Need help tuning AR15 gas system for 358 Wildcat please :)

[lar45]

Hi everybody, I'm working on a new AR15 rifle and have run into a snag with getting it to cycle and lock back.
The cartridge is a 358 Winchester short x 1.71", just short enough to fit an AR15 magazine. I'm loading Hornady 200 FTX to 2471 and Speer 180s to 2599fps with CFE-BLK.
The barrel is from DeadShot Barrels in Oregon, it has a mid length gas system.
They cut the chamber with a standard 358 Win reamer and set the headspace off of a case I sent to them with the bolt.
For loading dies, I just cut about .3" off the base of Lee dies and they seem to be working great.
For brass I'm using Winchester 308 Win once fired cases, cutting them off at the shoulder, then lube and run through the shortened sizing die, then trim to length at 1.71"

My first loads were with 1680. I started with a CAGB adjustable gas block. It came with the gas port drilled to .086" and would not lock the bolt back. I drilled the hole to .096" and now it locked back on the largest setting. I set the gas block back one notch and it wouldn't lock back, so I set it back to all the way open and thought I was good.
I tried some cast loads with the Lee 358-200 and they barely hit the target, so I gave up on that idea for now and went back to jacketed.
During load developement, I decided to switch to CFE-BLK as it's slightly slower burning and I got better velocities.
Now the gun started to not lock back. I went back to 1680 and it still wouldn't lock back on the last round.
I cleaned the inside of the upper and reoiled the BCG, but no change.
I then drilled the gas port to .116", but no change.
I oiled the recoil spring and buffer, no change.
I wondered if maybe part of a gas check got stuck in the gas block, so I replaced it with a standard gas block, no change.
I'm at a max load with CFE-BLK and I'm getting great accuracy and velocity, so I can't load any hotter.
My other thought is to open the gas port even more, but I think something else must be wrong as it used to cycle when I was first breaking it in after the gas port was at .096".
I am open to any and all suggestions.
Thanks
Glenn.

[cwtebay]

What buffer weight are you using?

Sent from my Pixel 5 using Tapatalk

[lar45]

I'm not sure on the buffer weight. I'll go weigh it.
2.9 oz

[Barry54]

I like the looks of that cartridge!

For testing, take the weights out of your buffer and see if it locks back on an empty magazine.

I bought an ultralight buffer for a lightweight build. I’ll post a link when I find it.

https://www.tacticallink.com/Taccom-...-1022275889370

Someone smarter than me will probably know, but I suspect you need a shorter length gas system. Do you have a lightweight bolt carrier you could try as well?

[imashooter2]

Is the gas port in the block aligned with the barrel? Gas key tight?

[Fitz]

I run a 358 Yeti and run a J&P captured spring , they come with 3 different weight springs to tune with and sell different weights for the buffer, have you verified that the gas block is set with the barrel gas port some barrel makers have the block set back around .030 from the wall.

[cwtebay]

I run a 358 Yeti and run a J&P captured spring , they come with 3 different weight springs to tune with and sell different weights for the buffer, have you verified that the gas block is set with the barrel gas port some barrel makers have the block set back around .030 from the wall.

This^^^^^

Sent from my Pixel 5 using Tapatalk

[lar45]

I'll see if I can run a bore scope down and check.
My cartridge should be very close to the Yeti. I was just too late to the Yeti party. I Don't think the barrels and bolts are available anymore, unless you find one on the used market...

[lar45]

The gas key is tight.

[DDriller]

On my .30 HRT I opened my port to 0.125 (full opening of my gas block hole) to get it to work with a piston system on a 12" barrel. With the adjustable I wouldn't worry about opening it up if changing to a lighter buffer doesn't fix your problem.

[Barry54]

On my .30 HRT I opened my port to 0.125 (full opening of my gas block hole) to get it to work with a piston system on a 12" barrel. With the adjustable I wouldn't worry about opening it up if changing to a lighter buffer doesn't fix your problem.

I opened a 300 blackout to 1/8” as well. That size hole seems big in a 30 caliber barrel but percentage wise, isn’t as much in 35 caliber. Hopefully it will be enough for the OP to make the new rifle run.

[Outer Rondacker]

Sorry I am short on time this morning but will Check back later. I recently had a bad buffer tube give me the same trouble in a 300blk. If the lower is new check the travel on the bolt. Just a suggestion. The buffer I had was not machined deep enough to allow the buffer and the bolt to achieve full travel.

[lar45]

The lower is new as well. I will try it on a different lower to see if it runs there.

[Moleman-]

What is your gas port pressure for the loads you're using?

[lar45]

What is your gas port pressure for the loads you're using?

As close as I can tell with Quickload, the gas port pressure at 9" is between 10-12kpsi for the 200s and 180s.

[lar45]

Now I can't find my bore Scope It only worked with my phone from 5 years ago...
Got on Amazon and ordered a new one...

[Moleman-]

As close as I can tell with Quickload, the gas port pressure at 9" is between 10-12kpsi for the 200s and 180s.

I'd think you should be fine with a smaller gas port then. I've made a few midlength 450BM barrels and used a .081" port on them which has a lower port pressure. Are you getting ejector swipes?

The gas systems are a little weird. Too low and too high port pressure can mimic the same result of not cycling. The ID of the gas tube is around .116"-.118" depending on who made them. Once you hit about .090" gas port size you're getting into deminishing returns as opening the port further has less and less effect as just so much gas at "X" pressure is going down a .116"-.118" tube. I'd really check the gas port alignment. If your barrel isn't dimpled you can take the rear set screw out of the gas block then install the gas block upside down centering the rear setscrew hole over the port and measuring the gas block/barrel shoulder gap with feeler gauges to know how much to stand it off when putting it back together. also check the passage in the block to gas tube alignment as I've had that be off as well. Might also check gas tube drag/alignment by removing the bolt and seeing if the carrier key is rubbing on the gas tube.

[lar45]

Thank you very much for the detailed information.
I'll check all of that and try again.

[Rapier]

The AR system is totally about timing. If you are going to change loads you really do need an adjustable gas block. Then you full close it, then open 1/4 turn, try, open a click at a time, until you get full function. Do not change more than one thing at a time, ever. The AR system does exactly the same thing UP and OP, so you change three things and end up right where you started.
Been doing this since 62. Had 384 ARs at one time.
Last wonder guns I got in, new in the box, would not even function subs or super factory ammo, they were so messed up, so no deal, even the big makers set up ARs that will not function.
The 358s and larger bore guns went to tungsten extra heavy buffers to get MORE weight. Counter intuitive, slow the BCGs down to drop the pressure so the bolt can open at the proper time on the pressure curve. So go back and think slow down, not speed up.

I shoot my two 358 AR-15s with the adjustable gas block, near full closed when at 2,500 with a 200. I use 1680
This is the round, based on the 6.8 SPC. Resembles a rimless 357 Herrett.

[lar45]

Ok, the new borescope came in.
I put the adjustable gas block on and it's lined up with the port.