Tuning suppressed sbr questions

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TexasEric
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Tuning suppressed sbr questions

Post by TexasEric » Fri Jul 27, 2018 6:58 am

I have been away from the forums for a while. I am back now. Thanks for all your time and help with this build. Dellet, Rebel, Dr Phil this is targeted to you. Thank you.

I am going to assemble my AR SBR in a couple weeks. My can should be out of jail in a now-ish to a couple weeks.

I plan on buying several different brands of factory ammo to do this.

I plan on buying 2 or 3 different tier subsonics, and the same with supers for tuning. Cheap to high quality is my tier system. I want the gun to run every it is feed.
With one exception, I don’t really care about firing subsonic unsuppressed. Ideally it would be nice, but not a hard requirement.
The can will probably spend most of it’s time on the sbr. After I purchase another, it will have a can on at all times.

Should I start with subsonics suppressed, and tune the gas adjustable gas block for that? Then move up to supers suppressed? Making needed adjustments along the way?

Also what is ideal ejection pattern, where my brass lands. I know the supers will be over gasses. What should I look for for supers and subs?

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alamo5000
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Re: Tuning suppressed sbr questions

Post by alamo5000 » Fri Jul 27, 2018 1:48 pm

Do you have an adjustable gas block? I assume so.

My method to the madness is as follows:

Start with one type of ammo, try to cherry pick the lowest pressure ammo of the lot. Open your gas block to allow full or nearly full flow.

Now, unsuppressed shoot a single round and see if you have bolt hold open. If so click down one or two clicks with your gas block. My gas block has 15 positions so that should give you an idea of how many shots you need to take.

My gun likes position 6 or 7 so if I went one shot per click you are looking at 7 to 8 shots.

When you get to the point where there is no bolt hold open click back to the position where it still functioned. In my case I might click back two positions since I have so many options.

Now shoot one round of each other ammo (IE load one round in the mag) and see if there is bolt hold open. If there is you are good to go.

I tune mine (for general use) to function with and without a suppressor using all ammo (barring my own special home brew stuff that requires special gas settings).

When you add the suppressor you will generally have reliable function with whatever you use.

---

Also repeating myself from other threads, if you have trouble with feeding and whatnot the problem might not be in the front of the gun, but rather in the back. Then we get into discussions about heavier buffer weights or other back end options.

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Dolomite_Supafly
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Re: Tuning suppressed sbr questions

Post by Dolomite_Supafly » Sat Jul 28, 2018 10:41 pm

I do just the opposite. I bottom out the setscrew and count the turns out until it locks open with an empty magazine with the highest, then write that down. Next I shoot the subsonic ammunition and count turns until it locks open on an empty magazine, then write that number down.

That way you have a known starting point and a known adjustment.
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TexasEric
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Re: Tuning suppressed sbr questions

Post by TexasEric » Wed Aug 01, 2018 7:10 am

I have talked to some of the great minds on the forum, Dr Phil still waiting to hear from you on tuning. Pm coming your way.

Any other advice on tuning, and what ammo do you guys recommend for tuning. I want the gun to eat everything it is feed.

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Re: Tuning suppressed sbr questions

Post by alamo5000 » Wed Aug 01, 2018 7:39 am

When I tuned the gas for my most recent gun I used a variety of ammo. I did the initial tuning with some cheap 150 grain stuff. Once I got it in the ball park I would try other lighter and heavier ammo to make sure. Low and behold I discovered that with the 150 grain gas block settings it would not fully extract with certain 220 grain subs. I opened the gas flow one or two clicks for fine tuning and viola.

While technically it would be ever so slightly over gassed with the 150 gr supers, but that's ok. It was not anything at all to worry about.

Don't use one ammo. Use various grain weight ammo of various brands that you can find on the shelf local to you.

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Re: Tuning suppressed sbr questions

Post by hotwing » Wed Aug 01, 2018 9:13 am

I use the same method as DS... close it completely & count the clicks out. Different settings for different loads (practically 2 - subs & supers).

Always cycle it full closed & open after every session to prevent buildup inside (ask me how I know) & keep things moving easily.

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Re: Tuning suppressed sbr questions

Post by steven11b » Wed Aug 01, 2018 12:47 pm

I start closed, once it fully cycles I usually turn it out 2 additional clicks. I do that so that when the rifle becomes dirty or I change the load/round it will still function 100%. Adding the 2 additional clicks does allow more not needed gas flow but its not really noticeable as the shooter and adds to the reliability. Not having to adjust it for different loads besides going from subs to supers simplifies the system.

I notice that many people use one round in magazine when performing this. I would load a full magazine to test cycling as that adds some resistance differences to the BCG. Basically test it as its intended to be used. You can do a few single rounds to obviously test the BHO.
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Re: Tuning suppressed sbr questions

Post by rebel » Wed Aug 01, 2018 9:14 pm

Eric, my answer via pm mimics DS's method.
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Re: Tuning suppressed sbr questions

Post by Dolomite_Supafly » Thu Aug 02, 2018 2:21 pm

TexasEric wrote: Any other advice on tuning, and what ammo do you guys recommend for tuning. I want the gun to eat everything it is feed.
To have a gun that will run everything you are going to have to compromise.

It is possible to have a gun that will run everything without adjustment but the trade off will be that it will be over gassed.

If you don't want an over gassed gun the trade off is you must adjust the gas for each load.

The best thing to do is drill your port at .120" and use an adjustable has block. That is the only way to ensure the gun will cycle the first time out.
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dellet
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Re: Tuning suppressed sbr questions

Post by dellet » Thu Aug 02, 2018 3:39 pm

Dolomite_Supafly wrote:
TexasEric wrote: Any other advice on tuning, and what ammo do you guys recommend for tuning. I want the gun to eat everything it is feed.
To have a gun that will run everything you are going to have to compromise.

It is possible to have a gun that will run everything without adjustment but the trade off will be that it will be over gassed.

If you don't want an over gassed gun the trade off is you must adjust the gas for each load.

The best thing to do is drill your port at .120" and use an adjustable has block. That is the only way to ensure the gun will cycle the first time out.
I need to disagree with drilling to .120", even if you plan to use an adjustable block.

Then I need to say that there really is nothing wrong with doing it.

Most people really don't have any idea how over gassed these things really are, in normal shooting conditions. A big reason for that is the tendency to grab a bunch of parts and hope they work. Then post about it on forums. People think there are more problems than there really are, because no one needs help if it works.

I have had the chance to talk to a few ammo manufacturers over the years. They all have one thing in common in how they develop subsonic loads.

All factory ammo needs to be able to cycle worst built and designed carbine gassed rifle without a suppressor. Think about that for a minute. We regularly have people come here for help with suppressed, pistol gas guns, that can't work with factory ammo. :shock:

I keep my port sizes to a minimum. That means .105" for carbine and .097" for pistol. I still use adjustable blocks.

Now I need to contradict myself again. I have one barrel that has a .110" port and carbine gas. They drilled it wrong on the order, not that big of deal so I accepted it.

The other is a 10" carbine gassed barrel with a .125" port. Not supposed to work. It works fine with factory subs suppressed and factory supers without a suppressor. It also has an adjustable block and I dial down both subs and supers.

I use the smallest port possible, so the adjustable block does as little work as possible. This takes more time and effort, that I am more than happy to spend. I prefer to size the port for my favorite sub load and only need to cut it back for supers.

The point of all that is these things are way over gassed to begin with, unless you regularly 5000+ sub rounds at -40 degrees without a suppressor and you life depends on it cycling.

Controlling the amount of gas is a necessity for me, there are a few ways to go about.

No disagreement with what Dolomite said, just a little different way of doing things.
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