69 or 77 grain SMK

**sdsuttu** · 07-09-2014, 11:16 PM

Just purchased a Savage fp-sr in 223. It has the 1:9 twist barrel. I am debating between the 69 grain and 77 grain SMK. Any reason to lean one way or another? I have read that the 1:9 twist barrel will stabilize the 77 grain SMK because the bullet has a relatively short bearing surface. I plan to shoot out to 600 yards so I suspect the higher BC on the 77 grain can't hurt anything. Does anyone have personal experience with the 77 grain SMK not stabilizing in a 1:9 savage. Thanks.

jb6.5 · 07-09-2014, 11:43 PM

I shoot 69gr nosler's with my 223. 700 yds is not a problem as long as the wind stays down.

**ngoforth** · 07-10-2014, 02:31 PM

I shoot the 69 smk with great results for my ability but have not tried them at 600. If its possible why not try both and let the gun decide for you.

**earl39** · 07-10-2014, 03:25 PM

Mine shoots the 77's just fine.

**darkker** · 07-11-2014, 03:14 PM

Bearing surface really has nothing to do with being able to stabilize a projectile, it has to do with difficulty in getting things lined-up for accuracy.

Twist, connected to velocity; imparts a stabilizing spin in RPM. Stability is important for a LENGTH, not a weight, not a bearing surface.

People who tell you that a twist will stabilize a certain "Weight", either don't know what they are talking about, or are making a huge generality with a lot of ASSumptions.

Also note that rotational decay happens MUCH slower, than a velocity decay. So if you have a bullet on the lighter side of stable, farther down range the bullet will have essentially the same RPM, but much less velocity; thus resulting in more stability.
Between myself and a couple shooting friends, the 77gr SMK from a 9-twist will keep things pointed in the correct direction past 1,200 yards. But that bullet passes Trans-sonic with flawless survivability.

For an estimation(not an absolute) you can look-up lengths, and use this calc:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Just click on the "Length" tab on the left, look-up the bullet. Then return to the original screen and plug in the numbers, along with your specifics.
Here is your RPM math lesson for the day:
MV * 720 / Twist = RPM

**rotts4u** · 07-11-2014, 09:55 PM

My Savage 223 shoots the 70 Berger and the 75 Hornady BTHP best. It also likes the Nosler 60 Ballistic tip a lot too. Between the two you mentioned I get better groups on the 69grain.

**thermaler** · 07-12-2014, 06:35 AM

Originally Posted by darkker

...
Twist, connected to velocity; imparts a stabilizing spin in RPM. Stability is important for a LENGTH, not a weight, not a bearing surface.

People who tell you that a twist will stabilize a certain "Weight", either don't know what they are talking about, or are making a huge generality with a lot of ASSumptions.

I guess I'm one of those ignorant asses. I'm not a math /physics wizz, but assuming the bullet caliber (and design type) remains constant, how do you increase the length without increasing the weight and bearing surface? And related to that, my understanding is that it is possible to "overtwist" a lightweight --errr shorter?--bullet so that it can become more structurally unstable.

**BoilerUP** · 07-12-2014, 07:46 AM

77 HPBTs will work just fine in a 1:9, contrary to what one might read on ARFCOM.

I had a Savage 12FV that was a no-joke, sub-half MOA shooter out to 200yd with a simple recipe of 75gr Hornady HPBT, 24.0gr Varget and CCI-200s in literally any brass.

**darkker** · 07-12-2014, 12:32 PM

Originally Posted by thermaler

I guess I'm one of those ignorant asses. I'm not a math /physics wizz, but assuming the bullet caliber (and design type) remains constant, how do you increase the length without increasing the weight and bearing surface? And related to that, my understanding is that it is possible to "overtwist" a lightweight --errr shorter?--bullet so that it can become more structurally unstable.

The answer is about bullet shape and construction. Yes, GENERALLY speaking, longer will be heavier. Now the specifics, from 2 examples. In 223, look at the 77gr. SMK & 75gr. Amax. The Amax is lighter, yet notably longer and needs more RPM to be at the same level of stability. Second example in 308: look at the 150gr. Bullets. The round nose is MUCH shorter than any other shape, from the same weight and mfg.

As for "over-twisting" the weight of the bullet, other than in generality doesn't matter. The jacket is what is the factor. IF the jacket is too thin for the RPM, there becomes a shift in power between centrifugal and centripetal force. Same example of kids on a Merry-go-round. Low RPM and all the kids giggle, to much and they try to get ejected from the center of rotation. If the jacket cannot hold the core together, then like the kids, the core begins to eject from the center of rotation.

The lightly constructed jackets typically talked about, are bullets that were designed for slower twists/velocities from days of old.
Examples are: TNT, SXSP, Dogtown, Varmint nightmare, Hornet bullets.

Those have an RPM limit of approx. 220-240,000. MOST modern varmint bullets are between 290-320,000 RPM

**earl39** · 07-13-2014, 07:16 PM

Just got back from a match and can say the 77gr SMK will fly true to 1000 yds for sure. Shot a 190, 194, 181 today in FTR class. Load is book hot but no pressure signs so i will just say it is RL-15 running 3000fps. Thats right i have the same bad habit as Scope eye. Shot out of a 12FV with a 9 twist barrel.

**foxx** · 07-13-2014, 09:40 PM

Just to add to the. chatter... ( I agree with everything EVERYONE has said, by the way. Though I don't like the WAY it was all said.)...

Sometimes a a barrel is called 1-9 twist but it is actually closer to 1-8.5 and so it shoots longer bullets okay when another 1-9 wont because it is a tually a 1-9.5 or something like that.

Or so I have heard

**earl39** · 07-13-2014, 11:07 PM

Originally Posted by foxx

Just to add to the. chatter... ( I agree with everything EVERYONE has said, by the way)...

Sometimes a a barrel is called 1-9 twist but it is actually closer to 1-8.5 and so it shoots longer bullets okay when another 1-9 wont because it is a tually a 1-9.5 or something like that.

Or so I have heard

this is can be very true expecially with button rifled barrels. Most cut rifled barrels are true to the twist number.

**earl39** · 07-13-2014, 11:08 PM

double post

**Steelhead** · 07-13-2014, 11:38 PM

Originally Posted by foxx

Just to add to the. chatter... ( I agree with everything EVERYONE has said, by the way. Though I don't like the WAY it was all said.)...

Sometimes a a barrel is called 1-9 twist but it is actually closer to 1-8.5 and so it shoots longer bullets okay when another 1-9 wont because it is a tually a 1-9.5 or something like that.

Or so I have heard

I have a 16" 1-9 barrel that I think the above applies-it shoots 77's quite well.

**scope eye** · 07-14-2014, 07:48 PM

Originally Posted by earl39

Just got back from a match and can say the 77gr SMK will fly true to 1000 yds for sure. Shot a 190, 194, 181 today in FTR class. Load is book hot but no pressure signs so i will just say it is RL-15 running 3000fps. Thats right i have the same bad habit as Scope eye. Shot out of a 12FV with a 9 twist barrel.

Since it is you Earl I will take that as a compliment.

Dean

n4ue · 07-15-2014, 05:45 PM

Originally Posted by darkker

The answer is about bullet shape and construction. Yes, GENERALLY speaking, longer will be heavier. Now the specifics, from 2 examples. In 223, look at the 77gr. SMK & 75gr. Amax. The Amax is lighter, yet notably longer and needs more RPM to be at the same level of stability. Second example in 308: look at the 150gr. Bullets. The round nose is MUCH shorter than any other shape, from the same weight and mfg.

As for "over-twisting" the weight of the bullet, other than in generality doesn't matter. The jacket is what is the factor. IF the jacket is too thin for the RPM, there becomes a shift in power between centrifugal and centripetal force. Same example of kids on a Merry-go-round. Low RPM and all the kids giggle, to much and they try to get ejected from the center of rotation. If the jacket cannot hold the core together, then like the kids, the core begins to eject from the center of rotation.

The lightly constructed jackets typically talked about, are bullets that were designed for slower twists/velocities from days of old.
Examples are: TNT, SXSP, Dogtown, Varmint nightmare, Hornet bullets.

Those have an RPM limit of approx. 220-240,000. MOST modern varmint bullets are between 290-320,000 RPM

This is a great answer but you leave out a couple of things. Ogive shape and FB vrs boat tail construction, in addition to hollow point, spitzer, or plastic tip, will all influence both bearing surface, aerodynamics, etc. The hollow point versus spitzer will have it's c/g biased more to the rear.

I 'suppose' that's why Sierra's Match bullets (HP) are so accurate. Even though they are HP. it's opening is tiny, and Sierra states they are not designed for hunting. I shoot both the Sierra 52 gr HPBT and the 53 gr HP (flat base)......
I have a Colt HBAR that I thought shot pretty good with the loads I worked up for my other 223s. One day, I tried some 69 gr Sierra MKs. I was amazed how well they shot.
The downside? I had to put in a mag follower that basically turned the AR into a single shot, since the rounds were now SO long they wouldn't fit the mag. Not the bullet's fault, my AR just has a long 'throat'..... ha ha
Since I use the rifle for target shooting, it's fine with me. If I want to burn ammo, I use a S&W M&P with a Slide Fire stock. Good thing my boss buys 223s 10K at a time.....

ron