Unreliabiliity with IMR 4198 in AR with Rifle Length Gas System

[luzyfuerza]

One of my favorite loads for bulk ammo using 55 grain bullets in .223 ARs is 20 grains of IMR-4198. This load has cycled perfectly in the half-dozen or so guns with a carbine-length gas system that I have tried it in, and, depending on the bullet used, is quite accurate.

IMR-4198 has been a favorite for me for bulk reloading because it uses 20% less powder per round than other common powders for .223.

The other day, a friend who shoots an AR with a 24" barrel and a rifle length gas system tried these loads. The 4198 loads wouldn't cycle in his gun, with lots of FTFs and FTEs.

Chronograph data showed that velocities for these 4198 loads were consistent with a variety of factory ammo and with other reloads that did cycle his gun successfully. For example, loads made with IMR-4895 using the same bullets with similar velocities cycled just fine.

Cleanliness isn't likely a factor; a magazine of 4198 loads wouldn't cycle, the same magazine was loaded with factory ammo and the gun cycled perfectly, and finally more 4198 loads were tried, and the gun balked as before.

I swapped buffers, buffer springs, and BCGs (one component at a time) between a carbine that loves the 4198 load and his rifle with no effect. Changing magazines had no impact.

His gun has been completely reliable with the tens of thousands of factory rounds that he has shot through it previously.

I haven't measured his gas port or inspected the condition or position of his gas block. If these were a problem, though, I would think that the gun likely wouldn't cycle with factory ammo or loads using slower powder.

My question: Have any of you observed cycling issues in guns with rifle length gas system with loads that use faster-burning powders like IMR-4198?

 

[Kaldor]

I have used IMR 4198 in my AR. My load was 21.7gr, CCI BR2 primer, 55gr Vmax, LC brass, loaded to just shy of mag length. Disclaimer: This load is above book max according to Hodgdon, but is right at max according to Lyman. Use at your own risk. Very light recoil. 4:30 ejection. Barely enough to cycle the rifle, lock back bolt, or pick up next round. Accuracy was decent. Been a couple years, and I didnt keep detailed notes because I only loaded less than a single pound of it because it was given to me.

Would I use it again? Nope. Doesnt meter worth a crap in my Hornady rotary drop, and Im not single measuring every charge.

Rifle:
Green Mountain 18" barrel, rifle gas
Spikes H buffer
Aero Precision M16 BCG
regular gas block

My gun runs like a sewing machine, quite often cycling on very very light loads that most other ARs choke on.

The issue that some ARs have with IMR-4198 is that because it burns so fast, the port pressure on the rifle gas system is too low to operate the gun. Your carbine length guns have a higher port pressure because it has less time to lose port pressure due to a shorter gas system.

 

[blue32]

I encountered problems with starting loads of H4198 in a mid length system. I would guess either H4198 or IMR4198 would need close to a max load in order to achieve enough gas port pressure in a rifle length system. Its a pleasure to shoot if you can get enough pressure though.

 

[cpt-t]

My best load for a 223 in both a Bolt Gun or AR is 21.0grs of IMR 4198 with a Speer, Hornady, or Sierra 52gr BTHP Match Bullets. I think the Speer Bullet shoots the best for me, but I use what ever I can find at the time. The 52gr Hornady A-MAX and 50gr V-MAX with 21.0grs of IMR 4198 shoots very well for me also. All of these shoot under an inch, at a 100yds off of a bench. These are all I have loaded for many years.
ken

 

[Kaldor]

My best load for a 223 in both a Bolt Gun or AR is 21.0grs of IMR 4198 with a Speer, Hornady, or Sierra 52gr BTHP Match Bullets. I think the Speer Bullet shoots the best for me, but I use what ever I can find at the time. The 52gr Hornady A-MAX and 50gr V-MAX with 21.0grs of IMR 4198 shoots very well for me also. All of these shoot under an inch, at a 100yds off of a bench. These are all I have loaded for many years.
ken

You may be right for your particular gun, and in a perfect world this would be true. For as many people, like you and me, that have no issues, there are others that will have issues.

What length is your gas system?

 

[243winxb]

cycling issues AR 15 223 H4198

AR and H4198 http://www.thehighroad.org/showthread.php?t=502784

 

[Ironicaintit]

my preference is 24 grains of 3031, but i do have a bunch of 55 grainers that are loaded with 21.5 grains of IMR4198 that shoot great and reeeally accurate in my 16" and 20". Luckily, I dont recall ever having any cycling issues. But mine arent 24" either

 

[GooseGestapo]

Too light of charge. 21.6 is what I've always used with 4198 in .223 (55gr bullets), howver I haven't used it since the late '90's. I've always found BLC2 to be superior. Only time I use something besides BLC2 is with 65gr or Heavier, I use RL15.
btw; imo, CFE223 is for practical purposes; is BLC2 with copper fouling reducer added...ymmv. Slightly higher charge weights for similar velocities.

Back in '08, I bought an AR (16.5") Bushmaster to replace one I'd traded off several years previous. I hoped to be able to shoot cast bullets in it, as all FMJ bullets had dried up.
I tried 4198 as I had/have several pounds of it. 19.8gr was the lightest charge that would cycle the action with the 50gr SptGC bullet I was loading. Velocity was too high for usable accuracy.

 

[Kaldor]

You guys are missing the point here. He is asking why doesnt it work.

The reason it doesnt work is not barrel length. This is a gas system issue. 4198 just doesnt have enough power in this particular rifle. There are potentially other issues at play here as well. Buffer & spring could be too heavy, but he checked that against a known working combo. Bolts can cause issues, how clean it is, is it lubed, are the gas rings worn, how easy does the bolt move in the upper, is the chamber clean, does the bolt close easily?

His problem simply is this: The rifle length gas system in combination with some other unknown factor, is causing the bolt not to cycle correctly with this particular powder charge because it is not creating enough gas to run the gas system which in turn drives the bolt.

If he wants to run this powder in a rifle length gas system, he likely needs to up his powder charge as others have suggested. But even then, this particular combination of parts may still not work, or he may get to where he needs to run an unsafe load to get it to cycle.

For what its worth, he could probably get away with 22gr of H335 which would cycle both rifles, and still give decent accuracy. And it meters a hell of alot better!

 

[243winxb]

From my link/post above The gas port pressure curve is a critical part of internal ballistics for cartridges used in gas operated firearms. Gas operated weapons are generally tailored to a narrow range of powder burning rates and characteristics. If the port pressure is too low the weapon will fail to function and if to high the weapon may function too forcefully or rapidly causing extraction or cycling problems. When using the fast H4198, the pressure peaks very fast and is done producing pressure sooner than your slow powders. With such a wide range of bullet weights from 40gr to 80gr, matching the gas port location and size is critical. If the gas port was moved closer to the chamber and drilled larger, H4198 may work.

 

[Kaldor]

From my link/post above The gas port pressure curve is a critical part of internal ballistics for cartridges used in gas operated firearms. Gas operated weapons are generally tailored to a narrow range of powder burning rates and characteristics. If the port pressure is too low the weapon will fail to function and if to high the weapon may function too forcefully or rapidly causing extraction or cycling problems. When using the fast H4198, the pressure peaks very fast and is done producing pressure sooner than your slow powders. With such a wide range of bullet weights from 40gr to 80gr, matching the gas port location and size is critical. If the gas port was moved closer to the chamber and drilled larger, H4198 may work.

Exactly the scientific answer here!

 

[David4516]

4198 works in my AR but it's a 16 inch with a carbine gas system. Someone mentioned switching to H335 and I have to agree. I don't have a problem with 4198 it's just that I've had so much success with H335. I'm getting much better velocity with H335 than I am with 4198. In fact of all the powders I've used for my AR-15, 4198 has consistently given me the lowest velocity. So I'm not surprised to hear that you've had issues with the longer gas systems...