150 SMK, 155 SMK & 155 Palma SMK ???

[boltgunluvr]

I keep reading more about shooters that have gone to the 150-155 SMK bullets over the 168 SMK. Looking for some input as to a legit reason. My Rem700 sps V shoots the 168 SMK at 0.5 in @ 100 yds using Win brass/primer & 42.7gr of Varget. Great for factory rifle. I don't chrono. Do the 155s really shoot that much better???

 

[stockdoc]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

I just told another guy here about the 155 scenars. They shoot really well out of my 308 at about 2935fps or so with 46 grains of varget. They have a higher bc than the sierra's and fly better in the wind. Worth the try.

 

[jkonzal]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

I shoot the 155 A-Max and they work great for me (1:12 twist)!!! I also use 46 grains of Varget and they run about 2910 fps. I would also submit that 0.5 in @ 100 yards doesn't say much. A lot changes even just going out to 200 yards. If you are shooting long range, you really should have a 200 yard zero. IMHO.

 

[RugerSlinger]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

The reason people are shooting the 155 SMK is because it has the same BC as the 175gr SMK and you can push them faster.

 

[ksthomas]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

Boltgunlvr,

Need to separate a few things here, just to make sure we're all on the same sheet of music; one, forget about anyone who recommends the 150 SMK for LR work, it won't do it. Neither will the 168, but you're already aware of that. The 155s will, but they're not really the best bullets out there suited to the task. The weight of 155 is what is specified as maximum for the international Palma rules, and is <span style="text-decoration: underline">required</span> maximum weight for this type of competition. Most US shooters, if they're not going to be shooting international matches where the rules demand this weight, will set up for a heavier bullet, and use them for such shooting. The 185s and 190s are probably the first choice here, and work well out to 1,000 yards.

The 155s (Ours, Berger's, and Sierra's) all work well at 1,000 (and this, after all, is what they're designed for), but they are at their best in guns that are set up specifically for them. They're unusual bullets, and violate some of the basic "rules" for "correct" bullet design; reasonably sharp ogive, slightly longer boat tails and bearing surface of less than one caliber. Because of this they have some definate requirements from a barrel to be at their very best. This usually means a 29"-30" barrel, a 1x13" twist in a tight bore, tight groove rifle chambered with a short throated Palma reamer. Driven to right around 2,950 fps, these bullets will stay supersonic at 1,000, and are generally very good shooters. But understand, they're 155s because that what the rules demand, not because that's the "ideal" weight for a long range bullet in a 308 Win.

They're worth a try if you'd like to tinker, but if you don't get the results you're looking for pretty quickly, I'd abandon the idea and head straight to a heavier bullet.

 

[shooter.dm]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

Very good point. I beleve one reson why 155s is because they shoot a lil bit flatter but down side is winddrift sucks

 

[tolnep]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shooter.dm</div><div class="ubbcode-body">Very good point. I beleve one reson why 155s is because they shoot a lil bit flatter but down side is winddrift sucks </div></div>

well. this is a bit confusing.

i got the impression that the ballistic coefficient was key to determining 'wind drift' and performance out to some distance. the BC of the 155 scenar is very good.

if you check a lot of the forums, the 175 smk and the 155 lapua scenar are pretty popular for shooting out to 1000 and the 168s are simply bad juju unless you are at some high altitude and even then the other bullets are better choices.

this is not to say the referenced heavier bullets are good but there seems to be more preference for 155 scenar and 175 smk and 178 amax sometimes for 1000 yards. the heavier bullets come up but not so often (it seems).

 

[ksthomas]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

If the BC's the same, and the velocity's the same, the wind drift will be identical. You've got it exactly correct.

 

[ronnl001]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kevin Thomas</div><div class="ubbcode-body">If the BC's the same, and the velocity's the same, the wind drift will be identical. You've got it exactly correct. </div></div>

Respectfully, I don't believe this is an accurate statement. Heavier bullets buck wind better than lighter bullets at the same velocity and bc. For example, my knights ballistic app shows approximately 10% less wind drift between the 175 and 155.

With additional speed, this is not to say that performance of the 155 might meet or exceed the 175 but, I still do not believe that the above statement is ballistically accurate.

 

[boltgunluvr]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kevin Thomas</div><div class="ubbcode-body">Boltgunlvr,

Need to separate a few things here, just to make sure we're all on the same sheet of music; one, forget about anyone who recommends the 150 SMK for LR work, it won't do it. Neither will the 168, but you're already aware of that. </div></div>

The 168s do work for me. Always been consistent for several years.

 

[boltgunluvr]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

Any more info about 155s out of factory 1 in 12??? I'll probably just do a little more homework on the 175s.

 

[oneshotkyle]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

my new sps-v seems to like the 155 scenars with 45.5g varget in new lapua brass. i ordered more 155 scenars, 155 sierra palma's and 155.5 berger fullbores to try also.

 

[Chanonry]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ronnl001</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kevin Thomas</div><div class="ubbcode-body">If the BC's the same, and the velocity's the same, the wind drift will be identical. You've got it exactly correct. </div></div>

Respectfully, I don't believe this is an accurate statement. Heavier bullets buck wind better than lighter bullets at the same velocity and bc. For example, my knights ballistic app shows approximately 10% less wind drift between the 175 and 155.

With additional speed, this is not to say that performance of the 155 might meet or exceed the 175 but, I still do not believe that the above statement is ballistically accurate. </div></div>

Actually no it is largely correct. Run it on JBM you can keep a constant bc but vary the weight => no change in wind drift. BC is a function of section density and form factor (i.e. shape). So heavier with the same bc implies a worse form factor so the effects cancel out.

You are of course correct that in practice everything else is not equal, you cannot launch a 175 at the same speed as a 155 so the heavier bullet is often a more practical choice if you are trying to minimise wind drift but with a 155 with a highly efficient form giving a bc normally found in a heavier bullet can give ballistic advantages if it is be launched at higher velocity

This gives less drop (shorter time of flight) and less drift (less lag time). You also get less recoil. Minor effect may well be different however

 

[tolnep]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chanonry</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ronnl001</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kevin Thomas</div><div class="ubbcode-body">If the BC's the same, and the velocity's the same, the wind drift will be identical. You've got it exactly correct. </div></div>

Respectfully, I don't believe this is an accurate statement. Heavier bullets buck wind better than lighter bullets at the same velocity and bc. For example, my knights ballistic app shows approximately 10% less wind drift between the 175 and 155.

With additional speed, this is not to say that performance of the 155 might meet or exceed the 175 but, I still do not believe that the above statement is ballistically accurate. </div></div>

Actually no it is largely correct. Run it on JBM you can keep a constant bc but vary the weight => no change in wind drift. BC is a function of section density and form factor (i.e. shape). So heavier with the same bc implies a worse form factor so the effects cancel out.

You are of course correct that in practice everything else is not equal, you cannot launch a 175 at the same speed as a 155 so the heavier bullet is often a more practical choice if you are trying to minimise wind drift but with a 155 with a highly efficient form giving a bc normally found in a heavier bullet can give ballistic advantages if it is be launched at higher velocity

This gives less drop (shorter time of flight) and less drift (less lag time). You also get less recoil. Minor effect may well be different however </div></div>

it was my assumption that if you could get 155 scenars to work with a load on the high end that the potential was at least as good as 175s if not better since you can launch them at a faster speed.

thats why i found the issues of 155s not being the best choice (heavier bullets being better) confusing. intuitively heavier seems better but BC rules and given two bullets with equal BCs, the faster bullet will be the better performer.

 

[ksthomas]

Re: 150 SMK, 155 SMK & 155 Palma SMK ???

Okay, a little explanation here. BC is simply a drag comparison to some "standard" upon which a given table is based. The G1, G7, G5, G6, whatever. It has nothing to do with weight or caliber, beyond what it takes to yeild a certain BC with a given drag model. Now, larger and heavier bullets, having the exact same shape and design as a smaller bullet otherwise identical to it (these are called homologues) will have a higher BC. That's probably where you're getting this impression from. But, if two bullets, one a .338" and the other a .204" have the same BC, their flight characteristics will be exactly the same IF they're launched at the same velocity; wind drift, drop, remaining velocity at a given range, etc., all identical.

Now the odds of these two bullets actually having the same BC with a model that's valid for both of them, not very likely. Here's where we need to get into different drag models and so on. The chances that both are going to be normally used within the same velocity ranges, again, not likely. Stuff gets complex in this end, and that's where you need to toss some additional qualifiers into the mix.