Range Report why the 155gr. scenar for .308

#51
Re: why the 155gr. scenar for .308

Can someone tell me if the 155 has any gains over a 175 moving at 2900 to 2925 out of a 308. That is with the 155 moving at 2950 to 3000. I dont have any comp programs to get that info and my bbls wont shoot the lapuia 155s
 
#52
Re: why the 155gr. scenar for .308

OAL 2.920 Win Brass
read that again its important
47.8gr varget under da skinny
zero pressure issues no ejector wipe, shoots good
 
#53
Re: why the 155gr. scenar for .308

Nesika
if you can run 175@ 2900fps then you should be able to hit 3100fps+ running skinny
hell i hit 3050 out a 26" barrel big gobs of IMR dont ask its crazy big load
 
#54
Re: why the 155gr. scenar for .308

Nesika should be so close you wont see more than .25-.50moa difference if you change over

Now today I had my Scenars at 3150fps (2.92OAL, 46.5 grains H4895, Lapau Case and 155 Scenar) but that load is on edge of almost too much

 
#56
Re: why the 155gr. scenar for .308

I have 30" and that is my real hot loads. My typical load is 46.0 grains and I am running 3090-3100fps

The 46.0 grain load has been safe from 70-100 degrees, but your rifle may vary.

These are long laoded and pumped way the f up to fight wind at 1000-1200 yartds.

Last year I ended up running right at 3000 fps but this looking for a slight edge
 
#57
Re: why the 155gr. scenar for .308

Interesting discussion here with respect to jumping the Scenars. SMK 175's in mag length cartridges jump ~ .140" out to the lands in my Rem 5R. I used a stoney point to make the measurement. For those having good luck with them, are you guys jumping anywhere's near that amount??

BTW - I took the "shoot the heck out of it before working it" with the 5R. I have 2000 through it and another 1K-2K to go before rebarreling and reducing the freebore.
 
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#58
Re: why the 155gr. scenar for .308

Running a skinny hot eqautes to 260 performance pert much, 26" barrel or shorter skinny just makes more sense.
I hope to start to start competing next year F/TR and open class, pending many things which must get done first. $$ thing this hobby aint cheap and comps are $$
 
#60
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tactical</div><div class="ubbcode-body">I have 30" and that is my real hot loads. My typical load is 46.0 grains and I am running 3090-3100fps

The 46.0 grain load has been safe from 70-100 degrees, but your rifle may vary.

These are long laoded and pumped way the f up to fight wind at 1000-1200 yartds.

Last year I ended up running right at 3000 fps but this looking for a slight edge </div></div>

Did you consider the 210 bergers (or JLKs)? According to JBM with a 10mph wind, at 2,700, the 210 bergers would beat the 155s at 3,100 by about 6 inches at 1k. My F class rig is still a work in process but I'm strongly leaning towards the 210 JLKs. I hear that 2,700 with a 32" barrel is very doable.
 
#61
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mk4</div><div class="ubbcode-body">Scimitar,

What kind of velocity are you getting with that load?

Overall Length?

I've tried the Scenars several years ago but to no success. Only thing, I don't recall trying any Varget. Used some Ramshot TAC, IMR4895 and maybe H4895.

Lapua brass is great.

</div></div>


Sorry missed that a while back. I have two guns that are chambered to engage a 175 SMK
in the riflings at 2.800 COL. The 155 Scenars are seated to 2.820 and I get a velocity
of 2900 FPS out of my 700 GAP with a 26 inch AI barrel. Out of my shorty Gap Howa with a 21 inch FN hammer forged barrel I get 2780 FPS.
 
#64
Re: why the 155gr. scenar for .308

The 155's provide an improvement in velocity with no loss of BC. If your barrel likes them (tight bore) and restricted mag length forces you to jump the bullet, then have at it, they jump well.

But I don't like the way the 155's perform at extended range: as they begin to run out of steam they suddenly drop like a rock.

I prefer 175JLK's seated to the lands (BC .545). And, for 800 meters-plus, the 180JLK long boat tails using the same powder charge as the 175's.

45.0 varget in a Lapua case gives me 2700fps at 70 degrees with a 180JLK LBT (BC .580): Stable in a good 12-twist barrel and much better performance in crosswinds at 1000.
 
#65
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">The 155's provide an improvement in velocity with no loss of BC. If your barrel likes them (tight bore) and restricted mag length forces you to jump the bullet, then have at it, they jump well.

But I don't like the way the 155's perform at extended range: as they begin to run out of steam they suddenly drop like a rock.

I prefer 175JLK's seated to the lands (BC .545). And, for 800 meters-plus, the 180JLK long boat tails using the same powder charge as the 175's.

45.0 varget in a Lapua case gives me 2700fps at 70 degrees with a 180JLK LBT (BC .580): Stable in a good 12-twist barrel and much better performance in crosswinds at 1000. </div></div>


What length is that 12-twist if you don't mind me askin?
smile.gif

 
#70
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Torfinn</div><div class="ubbcode-body"> What length is that 12-twist if you don't mind me askin? </div></div> 24" AE. Shoots the 180VLD's and 175 VLD's just fine.
 
#71
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mk4</div><div class="ubbcode-body">I'd be interested in hearing from anybody using the 155's with any success shooting a 1-12" twist in a 20-22" barrel. Loads and velocity. </div></div>

Im using 155 Scenars in a 24" tube wtih 47.8 gr Varget in 1:12 twist.

Case: Winchester
Primer: CCI 200
Powder: Varget 47.8
BUllet 155 Scenar
OAL: 2.948 or 0.015 from the lands
MV: 2925-2950
0.33" 5-shot groups at 100.
 
#72
Re: why the 155gr. scenar for .308

I am loading 155's with 45.0gr of Varget and get a little crunch when seating the bullet - just want to check if anyone else is getting a "compressed:" load with 45.0 grains of Varget - I didn't see any past comments about 155's compressed.
 
#74
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BV 700P</div><div class="ubbcode-body">I am loading 155's with 45.0gr of Varget and get a little crunch when seating the bullet - just want to check if anyone else is getting a "compressed:" load with 45.0 grains of Varget - I didn't see any past comments about 155's compressed.</div></div>

What case do you use? Also, what is your COAL? I have 47.4 grains of Varget in my Lapua brass at 2.910" and it is not a compressed load. I would check my bullet seating depth and make sure that it is accurate. Even with Lake City brass, which has the least volume, I don't think that you would get a compress load at 45 grains. Be safe.
 
#76
Re: why the 155gr. scenar for .308

COAL is 2.800 with Federal Cartridge cases. It didn't seem right to be getting a compressed load with 45.0gr of Varget.
 
#78
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palma</div><div class="ubbcode-body">COAL of 2.910 would jam the lands in most .308s. Look at the lengths above. </div></div>

In my AIAW, the chamber length is 2.920".
 
#81
Re: why the 155gr. scenar for .308

In a May 16, 2011 Berger Bulletin, Bryan Litz wrote about the concept of “form factor” and how it could be used to analyze the efficiency and performance of a given bullet. The form factor is the sectional density of a bullet divided by its G7 ballistic coefficient. The G7 ballistic coefficient is used instead of the G1 because the G7 standard is a better match for the longer boattail type bullets most of us shoot, and should be more constant over a wider range of velocities, as compared to the G1.

The form factor measures how efficiently a bullet flies (drag), independent of its weight. Form factors of 1.000 or greater are bad; form factors of 0.999 to 0.950 are better; and form factors of 0.950 and below are the best.

Doing the math for the Lapua 155 Scenars (.308): 0.223 (sectional density) / 0.236 (G7 BC) = 0.987 (form factor).

So… this is another reason to shoot the 155 Scenars.
 
#83
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WyomingShooter</div><div class="ubbcode-body">How does the Hornady 155 A-Max compare to the Scenar? With thanks and best regards from the Big Empty, ELN. </div></div>

Doing the math for the Hornady 155 Amax (.308): 0.223 (sectional density) / 0.212 (G7 BC) = 1.099 (form factor).
So... looking at the form factor, the Amax does not appear to be as efficient through the air as the 155 Scenars.
 
#84
Re: why the 155gr. scenar for .308

Thank you sir. "Form factor" is new to me. Is it possible to calculate the difference in drop and/or drift at a given distance using "form factor"? For example, let's say we're driving both the 155 Scenar and the A-Max at a MV of 2850 fps. Can we calculate how much more the A-Max will drop at 1000 yards? With best regards, ELN.
 
#85
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WyomingShooter</div><div class="ubbcode-body">For example, let's say we're driving both the 155 Scenar and the A-Max at a MV of 2850 fps. Can we calculate how much more the A-Max will drop at 1000 yards? </div></div>

Google and use: JBM ballistics. Use the bullets from the drop down list with the [Litz] lable.
 
#88
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WyomingShooter</div><div class="ubbcode-body">Thanks Mitch. I use JBM and some other similar software. Is the "form factor" applied in JBM? Best regards, ELN. </div></div>

I don't know that any of the ballistics models use the form factor of a bullet, but then again I don't claim to know a lot about the internals of these models. Form factor is the sectional density of a bullet divided by the G7 BC of that bullet. The JBM model has a bullet library that includes the G7 BC for some of the bullets. These are the ones with "(Litz)" after the bullet name.

The bullets that I shoot most often are the Amax 208 and 178, the SMK 168 and 175, and the Lapua Scenar 155. I manually calculated the form factor on these bullets and found that the Amax 208 and 155 Scenars were the only ones that had a form factor below 1.00. These 2 bullets have less drag than the G7 standard, so that's why I shoot them (and only them) right now.

Read Bryan Litz's May 16, 2011 Berger Bulletin on form factor to better understand what it is and what using it tells you about the bullets you shoot. Then get a calculator and calculate the form factors for the bullet(s) you shoot to see how efficiently they fly.

Once you find one or more bullets that have acceptable form factors, use OCW or ladder tests to find their optimal powder and charge weight, experiment with different seating depths to find the tightest groups, and then shoot the daylights out of that load. That's what I'm doing.

Bob
 
#89
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: WyomingShooter</div><div class="ubbcode-body">Is the "form factor" applied in JBM?</div></div>

To the best of my knoledge, No, the form factor is not applied to the bullets labeled [Litz]--what is applied is something much better. The bullets are loaded up by Bryan Litz himself and shot over chronometers and measured for drop at distance. From this data a G7 BC is computed and Bryan then generously supplies the data to JBM for all to use.
 
#90
Re: why the 155gr. scenar for .308

Form factor was traditionally used the other way around: a theoretical form factor was calculated from the geometrical properties of the bullet, and then BC was defined as the sectional density of the bullet divided by the form factor.

But to get correct BC at mid/long range (or form factor) you have to shoot the bullets and measure velocity decay at several ranges. Once you have the correct BC you also can have the correct form factor.
 
#91
Re: why the 155gr. scenar for .308

I have been playing with them for the last little while with my .308. I load mine like so and see about .75moa, and am going to start playing with seating depth next

50.5gr Alliant 2000MR
155 Scenar
Lake City brass
2.875" seating

the round chrono'd at 3000fps on the dot as my average speed and can feed from my AI mags.
 
#92
Re: why the 155gr. scenar for .308

I get 2875 fps running the 155 scenars out of a Gap 10 with an 18.5" Bartlien 11.25 twist. These are crazy accurate out to 950 yards and then they seem to drop like rocks.
155 scenar
45.8 grains RE15
LC brass
CCI primers

Loaded to mag length.
 
#94
Re: why the 155gr. scenar for .308

A few years ago, Don Miller developed a formula for calculating the stability of a given bullet in flight. Based on a bullet's caliber, weight, length, barrel twist, muzzle velocity, and some environmental conditions, Mr. Miller calculates the "Gyroscopic Stability" (SG) for any given bullet. To achieve an adequate level of stability (and accuracy), the SG should be at least 1.40 and should not exceed 2.0.

An article in accurateshooter.com entitled "Calculating Bullet RPM — Spin Rates and Stability" (June 2008), has a link to Mr. Miller's formula in an Excel spreadsheet that permits you to calculate SG for any given bullet.

To put this in perspective, my friend Greg has a barrel with a 1:12 twist. Using the Lapua 155 Scenar in .308, his round needs to generate a muzzle velocity of 2950 fps to achieve an SG of 1.40. In my gun, which has a 1:10 twist, the 155 Scenar will generate an SG in excess of 2.0 at only 2900 fps.

So... if Greg and I were both shooting the same 155 Scenars at 2925 fps, his accuracy would suffer because his gun is not spinning the 155 fast enough to properly stabilize it. My accuracy would suffer because my gun is spinning the 155 too fast to properly stabilize it.

Something else to think about I guess.
 
#96
Re: why the 155gr. scenar for .308

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">squarenut, if you use the Miller formula you will see that gyroscopic stability changes VERY little with +/- 100 fps...

http://accurateshooter.net/Blog/millerformula.xls </div></div>

I agree Tiro. Your point is well-taken.

What this exercise tells me is that, when I shoot the 155 Scenar out of my gun, I need to stay south of 2900 fps (using standard atmospheric settings) to effectively stabilize the bullet and achieve accurate results. North of 2900 fps begins to affect my ability to stabilize the bullet, as well as my accuracy.

To your point, for the 208 Amax (which is what I shoot the most), I cannot physically make a bullet that would have a muzzle velocity that will push the gyroscopic stability number north of 2.0. I hit 1.40 at about 1950 fps and inputting wildly exaggerated muzzle velocities in the formula still doesn't push the gyroscopic stability number anywhere near 2.0.

So... I am comfortable knowing that, at the muzzle velocity of my current load (2625 fps), the 208 Amax is rotating and stabilizing as it should. Any variation in my results is most likely due to poor shooting technique. I will ladder test a 155 Scenar load within the next week or so. If I get a good node (or 2) and the chronograph readings are south of 2900 fps, I will be comfortable with that as well.

The more I read and learn and experience for myself, the more fascinated I am by the science of what happens once you pull the trigger.
 
#97
Re: why the 155gr. scenar for .308

I'd really like to hear from somebody who has used both the 155 Scenars and Sierra's new 155 Palma bullet.

I've been running 155 Scenars for about 4 yrs with good results. I've got a 26" Mike Rock 11.25 twist barrel and have been pushing the scenars at 2900+ with 45-46grns H4895. The only thing I don't like is the powder compression you get with magazine length loads. I've tried Lapua and Winchester cases. Winchester cases have more volume and a little less powder compression, but I'd prefer to use Lapua cases. I want to avoid compressed loads as I've noticed increased seating depth variations when compared with non-compressed loads.

The new Sierra 155 palma bullet is shorter than the Scenar by .081 inches so I'm thinking they might eliminate (or mostly eliminate) powder compression with mag length loads. Being a shorter bullet they should also stabilize better in the 20" 12 twist barrel of my Remington 700 LTR. I tried the 155 Scenars in my LTR and they didn't group very well. I ran the Miller stability calculations on the JBM site and the results confirm my theory that the Sierra 155s might perform better in my 700 LTR.

Thanks for your help!
 
#98
Re: why the 155gr. scenar for .308

Try XBR 8208 with the Scenars. I have run compressed Varget loads for years, but switched to XBR and can get the same velocity with less powder. I am running around 2950 with a 26" Rock tube, but can run it faster.
 
#99
Re: why the 155gr. scenar for .308

I tried everything to get the 155 SMK palma bullets to group out of my 20" gas gun, no joy. I am back to my old standby 155 scenars with 46.0 of varget in lc brass, mag length. Very predictable results out to 850-900 yards. At 1K it opens up to about 2 MOA.
YMMV-Rob
 
#100
Re: why the 155gr. scenar for .308

I've shot both the Lapua and SMK version, and much prefer to SMK (2156) due to cost. Performance is very close between the two. 8208XBR is the powder for 155 class bullets in 308. I'm at 2925 out of a 24" barrel with no pressure signs, and very good accuracy. the 2156 smk likes to jump...alot.
 
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