Sierra Palma Match 155 and IMR4064

[Bart B.]

Interesting, Jim, that you get better accuracy with the Scenar's.

Lapua states their accuracy at 300 meters with their Scenar 155 averages about 2 inches; biggest groups are going to be close to 3 inches. Darned near 1 MOA.

Sierra gets 1/4 MOA average or better with their Palma 155's at 200 yards.

 

[Jimro]

Bart B.

Jim's experience with the Scenar 155 being about equal to the 175 SMK makes sense to me, those bullets are abou the same length. The Sierra 155 is much shorter, so it seems like a twist optimization problem, in other words, Jim's barrel has too tight a twist and is over spinning the short bullets.

Alternately, it could be that the bearing surface is allowing more resistance giving a more complete/consistent powder burn with the Scenar and 175 SMK.

Could be a lot of things, but those are the two most likely in my mind.

Jimro

 

[Bart B.]

Sierra's 155's have shot with equal accuracy testing near 1/4 MOA at short range and near 1/2 MOA at long range in twists from 1:10 to 1:14. John Whidden proved that fast spinning ones do with his 1:10 twist Palma barrel with the bullets leaving at 3000 fps.

Well balanced bullets are very accurate over a wide range of rpm's as they leave the barrel. But most people don't understand that. Bullet rpm equals velocity in fps times 720 divided by twist in inches.

Some people using 26" 1:10 and 1:11 twist barrels shot Sierra 155's about 1/2 MOA at 600 yards in the first matches they were used in.

 

[Jimro]

http://www.riflebarrels.com/articles/bullets_ballastics/bullet_imbalance_twist.htm

Very good isn't the same as "mathematically perfect." And it could also be something as simple as barrel harmonics hitting a "scatter node" with that particular bullet in that particular rifle.

John Whidden seems to make magic when he builds a Palma or F Class rifle, so I wouldn't want to say that a John Whidden 1:10 twist barrel is indicative of what ever 1:10 twist barrel out there will do.

Jimro

 

[HiBC]

For my own clarity,there are two Sierra 155 gr Match bullets,the 2155 and the 2156.

Only a few years ago,the 2155 was the 155 gr Palma.Fairly recently,within the last few years,a new 155 Palma was introduced.It has a BC over .500,its the 2156.

Now,the 2155 old Palma is called the 155 MK,and the new 2156 is the Palma.


When the 2156 came out,i bought a box to try side by side with the 2155

It was just comparing a Varget load from an AR-10 T and a DPMS LR308L.

They were loaed to 2.800 mag length.

The old style 2155 shot very well.The new 2156 ,like the OP's experience,was going about 2 moa.

I do not blame the world class Sierra Palma bullet,I fully accept something about our rifles/loads makes it unhappy.

I noticed in the 6mm BR article the 155 gr Sierra bullet was called the MK,not the Palma,if I had the right article.

Are we all talking about the same bullet?

 

[Bart B.]

I'm not aware of any difference in accuracy between them. The newer one has a slightly different shape giving it a slightly higher BC. It'll drift a tiny bit less in a given crosswind. And a 20% spread in accuracy across several lots of each is normal. Given a choice of a lot of the old ones being more accurate than a lot of the new ones, I'd pick the old ones.

 

[old roper]

I think looking at the two 155gr bullets from Sierra sure look different.

http://bulletin.accurateshooter.com/2008/12/sierra-introduces-new-308-155gr-palma-bullet/

Bart, I read what you posted about the 1/13 twist barrel and since I didn't write the article you may want to contact Bryan Litz.

 

[DAVID NANCARROW]

Well, darn me for not reading the news. The old Palma match bullets did okay in my rifle, but I looked at the box and sure enough, I am trying to run the new 2156. Apparently, the old Palma is now simply the 155 Match King according to the article Old Roper.
Guess I am going to find out if the new Palma can do as well as the old style in my rifle. The 2155 did just a shade under moa at 100 IIRC, but that was years ago and I don't recall the powder combination.

 

[Bart B.]

With your factory barrel, I think you'll need to shoot 20-shot (or 30-shot's better) test groups with each bullet to make a meaningful comparison. I doubt you'll see much difference.

 

[DAVID NANCARROW]

Good idea, Bart. Back to the press I go.

 

[DAVID NANCARROW]

Sorry to be so late in getting back to those who have tried to help. Between the VA hospital and all the rain, its been interesting to say the least. The hunt for the elusive accuracy load for the 155 grain palma match continues, although I may just have to settle for the 155 grain Match King instead, which groups well out of my rifle. With the exception of the center bullseye, all loads were 10 shots each. The center target was 30 rounds, all of which were under windy conditions.

Upper right target was 47 grains of IMR4064. This load shot worse than the 44 grain load I had issues with earlier.

Upper left target was 47 grains of Reloader 15.

Lower left target was 47 grains of Varget.

Lower right target was 47 grains of H4895.

The center target was 41 grains of Reloader 15 and Sierra 175 match Kings, fired last. I don't know what anyone can make of these groups, and my shooting today was not up to my usual, but I am coming to believe that in order to get the 155 to group well, I am going to have to go to their standard 155 MK.

The rifle is a bone stock Remington Varmint Synthetic built back in the late 90s, the trigger I adjusted myself and the action screws are torqued to 45 inch pounds. The scope is a Leupold Vari X III on Leupold dual dovetail rings.

Brass is new Lapua, full length resized, COAL 2.815. Federal 210M primer. Remington's seem to like a really long leade, and I loaded to magazine length.

Thoughts?

 

[HiBC]

That is the sort of results I got with the new Palma bullet.

I also have little doubt that the old Palma,now the 155 MK,will shoot like your center target 175 MK's.

I know nothing about Palma.My wild guess:Its a specialized,edgy competition.Staying supersonic at 1000 yds is important.Many MK's are very forgiving bullets.They want to shoot.That characteristic may cost a little BC.

Maybe ,to get the over .500 BC cutting edge bullet to shoot,it takes a particular design chamber reamer/bore/groove/rifling form...etc.I bet Elliot Reamers or PTG or Manson could fix you up.

Just my guess.Given,I got similar results with the new Palma,I just shrugged and used a different bullet.

 

[DAVID NANCARROW]

Thanks for the input HiBC. After studying these new Palma Match bullets, the boat tail is a lot longer and the front half of the bullet almost looks like a VLD, and the bullet itself is as long as a 168 grain MK. That doesn't leave much to grab the rifling. Makes me wonder if the bullet needs to be a lot closer to the lands for good performance, maybe with a faster twist in combination than what I have.
Because upping the charge scattered them more, I am going to drop down to a starting load and see if anything good happens. If that does come out to be true, this will be the first bullet that I have tried in this weapon which responded well to smaller charges. In everything else I have tried in every grain weight I have tested, my best result has been with max or nearly max charges.
Dropping the charge down to minimum sort of defeats what I was trying to accomplish, but its not necessarily what we like-more of what the weapon likes.

 

[Bart B.]

I don't think there's much difference in boattails between those bullets. But their front half shapes are different.

Both have shot 1/4 MOA at 100 - 300 yards (1/2 at 600, 3/4 at 1000) from all sorts of chamber, bore, groove and twist dimensions. 4-groove barrels are a little better than 5- or 6-groove ones for some reason. But barrel lengths need to be at least 28 inches to get 2900+ fps so they'll stay supersonic through 1000 yards.

If one's reloads with either are what the pictures show in David's photo, it's not any issue with the bullets. Some part of the reloading process made ammo that shot those 3- to 4-inch groups ended up making bad stuff. The way the rifle was held and fired may well be an additional contributor.

IMR4064 is a bit on the slow side for best results with Sierra's 155's. But it will still put bullets into 1/3 MOA at 100 yards from good rifles shooting good ammo. Here's a list of things to check on ammo loaded with those 155's:

*What is bullet runout on the loaded rounds? Anything under .003" is good enough.

*Do seated bullets, after being pulled, have deep scratch marks on them? If so, the case mouths are way too rough and score the bullet jacket enough to make them shoot less accurate.

*Did you try seating bullets out as far as possible? Sierra's 155's typically need little or no jump to the rifling for best accuracy. Longer jumps with short bearing surfaces in large chamber throats is detrimental to good accuracy.

*Were your sized cases such that their shoulders were set back only a thousandth or two? Any more typically means less accuracy.

It's hard to say what the cause(es) may be, but something is sure not so good with your 155's when reloaded. Especially when the 175's did pretty good.

 

[DAVID NANCARROW]

Actually, there is quite a bit of difference between the MK 155 and the Palma Match. The boat tail is a different angle and is nearly a third longer in profile.

The ogive is quite a bit farther back on the Palma in comparison, which might help explain why the PM gets a .503 ballistic coefficient. My rifle is blessed/cursed with a long leade as a most Remington 700's that I have worked with. Getting the bullet closer to the lands will leave me with almost no bullet in the case. I am beginning to believe that is where the problem lies. It may well be that bullets with short bearing surfaces do not like a large jump to the rifling, which of course I am spitballing here, but seems to make the most sense. The other possibility is brand new brass, resized and trimmed to length. It may be that now the shoulder is blown out to chamber dimension that it might help. However, I have little confidence that is going to make that much difference in the group size. I might be surprised but I am skeptical.

I can shoot 1/2 to 3/4 MOA with the standard MK in 155 over 47 grains of Reloader 15 from a sandbag front rest. Finally found my old load data from quite a few years ago.

The loaded ammo runout was a max of .003 with most of them around .001.

The rounds fired came off a bipod rest. Including the 175s. Ive come to the conclusion that I will either have to rebarrel what I have or be content with the standard match kings in 155 for groups.

 

[HiBC]

Bart,once again,I know nothing about Palma.

I don't think Sierra makes any bullets that do not shoot,and I have no doubt the new Palma bullet will shoot well enough to bring home a world championship.

But,we specifically loaded to compare the two .Necks and flashholes deburred,same 2.800 mag length,same press,same Forster dies,same Krieger bbl and chamber,same AR-10 T,same shooter,same day,

the current 155 gr MK ,the old Palma that you brought the tropies home with,shot on a dime at 100 yds,and the new 155 gr Palma went 2 in or so.

But anAR-10 T is not a Palma rifle.I've never seen a Palma rifle.

My guess is,the folks who build Palma rifles have their way of doing things,and Sierra knows how to build a heckuva bullet to shoot in those rifles.My guess,they did not compromise anything for general use,they made a world class Palma bullet for world class Palma rifles.

But,that Palma rifle maybe was not set up to be optimal with the full spectrum of off the shelf .308 factory ammo,hunting,military,and target...like the Rem 700 .

They left us the excellent 155 MK.

 

[Bart B.]

Last time I asked Sierra, they use the same test barrel for both 155-gr. bullets. Best lots of them shoot under 1/4 MOA in their 200 yard indoor range. I also think they use the same load recipie for both.

A Palma rifle is no different than any other rifle except for its barrel length being long enough (29" or more) so 155's leave at least 2950 fps with normal peak pressures. Stock shape, barrel contour, action type, sights and all that stuff has all sorts of variables. Metallic sights are required; no scopes. 155's of either type have done well with a varitey of bore and groove diameters as long as the groove diameter's a bit smaller than bullet diameter and groove count is 4. Chambers are usually short throated so bullet jump to the rifling can be minimized with cartridge OAL at 2.800" which is pretty much the international standard for Palma matches. For international competiton, weight's usually limited to 6.5 Kg.

I don't think Rem's 700 is set up to be optimal for any ammo type. If it was to be so, smart people in their barrel making shop would make groove diameters down in the .307" range and short throats so virtually all ammo would shoot optimally accurate.

If an AR10 can't shoot both 155's with the same accuracy, I suspect a timing issue causing different barrel whip issues pushing one of them more random in exit direction. Bolt action rifles don't seem to have that issue. The accuracy difference between the two 155's when tested at 1000 yards is about 1/10th to 2/10ths MOA or less depending on who's testing and the load used. Which means at 100 yards; it's virtually zero. Sierra says they're equal in their test range, as I remember.

Contact Sierra then explain your frustration with accuracy differences. They may have a solution or explanation that satisfies you.

 

[DAVID NANCARROW]

Thanks for the update Bart. I really do think that the Palma Match bullet is set up for competitors using the short throat as you say, which is why they wont group all that well with a long throated barrel. I figure that I have a few thousand rounds left with my current factory barrel before its time to change it out, and at that point will contact Krieger or one of the other well known barrel makers and get their input as to chambering and leade angle. I wont even try the VLD style bullets because they aren't very tolerant of bullet jump.

I do not wish to turn my Rem into a specialty rifle just for the Palma bullets, but I would think that a chamber/leade combination could be found for bullets between 150 and 180 to 200 grain weights. I am not certain that I will stick with the 1:12 twist-some folks are getting good results with a 1:11.25 as well as the 1:10. At that time I will be getting the action squared at all the critical dimensions.

But, for a factory rifle, it really doesn't do too badly when fed what it likes. On the average, its a 3/4 MOA rifle out to 300 yards, not too bad for a production line stick.

 

[Bart B.]

A standard SAAMI spec chamber will do well with all bullet weights from .308 Win. cases. I've shot 150's through 200's in 1:10, 1:11 and 1:12 twist barrels. Lighter ones had near 1/10th inch jump to the rifling when seated to 2.800" for magazine feeding. Heavier ones, 200's for example, had to be seated out touching the lands to get 48 grains of drop-tubed IMR4350 under them without crushing the powder kernels.

 

[Grunt96]

IMR4064 is best with 165 and heavier bullets in the 308 Win. I've never gotten the accuracy from 150 gr match bullets with 4064 that I have with heavier pills.

For 155's I'd recommend H4895 or as an alternate IMR4895.

Jimro

Thanks, I have some IMR4895 that I have yet to open. I'll give that a try.