77gr gas gun struggle

[jlorenzo]

My PSA (upper/lower, bolt/carrier) with a 20" White Oak 1 in 8 twist Three Gun barrel will shoot 75 grain Hornady BT with RL-15 into 5 shot .75" group consistently at 100 yards. I did ream the takedown pin bores and install oversize pins. I seat the Hornady 75's to 2.25" with no crimp. I use a Redding bushing die and bump the shoulder back .004". I shoot for .0015" to .002" neck tension. I run a Geissele SSA two stage trigger.

I had luck with RL15 and those bullets as well, still not quite as tight as I would like which may be me. Also wanted something a little more temp stable.

 

[jlorenzo]

Wylde or 556?

How was the fit on the barrel extension? If it was loose tighten in up with some shims and heat fitting.

how are you processing your brass? Die type, trimming, chamfering, ect?

How are you measuring your charges?

How are you seating your bullets?

You may want to try a stainless steel mag with thin front and back walls. You can load out to 2.3ish with those. That can help in many cases especially with the 75s.

If there is any part of the gun that has wiggle room and it doesn't need to move try to tighten it up to eliminate unnecessary movement.

What is your optic?

How are you shooting for groups? Position, rests, conditions, ect.

Make sure there is no contact on the barrel and if you have the tool lap the receiver face.

Wylde, It slid in not loose but not super tight. I have had tighter and looser fits.
I size with Hornady custom die, bump shoulder .0035ish, trim to 1.75 every firing now, just started annealing but haven't shot that brass yet. Standard chamfering and deburring on RCBS prep station with Lyman vld tools.
Charges thrown on a Frankford Arsenal intellidropper, I weigh charges again on a seperate scale to see how its doing. Throws consistently.
The lower wiggles a touch, I have an accuwedge in it.
Optic is a Athlon Ares ETR 3x18
Shooting for groups on magpul bipod and basic rear bag. Might move to a grooved rear bag, looking to pick up a front rest for F class anyway.

Honestly I think its mostly me and just havent found the load. I was getting single digit SDs with 8208 and the groups showed promise. I think Ill be able to find one that works. Also got some 69gr SMKs to try because I wont be shooting this gun much past 600y I am realizing. Still have a bunch of 77s and 75s.

 

[jlorenzo]

Do you use a concentricity gauge on your ammo. Last time I had an accuracy issue with 75+ i found that the bullets didn't fit my seating die well and concentricity was all over the place. If i sorted my ammo after; i found sub 1" groups at 209y, indicating this was a key loading component.


Barrel nut torque? Mil spec is 30-80ftlbs; most accurate assemblers that i know torque to 30 and increase until barrel nut clears the gas port with no gas tube contact. Or use a WOA like barrel nut that doesn't contact gas tube no matter what.

Facing off the receiver can help too; and I'll add that I've never found a barrel to shoot all heavies equally, Nosler, Sierra, Hornady, Berger try them all, the barrel will choose.

24.0gr Varget is 2650-2700fps from a 20" barrel. That is about as expected. If you want more velocity; you're asking for trouble when the weather changes. By all means, do what you gotta, just saying; consistency is key, my suggestion ignore velocity it's a gross measurement at best. The target tells all.

-Mac

I do not have a concentricity gauge. I will look into it.
The barrel nut is around 57 ftlbs I think. The barrel nut doesnt contact anything, this is an Aero enhanced upper with the chunky receiver extension.

 

[mac86951]

I do not have a concentricity gauge. I will look into it.
The barrel nut is around 57 ftlbs I think. The barrel nut doesnt contact anything, this is an Aero enhanced upper with the chunky receiver extension.

Yea take a look at the ammo then; i was seating 77s and 1 outta 3 would be horrendous runout, easily seen by rolling the loaded rounds on a table. Start there and save your $. Measuring up near me play, 0.005" or less TIR grouped the best. Who knew, bullets starting straight come out straight...

Highly recommend trying other components as some combos just don't fly in some ARs. Varget ~23.5-24.0 is common, as is N140 same weights. H4895 is another great powder for 77s.

TAC, H335, ar comp, CFE 223, imr 8208, R15, 203B, and all the others I've tried, 748, WC846, all shoot great if you load for the conditions. In the high desert, it means a summer load, winter load, and sometimes a mid-temp load; but those nice mid-range temps have 80mph winds, so... Those are the best days! 600y you hold upstream edge, 2 targets over.

-Mac

 

[jlorenzo]

No luck with Tac but my bolt gun likes it, CFE 223 was awesome velocity with no pressure but patterned more than grouped, been looking for some H4895 for my bolt gun for over a year and haven't seen it once.
I have IMR 4895, have yet to load anything with it. I am using N140 in my bolt 223 and liking it.

8208 is what I am going to pursue. Saw good results right away that should be able to tune a load up with.
This was in 20 mph wind, notice the ripped target. Almost couldn't staple it to the board. Also my fundamentals weren't great that day.

 

[darkangel_r2]

Wylde, It slid in not loose but not super tight. I have had tighter and looser fits.

If you can a stainless steel shim and some heat fitting can very solidly bed that.

I size with Hornady custom die, bump shoulder .0035ish, trim to 1.75 every firing now, just started annealing but haven't shot that brass yet.

Check the die without the expander ball to see how tight it sizes the neck without it. If you don't need the expander don't use it. Are you measuring the brass after every cycle? Like you pick a fired one and adjust the die .0035 from that shoulder dim? If that is the case I would not do that. Either have a master piece of brass with the exact dimensions you want all your resized brass to have or use a wilson (or similar) case gauge to insure one lot of reloads is identical to another. Also I don't like the Hornady seater with the neck sleeve thing. If thats what you are using try a different type of die. Forster ultra and redding comp seater work well.

The lower wiggles a touch, I have an accuwedge in it.

Good start, I use those too. See if you can shim it to make it even more solid.

Honestly I think its mostly me and just havent found the load. I was getting single digit SDs with 8208 and the groups showed promise. I think Ill be able to find one that works. Also got some 69gr SMKs to try because I wont be shooting this gun much past 600y I am realizing. Still have a bunch of 77s and 75s.

The best advice I can give is try to make everything as consistent as possible so you only vary the thing you are testing.

I prefer the 77s. They seem to go transonic better than the 75s and 69s. But as you say inside 600 there will be no issue with any. 69s seem more jump tolerant though. Get one of those stainless steel mags that allows longer seating and see if that helps a little too.

 

[darkangel_r2]

8208 is what I am going to pursue. Saw good results right away that should be able to tune a load up with.
This was in 20 mph wind, notice the ripped target. Almost couldn't staple it to the board. Also my fundamentals weren't great that day.

23.2 is a stout charge of xbr. Do you have a chrony? If you haven't already you may want to check a little lower. 223 hits 55k psi at about 2650 in an 18" with 77s and xbr. Now a wylde chamber can go hotter without issues, so I'm not that concerned about your charges but the sweet spot for you might be below 23.

 

[6bra1k]

my opinion..is just that
i think you keep buying low end 2nd tier or less parts and expect the world.
current bolt is no better than a psa.
you bought a good bbl but keep associating it with lower stuff.
scope is marginal in my opinion
what is the intent of the rifle ??

 

[darkangel_r2]

my opinion..is just that
i think you keep buying low end 2nd tier or less parts and expect the world.
current bolt is no better than a psa.
you bought a good bbl but keep associating it with lower stuff.
scope is marginal in my opinion
what is the intent of the rifle ??

The only thing a custom bolt and carrier can do is give better head space dimension and reduce tilt in the carrier. Depending on chamber dimensions a standard or small base die and sizing the shoulder a little long (turn off gas for a few shots to get a fire formed piece from your chamber) can eliminate the the need for a headspaced bolt.

And a high end carrier with reduced slop between the upper and bolt carrier to combat tilt (they do not cure it only reduce it) comes at the price of potentially reduced reliability. Tilt is probably better addressed by custom mods done by the shooter. There are extended buffer tubes that have surface forward of the buffer detent that can be used as a contact point to eliminate it. You can shave the edges of your buffer and use a stronger spring to insure more forward force on the back of the carrier to even it out, anti tilt buffers, ect. These all cost less than a high end bolt carrier designed to mitigate tilt which only partially eliminate the problem.

Treat your ar15 like its your piece of art. Put some sweat work into it and you can get a lot out of it.

 

[Jeff Porter]

23.2 is a stout charge of xbr. Do you have a chrony? If you haven't already you may want to check a little lower. 223 hits 55k psi at about 2650 in an 18" with 77s and xbr. Now a wylde chamber can go hotter without issues, so I'm not that concerned about your charges but the sweet spot for you might be below 23.

Thread drift alert.... I agree a standard 223 chamber 23.2 is getting on the warm side, I run 77's with that load and up to 23.5 in a Wylde 20" Shilen ratchet.

But... In a Wylde chamber with a +2 gas system and an H3 buffer... I was getting 2800 fps with an 88 ELDM and had no flattened primers or ejector swipes at 24.5gr 8208 in LC brass with 205MAR primers. I would have thought I would have been popping primers about 24.0. - Usual disclaimers please work up to this load. If you are not trying to shoot 1000 yards on an E target - no need to get this hot.

 

[darkangel_r2]

Thread drift alert.... I agree a standard 223 chamber 23.2 is getting on the warm side, I run 77's with that load and up to 23.5 in a Wylde 20" Shilen ratchet.

Yep as I stated I wasn't too concerned about his pressures I was simply pointing out that he was starting pretty hot and may be a more accurate load lower with still acceptable velocity.

But... In a Wylde chamber with a +2 gas system and an H3 buffer... I was getting 2800 fps with an 88 ELDM and had no flattened primers or ejector swipes at 24.5gr 8208 in LC brass with 205MAR primers. I would have thought I would have been popping primers about 24.0. - Usual disclaimers please work up to this load. If you are not trying to shoot 1000 yards on an E target - no need to get this hot.

Are you saying you are feeding these monsters from an ar15 mag???

 

[Jeff Porter]

Yep as I stated I wasn't too concerned about his pressures I was simply pointing out that he was starting pretty hot and may be a more accurate load lower with still acceptable velocity.

Are you saying you are feeding these monsters from an ar15 mag???

No, single load

 

[jlshaw]

Run 24 to 24.5 grains of Varget, RE15, N140, or 4895 in a Lake City, WIN, or Lapua case.
Put a 75 or 77 on top of it and load to 2.245 to 2.25.
Stuff it in a magazine and shoot it.
If it won't shoot under .75 to 1 MOA there's probably something wrong with your gear or technique.

This has worked for many years on my White Oak barrels.

Most competitive highpower rifle shooters would concur.

 

[jlorenzo]

the 23.2 load of 8208 was 2695 w/77s.
23.8 was 2762 with single digits SD of 7.4 and ES of 18. I'm gonna start working with that one I think. I didn't see pressure with any of the charges even 24.0.

 

[Bamban]

The only thing a custom bolt and carrier can do is give better head space dimension and reduce tilt in the carrier. Depending on chamber dimensions a standard or small base die and sizing the shoulder a little long (turn off gas for a few shots to get a fire formed piece from your chamber) can eliminate the the need for a headspaced bolt.

And a high end carrier with reduced slop between the upper and bolt carrier to combat tilt (they do not cure it only reduce it) comes at the price of potentially reduced reliability. Tilt is probably better addressed by custom mods done by the shooter. There are extended buffer tubes that have surface forward of the buffer detent that can be used as a contact point to eliminate it. You can shave the edges of your buffer and use a stronger spring to insure more forward force on the back of the carrier to even it out, anti tilt buffers, ect. These all cost less than a high end bolt carrier designed to mitigate tilt which only partially eliminate the problem.

Treat your ar15 like its your piece of art. Put some sweat work into it and you can get a lot out of it.

Here is my anti tilt mod. Buffer tube needs to be bored out to accommodate the SS sleeve. The pressed in brass carrier weight was before the H3 was available

 

[jlorenzo]

Here is my anti tilt mod. Buffer tube needs to be bored out to accommodate the SS sleeve. The pressed in brass carrier weight was before the H3 was available


View attachment 1337882View attachment 1337883View attachment 1337884

What difference did you see after installing this? Mind giving a rundown on the construction and how it functions?

 

[Alaska Bush Man]

My 5.56 load for my MK12
IMR 8208 @ 23.4
77 MK
CCI 41 in LC brass
Mild crimp with Lee factory crimp die
IMR 8208 is a up coming star in the 5.56 with 77MK in match shooting. Also the new RL 15.5 been hearing good things also with heavies.

 

[Alaska Bush Man]

the 23.2 load of 8208 was 2695 w/77s.
23.8 was 2762 with single digits SD of 7.4 and ES of 18. I'm gonna start working with that one I think. I didn't see pressure with any of the charges even 24.0.

23.8 is the ADF load MK262Mod1
I load 23.3 for 2700 fps in 18”
IMR 8208

 

[Hohn]

23.8 is the ADF load MK262Mod1
I load 23.3 for 2700 fps in 18”
IMR 8208

I’ve found accuracy with 8208 as low as 22.1 under a 73 ELD (200-14x at 300) and as high as 23.6 under an 80 ELD (200-8x at 600). To date it’s the most consistently accurate powder I’ve tried in my gas guns.

RL15, AR comp seem great too, but 8208 is just a bit more accurate. I’ve got some aa2520 and n135 I haven’t tried yet.

 

[Hohn]

What difference did you see after installing this? Mind giving a rundown on the construction and how it functions?

Don’t waste your time on such mods. They are dubious in utility at best. Any carrier meeting mil spec is sufficient. I will suggest a JP enhanced bolt be fitted.