150 SMKs and the 6.5 x 284 ***UPDATE***

[Berger.Fan222]

Yep, this is the problem with "faster is better" as relates to twist. At some point the bullets blow up in flight. We've even seen it with 1 in 8" twists in 6.5-.284 for some bullets.

One promising theory is that melting of the lead just under the jacket plays a role so that keeping the barrel cooler and/or reducing barrel friction with coated bullets may help. This theory seems consistent with our observation that we've never seen blow ups in the first 10 shots from a cold barrel - always later. Lapua Scenars seem more resistant than SMKs and AMAX.

 

[243Mendoza]

Yep, this is the problem with "faster is better" as relates to twist. At some point the bullets blow up in flight. We've even seen it with 1 in 8" twists in 6.5-.284 for some bullets.

One promising theory is that melting of the lead just under the jacket plays a role so that keeping the barrel cooler and/or reducing barrel friction with coated bullets may help. This theory seems consistent with our observation that we've never seen blow ups in the first 10 shots from a cold barrel - always later. Lapua Scenars seem more resistant than SMKs and AMAX.

Are you saying barrels are getting over 650deg (melting point of lead)?

 

[Berger.Fan222]

Are you saying barrels are getting over 650deg (melting point of lead)?

No. It is not a static situation. But a combination of the barrel temperature and the friction may occasionally raise the lead above it's melting point. Lead has a much lower heat capacity than steel. Adding a given amount of heat from friction will heat lead up a lot more than steel.

The heat transfer is a very complicated issue with friction, the barrel temperature, the starting temperature of the bullet, and the jacket thickness all playing a role. Increasing the friction, barrel temp, starting temp of bullet, or twist rate all increase the odds of a failure in flight. Increasing the jacket thickness decreases odds of a failure in flight.

 

[lee1982]

I have never had a blow-up with an 8 twist either. But add an additional 1/2 twist and many, many thousands more RPM's, and it may be on the horizon. If I do rechamber the barrel it will be with a 6.5 Creedmoor or 6.5 x 47 Lapua and I doubt at 2600-2700 you would get any blow-ups..

I've taken the 147 eld to low 2900's in a 7.5t and haven't had them blow up yet. You might buy a box and try them. Their actual g7 is in the .34-35 range at the speed you are going, and they have been very accurate and easy to tune for me. I have always been a big fan of berger, sierra, and lapua, but the 147's have become the defacto bullet for my 6.5's.

Thanks for the info on the 150's as well.

 

[Park ranger]

I’m pushing 150’s in my 6.5 Creedmoor at 2780 and not having any problems. 7.5 twist. I know that’s not as fast as OP, but still a nice load. Cleans with 50% x count.

 

[muleystalker]

Same question: Will the 142s hold up under the stress of a 7.5 pushing them at 2950-3000 when the 150s are blowing up at 2930?

An easy way to find out is shoot a couple out of the 6.5x284 as it is chambered now and see if they will hold together.

 

[ShootDots]

***UPDATE*** : As promised, here is the update on this project. After speaking with BOTH Sierra and Krieger, it was determined the 1-7.5 twist with conventional rifling was the culprit in bullet blow-ups. Krieger was so kind as to send me a barrel that was in "5R" configuration and because the Berger Twist Rate Calculator, after entering in all the necessary info on the 150 SMKs, states that a 1-8 twist with velocities at or above 2900 f.t. will give you a stability factor ABOVE 1.5, which will give BOTH stability as well as wring all the B.C. out of the bullet.. So I ordered a 5R-8 twist.

A few weeks ago I graciously accepted the free barrel from Krieger and had it chambered up in 6.5 x 284. I loaded up 53.8 to 54.7 of H1000 which I thought would give me "about" 2885 to 2960. This was based off the Conventional rifling barrel I sent back. Evidently, 5R rifling is considerably more "slippery" as the 53.8 load started out at 2970! Whew! This was going to be interesting. Well, long story short, it shot like dog do do.. I thought "well lets slow this down and see what transpires". So today I went out with 52.3 to 53.3 of H1000.. I got velocity from 2860 to 2940, exactly as I had hoped for. However, it shot like dog do do too!

Last night I was "consulting" with my old riflesmith in Houston. He builds both F-Class rifles as well as PRS rifles aplenty! He also has the desirable habit of spending $$$s for extensive testing of barrels and bullets. It is his "experienced opinion" that the NEW Sierra bullets are not the "less than stellar" projectiles that we have a tendency to portray them as. It is his opinion, after MUCH testing, that those 150s NEED a "straight" 1-7 twist. He has done several barrels in that twist and the 150s shoot great! He believes we are NOT using enough twist to gain the accuracy on these VERY long bullets. Although the Twist Rate Calculator states differently than his findings, he believes that may not be an accurate of a gauge, with ULTRA long bullets, as we think it is. After today's testing I am in agreement with him. I do NOT believe that the barrel is bad neither do I believe the bullets are bad>>>I have the wrong twist! So, I just ordered up a "straight" 7 twist. However, I may have to slow the bullets down somewhat>>I won't know till testing on that starts in ????...

 

[FatBoy]

good news is the barrel will probably shoot the 140s or 142s just fine.

 

[ShootDots]

good news is the barrel will probably shoot the 140s or 142s just fine.

Of that there is NO DOUBT Chris! I will be using the 142s with either VV N165 or RL-23..

 

[muleystalker]

I’m pushing 150’s in my 6.5 Creedmoor at 2780 and not having any problems. 7.5 twist. I know that’s not as fast as OP, but still a nice load. Cleans with 50% x count.

What powder are you using and is the barrel a 4 groove or 5R?

 

[muleystalker]

***UPDATE*** : As promised, here is the update on this project. After speaking with BOTH Sierra and Krieger, it was determined the 1-7.5 twist with conventional rifling was the culprit in bullet blow-ups. Krieger was so kind as to send me a barrel that was in "5R" configuration and because the Berger Twist Rate Calculator, after entering in all the necessary info on the 150 SMKs, states that a 1-8 twist with velocities at or above 2900 f.t. will give you a stability factor ABOVE 1.5, which will give BOTH stability as well as wring all the B.C. out of the bullet.. So I ordered a 5R-8 twist.

A few weeks ago I graciously accepted the free barrel from Krieger and had it chambered up in 6.5 x 284. I loaded up 53.8 to 54.7 of H1000 which I thought would give me "about" 2885 to 2960. This was based off the Conventional rifling barrel I sent back. Evidently, 5R rifling is considerably more "slippery" as the 53.8 load started out at 2970! Whew! This was going to be interesting. Well, long story short, it shot like dog do do.. I thought "well lets slow this down and see what transpires". So today I went out with 52.3 to 53.3 of H1000.. I got velocity from 2860 to 2940, exactly as I had hoped for. However, it shot like dog do do too!

Last night I was "consulting" with my old riflesmith in Houston. He builds both F-Class rifles as well as PRS rifles aplenty! He also has the desirable habit of spending $$$s for extensive testing of barrels and bullets. It is his "experienced opinion" that the NEW Sierra bullets are not the "less than stellar" projectiles that we have a tendency to portray them as. It is his opinion, after MUCH testing, that those 150s NEED a "straight" 1-7 twist. He has done several barrels in that twist and the 150s shoot great! He believes we are NOT using enough twist to gain the accuracy on these VERY long bullets. Although the Twist Rate Calculator states differently than his findings, he believes that may not be an accurate of a gauge, with ULTRA long bullets, as we think it is. After today's testing I am in agreement with him. I do NOT believe that the barrel is bad neither do I believe the bullets are bad>>>I have the wrong twist! So, I just ordered up a "straight" 7 twist. However, I may have to slow the bullets down somewhat>>I won't know till testing on that starts in ????...

Did your gunsmith buddy happen to mention if he used the 4 groove conventional 1;7 or the 5R 1;7 twist barrels for the 150's? Thanks for the info, I've been wanting to order a barrel and the 1:7 was what i've been looking at.

Dave

 

[ShootDots]

Did your gunsmith buddy happen to mention if he used the 4 groove conventional 1;7 or the 5R 1;7 twist barrels for the 150's? Thanks for the info, I've been wanting to order a barrel and the 1:7 was what i've been looking at.

Dave

He most certainly did. He said that on virtually ALL of his very fast twist barrels, he ONLY uses 5R Rifling or you WILL blow bullets up, even at moderate velocity! The "cutting effect" of the conventional lands will greatly increase the chances of a blow-up.. If you go below 8 twist (6mm and 6.5mm) you need a 5R barrel. If you go below 9 twist on a 7mm barrel, he recommends a 5R. If you go to 8 or 8.5 he believes it becomes a necessity..

 

[sdean]

Heavy for caliber bullets have sold more barrels than wearing a barrel out practicing ever did. Benjamin will be on his 3rd to get one to shoot. Although the lucky dog got one for free!!! He is not alone. I just got a 1 in 8 to chamber for 183 sierras

 

[johnfred1965]

Wonder what type barrel and twist Sierra used when they developed that bullet?

 

[wboggs]

Wonder what type barrel and twist Sierra used when they developed that bullet?

It is past time for a spokesman from Sierra to speak up with all the information they gained during their testing. We need an honest accounting of barrels, twists, rifling types, velocities, and any other information they obtained. They clearly state on the product box that it requires a 7.5 twist or faster.
Customers depend on their company. It is not up to users to do extensive and expensive testing.
So, Sierra, what are the facts concerning this issue?
Bill Boggs

 

[ShootDots]

It is past time for a spokesman from Sierra to speak up with all the information they gained during their testing. We need an honest accounting of barrels, twists, rifling types, velocities, and any other information they obtained. They clearly state on the product box that it requires a 7.5 twist or faster.
Customers depend on their company. It is not up to users to do extensive and expensive testing.
So, Sierra, what are the facts concerning this issue?
Bill Boggs

There is another factor to consider. Did they test running L-O-N-G shot strings as you would in an F-Open match? Even in the first barrel (4 groove conventional rifling) it would not blow bullets up till at least 15+ shots down the bore.

 

[johnfred1965]

That made me think of another question: What FPS were they running? With the 26 Nosler and the 6.5/300 WBY, it should have been FAST!

 

[wboggs]

See thread 6.5 anarchy and the 150 smk. 3100 does not look like the bullets are blowing up.

 

[Longrange57]

See thread 6.5 anarchy and the 150 smk. 3100 does not look like the bullets are blowing up.

Nothing wrong with 150 SMK. I've shot hundreds with 2 different 6.5 x 47 Kreiger and 6.5 x 55 swede with Brux, both 26 inch barrel. Both 47's run at 2750, 450 primer, Lapua brass. Swede runs at 2740, CCI200, Lapua brass. One third moa the majority of the time. Usually by 4th or 5th string in competition at 530 yds they all three will still be half moa. I sort bullets by weight and occasionally find a few that I pull aside (less than 10%) and use those to foul barrel. All barrels are 8 twist. Many friends with 6.5 x 284's and 8tw...running about 2900-2920...no problems. All of this with H4350 and jammed .010. I do buy them 500 at a time....maybe I got a good batch. These rifles also shoot 147ELD-M, and 140 Hyb Berger very well. Best groups have been with Berger but using the 150 due to ballistics and trying to cheat the wind. 2900 and 7.5 twist would put bullet rpm at about 280,000. This could potentially be a problem with certain barrels, but I can promise that 250,000 rpm is no problem for the SMK. If I were shooting groups at 3-500 I would use 140 hyb, but 150 SMK or 147 ELDM may become the norm in the wind at 1,000.

 

[1shot]

I have also been testing the 150's. My setup is a 32" Bartlein 5R barrel, chambered in a 6.5 GWI. This a reformed 6.5x55 Swede with the same powder capacity as a 6.5-284. I have tested the bullets in excess of 3,100 fps. with no issues other that it trashed the brass quickly. Additionally, I have tested the bullets both moly coated and bare. So far, I have shot six 20 round matches with sighters with -0- bullets failures. As an aside note, I also shoot Sierras 110 and 183 bullets, and both of them like a .015 jump. Since all three bullets are of the same form, I assumed (we all know what happens when we assume right?) that the 150's would like that jump as well.
Long story short, in my combination they didn't show me any real long rang accuracy until I started to jam them. Thanks Ben@shootdots for that. For what its worth, two of those six matches were 199 with a 30-50% X count while FF brass at 1,000 yds. so the bullets will shoot!
Regards,

Lloyd