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

[mehavey]

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[mehavey]

More to the OP's point, the "AR" per se, can handle 77SMKs just fine -- with the proper twist:
twist:

[lokidansk]

Yes Mehavey 1:7. Sorry

[Metal god]

The OP stated he is using a 24" barrel . If the blackhills is getting 2750 from a 20" barrel . The OP should get at least 2880fps from his 24" barrel . That's why I used 2850fps as my base velocity . A 1-9 twist will stabilize a 77gr smk , just not well . ( so who's going to be the one that says a bullet is either stable or it is not ? )

I think uncle nick had it right

The 75gr Hornady is an option but my guess is that it will not do much better . How ever the Berger 73 gr Match BT Target bullet has a recommended twist of 1-9 . They cost a bit more but if the 69gr smk is not good enough I'd try the 73gr Berger http://buybergerbullets.3dcartstores...rget_p_31.html.

[Jimro]

Metal God,

Let me put some math to my previous post.

69 SMK's are nominally 0.900" and the 75 Hornady 0.981, and the 77 SMKs 0.994, the 73 Bergers (match target) are a 0.970 length. In inches.

Stability factor for a 1:9 barrel shooting the 69SMK at 2,800 is 1.656
Stability factor for a 1:9 barrel shooting the 73BGR at 2,850 is 1.420
Stability factor for a 1:9 barrel shooting the 75HDY at 2,850 is 1.412
Stability factor for a 1:9 barrel shooting the 77SMK at 2,750 is 1.378

Since we know that the OP is looking at marginal stability at longer ranges we won't know if the increase in stability to the 75HDY from the 77SMK is enough to get him to the 600 yard line for competition. My recommendation is to try, after all a box of 75gr HPBTs is relatively cheap.

69SMK 0.169 G7 BC
73BGR 0.176 G7 BC
75HDY 0.183 G7 BC
77SMK 0.190 G7 BC

The one other factor that gives me some hope for the 75HDY is that it is a secant profile bullet which maintains flight stability better than the tangent ogive bullets (like either SMK), at least until you hit the transonic region, so it is more likely that the OP will get longer stable flight.

But, if the 75HDYs still provide no performance advantage, the 73 Bergers would be a logical next solution.

Jimro

[TimW77]

"so who's going to be the one that says a bullet is either stable or it is not?"

The bullet at/on the target...

You are not going to beat the laws of physics no matter how much you kick the dead dog...

T.

[Road_Clam]

So here's where I'm at. I want to try one more powder which is my fav ball powder good ol' Win 748 . Hopefully get out tomorrow and see what happens at 200 meters. If I don't find anything around 2 MOA or better (which is the best I've gotten so far using Benchmark powder) I'll go ahead and load up my Benchmark recipe and shoot them at 600 yds next Fri . I'll put the "stable or not " speculation to bed. Stay tuned for an update..

[Unclenick]

Road_Clam,

Check out the different stability estimators at the JBM site and at Geoffrey Kolbe's site. Sierra suggests the stability factor should be within about 1.3 to 3.0 for "hunting accuracy" and between 1.4 and 1.7 for high precision shooting. If find those numbers work petty well.

[Road_Clam]

Got out the the range yesterday and to my surprise I had excellent results with Win 748 powder and the 77's. While I didn't observe much better accuracy than Benchmark powder I did see some data that suggested more consistent accuracy. Found a good node at both 23.4gr and 24gr. The velocity averages were 2656 and 2753 respectively. Slightly better overall accuracy average with the 24gr charge. Excellent stability at 200 meters. So i'll think I load up the 24gr/W748 load and see what happens at 600 yds.

[Jimro]

Pleast post your results. The ballistic calculators say you should be good, but reality trumps all.

Jimro

[bfoosh006]

Your rifles 1n9 twist doesn't like the 77gr bullet.... If you ever consider a new barrel get at least a 1n8 or faster.

I also suggest you try some 75gr Hornady.

[Road_Clam]

A stability question to the mid range experts , in my situation experimenting with the less than ideal 77gr's will stronger winds elevate the possibility of bullet instability ? My 600 yd range is notorious for being a challenging multi-directional wind tunnel !

[Metal god]

Short answer yes . uncle touched on it a little . I'll use an example . If you have two tops . One spinning very fast the other spinning just enough to stay upright . The top that is spinning very fast will be much harder to destabilize then the slower one . Even though they are both stable while spinning .

[Jimro]

A stability question to the mid range experts , in my situation experimenting with the less than ideal 77gr's will stronger winds elevate the possibility of bullet instability ? My 600 yd range is notorious for being a challenging multi-directional wind tunnel !

Yes, and rapid direction changes will increase bullet yaw speeding the destabilization effect.

However, if you can't get the 77 SMKs to work for you, and the 75 Hornadys aren't any better, try working up to max loads with 68 Hornadys or the 69 SMKs.

A 68 Hornady at 3000 fps has less drop than a 77 SMK at 2800 fps, and only 0.3 MOA difference more windage out to 600. The ballistic data for the 69 SMK is essentially the same for drop and windage.

If you can get the 75 Hornadys to 2900, you can match the 77SMK wind corrections when the 77 SMK is launched at 2800.

The go to powders for all the loads listed are H4895 or Varget. Both are "temp stable" and can on paper achieve the velocities listed for the 68 through 75 gr bullets.

Hope this is helpful.

Jimro

[Road_Clam]

Thanks guys for all the help and tips, much appreciated !

[oley55]

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.

Road Clam, I feel your pain. I have tried, tried, and tried again to get a tight group with the 77gr MK HPBT out of my 24" 1:8. I have tried H335 and Varget and never got better than 4 (out of 5) bullets within 1/2" at 100 yds with Varget.

On the other hand my AR does quite well with 55gr VMAX/H335 and 69 gr MK HPBT/ Varget. Last week the 69gr MK HPBT, LC brass, CCI #41, 25.4 gr Varget gave me a nice 5/16" (5) shot group at 100 yds with a brand new Redfield scope. I'm using a stock mil-spec fire control unit and could probably do a little better with a decent trigger.

My 24" HBAR in 1:8 should be able to create a nice tight group with 77gr MK HPBT at 100 yds. But without a tight 100 yd group, I saw no purpose in going further out to see if the 1:8 would maintain stability . Not giving up on the 77gr bullet yet, but I'm out of bullets and need to get my hands on some different powder.

As other more technical/knowledgeable folks have advised, 77gr out of a 1:9 twist barrel is unlikely to meet your expectations.

Edited/Added: after rereading what others have posted, I think I will probably not waste anymore time/money trying to get the 77gr MK HPBT to fly out of my 1:8.

[Rimfire5]

1:8 twist barrels shoot 77 grain bullets just fine.

My 1:8 Les Baer shoots 77 SMKs under 1/2 MOA and also shoots Berger and Nosler 77 grain bullets under 1/2 MOA.
The new Sierra 77 TMKs shoot even better than the 77 SMKs in the Les Baer 1:8 twist averaging 0.395 for all groups versus 0.461 for all groups for the 77 SMKs.
The top 10 best loads include eight 77 grain bullets and two 69 grain bullets and average 0.249 for 5 round groups at 100 yards. In my rifles, I have found that the slower powders (CFE223, N140, Varget and Reloader 15) work best with bullets over 65 grains.

To provide some comparison for a 1:9 twist barrel, my CZ 527 Varmint bolt action 1:9 has accuracy drop from well under 1/2 MOA with bullets under 55 grs to 0.454 with 69 grain SMKs and to just under .7 MOA with 75 grain bullets. The CZ has problems cracking 1 MOA with 77 grain SMKs or any other 77 grain bullet so I don't waste my time loading heavy bullets for it.
Given the results with the TMKs in the Les Baer, I might load a few and try them in the CZ.
But in general, I would say that my 1:9 CZ has problems stabilizing a 77 grain bullet and begins to loose accuracy with bullets above 69 grains.

[Ifishsum]

Until very recently the only AR I had was a 1:9 (20" A2) and the heaviest I could get to shoot well were 69gr SMKs. They will get you by at the 600 yd line, they will be affected more by the wind though. Probably not much other choice for now, if/when you get serious about competition you will likely do as I did and get another upper with a faster twist to shoot the heavies.

[oley55]

not to hijack this 1:7 thread........but

RimFire5

That was/is my expectation, but after 150 rounds of 77gr SMK's fired, I was/am a bit frustrated. I really expected Varget to work for me, but it hasn't quite panned out. My rifle was built by someone else and the barrel has zero markings. The previous owner thought it was an ER Shaw barrel, but no way to tell.

What I do know is this barrel fouls easily and absolutely MUST be cleaned after 12-15 rounds. If not, the groups really open up. Surprisingly, after a cleaning it is a waste of ammo to fire fouler shot/s as it is dead on from the first round fired.

[Jimro]

Oley55,

Sounds like CFE223 is worth a shot for you. If it increases the number of shots between necessary cleanings, it might be a good choice if accuracy is there.

Jimro

[oley55]

Jimro, good suggestion me thinks.

frankly a semi-auto AR that requires such frequent cleanings pretty much negates the practical usage of an AR. I'll give CFE223 a try, otherwise I'll be looking for a different barrel.

[Unclenick]

12-15? Yikes! I once had a really rough military barrel on a Garand that started to fall apart in the middle of rounds 30-50 of the National Match Course (600 yard slow fire), and have heard of guns doing it after 20 rounds, but yours takes some kind of prize. A lot of barrels need ten rounds to really settle, so you are getting like zero good round time.

In your shoes I would do a couple of things. First, I would make sure I got the barrel truly clean so that I knew I wasn't starting out pre-fouled. No way to know how the previous owner treated it and old fouling can be a misery to get out.

The method I would use is to start with some Mobil 1 0W-20, and get the bore good and wet with it and let it sit 24 hours and then push a bronze brush from breech to muzzle, unscrew it at the muzzle, remove the rod from the bore, put the brush back on and repeat a couple or three more times. This is so you are only brushing in one direction. Then patch the oil out. Mobil 1 has very good carbon softening additives. The Army Marksmanship Unit uses it for this reason. If you have hard carbon deposits, the patches will come out blackened with visible carbon (not just gray steaks). If you get that, I would repeat this every day until black carbon stopped coming out.

Another excellent product for that is Gunzilla. It is actually a little faster working, IME, but oil is cheap if you have time to let it work. Gunzilla I have left in a bore for a month and a half while it kept getting carbon out of pits in an old Springfield barrel, so it's something to try if you are for some reason not satisfied with the oil results, but I expect you will be.

Next, I would spray some brake cleaning solvent down the tube to remove the oil. Brake cleaner, unlike carburetor cleaners, has no residual lube left behind.

The next thing I would apply is KG-12 copper solvent. This is not like the usual ammonia copper removers. It is a water-based chelating chemistry. If you let it sit 20 minutes it will absorb a huge amount of copper. The only drawback is it doesn't turn blue or green when it reacts with copper. It just gets darker orange. But three applications over an hour will remove more copper than I've yet found in a barrel.

At that point, if you know someone with a borescope, I would take a look, particularly at the throat and first two or three inches of the bore, where copper fouling is heaviest. If you don't have access to a scope, I would apply a copper solvent that does turn blue, let it sit five minutes and push it out with a plastic or other non-reactive jag, just to be sure I didn't see any color coming out.

At this point I would take Iosso Bore Cleaner or JB Bore Compound and push a patch down to the muzzle, remove it, push it through from the breech again, and go for a third or even a fourth time if it still seemed to be working. I would then get a fresh patch and repeat, and keep repeating every third or fourth patch until I had pushed through the bore the bore a total of about 50 times (48 is divisible by both three and four; close enough). Then I would repeat with Flitz.

Now take the gun to the range and see if you haven't made progress with the fouling problem. If not, you may need to look at firelapping or other more aggressive polishing methods. I don't like it as a first resort, because you very occasionally get a gun that sees adverse accuracy effects from doing it.

[oley55]

Nick,

yea after 12 rounds the group just starts opening up, but after 15 rounds it is really evident. After 20 rounds, 1/2" MOA becomes 2"+.

In the past I have soaked n cleaned for a couple days removing all trace of both copper/carbon fouling. But not inspected with a bore scope.

I have already fire lapped using the Tubbs fire lapping kit and I am reluctant to do it again. In retrospect I wish I had been more deliberate in my fire lapping methods. Knowing how quickly it fouls, I wish I had taken several days to complete the fire lapping rather than a single long day. I should have spent much more time removing fouling between each string of lapping bullets. Today my gut tells me after a few rounds I was merely fire lapping copper versus barrel steel.

I am thinking I have two options, go ahead and get a new barrel or thoroughly clean and then find someone (acquaintance or gunsmith) with a bore scope and then go from there.

[darkgael]

I rarely get to a 200 yard range. Mostly I shoot my old HBar with its 1-8 twist from prone at 100 yards. Most often I use the Sierra 77s over 24 grains of Reloader 15. Winchester brass and primers.
I am not a great shot but can usually keep all ten together at 100 yards.....the load has always been 10 ring reliable for 10 shots at that distance

[Road_Clam]

Well, long story short success ! Shot my 77 smk's out to 600 yds today and they performed very well. I briefed my fellow target puller as to my bullet experimentation and he communicated to me that the holes were perfectly clean NO signs of instability. Shot about 30 rounds and overall I was shooting between 1-3 MOA . Unfortunately no X's today as the wind was a bit brisk at times. I mostly scored 9's and 10's .
I started out at 200 meters just to verify my zero, my MOA and my velocities. At 200 meters I was at about 1.25 MOA . My chosen load was 24gr of Win 748 and a .020" jump. My velocities today were about 2728 (73F). Great day for shooting , mild temps, low humidity , and breezy. My 200M to 600 yd elevation dope calculated to about 14 MOA , and this was spot on as my first 600yd cold bore shot scored a 10 ring. For an AR platform my box stock Bushmaster Varmint is a dam good shooter. Took some time to dial in my 600 yd zero but my last 10 shot string scored : 10,9,9,8,10,10,8,10,9,10 (shooting at a standard MR 600 yd target . So to put this instability concern to bed, in a Bushmaster 1-9" 24" bbl AR-15 you CAN successfully shoot 77's out to mid range. Any other 1-9" rifle YMMV...