M4 AR 5.56 NATO 77 gr. SMK/Burger OTM QL/Node/OBT Help

[Ridgerunner665]

Calculating the nodes....

The vibrations travel through the steel at the speed of sound (the speed of sound in steel is 19,000-20,000 fps... depending on the type of steel)....

The formula is: OBT = (A*N + B)*L + C*N + D

N = node number
L = barrel length

To find node 4 for a 24" barrel:
OBT = (4.40803571E-03 * 4 + 2.68380952E-02)*24.0 + (-2.40148810E-03 * 4) + 4.39015873E-02 = 1.101 ms

To find node 6 for a 26" barrel:
OBT = (4.40803571E-03 * 6 + 2.68380952E-02)*26.0 + (-2.40148810E-03 * 6) + 4.39015873E-02 = 1.415 ms

Odd number nodes use different numbers...to find node 9 of a 26" barrel...
(4.42642857E-03 * 9 + 2.84942857E-02)*26.0 + (-3.18785714E-03 * 9) + 2.91180952E-02 = 1.777 ms


Explained here...down near the bottom.
http://www.the-long-family.com/OBT_paper.htm

 

[longrangehunter]

Possibility of increased muzzle flash when you're using a slower powder in shorter barrel. Could be bothersome at night. Thought it, but thumbs didn't type it. Sorry. Not sure what his setup is, or if he really cares, just my thought.

This is for home defense and predators at night while walking my Dog. That being said I run a USO 1-8 red dot with both my eyes open and a SureFire mounted to the end of the stock. I'd imagine if I had to shoot at a Wolf at night, it would be pretty fast and furious. Been there, done that during the day with this gun, but I'm looking to improve the accuracy because long range the last load wasn't very good, but I'm thinking since it's an AR, it not really designed for that? Plus an M4, SBR.

Good info so get it going. Yesterday was too windy to test and I can't today, so maybe tomorrow or this weekend I'll get on it.

 

[Wyo7200]

Sorry if that sounded bad... Was meaning if you cared about the flash at night or not.

Ar's can be as accurate as bolt guns. My 5.56 is shooting bug holes just as accurately as my .223 rem 700 sps. It's just finding that combination...

 

[longrangehunter]

Hey no worries Wyo, no offense taken. Muzzle flash is never good if you're blinded by it, but I'm not sure it would matter since the light is so bright off the end just below the barrel anyways.

 

[longrangehunter]

I did so testing today with H335, the Hornaday 68 BTHP and the 77 SMK. (I must have made a mistake and ordered more 73 gr. Berger OTM's vs. the 77 OTM's because I can't find them).
I did retest my old load using 23.5 VV N 140 and the 77 Berger Tactical OTM for speed:

09/2/14 avg. 2447 ES 75 SD 30 HI 2473 LO 2398

05/22/15 avg. 2443 ES 45 SD 16 HI 2470 LO 2424
______________________________________________________

Next was nothing more then running up the charge weight using a 68 BTHP Starting @ 22.6, 23.0, 23.4, 23.8, with a final 5 shots @ 24.0 that avg. 2651 ES 69 SD 32 HI 2689 LO 2651

Note: Shot #1 was (1) 77 Berger 77 OTM with 22.6 H335 CCI-41 in LC Brass @ 2.2600" for comparison
The rest were all the 68 BTHP.

Note: I had picked out 22.6-22.8 from what looked like Node #7 from the data above. But I didn't see anything that stuck out that I liked along the way and retested lower down the weight charge.

 

[longrangehunter]

This is a retest of the Hornady 68 BTHP and 22.8 H335 CCI-41 LC Brass @ 2.2600"

Nothing special about that bullet and back in the box they go!

 

[Wyo7200]

I was going mention, either the first or last bullet out of an at will almost always be a flyer. Load up 6 and test the group of 5.

 

[longrangehunter]

This gets more interesting but I felt the data above won't allow that much speed after seeing what 22.6 and the 77 Berger OTM only reached 2463-2463. Note that doesn't happen very much having the same FPS over both screens. I only have 29 of those left.

This is the same load as the Hornaday seated to the same depth. 22.8 H335 77 SMK CCI-41 LC Brass @ 2.260" COAL. I had seated the first one short @ 2.2490" which was also in a Military Winchester brass that had higher pressure due to both issues.

This is still really slow, but I'm not sure adding more powder is the ticket? I just don't see how I would ever reach those velocities listed from Mike in QL without going way beyond what's listed?

I bought those SMK's because I've always found that they just seem to shoot and finding a load comes easy with them. Since I have a thousand of them that I just opened I suppose those should work simply because they go to POA, although a bit slow, would a person or animal ever know it?

I usually take off anywhere from 20-35 FPS per inch of barrel depending on the cartridge. The MK 262 Mod 1 uses a non-canister powder to reach 2750, made by Black Hills using the 77 SMK. Most people say TAC will get you close, but I tested it last year and didn't like the accuracy. If I deduct 20-25 FPS per inch times what I've read in most reloading manuals I'm in the 190-240 range loss. So it's hard to ever see these going anywhere near those velocities listed above? Maybe I'm wrong with the pressures being developed from what I read in a manual's data/velocity but I'm a little hesitant running up to those velocities I see above.

 

[longrangehunter]

I was going mention, either the first or last bullet out of an at will almost always be a flyer. Load up 6 and test the group of 5.

Honestly I've tested those bullets before with a few other powders and they just wont shoot very well in this gun. I just wanted to test the powder for how it acted since I had read the 77 SMK can spike during powder charge increases, those were just Guinea pigs since I had them laying around and don't care for them.

Over the years I've come to the realization that when I see a group that bad, I move on to something else. First or last they're just to far apart for testing unless something is changed, seating depth or the powder charge or the powder altogether. I just move on and pick another combination that I feel might work better rather then waste burning up powder or worse a barrel.

 

[Wyo7200]

Gotcha! I chuckled a little bit reading "although a bit slow, would a person or animal ever know it?".
If it's accurate and does what you want out of it, I wouldn't worry about speed. Anything on the receiving end of that bullet will be hurting enough to retreat or be dead. besides, at 2463fps, it is 2400 fps more and heack-of a lot more energy than the old bow and arrows, atlatl's, slings, and spears that have been used for thousands of years to kill game.

 

[longrangehunter]

Precisely! I had wandered off the Data page a bit since I changed two components...... Lake City Brass and used a 77 Sierra Match King. Both of which was because I had the most of them, 1,000 of each, so I made the call to test using those two components.

I may still test using RL-15 since I have 6 lbs. of it vs. <2 lbs. of H335, but I should have enough H335 to make about 500 pieces if that powder works the best? Speaking of which, I opened that jug back in 02/2005 when I was testing a 257 Roberts, just goes to show you if stored properly this stuff will save well.

My only issue, if it is one, is that RL-15 will be a compressed load and the Redding Competition Seating Dies warranty goes out the window if you brake them seating compressed loads! Fifteen years ago they never said anything about that, and now they point it out in big lettering that it wont be covered. :roll:

Honestly looking at the print out from the chronograph using 22.8 H335 77 SMK, if I had omitted the one short seated round, all 5 had very low ES. A few FPS apart from each other, which is what I like to see when testing. :mrgreen:

2374-01-2380
2370-02-2376
2375-04-2380
2400-05-2408
2377-06-2384

This is rare to see, and what makes a load accurate in most cases. Those are numbers will print very small groups if the gun is capable of it, and why I shouldn't even bother looking for another load :?: Even if I gain a few fps, those readings are tough to beat. Omitting the #3 reading, would have brought the ES, and SD down to levels that you just don't see that often. Hard to come by really and why it shot so well.

 

[.300winmag]

Can't help with QL, but I've shot out three AR barrels in high power using 77gr. SMK's and every barrel I put on them has all shot the same load, 24.0grs or Varget. I go there and never look back

 

[longrangehunter]

That's what I use in my bolt gun 223, and my 6.5x47 Lapua. So that powder is kind a already spoken for unless I go find more?

 

[.300winmag]

That's what I use in my bolt gun 223, and my 6.5x47 Lapua. So that powder is kind a already spoken for unless I go find more?

Copy that. I've not used anything but Varget and RL-15 for 77's, 75's and 80's. I did find an awesome load for Berger 82's using another powder, would have to check my records to verify which one. I will check asap and see what that is. Out of curiosity, what bullet and charge are you running in your 6.5x47? I've got one and have been wanting to try Varget out of it, but haven't.

 

[longrangehunter]

6.5x47 L
123 Scenar
37.7 VarGet
CCI-BR4
Lapua Brass @ 2.070" CBTO =.045" off the lands.

 

[.300winmag]

6.5x47 L
123 Scenar
37.7 VarGet
CCI-BR4
Lapua Brass @ 2.070" CBTO =.045" off the lands.

Thanks! I'll give that a shot. Looked up my records and for 82gr Berger's, I used 23.8grs of H4895 seated to 2.260" OAL (max mag length). Made it nice because they shot well, bucked the wind with that high BC and I didn't have to worry about having 200&300 mag length rounds loaded with 77's and then have to switch to a single feed 75gr A-max or 80gr Sierra. Looks funny when loaded but it shot well out of my practice upper and comp upper. Plan on using it in an upcoming 600 yard any any match coming up soon over my 6BR....been too long since I shot the black rifle.

 

[Alaska]

I use TAC in my MK 12 mod 0
24.1
77 SMK
LC Brass
CCI 41 primers
Lee Factory Crimp

 

[Dwh7271]

How do you feel the 24 gr charge worked? Reason I ask is although it's toward the top end there should be an area around 24-24.2 that should work. Burn percentage is good up there also.

 

[longrangehunter]

So I stole the USO Scope for the MK12, I now have installed a Trijicon ACOG TA31RCO-M150CP w/a Green reticle. This is calibrated for the M4's 14.5" Barrel, very clear and bright glass, and works with both eyes open. I tested it out today to zero the scope, easy to punch little groups at 100 yards for only a chevron for POA. Only took 1 round to hit the target after a very low and left first round hit in the cardboard, by the 5th round I was done and ready to get off the bench after 10 rounds. But another day maybe, the snow is so deep it's very hard to find your brass in 18"-24" deep snow!

This load works very well in the M4 barrel length, and I'm very happy with the outcome for a short-midrange weapon.