Gunsmithing Need help finding right 75 grain load for 1:7 twist 5.56 build

[onthex]

Here is the background: I have built two AR-15 rifles that are tack drivers. Each has a 1:9 twist barrel and both will easily shoot sub-MOA at 100 yards with quality 55 grain factory ammo. One of these (an FA M4 Match 1:9 20" barrel) also shoots 75 grain BTHP Match ammo well out to 500 yards, but after that accuracy goes to hell because the spin rate is not fast enough and the bullet becomes unstable. For a while now I have wanted an AR 5.56 that I could shoot steel out to 800 with, so last week I completed my latest AR 5.56 build with a Ballistic Advantage Hanson Performance series barrel, 18" with a 1:7 twist and a Radical Firearms NADA Zero Impulse brake.

I have found a number of 55 grain 223 rounds that this gun will shoot 5 shot groups under an inch with. The first pic below is of one 5 shot group at 100 yards with Beck 55 grain V-Max ammo that measures .72 inches. The second is a 10 shot group with Echo Ammo's 55 grain AMAX load (no longer available). I feel pretty confident that the three rounds on the bottom were caused by me, not the rifle.




So here is the problem: I have yet to find a 75 grain load that this gun will shoot a 3 shot group inside of two inches with. My gunsmith recommended I remove the brake as it could be jacking with the barrels harmonics. Could this be the case? Given the great groups I am shooting with 55 grain ammo I do not want to give up on this barrel yet, but I also do not need a third 55 grain tack driver when the goal is to shoot heavier bullets at distance. Any advice would be greatly appreciated.

 

[FatBoy]

24.0-24.5gr RL15 or Varget in a LC or Winchester case with a 205 primer. Works great from 69-77gr in Wyldr chambers.

Find out what chamber this rifle had. If it's set up with a short throat, this may be the issue.

 

[308pirate]

24.0-24.5gr RL15 or Varget in a LC or Winchester case with a 205 primer. Works great from 69-77gr in Wyldr chambers.

+1

 

[onthex]

Thanks @FatBoy It is chambered in 5.56. This is the barrel: https://ballisticadvantage.com/18-inch-556-hanson-mid-cmv-performance-barrel.html

 

[Soulezoo]

My best load (equal 1/2" groups @100 from 2 rifles, one a 16" ss BCM, 1 in 7 twist, the other a 16" F1 barrel with Wylde chamber, 1 in 7 twist) uses 23.4 grains of 8208 XBR in LC cases and wolf primers with Hornady 75gr hpbt. Also use 77gr smk's.
There are a couple of other powders that will give a few more fps, but are not as consistent.

 

[onthex]

Any thoughts on the brake effecting the harmonics of the barrel? I have not tried removing it yet, but I am willing to give that a shot if it would help.

 

[Soulezoo]

I've never encountered that before, so can't really speak to it.

 

[Onyx Z]

Any thoughts on the brake effecting the harmonics of the barrel? I have not tried removing it yet, but I am willing to give that a shot if it would help.

A bare muzzle *should* provide the best results.

But first, try 23.4gr XBR behind a 75gr/77gr pills with a SRM primer in LC brass. Works well in every rifle I've tried it in. Work up to this load checking for pressure signs as it is over max.

 

[Soulezoo]

Thinking on this a little more, I think there "may" be some validity to the brake causing an issue, but I really can't see it causing THAT much an issue.

Browning had/has the BOSS adjustable brake to tune the barrel and load. Obviously, groups and poi were affected by the adjustment. So, it's conceivable to me that the brake can have a negative effect if not installed or clocked correctly.

 

[Onyx Z]

Thinking on this a little more, I think there "may" be some validity to the brake causing an issue, but I really can't see it causing THAT much an issue.

Browning had/has the BOSS adjustable brake to tune the barrel and load. Obviously, groups and poi were affected by the adjustment. So, it's conceivable to me that the brake can have a negative effect if not installed or clocked correctly.

The idea behind a bare muzzle is that the crown of the muzzle is the ONLY thing affecting the bullet as it leaves the barrel. Brakes have ports, holes, etc. at all different angles and locations that could affect the bullet as it travels through the brake. This is all theoretical of course.

 

[cwinner]

Any thoughts on the brake effecting the harmonics of the barrel? I have not tried removing it yet, but I am willing to give that a shot if it would help.

I would not think the break would affect it, especially cause the 55's shoot good thought it......you could check and make sure the bullets aren't hitting it on exit and may need to open it up slightly

Like the others stated, more likely the throat in the chamber.... what's your OAL to where the bullets touch the lands? I'd check that and see how much your jumping them or not.

I spun up a 18" with a 1:7 Krieger with the WYLDE chamber and it's easily sub-MOA with 23.0 ish gr Varget (suppressed) and the cheap Hornady 75gr BTHP.

 

[onthex]

Ok, so I removed the brake, shot five groups with five different factory loads (I did not have time to work up anything on my own), and I got some very interesting results!

A bare muzzle *should* provide the best results.

As @Onyx Z suggested, all of my groups improved with a bare muzzle. Here they are:

First group is an Echo Ammo 55 grain AMAX with an actual avg muzzle velocity of 3140 out of my gun and an SD of 6.8. Best 5 shot group I have recorded with this gun to date. Measured just over 1/2 inch.


Second group is a Beck Ammo 55 grain V-MAX. Average muzzle velocity 3210, SD 8.2. I definitely pushed the errant round, or this would have easily been under 1/2 inch group. That round was the fourth of the group, and it was in the middle of the velocity range, so I feel confident it was on me.

Now here is where it gets interesting. Group three is Hornady Super Performance Match 75 grain BTHP. Avg muzzle velocity was 2900 fps with an SD of 11.2. I actually shot two groups with this ammo to make sure it was not me. Below is the first group. As you can see, it is measures about 1.85 inches. The second measured almost 2.25!

Next is a group with Hornady Black 75 grain BTHP. Average velocity was 2710 with an SD of 17.1. This was the highest SD of all, yet the group was not that bad coming in at just over an inch!

Finally after becoming concerned that maybe this barrel can't handle larger bullets I tried a Hornady Match 68 grain BTHP. Average velocity was 2920 with an SD of 12.4. I found it strange that this round had a POI well to the right of the others, and it also was the second worst of the bunch.


Based on this data I have decided that the brake definitely has an effect, but it is not the total problem. I will be contacting the folks at Ballistic Advantage tomorrow for brake suggestions, as I am definitely going to replace the Radical NADA that I had on it. With that said, it appears to me that this barrel has potential. I am no expert, but a half inch 5 shot group out of an AR seems pretty impressive to me. The question is - Can I do that with a 75 grain bullet? Based on the results that I got today it looks like I need to work on something with a velocity in the 2700 fps range. I am certainly a novice in this area, and any feedback/observations based on the above data would be greatly appreciated. Thanks!

 

[FatBoy]

My 18" SPRs run around 2650-2675 with 24.5gr RL15 and a 77.

I wonder if your chamber is throated for heavier bullets? 5.56 chamber is pretty generic. I get that mag fed is mag fed, but something is different. I'd try to get a measurement to the throat and I'd get a real measurement of the actual twist with a tight patch and a cleaning rod.

Also. WTF is Hornaday putting under their 75 load? 2900fps from an 18" barrel is ludicrous speed.

 

[onthex]

@FatBoy I am going to get a measurement to the throat tomorrow, and I am also going to measure the OAL of all five loads to try to refine my data. I am quickly learning that a multitude of factors must be considered to get the "big picture" when it comes to ballistics.

As far as the Hornady 5.56 75 grain BTHP SF Match round goes, their ballistic chart indicates 2910 out of a 20" barrel, but we got almost that out of an 18" today. It could be that the chronograph that we were using is out of calibration, but all of the others were significantly slower than the 20-24" barrel baseline that their respective charts show, so I am guessing that the folks at Hornady are loading this round really hot.

 

[FatBoy]

The Hornaday not shooting at that speed doesn't surprise me. I dont know how they get it going that fast but it's got to be hell on the jackets.

Now, Black Hills not shooting 3/4MOA, that's a problem. Twist would be my first check. Could have just been stamped wrong at the factory.

 

[G17C]

Give the Speer 75 grain Gold Dot factory load (.223) a try. If it shoots well, you will have also found a load with superb terminal ballistics.

FWIW, this is an accurate load out of my BCM 16" ELW BFH upper, consistently holding just over a MOA with a 2.5X scope.

 

[tlsmith22]

I run the Black Hills 77 grain in my MK12, its very accurate factory ammo. I tried the same ammo in my KAC RECCE and it doesn’t shoot them well at all. I tried the FGMM in the KAC and it loved them but the MK12 doesn’t. I cant explain it...lol

 

[5pins]

It could be something as simple as your barrel not liking Hornady match bullets. An easy thing to try is getting some ammo using a Sierra Matchking bullet.

 

[onthex]

Thank you all for the input. I have ordered four other premium factory loads (Sierra, Nosler, Speer and Berger bullets) that I am going to try. Yesterday I ran a VG^ Precision muzzle brake, and all of my groups improved. I shot one group (5 shots) with the Hornady Black 233 75 grain BTHP that measured .93", and I shot a group using the Beck Ammo 55 Grain V-MAX load that measured .38"! I am now at 141 rounds through this barrel, and I believe that it is starting to break in. I'm gaining confidence that I can get a .5" group with the right 75-80 grain bullet and load - It is just a matter of finding it. This week I am going to load a couple of the recipes that you guys have given me and try the factory ammo when it comes in. I will let you know how it goes.

Thanks again for all the good feedback!

 

[RPR300WM]

75gr hornady bthp
24.5gr H4895
Remington 7 1/2 primer
LC brass
2.26" coal

5.56 or Wylde chamber only. Not .223 no wylde

 

[10X Rifles]

Are you sure it's a 1-7 twist? Sounds more like it's a miss marked 1-9.

 

[AccuSol-ERN]

I am definitely keeping an eye on this post.

I am having a similar experience with bulk hornady 75bthp.

I recently threw together some PSA nitrided 1:7 m16a4 configs as general purpose cache DMR rifles. I put a vortex 1-8 in a larue qd mount expecting 1moa. I first tried TAC in LC fully prepped once fired cases with 75gr hornady bthp.......holy shit......it was between 4-5moa at 100yds with all charges .3gr intervals.

I had some prime 77gr ammo I tried......it shot around 1moa.......ok......must be something lose on the rifle. I made sure everything was tight and tried again with TAC......same results.

Next I tried Varget and it shot better.....but still around 2-3moa at 100yds. Again I shot some Prime 77gr and it shot 1moa or slightly less.

Can the Hornady's bulk 75bthp really be that terrible???

I really wanted to find a budget load that worked in all 3 rifles (same config) and start cranking them out on the 650.

Anyone else have a similar experience?

 

[TonyTheTiger]

Thats been my experience with TAC in multiple barrels with several bullets.

 

[onthex]

I have tried several factory loads now other than the Hornady Match loads, and they all group better than the Hornady 75 gr BTHP out of my gun. The best has been a Federal Premium with Berger Gold Medal 73 gr OTBT. I am still waiting in some Black Hills ammo with the 77 gr ballistic tip, but I think I am getting close to finding a factory round that will group out of this barrel. I am also going to experiment with a few handloads this week as soon as my brass arrives.

 

[AccuSol-ERN]

Anyone try sierra 69tmk?

I know they are higher than giraffe pussy.....but if I can get a "one load for all" it will be worth the extra cost.

 

[david walter]

Been told:

For varmints the 69gr Sierra Tipped Match King.

For deer the 70gr Berger VLD.

Both bullets over 24.5grs of Benchmark.

Rem 7 1/2 primers.

PMC or Starline or WIN Brass.

2.255 OAL.

You should get 2825fps from a 16 inch.

 

[Wormydog1724]

21.6gr H322
CCI#450
whatever brass
77gr SMK, 75gr BTHP, 77gr OTM

 

[david walter]

I’m also hearing 26.5 grains of lever evolution in commercial brass under a 75 for BTHP is the ticket for 50-100 more FPS.

 

[Snuby642]

Removing any brake suppressor or flash hider will change your barrel harmonics.
Does not mean said device is bad, it's just changing weight and vibrations.

I belive it possible to develope a load for any of them but have zero confidence
as to running the same load well in anything else.

Have a couple of barrels that run poor groups till suppressor is in place.
One that will not run brandx with suppresor adapter but runs with suppressor or thread protector.

If you plan to reload it's not a problem, I would just test loads till one was found.
None of your muzzle divices are probably "bad", just different.

Take any factory ammo tack driver you have and change muzzle device.
I think you will see groups size change. Mine have.

Imho

 

[AccuSol-ERN]

Good info.

I ordered some 69tmk. Gonna try CFE223 and TAC, as they run better through the 650

 

[Snuby642]

I do like cfe 223 for 55gr

 

[Snuby642]

Doing load development on the dillon?
What are you getting for powder consistency?
We have a dillon, but use single stage and hand trickled loads for development.

That may explain some of the odd velocity

 

[AccuSol-ERN]

Nope no load development on the 650.......I work up a load on a single stage....once accuracy is found I find charge weight limits low/high of where the group opens up and set that up in the 650 and proceed to crank 'em out. I figure a little "tolerance" in the 650 is worth the time savings.

I will post back when I test out the 69tmk with cfe223 and imr8208.

 

[onthex]

Removing any brake suppressor or flash hider will change your barrel harmonics.
Does not mean said device is bad, it's just changing weight and vibrations.

I belive it possible to develope a load for any of them but have zero confidence
as to running the same load well in anything else.

Have a couple of barrels that run poor groups till suppressor is in place.
One that will not run brandx with suppresor adapter but runs with suppressor or thread protector.

If you plan to reload it's not a problem, I would just test loads till one was found.
None of your muzzle divices are probably "bad", just different.

Take any factory ammo tack driver you have and change muzzle device.
I think you will see groups size change. Mine have.

Imho

@Snuby642 you were right on about the muzzle device. I have experimented with 5 on this gun, and they all change the point of impact at least 5 inches at 100 yards. They also all group differently with various loads. However, I found that I get the most consistent groups regardless of load out of a VG6 Episilon 556, so it has found a home on this gun.

 

[onthex]

UPDATE: After going through a dozen different factory loads (and a couple hundred bucks!) I have found two that this gun really likes- Federal Premium Gold Medal Berger 73 grain OT Match and Black Hills 77 grain Sierra TMK. I can consistently get 5 shot groups inside 1 inch, and I have shoot several three shot groups in the same hole.

With both loads I have shot several groups with 4 inside half an inch, but not all five. It seems that one always sneaks out of the main group! I am sure that sometimes this is shooter error, but I also think I can chalk it up to the fact that factory ammo will never be 100% consistent.

While this barrel is definitely more finicky than my other 5.56 barrels, it is still a shooter. I feel pretty confident that with the right hand load I can get 5 shots inside half an inch. Hopefully this weekend I will find out!

 

[AccuSol-ERN]

Just wanted to report back with my results with the 69tmk and cfe223 and 8208.

Apparently my rifle doesn't like the Hornady 75hpbt worth a damn. My rifle went from 3-4moa to .75moa with 69tmk and 25.4gr cfe223. I also shot 8208 and it shot great (a little better than the cfe223 actually) at 24.0gr. but given I will be bulk loading this with a Dillon 650 I decided to stay with the cfe223 load. The CFE load had a larger acceptable accuracy window (1moa from 25.1 to 25.7) and should run smoother through the 650.

Rifle is a 20" melonite PSA, MOE stock/handguard, oem trigger with JP spring kit, vortex 1-8 strike eagle in Larue QD. Nothing special just a decent blaster.

Sorry for the hijack, just trying to help others who may be banging their head against the Hornady 75hpbt too.

Ern

 

[onthex]

Just wanted to report back with my results with the 69tmk and cfe223 and 8208.

Apparently my rifle doesn't like the Hornady 75hpbt worth a damn. My rifle went from 3-4moa to .75moa with 69tmk and 25.4gr cfe223. I also shot 8208 and it shot great (a little better than the cfe223 actually) at 24.0gr. but given I will be bulk loading this with a Dillon 650 I decided to stay with the cfe223 load. The CFE load had a larger acceptable accuracy window (1moa from 25.1 to 25.7) and should run smoother through the 650.

Rifle is a 20" melonite PSA, MOE stock/handguard, oem trigger with JP spring kit, vortex 1-8 strike eagle in Larue QD. Nothing special just a decent blaster.

Sorry for the hijack, just trying to help others who may be banging their head against the Hornady 75hpbt too.

Ern

No hijacking worries. Glad to hear I am not the only one having trouble with the Hornady 75 BTHP. I actually did another AR build this week with a match barrel in 1:7 twist that hates them, too!

I have not tried the 69 grain TMK, but my AR loves the 77 grain. I just ordered some 69 TMK, and I am going to try your recipe with the CFE223. I'll let you know how my gun likes them.

 

[idahoorion]

Frontier 556 75 grain, I cannot load better than my 8 twist 24 inch will shoot this load, magnetospeed in high 2800's and if I look,online pretty cheap too.

idahoorion

 

[[email protected]]

24.0-24.5gr RL15 or Varget in a LC or Winchester case with a 205 primer. Works great from 69-77gr in Wyldr chambers.

Find out what chamber this rifle had. If it's set up with a short throat, this may be the issue.