77gr gas gun struggle

[jlorenzo]

Been trying to get 77gr Sierras and 75gr Hornady bthps to shoot in my White Oak 18" SPR barrel, not getting the best results, the Hornady bullets kind of suck I think. Had a some good groups with RL15 and Tac. Still just not quite there. I can shoot pretty well with my other guns and am aware of how to drive a gas gun.
I have some 8208 XBR on the way which I have never used before. I am wanting to use Tac or the 8208 XBR for this gun and save my other stuff for another gun.
Ive run 2.25 mag length and had better results around 2.23-2.24 coal with both bullets. Keeping the powder a touch on the low side so the gun is beating itself up.

Any suggestions on what to do/try?
This is an Aero enhanced upper that has the built in receiver extension instead of the barrel nut, very solid. I have the Larue MBT2s trigger which is great. Cant help but wonder if the bolt has something to do with it, its a nickel boron coated PSA bolt. The last cheap thing on the gun.
I know the White Oak barrel is capable, I just didn't expect to struggle quite this much. It doesn't shoot horrible but it isn't impressive either. So far.

Is it bad to switch bolts after having shot with one for a few hundred rounds?

 

[jlorenzo]

Here is how 24.0gr of Tac at 2.25 COAL shoot out of the gas gun and the single group is out of my Bartlien barreled Tikka. Same load.
twice fired LC, CCI 41s.

 

[troupe]

Round count on the barrel, twist, and a comp ?

 

[Jeff Porter]

23.2 - 8208 - load the smk77 to 2.250”. Try 2.235” OAL with the 75’s.

 

[Twdmar]

Try another bolt. White oak barrels are pretty consistent, not sure about the psa bolt. I have always used white oak bolts and barrels together. Tac works very well with 77s normally.

 

[BoilerBobcat]

I didn't believe it until I tried it with a service rifle AR, but adding a light crimp on the necks with a Lee collet crimp die tightened groups up with 77gr Sierras (and Noslers) and 24.0 gr of TAC at magazine length. Folks told me that somehow TAC shot better (and cleaner) with a crimp and I was skeptical until I tried it myself. Granted, this was to hold X/10 ring on a NRA sling target.

 

[Alaska Bush Man]

Been trying to get 77gr Sierras and 75gr Hornady bthps to shoot in my White Oak 18" SPR barrel, not getting the best results, the Hornady bullets kind of suck I think. Had a some good groups with RL15 and Tac. Still just not quite there. I can shoot pretty well with my other guns and am aware of how to drive a gas gun.
I have some 8208 XBR on the way which I have never used before. I am wanting to use Tac or the 8208 XBR for this gun and save my other stuff for another gun.
Ive run 2.25 mag length and had better results around 2.23-2.24 coal with both bullets. Keeping the powder a touch on the low side so the gun is beating itself up.

Any suggestions on what to do/try?
This is an Aero enhanced upper that has the built in receiver extension instead of the barrel nut, very solid. I have the Larue MBT2s trigger which is great. Cant help but wonder if the bolt has something to do with it, its a nickel boron coated PSA bolt. The last cheap thing on the gun.
I know the White Oak barrel is capable, I just didn't expect to struggle quite this much. It doesn't shoot horrible but it isn't impressive either. So far.

Is it bad to switch bolts after having shot with one for a few hundred rounds?

23.8 of 8208 is ADF military load
CCI 41 primer in LC brass
77 MK
I load 23.3 in my 5.56
Great choice of powder
Suggest look at ADI load data for best results

 

[SKWERLZ]

23.2 - 8208 - load the smk77 to 2.250”. Try 2.235” OAL with the 75’s.

23.2-23.5 of 8208
#450 primer
Very common and successful load with 75 and 77’s

 

[Jeff Porter]

it does ok in a 200 yard rapid fire string.

 

[Jeff Porter]

 

[Woofie]

The first AR15 I built up from scratch is a SPR with a 1:7 18" White Oak barrel. It has a FailZero plated BCG (I have been happy with Fail Zero in another .223, an AR10 and a 458SOCOM). Other than a Geisselle trigger and a Magpul MOE stock everything else on the rifle is Seekins, down to the gas block.
I have been happy with build, it shoots well out to 1,000 yards but is a bit wanting past 7-800 due to the 18" barrel. It prefers 77 SMKs or the Nosler or Berger equivalents. I have also loaded Hornady 75 HPBTs with success. The rifle also likes the Speer 70grn SP. My only complaint about the barrel, which shoots well, is the "scab" down bore from the gas port which I assume came from a burr left after the gas port was cut/drilled.
I haven't loaded the 75s for a while, but probably should as I have a box full of them and yes, there is a component shortage Looking at my chrono record database I used W748, Varget, RE15 and CFE223 with the 75s. RE15 was the best, and actually gave the most velocity. I have also done well with BLC2, A2520 and TAC in this gun. You should do well with TAC in this gun, which I think of as a spherical H4895.
If you have a friend who can lend you different BCG to try a few shots, that would held to confirm or eliminate one of the concerns.
I'm assuming you installed the barrel yourself? So you know it is a snug fit in the upper? If all else fails you might think about reinstalling it using Green Loctite as a bedding compound. I typically DO NOT do this as Seekins uppers are nice and snug, but it has worked for some folk I know.
One other thing you might try is to look for some IMI 77grain Razorcore ammo. It is, IME, consistently the most accurate and powerful 5.56mm ammo I have used. Or maybe some Hornady Frontier 75grn Match (sgammo.com has some) and use those as a benchmark for your handloads? You may have done this already, but it's worth mentioning.
Good luck with your frustrations.

 

[6bra1k]

get a real bbl....20-24"

 

[tommeboy]

check out johnny's reloading bench on youtube. He did a huge series on shooting the 77gr bullet trying to match the Military load. He uses a 18" WOA barrel also. He used almost every powder that is suitable for this bullet. There are at least 20 vids he does.

and maybe it is you. Shooting an AR is different from shooting a regular bolt gun. I had trouble at first till got some time behind one. Lots of things going on when the trigger is pulled and it takes practice to get good at shooting one of these things. A friends gun shoots 1.5"+ groups with him shooting the gun. When I shoot it it drops to about a 0.90" groups.

 

[Crazyornothing]

Ironically I started shooting lighter bullets in my 1-8 twist WOA 20 inch service rifle and it seems to love them more than my 77s. My Shilen prefers heaviers way more. Same twist! Same service rifle profile. Try shooting some 55 grain match or varmint bullets. Mine will also shoot tiny groups with 40 grains as well. With 24.7 G of Tac I get great accuracy with multiple 55 grains at lower pressure. Weird how my WOA prefers lighter. A 40 grain Vmax at 3600 is hardly much drop at 500! The 77s will still shoot sub MOA at 2760+ FPS but not quite like these lighter ones want to touch the same holes.

Also, I clean my barrel every 50 rounds or so but this last time I didn't and couldn't notice a difference but it did seem like it took a 100 rounds before I started seeing it's potential with lighter bullets. I prefer my Shilen for the 77s and WOA for 40-68 grains.

 

[Crazyornothing]

Try another bolt. White oak barrels are pretty consistent, not sure about the psa bolt. I have always used white oak bolts and barrels together. Tac works very well with 77s normally.

Yeah I would swap the bolt just in case. Also 2 thousands next tension, expander mandrel, and mighty armory 223 FL match die has done me very very well. 4 thousands primer seating depth with 21st century also is money.

 

[Karlandco]

Neck tension? Oal movement after cycle? How's the meplat look after chambering? Is it bumping em back into the case them upon chambering and/or using the cycle as a kinetic bullet puller. Tuning neck tension, buffer weight, spring and gas system is a juggling act. Try hand feeding right into chamber, lock the bolt in and shoot 3. If it improves you'll know.
If you let it rip one out of the mag into the chamber, then Eject it, you can measure to see if the oal changed. However this is not a good duplication of the cycle as when a live round cycles the action. Instead load 2 rounds into mag. Cycle action and fire 1 round down range. Eject the second out of chamber and measure that one. This exactly duplicates the all variables for examination. I'm sure ya know load developing gassers involves more steps than bolt guns. It can surly be a back n forth game until you waive the white flag.

 

[Jeff Porter]

23.8 of 8208 and 69’s shoots well in my 20” if you do try lighter bullets. I haven’t shot it past 500 yards but it was 1moa there.

 

[karrarararararar]

I didn't believe it until I tried it with a service rifle AR, but adding a light crimp on the necks with a Lee collet crimp die tightened groups up with 77gr Sierras (and Noslers) and 24.0 gr of TAC at magazine length. Folks told me that somehow TAC shot better (and cleaner) with a crimp and I was skeptical until I tried it myself. Granted, this was to hold X/10 ring on a NRA sling target.

I would do the same when I was loading shortline ammo. 24.0 grains of Tac with a light crimp. I noticed lower SD's when I crimped.

I will add for OP, don't worry about beating the gun up. Full power loads will not hurt an AR-15.

 

[jlorenzo]

Round count on the barrel, twist, and a comp ?

3-400, 7 twist, A2 flash hider

 

[jlorenzo]

get a real bbl....20-24"

I do wish I had gone with a 20", even finding the 18" was a struggle the last two years. Even still good luck getting either any time soon. I figured between my 26" bolt gun and the 18" gas gun I had a pretty versitile spread. That said, next time I will be going 20 on the gas gun.