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Discussion Starter · #1 ·
I'm getting ready to buy my first XCR-L and I want it to be my Quiet Gun. We all have plenty of loud guns that shoot supersonic, so I would like this one to be dedicated to plinking ONLY Sub-sonic 300 BLK and Always shoot it With a Suppressor.
My concern is that I've heard shooting suppressed 300 BLK can be unreliable when using Sub-sonic ammo but Sub-sonic ammo is the only ammo I want to shoot in this particular gun.

Robinson Armament even says on their website quote " ....some barrel lengths may not work well with all calibers. For 9.5 inch barrels or to shoot Subsonic .300 BLK ammo, a shorter gas system is required that puts the gas block inside the upper (Buried). For barrels longer than 9.5 inches, it is best to use a longer gas system which puts the gas block outside of the Upper( Exposed)....unless you're shooting Sub-sonic 300 BLK, the Micro and Mini are not recommended for use with a suppressor unless it is a Flow-through suppressor or one with very little back pressure.

1. None of my suppressors are flow-through design with little back pressure so does this mean that the Micro and the Mini are less reliable with Sub-sonics than the longer standard barrel configurations ?

2. What is the Most Reliable barrel length for shooting suppressed 300 BLK Sub-sonics ?

3. For only shooting suppressed Sub-sonic 300 BLK, without a Flow-through Can, what would be the Quietest configuration that is still 100% reliable ?

4. Can I get either Micro or a Mini in 300 BLK and is one more reliable than the other when shooting suppressed Sub-sonics ?

5. How hard is it to adjust the gas if it is Buried ?

6. I think I want the gas block Exposed, but can get a 300 BLK with an exposed gas block on a Mini or only a Micro ?

7. Does the Robinson Armament website configurator actually show all of the possible combinations of configurations or are there other options not shown ?

Bottom line is I would hate to pay $2,400 for a gun and then pay one dollar per round for Sub-sonic ammo only to have an unreliable gun that jambs on me at the range.

Any Advice would be greatly appreciated. Even if you can't answer all 7 questions, please chime in on any that you can give advice on.

Thanks
 

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1. 300blk comes in "blackout" or micro length gas. Usually determined by which upper you're putting it in. Rest of the calibers can be had in any gas length. Longer barrel is going to keep the system under pressure for more time, potentially helping reliability in low pressure rds but in high pressure rounds like 556 a short gas system with a long barrel and a suppressor kind of sucks.

2. Broken in gun and appropriate gas setting is going run on any length. I've got a 7.5 micro that runs fine as long as I set it up correctly. 9.5 will give you more dwell time to help with pressure if you're running really low pressure stuff.

2 and 3 are redundant.

4. Figure out your barrel length and upper configuration to help determine which gas system you want. It's a small difference in length but plays into being able to reach the adjuster. Still a little redundant after 2 and 3.

5. Easy with the correct pairing of gas length and upper.

6. Only micro upper will expose the gas block on a 300.

7. Not all are shown. Not sure they still offer every possible combination. I was told "mini" gas a special order the end of last year.

Bottom line. Figure out what's most important; barrel length, upper length, gas system length. That will narrow down some options.
 

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Guys who are running sealed cans...how many rounds do you get before fouling in the magazines/bcg start causing reliability issues? Seem to remember some folks saying around 300 rounds....but that was (IIRC) in ARs and may not have been talking XCRs.
 

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To be clear, if you order an XCR in .300 blackout with a standard length upper, Robinson will default to the “blackout” length gas, which is “buried.” It’s not difficult to turn the adjustment dial.
Assuming reliability refers to proper cycling, I think that the issue is that subsonic .300 BLK varies a lot. One brand may cycle perfectly on gas setting 3 and another brand needs gas setting 4, etc. Personally I’d go with a 9.5” or 12” barrel.
 

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Discussion Starter · #7 ·
This XCR Forum is great, everyone is nice and very knowledgeable. I thank all of you that help me and others learn.

Questions:

1. Since Robinson Armament puts a Detent on their Exposed gas valve for a reason, are there any issues with the gas valve not having a detent on the Buried gas blocks ? Can it move unintentionally ?

2. Thanks guys, based on your good feedback, a longer barrel gives me more dwell time so that would help Sub-sonics cycle more reliably. So I would like to get a 9.5" or 11", or 12" barrel but the configurator shows the Mini in 300 Blk only comes with a 7.5 inch barrel. However the configurator shows that 9.5", 11" and 12" barrel lengths are available on the Standard Short Gas system. Unfortunately, it shows the gas block is Buried on the Standard Short Gas model. Their picture looks like I could reach a detent on a Mini upper. I just personally like the Exposed gas adjustment valve, so is there any way to get Mini with a 9.5 inch barrel ?

3. From just the pictures I have seen, it looks like it would be much easier to adjust the gas valve if it is Exposed instead of Buried. Is there any configuration of a 300 Blk besides a Micro that would give me an Exposed gas valve ?

4. Are there any videos showing how to adjust the gas valve on a Buried upper ?

5. I have read that specifically with Sub-sonic 300 Blk a 1:5 Twist gives much better accuracy than a 1:7 Twist because it stabilizes those long heavy slow moving bullets better. Alabama Arsenal says his tests show " the groups get considerably tighter with the 1:5 twist, like going from 3 inch groups to 1 inch groups at 100 yards." Since I am going to only be shooting Subs in this gun, is there any way to get Robinson Armament to build me an XCR with a 1:5 Twist ?

Thanks again for any help.
 

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Someone recently asked a question about buried gas blocks having any issues with the adjustment turning due to the lack of detent. This was just a person with no XCR experience asking questions that had no real basis. The adjustment won’t turn on its own.
All of us here shoot one or more XCRS and we haven’t had the experience of the adjustment turning on its own. It’s a non issue. The adjustment is also very simple with the tip of a bullet or pushing the knob with a small hex wrench.

1:5 twist is becoming more popular but 1:7 is still the standard. Just call RobArms if this is really something you need. Personally I think it may be overhyped. 🤷🏻‍♂️
 

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You can use the tip of a bullet, brass rim or other tool to adjust it. Your usually only going to touch it when you change ammo types, and its a pretty easy adjustment. The buried block uses a spring and ball bearing to hold the dial in position, the exposed block has a spring loaded cup that rests in a slot outside the dial. There's more risk of bumping an exposed block, which is why it's held in place more robustly. Both won't move on you.

Unless you need the shorter upper or barrel length I'd just go standard upper and 9.5" blackout length. Its pretty comfy. You could probably ask for 1:5 but it'd be quite a wait. At 100yds a 300blk sub is going to have about 1ft drop compared to a super zero.
 

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Regarding gas system length and upper length... again...

300blk comes in blackout or micro gas length. Micro is slightly shorter and coincides with the micro length gas with the rest of the 7.5" barrels in the other calibers that will place the gas block in front of micro upper.

MICRO UPPER IS THE ONLY LENGTH UPPER THAT WILL GIVE YOU AN EXPOSED GAS BLOCK IN MICRO/BLACKOUT GAS LENGTH.

Mini length upper will cover blackout and micro gas blocks but will occlude the blackout length dial. It can still be reached via the front of the upper but it's more difficult to get a good purchase to adjust smoothly. Micro gas in a mini upper is easily adjustable through one of the side vents, buries the block and puts the shoulder of the threads just in front of the upper. I have this setup and it works great once you figure out the correct setting for the Ammo you use with your suppressor.

Standard upper requires a 9.5 inch or longer barrel. 9.5 will put the shoulder right in front of the upper. Blackout gas length will be easily adjustable through a side vent. Probably the "sweet" spot for barrel length. Enough to get the supers going without unneeded length for the subs. Unless you want the marginal extra fps with a longer barrel, I'd stay at 9.5. A 9.5 micro gas length will fit in standard upper but the dial is occluded.

I've assembled all the above configurations personally. I've shot the 9.5 blackout in a standard upper and 7.5 micro in a mini upper quite a bit.

If you contact RA direct, they CAN make whatever configuration you want, not sure they'll actually do it and it may add some time. I think getting a 1/5 twist will be the hardest thing to get.
 

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Discussion Starter · #11 ·
Thanks everyone for all the help, I really appreciate it. I'm ready to buy my first XCR-L and I have narrowed it down to either a 9.5" or 11" or 12" barrel.

I believe you guys, it's just that if you put yourself in my shoes, when I click on the RA configurator and choose a Standard XCR-L in 300 BLK with a 12 inch light barrel it shows a picture of an Exposed gas valve. I believe you guys that for 300 BLK to cycle reliably with Subs, it must have a very short gas system so I don't think the RA configurator shows the correct gas valve location on the Standard XCR-L 300 BLK 12 inch. I like the looks and the easy access of the Exposed gas valve, but for 300 BLK Gas Length if it is only possible with a Micro upper, then I will go just with a Buried gas valve. However, it seams like there are two different lengths of buried gas valves for 300 BLK.

Question :
1. The RA configurator does not distinctly specify them but are you saying there are two different gas lengths for the 300 BLK caliber, #1 Blackout length and #2 Micro gas length ?

2. You're saying a Standard upper using a Blackout length gas length will be easily adjustable through a side vent but a Micro gas length in a Standard upper will make the dial occluded. Did I understand that correctly ?
So you're saying a Micro gas length would be harder for me to adjust because the the dial would be covered by the handguard so should I order a Standard Upper with a Blackout length gas system ?

Thanks again everyone for helping me understand so much about these great guns. I really appreciate all of you taking time to explain everything and help me learn.
 

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Discussion Starter · #15 · (Edited)
The configurator showing the XCR-L Standard in 300 BLK with an Exposed gas valve is what was throwing me off. I definitely want to be able to shoot Sub-sonics so I know I need a short gas system.
Question : Are there two different gas lengths for 300 BLK Sub-sonics : one called " Blackout length " and a second one called " Micro length " ?

Thanks again for all the help. Have a Happy 4th of July !!
 

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It’s unfortunate that the configurator uses different terms than the company sometimes uses for communication. “Blackout length” is “short gas system”, which is what you get when you get a standard upper length XCR-L with buried gas. I wouldn’t recommend to anyone a longer length gas
System — ie exposed on a standard upper — for .300 blackout.
 

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The configurator showing the XCR-L Standard in 300 BLK with an Exposed gas valve is what was throwing me off. I definitely want to be able to shoot Sub-sonics so I know I need a short gas system.
Question : Are there two different gas lengths for 300 BLK Sub-sonics : one called " Blackout length " and a second one called " Micro length " ?

Thanks again for all the help. Have a Happy 4th of July !!

Yes, Blackout and Micro Length are the 2 lengths for subs...
 

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For the people in the back.......


 

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Discussion Starter · #19 ·
When you guys say " Blackout and Micro Length are the 2 lengths for subs " meaning two different Gas Lengths, then which one should I buy for 300 BLK Subs ? Blackout Gas Length or Micro Gas Length ? They both seam similar to me, why would you choose one over the other ?
Which one of them would cycle more reliably than the other for 300 Subs ?

Thanks again for any help.
 

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When you guys say " Blackout and Micro Length are the 2 lengths for subs " meaning two different Gas Lengths, then which one should I buy for 300 BLK Subs ? Blackout Gas Length or Micro Gas Length ? They both seam similar to me, why would you choose one over the other ?
Which one of them would cycle more reliably than the other for 300 Subs ?

Thanks again for any help.
Dude.
..... your questions have been answered multiple times by multiple people. Just like your other thread about quiet gas systems, there's not a single right answer.
 
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