pondskipper
Well-Known Member
- Joined
- Aug 23, 2010
- Messages
- 296
You are correct. I would never recommend anyone use a rifle length gas system with an 18" barrel, as they are always over gassed due to as you stated oversized gas ports because of the short dwell time. I always build an 18" with either a midlength or an intermediate length gas system. Now for 20" or 24" definitely go with the rifle length system, and usually I only use an adjustable gas block on suppressor builds. If you use a high quality barrel, such as White Oak, Wilson Combat (which by the way I would've used with their upper and lower and it's only 10.00 more than the White Oak barrel), and Ballistic Advantage, which I use quite a bit and get excellent accuracy out of. As a few people and the OP mentioned the key is to get everything running in harmony, which can be done many different ways, some, or even most that aren't that horribly expensive. You don't even need a Billet upper and lower matched set, just a good quality forged upper and lower set. It's all about who finishes the forged upper and lower and the QC of the company who does it. Palmetto is ok for an entry level first or second AR but there are way better quality companies out there who have excellent forged uppers and lowers, Aero Precision to name one. Also if you want to build a very accurate AR I usually recommend a 20" Heavy free floated barrel, fluted or non fluted with either a Billet match upper lower set, or a quality forged upper lower matched set. If you would like me to do a parts list for one of my custom match .223/5.56 20" barreled rifles I would be ok with listing it out for you all if you would like just let me know. I spent 15 years in the US Army and have been designing and building AR's for the last 10 years. Also I guarantee all of my rifles from 14.5" barrels on up to shoot under 1 MOA at 100 yds with quality ammo, and our match guns are guaranteed to shoot under .65 MOA at 100yds with quality match ammo. So yes AR's can easily be made to shoot sub MOA with the proper parts and combination of parts. Good luck with all you builds guys.You don't need an adjustable gas block on a rifle length gas tube. I can't find the test article, but max pressure is achieved very early in the bullets travel down the barrel. So don't quote my numbers. They are from memory. on a round loaded to about 53,000 psi The gas port on a carbine length gas tube gets about 30,000 psi The mid length was 22000 and the rifle length was 17,000. They did state slow burning powder and bullet weights could change these up and down.
I have friends with carbines and light weight BCG and when you open them up for cleaning after a few hundred rounds on a new AR the buffer tube weight face is marked up from getting slammed by the BCG. The small piece called a "cam pin" located underneath the gas key is already visibly warn already.
My mentor told me to use the heavy full auto bolts, longer gas tubes, and possibly even heavier buffer tube weights. It all slows down the cyclic rate. I've even messed with the buffer tube end hole diameter and using flat wound springs to quiet the cycle.
You want everything in harmony to eject your rounds every time. I have some that put all the casing in a pile about the two O'clock position and others clear back to around to nearly 5 O'clock
Could be the gas block because that is what operates the rifle so with the amount of gas going to the BCG changing all the time, if that's what's happening you will get a POI shift causing your zero shift. Also what brand of adjustable gas block are you using? You also need to make sure the set screw is tight on your adjustable gas block locking it in whatever position you adjusted it to or you will have problems with operation as well. Is your JP optic mount completely on your upper or does it span both the upper and your handguard/rail system? If it spans both and the handguard is not to the same spec as the upper you could have issues with movement and then your scope would be off the next day or later in your range session. Let me know about those questions and we should be able to get this fixed for you.Ok guys, I'm having a bit of trouble with the rifle maintaining zero and I'm not sure what it is. I've tried 3 different scopes on it now and they all are doing the same thing so I know it has to be something to do with the gun. I've checked, checked, and rechecked to make sure everything was right like it's supposed to be including the scope mount and barrel nut, but for the life of me I can't nail down the problem. The scope mount is a jp enterprises 34mm optic mount that's super strong so I don't think that's the issue. One thing I did notice was that when I slid the gas block and tube on when I was putting everything in the wilson combat upper was that the gas tube was pressed more tonone side than the other, I think the alignment slot for the barrel is a little off or the passage for the gas tube is off causing it to bind some and seeing as how it's basically connected to the barrel this could be causing the issue but you would think that is would cause accuracy problems and not problems maintaining zero. Any thoughts?
Scopes tested were Burris xtrii 2-10x42, 3-15x50, and
vortex razor hd gen II 4.5-27x56 from my 300wm so none of them are junkers lol.
You know, when I was reading through the "failure to maintain a zero" my mind immediately went to ... could it be the nut behind the trigger?Ok so I figured out the problem, and I'm a little embarrassed to admit it ...