Pressure Signs - M16 High Power Rifle

[grizlywinkleman]

Hey erbody,

Hoping you all can help me out. I started to refine my typical load as well as try a few other powders in my high power/service rifle M16A4. I was shooting 77gr SMK's in LC brass (mix of years since 2000 not separated), CCI 400 primers, 23.5gr Varget. I would get the occasional AR ejector marks once and awhile but nothing else.

I recently worked some ladder tests with 8208XBR (Top) and N540 (Bottom) with the same components in 2x fired brass. Here are my findings:

I started getting increasing pancaking of my primers, ejector marks, and occasional extractor marks/burrs starting at the second load of 8208 and the fourth load on N540. Totally normal in a ladder test right...?

Here is the problem, I loaded up some 10 shot groups of N540 at 24.6gr hoping to get a 600 yard load and 23.7gr of Varget (added .2 gr) hoping to get a little more than 2600 FPS. I first fired a 5 shot control group of 77 gr OTM AAC factory ammo (fly's at about 2815 out of my rifle; it's good stuff!). Everything seemed to have followed the trend of pressure signs. Pancaking is especially more prevalent. Here are a few pics:

I'm shooting a Bartlein Barrel that was manufactured at a time know for premature barrel extension wear out. Could these signs be a sign of that? The 23.7 gr load of Varget shot .863 MOA @ 100 and the function was fine. I've never shot a barrel out but I got the upper from a good friend and have put about 700 rounds through it.

Is my barrel that picky? I wouldn't expect such a drastic pressure sign jump with .2 gr of varget. I will be monitoring the 23.5gr load of Varget at my next practice. Maybe I'm over thinking this and need to just dumb down my loads but it really doesn't feel like I'm reaching for any extreme's. Perhaps I need to be humbled.

Any words of wisdom would be greatly appreciated. Thank you for your time.

Ryan

 

[Critter Picker]

Did you check for a carbon ring? The only way 700 rounds of .223/5.56 would wear out a barrel would be with a lot of mag dumps.

 

[grizlywinkleman]

I literally didn't even know about a carbon ring issue until you posted amd I quick googled it. Thank you! And no I have not subjected the rifle to any sort of mag dumping. I'll look into that next.

 

[Panhandlin Pat]

I've had that happen with long (still in spec, won't close on a no go gauge) head spacing. Took me a long time to figure out the issue, and Redding + competition shell holders solved the issue. My guess is the primer was backing out and then getting hammered back in, since the case head wasn't pushed into the bolt face. The lower pressure loads seemed to be worse. This of course being in a bolt gun

 

[badbull]

You hit 2815 with the N540 and that's what the factory stuff did in your rifle. I think that is your max fps for your barrel with the 77gr bullets. Since your bumping max, that small change in powder could cause the pressure signs to show IMO. But let us know if you have a carbon ring and if that changes things after you clean it.

 

[Mike6158]

If you find that you have a carbon ring it can be a bear to remove. I had one in my 7mm Rem Mag. It took a lot of work to get rid of it. I think the thing that helped the most was pushing a patch with carbon remover on it into the bore just far enough to let the carbon ring soak. I tried quite a few and CLR made the most difference. Some barrel mfg will void the warranty if you use CLR. Sharp Shoot R Carb-Out is pretty good. Iosso paste is good. They all work well. I clear them out of the barrel with a couple of 99.9% isopropyl alcohol patches. Anything lower in percentage will have water in it.

The carbon ring is hard. Think about where diamonds come from, carbon subjected to high heat and pressure.

 

[johngibbs222]

Excuse my question as I don't know about LC brass here in the UK but is it service ammo ie 5.56 or commercial 223 ammo.
If it's service ammo were the primers staked in and did you have to ream the pockets?
I had a very similar issue with service 7.62 ammo brand GGG, I over reamed the pocket and on the next firing the primers flowed into the countersink I made. Changed to Federal 308 cases with no primer staking obviously, problem vanished.
Another suggestion is to check the case usable powder volume, here's a link to the methodology I use ,
Check the various capacities of the mixed cases you have and you may find that the volume of some of your cases is less than others which can or may cause increased pressure signs.
FWIW there are those that say such pressure signs put you way above the actual service pressure but hey, it's your hands and face that could get injured and there's an easy cure for that.
Final suggestion, e-mail Vhitavuouri, their customer service is excellent.
Just a stab (or two) in the dark but just saying. HTH

 

[Mike6158]

I over reamed the pocket

I use a Dillon primer pocket swager to solve the crimped or staked in primer problem. That eliminates the risk of over reaming the pocket.

 

[cohunt]

Are you shooting your m16a4 in semi-auto or 3 round burst mode?

I didn't realize they came with bartlein barrels, but I suppose you could have rebarreled it,

Where is your brass landing with factory ammo? Where is your brass landing with your reloads? Ideal is 3:00-5:00 position, if it's forward of 3:00 you are over-gassed which can show false pressure signs.

How are you sizing your Brass? Bumping the shoulder a certain amount, or touching die to shell holder? Do you have head space gauges? Are you crimping the bullet? Are you loading to gi mag length or loading long?

I see you are mixing years on the LC brass (different head stamp years can have different case capabilities) are you checking case capacity?--- are you reaming or swaging your primer pockets? Are you checking case length and trimming if necessary? Annealing?

 

[TennJed]

Excuse my question as I don't know about LC brass here in the UK but is it service ammo ie 5.56 or commercial 223 ammo.
If it's service ammo were the primers staked in and did you have to ream the pockets?
I had a very similar issue with service 7.62 ammo brand GGG, I over reamed the pocket and on the next firing the primers flowed into the countersink I made. Changed to Federal 308 cases with no primer staking obviously, problem vanished.
Another suggestion is to check the case usable powder volume, here's a link to the methodology I use ,
Check the various capacities of the mixed cases you have and you may find that the volume of some of your cases is less than others which can or may cause increased pressure signs.
FWIW there are those that say such pressure signs put you way above the actual service pressure but hey, it's your hands and face that could get injured and there's an easy cure for that.
Final suggestion, e-mail Vhitavuouri, their customer service is excellent.
Just a stab (or two) in the dark but just saying. HTH

Plus 1 for varying case capacity. I've weighed different head stamp mil brass and the variance is pretty large, never measured case capacity but I'm sure they also vary considerably.

 

[FireFlyFishing]

My first thought when reading the OP is a carbon ring buildup. Bore scopes tell all in this department. Plus, they tell you when it's gone when you're trying to remove it. I've had good luck with a carbon remover I purchased at the LGS.

I use mixed headstamp LC brass, don't push the pressure envelope, and can stack a 30 round group in about 1.1 MOA. That's using 77 grn SMKs too. I'm running north of 2800 fps in an 18" DD barrel.

Edit: oops, I needed coffee this morning. It was the 55 grn blitz king running north of 2800. I think my SMKs are 2600+ish.

 

[badbull]

From my Sierra Reloading manual #6 for the 77 gr SMK COAL 2.260" 1-8 twist. Loading for AR-15 rifles .223 REM
N540 24.5 @ 2600 fps, Max 24.9 - 2650 fps. No data for 8208 XBR. Varget 23.5 @ 2500 fps, max 23.9 @ 2550 fps This is data straight from the manual(not mine) No 5.56 or Wylde chambering data in case you were wondering. You may already have this just trying to be helpful. The manual did show 2 faster powders TAC and A2520 if speed is your goal.

 

[Citified]

I'm voting for a carbon ring. Especially is he is not using a borescope. The other thought that comes to mind is case stretch. Are you checking overall case length to see if it is within specs?

 

[lyle2231]

From my Sierra Reloading manual #6 for the 77 gr SMK COAL 2.660" 1-8 twist. Loading for AR-15 rifles .223 REM
N540 24.5 @ 2600 fps, Max 24.9 - 2650 fps. No data for 8208 XBR. Varget 23.5 @ 2500 fps, max 23.9 @ 2550 fps This is data straight from the manual(not mine) No 5.56 or Wylde chambering data in case you were wondering. You may already have this just trying to be helpful. The manual did show 2 faster powders TAC and A2520 if speed is your goal

2.660 COAL????