5.56 powder testing results with 75 gr.

[budlight]

I tried to find an article that I read years ago about gas tube pressures. But don't quote me on actual testing. I had a couple of friends with 16 inch Wylde barrels and carbine length gas tubes. When they opened them up to clean them after lots of rounds their buffer tube weights were beat to crud. Mine on the other hand were 18 inch with rifle length gas tubes and I built my rifles with full auto heavy BCG's. Quality nickle boron or chrome.... I also bought barrels with a smaller gas hole. Like .072 VS maybe a .085 or something.

The article ran pressure tests. So lets say that you have a 55,000 psi load starting out. The carbine tube experienced 33,000 psi, the mid length gas tube was down to 22,000 psi and the rifle length gas tube was clear down to 14,000 with the given powder like H335 and a 55 grain bullet. The bleed off is terrific in short gas tubes and that is how they got data that shows the bullet velocity actually drops in an AR platform once the barrel starts getting out to 20 inches.

You want to make builds with rifle length or even longer like my 308 ar-10s. Run a heavy Bolt CGroup and then use light weight buffer tube springs and buffer weights.

Then use the slowest practical powder. That is why I went to h414 clear out to Hybird 100v in heavy pills with longer barrels. Then along came AR-comp and 2000 mr To me instead of having a barrel burner that is hard on primer pockets why not download slower powder in longer barrels with less twist rate

 

[LVJ76]

I flight plan 2600 fps for the 75s - very achievable with off the rack components at factory OALs. I've shot them at steel @ 475 yards, but its very difficult to spot hits. sometimes even hard to hear them hit steel.

Thanks Tyler. I have a few boxes of Hornady 60gr and 68gr that I've been wanting to load for and a few in 75gr, and see how they shoot.

I went up to 25.6gr of Varget with the 73gr ELD-M's and it clocked in at 2,782 with an 18" barrel, that should put you somewhere around 2,730 with a 16" barrel ... give or take a little. That was just in the load development I've done so far, I haven't shot them for groups or anything yet.

I was just shooting The Hornady 75gr HPBT's at 2,734 up to 500 yards pretty easily and hearing the steel well enough.

Thanks SteelBanger. I dont have the best hearing and with ear plugs on I hardly hear the hits at 500m out of the 223 but I can see them clearly.

Again thank you both and stay safe

 

[budlight]

I dont have the best hearing and with ear plugs on I hardly hear the hits at 500m out of the 223 but I can see them clearly.

Again thank you both and stay safe

You should consider electronic hearing protection. Relatively instant on and off. Muted bang and then a pop of the strike. They are actually interesting to hunt with because you can turn them up and hear the tiniest of sounds.

 

[LVJ76]

You should consider electronic hearing protection. Relatively instant on and off. Muted bang and then a pop of the strike. They are actually interesting to hunt with because you can turn them up and hear the tiniest of sounds.

Thanks Budlight, I've been looking in to them and plan on getting them soon.

Stay safe

 

[SteelBanger]

You should consider electronic hearing protection. Relatively instant on and off. Muted bang and then a pop of the strike. They are actually interesting to hunt with because you can turn them up and hear the tiniest of sounds.

I second this, electronic muffs make a huge difference in hearing your hits on steal with 5.56.

 

[budlight]

When you are buying muffs. get the highest DB reduction in your price range. I even have a couple of sets of cheaper Cabelas brand that I keep in my truck just in case I forgot to bring the best ones along.

Another thing is when the batteries are dead they work like a non electronic. The twin AAA size seem to last quite awhile.

 

[SteelBanger]

Another thing is when the batteries are dead they work like a non electronic. The twin AAA size seem to last quite awhile.

Until you forget to turn them off after your range session ... done that a couple times.

Lesson learned: keep a couple extra AAA's in your range bag!

 

[LVJ76]

I second this, electronic muffs make a huge difference in hearing your hits on steal with 5.56.

When you are buying muffs. get the highest DB reduction in your price range. I even have a couple of sets of cheaper Cabelas brand that I keep in my truck just in case I forgot to bring the best ones along.

Another thing is when the batteries are dead they work like a non electronic. The twin AAA size seem to last quite awhile.

I've been looking in to the Walkers Game Ear, I preffer the ear plugs over ear muffs, looking at the rechargeable ones.

Thanks again and stay safe

 

[nksmfamjp]

That sounds great. Good luck. My best groups so far are 0.48" at 100 with CFE223. velocity= 2384 FPS. Sd = 12.3
Seems kind of like a fluke group and Sd/velocity too low...

Trying to redevelop at 2900 fps, but not at a node yet

I hate to quote my own post, but thought I owed it to folks that the ~26 gr node was crap. One day I'd get 3 into 0.8", then trying to reconfirm, nothing under 1", but most over 2". Stepping down to work around 25gr where I had 5 shots into 0.6".

i go back to that 23.7gr load, but 2384 is jus too slow! Might as well jump back to 55gr loads

 

[budlight]

I hate to quote my own post, but thought I owed it to folks that the ~26 gr node was crap. One day I'd get 3 into 0.8", then trying to reconfirm, nothing under 1", but most over 2". Stepping down to work around 25gr where I had 5 shots into 0.6".

i go back to that 23.7gr load, but 2384 is jus too slow! Might as well jump back to 55gr loads

That is where the slow powders come in. 2000-mr being one of the best. Use cfe 223 for 55 grain and less. Also only buy barrels with rifle length gas holes.

 

[edward hogan]

The Hornady 75gr and Sierra/Nosler 77gr HPBT match bullets are THE Mainstay bullet for service rifle competitors. Many shoot these at the 600yd line. The proven load involves Win or LC brass, Rem 7.5 primers and RL-15 powder; these being fired in 20" AR-15 rifles.

The best books on the AR are volumes 1&2 of The Competitive AR by Glen Zediker. He also did a book on handloading. Very informative and easy reading. You might contact Sierra or Hornady for their gas gun accuracy loads, or look for the National Match forums for in depth load and bullet discussions.

If looking for best accuracy, why not begin with Sierra's Accuracy Load for their bullet? Always a good starting point and hard to go wrong with their bullets.

 

[nksmfamjp]

I wonder about h322....too fast?

 

[bpcrshooter]

24.8gr of varget, seat to mag length, rem small rifle primer.

 

[moosekiller99]

2,860 fps with this load. Slightly faster with CCI #41 primers but loses accuracy. Magnetospeed used to chronograph these loads on same day.