I read in a few places that the 155's wont shoot good out of short barrels. I just don't understand why? The run 150's out of AR platforms all the time. I do they perform 100 to 1000 yards? How do they compare to the 168 smk & 175 smk or amax & vld bullets?
- Thread starter madarcher427
- Start date
That is a bunch of BULLSHIT. What you are reading likely has to do with saying that 155s need to go really fast to have any advantage. This is somewhat true, but you really only need to be around 2850. You do not need a 30" barrel to do this. I have shot plenty of 155s out a 20" barrel for a few years and they did just fine. I've since moved on from 308, but the 155 palmas were my favorite
This is not an accurate representation of reality.
Some people have agendas, the guns don't care one way or the other.
If you can get a 155 up into the 2850 fps range (perfectly possible in 20") the 155s will make it to 1000 yards.
The 155s prefer to be over 2950 fps and make it to 1125 yards supersonically, but this generally takes 22"-24" barrels.
The 155s can be pushed over 3025 fps in 30" barrels (typically PALMA stuff.) The 155 SMK (2155) required this kind of velocity to be a good PALMA round.
ill give them a try ,Cant hurt anything . i wonder if a fast twist would help?
Typically the faster twist is for heavier bullets. It is actually a dab easier to get to your target velocity with a little slower twist (less friction).
I am running 155's in a 20" SPS Tactical and have been to 800 with them. It is a 1:12.
I am running 155's in a 20" SPS Tactical and have been to 800 with them. It is a 1:12.
Damn good shooting!
madarcher427,
As previously stated what you've been hearing/reading and telling us, is not in it's entirety close to being correct.
First, think bore dia. vs. case size. The .308 has a case size/bore dia. ratio that allows it to burn slightly faster powders than the .243 Win, .260 Rem and 7mm-08 Rem. Optimal powders for the heavier bullets are RE-15, IMR/H4895, and specifically Varget. These are medium burn rate powders. The smaller the bullet diameterthe slower the powder you can use.
That said, when you go down in bullet weight to 155 gr. you can use faster powders. IMR 8208, TAC, Win 748. These are basically standard .223 powders. Meaning you can get a lot of velocity out of them in a short barrel. The 155's all pretty much have a maximized BC forthat bullet weight because of Palma shooting. Combine good speed with High BC and you have a qualifiable 1k round.
So, FWIW, they will shoot just fine out of shorter barrels. You may get more velocity out of a longer barrel. As long as the load is accurate, that is what matters most. If you try to exceed the capable range of the 155's you will fail.
Something that never gets discussed on ballistic programs is how well a bullet stabilizes through and beyond the transonic range. This is really important, I think. No bullet remains completely stable through that range. And that means that some accuracy is given up. The bullet wobbles through the air when the sonic crack hits the base of the bullet. How it is balanced, length of boattail and rate of twist it is spinning at will determine if it regains stability. Meanwhile the wobbling is causing lateral aerodynamic movement of the bullet in relation to the vector it is following. It still wants to follow that vector. But, once it moves off that path it will parallel it , at whatever distance, until it either goes radically unstable or hits something, like earth or a target.
The 175's are better suited to shooting longer ranges as they tend to regain stability better. Again, a balance of weight and longer Boattail are attributing factors. A 1-10" twist never hurts, even though a twist as slow as 1-13" will stabilize them.
The 168's don't do well beyond the transonic range, which at seal level std. pres./alt. is about 850 yds. They don't fall out of the sky, but don't shoot super accurate either beyond this.
The 155's were (being Palma oriented from the start) optimized to go to 1k-1.2k. They don't require a 1-10" twist and are unusually long for overall weight in the boattail and ogives.
As noted above you can almost always get more velocity out of a longer barrel. It is, simply, longer push time for the expanding gases to work on the bullet. A short barrel doesn't mean you won't get enough velocity to make the bullet work. Getting to the edge of it's capability is something you will have to find out.
As previously stated what you've been hearing/reading and telling us, is not in it's entirety close to being correct.
First, think bore dia. vs. case size. The .308 has a case size/bore dia. ratio that allows it to burn slightly faster powders than the .243 Win, .260 Rem and 7mm-08 Rem. Optimal powders for the heavier bullets are RE-15, IMR/H4895, and specifically Varget. These are medium burn rate powders. The smaller the bullet diameterthe slower the powder you can use.
That said, when you go down in bullet weight to 155 gr. you can use faster powders. IMR 8208, TAC, Win 748. These are basically standard .223 powders. Meaning you can get a lot of velocity out of them in a short barrel. The 155's all pretty much have a maximized BC forthat bullet weight because of Palma shooting. Combine good speed with High BC and you have a qualifiable 1k round.
So, FWIW, they will shoot just fine out of shorter barrels. You may get more velocity out of a longer barrel. As long as the load is accurate, that is what matters most. If you try to exceed the capable range of the 155's you will fail.
Something that never gets discussed on ballistic programs is how well a bullet stabilizes through and beyond the transonic range. This is really important, I think. No bullet remains completely stable through that range. And that means that some accuracy is given up. The bullet wobbles through the air when the sonic crack hits the base of the bullet. How it is balanced, length of boattail and rate of twist it is spinning at will determine if it regains stability. Meanwhile the wobbling is causing lateral aerodynamic movement of the bullet in relation to the vector it is following. It still wants to follow that vector. But, once it moves off that path it will parallel it , at whatever distance, until it either goes radically unstable or hits something, like earth or a target.
The 175's are better suited to shooting longer ranges as they tend to regain stability better. Again, a balance of weight and longer Boattail are attributing factors. A 1-10" twist never hurts, even though a twist as slow as 1-13" will stabilize them.
The 168's don't do well beyond the transonic range, which at seal level std. pres./alt. is about 850 yds. They don't fall out of the sky, but don't shoot super accurate either beyond this.
The 155's were (being Palma oriented from the start) optimized to go to 1k-1.2k. They don't require a 1-10" twist and are unusually long for overall weight in the boattail and ogives.
As noted above you can almost always get more velocity out of a longer barrel. It is, simply, longer push time for the expanding gases to work on the bullet. A short barrel doesn't mean you won't get enough velocity to make the bullet work. Getting to the edge of it's capability is something you will have to find out.
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Time to bust out the Palma 155's!! I want to make a "poor mans" .260/6.5 CM with them. Well, at least try....I have a 20" 1:10 as well.
As much as I want to hold on to them, as I may need them, I have 6 boxes of Lapua 155 Scenars that need another home.
