Anyone have good sucesss running 77 SMK's in an AR ?

[Road_Clam]

Hello folks,
Been working up some 77gr SMK's in my 1-9" twist Bushmaster Varmint AR and thus far have tried Benchmark and 8208 XBR powder. Found some "OK" accuracy around 1 MOA , but nothing consistently sub MOA. Any of you have any accurate loads ? I even tried seating the bullet for a .020" bullet jump (which at that length I had to single feed the bullets as they were too long for mag feed), didn't notice much better accuracy from simply loading to Lyman's suggested mag length. I'm thinking maybe my AR just doesn't like the 77gr.

[g20gunny]

Could possibly be your twist rate, how long is your bbl? My 14.5" will run moa or better all day with about any handload I put through it but it is a 1/7" twist. With a 20" 1/9 I would think you could get enough speed to stabilize them unless your barrel really just doesnt like it. Fwiw I usually stick with H322 or H335.

[steve4102]

thinking maybe my AR just doesn't like the 77gr.

You could be right with the 1-9 twist.

Benchmark and 8208 might be a little fast for the 77gr, ya might want to give a slower powder a try before you give up on the bullet.

[skizzums]

If you just like the idea of being heavy, hornaday 75gr are a bit shorter than the smk and will likely do better with your faster twist. But I would like to see you shooting the 69gr smk first, I think you may find your sweet spot there

[Road_Clam]

My bushmaster uses a 24" bbl. So maybe I do need to experiment with a slower powder. Many loaders swear by the 77's and xbr but not working in my barrel. I also have some 4064 , varget and RL15 still have about 300 of the 77's so hopefully find a sub moa load. I woul like to be able to use the 77's at my club's 600 yd range when it gets windy.

[Metal god]

Have you tried Fed GMM or Blackhills match ammo using the 77gr smk yet . Reason I ask is to insure your rifle likes the 77's or even capable of shooting sub moa . 4064 is good I have a hot load ( over max ) of 25gr using a 69gr smk

23gr IMR 4895 and 77gr smk works good for my service rifle . .8 moa 10 shot group . It's a longer extruded powder . Not the best metering powder , It takes a little more effort to get the charge dead on but it's a real good powder .

[skizzums]

i'll add that I shoot with other high-power shooters, most that have a 1:9 twist all run the 69gr SMK's. if you wanna try 4064, go for it, that it what I use. I run a compressed load (WARNING: OVER MAXIMUM PUBLISHED DATA) of 4064 with 77gr SMK(or hornaday 75gr, PPU 75gr), about 23.5gr, seated maximum mag length. has proven pretty close to MOA, about 1.5 I guess, accurate out of my 16" 1:7 twist.

here is 200yard target with 77gr and 4064
top left:hrn ,top right:SMK, bottom PPU


obviously you already have the bullets, so why not make the best of it, but I think you will regret putting to much energy into making them work. I think 1:8 is really as slow as you can go getting long range accuracy from 75gr+. maybe I am wrong, but I think you'll be best served with 69gr SMK's instead

[Road_Clam]

Originally Posted by Metal god

Have you tried Fed GMM or Blackhills match ammo using the 77gr smk yet . Reason I ask is to insure your rifle likes the 77's or even capable of shooting sub moa . 4064 is good I have a hot load ( over max ) of 25gr using a 69gr smk

23gr IMR 4895 and 77gr smk works good for my service rifle . .8 moa 10 shot group . It's a longer extruded powder . Not the best metering powder , It takes a little more effort to get the charge dead on but it's a real good powder .

I tried some 77gr FGMM a few years ago and that ammo shot poorly. It only shot about 2.5 MOA. After that I stayed away from 77's and focused on 69's (which does work great in my AR). I just was hoping to find a 77gr load as I'm sometimes struggling shooting in the heavier winds at my 600 yd range. Thus far my most consistent and accurate loads are using the 52gr SMK, but my 600 yd range has a 69gr bullet weight minimum rule.

[Metal god]

I think that answers your questions .

but I think you will regret putting to much energy into making them work

I agree , you could end up spend to much time and components trying to get the 77's to work only to find they will not to your liking .

Sounds like your best bet really is to see if you can find someone to trade 69's for your 77's or buy your bullets .

[FrankenMauser]

77 gr SMKs run 'okay' in my 1:7" carbine.
They are HORRIBLE in the 1:9" mid-length. (Well beyond the typical poor performance of that barrel.)

69 gr SMKs run great in the 1:7" and are about as good as it gets in the 1:9". (Both 16" bbls.)

[TMD]

I have a Stag Model 6h varmiteer which has a 1/8 twist24" heavy stainless barrel with a 5.56 chamber. Stag guarantees .5 moa and it will do it but not with the 77gn SMK. Best I can get with them is slightly under MOA. With 69gn SMK's it will shoot .250" groups all day long.

[surveyor]

100 yds 1:8 20" wylde chamber varmint contour
Lc brass, 77 smk, varget, cci primer,
Load is over max listed


Same load at 300 yds shot from 30" bolt 1:7
20 rds

[9MMand223only]

Rl15 23-24 grain, VVN140 similar, or Varget, similar

are going to be as good as you can do on this earth with those bullets with new lapua brass, everything measured the same, and good barrel

[mehavey]

RoadClam
You need a 1:7 Twist barrel (1:7.7 Max) for that bullet.
(Look at the end of the box the bullets came in)

[skizzums]

am I incorrect to think that more velocity could mean better stabilization for our OP?

[Metal god]

am I incorrect to think that more velocity could mean better stabilization for our OP?

No I think it should help . Yes a 77gr smk thru a 1-9 is not going to stay stabilized out to 600yds . A max load out of a 1-9 24" barrel should stabilized the 77s to at least 300yds .

My general calculations say a 77gr smk with a muzzle velocity of 2850 from a 1-9 twist should stay marginally stable to 350yds .

Sierra 77gr smk bullet
https://www.sierrabullets.com/store/...HPBT-MatchKing

223/5.56 twist rate thread
http://thefiringline.com/forums/showthread.php?t=530927

Twist rate calc
http://www.bergerbullets.com/twist-rate-calculator/

Ballistic calc
http://www.hornady.com/ballistics-re...ics-calculator

In short the 77s are not going to work for what the OP wants them to do which is shot 600yds . It's not even going to be worth trying . How ever the math does seem to indicate that they will be stable for a few hundred yards .

EDIT:

I just did the math on my 77gr load I use in my 1-8 service rifle . I barely stay fully stable out to 600yds .

[FrankenMauser]

Velocity and twist rate go hand-in-hand.

As one increases, the other can decrease; and vice-versa.

That's why bolt guns (particularly with long barrels) can usually get away with shooting bullets that tend not to do well in ARs (where you lose velocity due to it being gas operated, and barrels tend to be shorter).

[Road_Clam]

Thus far the 77's seem to be stabilized but I've only tested at 200 meters. Just for my own info I think I will load up my best recipe thus far, then try them at 600 yds. For me, this is not about success and failure but gaining reloading experimentation knowledge in the whole.

[Metal god]

That's a good idea . My calculations show you will be right on the cusp of marginally stable and completely unstable . My guess is some may make it there while others may key hole . For me the numbers would be to close to bad for me to use the 77s out to 600yds .

[Unclenick]

As previously suggested, the 77 is marginally stabilized by a 9" twist at most velocity ranges. It's not outright unstable, but it doesn't recover from initial yaw very quickly with that amount of twist you have, and that tends to make it sensitive to minor sources of drift, like tiny imperfections in the muzzle crown, opening groups up. Going faster helps some and may even fix it. Shooting in lower air density, like on warmer days may help. Some 9" twist guns shoot these bullets OK, though I don't recall hearing of one in which they did great.

If drag didn't grow in the transonic range, the added velocity wouldn't make a difference, as the faster RPM's from going down the tube faster would simply be offset by the greater drag associated with the higher velocity. But there is a big jump in drag coefficient at the speed of sound (the "sound barrier") which falls off as you go faster, and that's why more speed helps. You are getting further away from the lump in the drag coefficient curve.

Stability downrange is actually not a problem. Spin decays more slowly than forward velocity does, so the projectile actually tends to become more stable as it goes down range. But if it becomes more stable already drifting off the intended path, the groups still open up.

[mehavey]

To make up in speed for what the OP misses in twist requires an unacheivable increase in muzzle velocity.

If the 77SMK is nominally moving out at 2,750fps-or-less (which is the measured velocity of BlackHills 77SMK ammunition in my 1:7.7 20" barrel), I would need to increase that to 3,220fps to accommodate a 9-twist.**

'Just ain't gonna happen, especially with shorter AR barrels



**(Note: That same 20" barrel twist in an earlier 1:9 would not stabilize the 77SMK)

[Jimro]

Instead of the 77 SMK, try dropping down to a 75gr Hornady BTHP. Not the Amax, just the regular 75gr Hornady.

It is slightly shorter, you can launch it slightly faster, and stability is slightly better from a 1:9 twist. Might be what you need to get a long range load for your rifle.

Jimro

[lokidansk]

77 SMKs
23g w748
2.26 "

20" PSA CHF barrel--- 1:7

I just picked up some TMKs, havent had a chance to
try them out yet.

[mehavey]

That's a 1:7 barrel [right?]
http://palmettostatearmory.com/index...rifle-kit.html

[mehavey]

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