them through the Berger Ballistics Solver and at 3,000 fps MV for Bisley on a 'standard' day (29.92 inches HG at sea level; 59-deg F air temp), you get at 1,000 yards (theoretically):

 

Older SMK (0.214 BC): ............ 1,181 fps / 10.56 inches movement per 1 mph 90-deg wind change

Scenar-L (0.221 BC) ................ 1,225 fps / 10.04 inches etc

Scenar (0.236 BC) .................. 1,315 fps / 9.07 inches etc

 

However, that's on the basis of perfect bullet stabilisation from the imparted rifling spin. Berger's Twist Rate Calculator predicts the Scenars will see a ~9% actual BC reduction with a 13-inch twist under the same external conditions at 3,000 fps MV to 0.215 for the Scenar and 0.202 for the Scenar-L. So the older Scenar has no BC benefit over the SMK, and the Scenar-L is actually worse. (The SMK is perfectly stabilised so retains its nominal 0.214.)

 

So, theoretically anyway, irrespective of which design groups better at 1K in a 13-twist, the SMK sees no extra windage effect over the old Scenar, and outperforms the newer 'L' variant.

 

Clever man though Bryan Litz is, this may all be b*ll*x in real life on Stickledown, Altcar, Diggle, and Blair, but the evidence suggests the old 155 SMK may be the better choice in your other half's rifle on a number of counts. If she ever tries the two models side by side at 1,000, I'd love to hear the results.

 

 

 

[Richiew]

My AI AT didn’t like the lapua designs being a 1:12” twist . The only difference was the L design has a better point part similar to a normal bullet being put through a pointing die . 155 Amax , 155.5 Berger were the best options. Could nt get them over the high 2800s .

At eskdalemuir my 308 ran out of steam at 900 yards , no problem with hits upto this distance but 1000 and 1014 targets were either hits or over the top or under the target. 
26” barrel though so you might be ok with your longer barrel . 
 

[nigdnn]

Laurie, Richiew, again thanks chaps, so maybe i should then keep the scenars for 600 yards max or try to get some Berger 155.5 as i belive these are supposed to be better.

Ok so also in stock I have 190 SMK   185 Berger VLD   175 SMK and some old Lapua 185 D46 

Comments and suggestions on these would be appreciated

Nig

[Richiew]

Your 1:11” should be ok for the heavies . Berger 185s juggernaut are very good at 44.5 grain of N150 give 2660fps so might be worth a try for the 1000 yards in your barrel. All the above bullets are well made and will stay stable to the target . 
Good luck