300 blackout AR not cycling

[bigjake]

I sure could use some possible fixes for the blackout upper I got a good deal on at the local gun show, ( gee, I wonder how I got such a good deal?)

Anyway, The thing is short stroking or wont put another round in the chamber. I read a bunch of stuff online from drilling out the gas hole to a weaker spring to a lighter buffer weight, not to mention ammo and mags. I tried all different mags and all kinds of different load combos.

I want to start casting boolits for this rifle. That's all I want to shoot out of the gun, No copper, I use enough copper in the 5.56.

Has anyone come up with something different than what I have read?

thanks

[mdi]

How does it work with factory ammo?

[BK7saum]

I'd check with factory ammo first , then start looking for problems or changing stuff out. One possible issue to look for is poor alignment of the gas port and gas block. Sometimes they don't line up or aren't lined up and you're getting reduced gas.

[LUCKYDAWG13]

I'd check with factory ammo first , then start looking for problems or changing stuff out. One possible issue to look for is poor alignment of the gas port and gas block. Sometimes they don't line up or aren't lined up and you're getting reduced gas.
I'm thinking the same thing I would start with factory ammo then a new mag then play with the gas block
but i would bet its a misaligned gas block

[charliehough]

What bullet are you shooting thru your blackout

[Pumpkinheaver]

Do not drill the gas port bigger!!! Check the screws in the gas key first, make sure they are tight, they should be staked in place as well. If that's good then check the alignment of the gas block and the port in the barrel. Check back in after you have done that.

[Pumpkinheaver]

Also are we dealing with a carbine mid length or rifle length gas system?

[osteodoc08]

We need more information.

What Gas length do you have? Carbine or Pistol. I've never seen a rifle length gas system on a 300BO.

What reloads are you shooting? Need details.

What weight buffer are you using?

Have you cleaned it? Any corrosion, heavy grease, etc?

How does it cycle manually? Gritty? Smooth? Difficult?

What type of gas block does it have? How is it attached?

[Gtek]

Agree with not drilling until you look and confirm and research out from end to end. Most barrels are not cut for floater front guards, if gas block is against shoulder you may have a restriction of around forty percent of orifice. Remove gas block to measure orifice in barrel and record size then find somebody with a HAWKEYE or 90 degree type visual aid to confirm alignment on install, trust no ones set screws, keys, pins. Pull gas tube and inspect just for feel good. Visual on bolt key, sealing rings, then understand what gas system you have and burn rates/powder choices and projectile weights that will be needed and used. IMHO this platform is not for the uninformed due to all the different configurations available. Figure out what you have and then absorb all the information you can sponge, then they are a hoot to shoot!

[Steve Steven]

I have just helped a friend with a Blackout which would not cycle. We drilled the gas hole out to .106", cut the spring 1" and still no cycle. Load was 125gr Nosler with 14.8gr Win296 a 1800FPS load.

He came up with a reduced strength recoil spring from Nemo (http://www.brownells.com/rifle-parts/receiver-parts/recoil-parts/recoil-springs/300-blackout-carbine-buffer-spring-prod56149.aspx) which he ordered, we will see if that will help.

Steve

[6bg6ga]

90-95% of the problems I have seen with the 300 blackouts have stemmed from a carbine or full length gas setup. Want a 300 to work with everything? Set it up correctly in the first place then. I read all the horror stories about not cycling before I built my first 300. I settled on a PISTOL length gas system and the three 300's I have built for myself and my wife work flawlessly with ALL ammo that is fed to them. I can run below minimum loads in my 300's and they still cycle. They may not throw the brass out 30 feet and instead put it 3 feet to the right of the gun but every shot every time they work. Got an adjustable gas block? If not put one on and adjust it and it will probably work and if it doesn't pull the barrel and replace it with a pistol length gas system and be done.

[GooseGestapo]

I went through something similar.

I bought a used .300bo barrel. It's a mid-length gas system on 16.5" bbl. Built upper from assorted parts I had laying around.
I too had short cycling. Ended up drilling port to full .120" (1/8").
Still, to get it to cycle, I had to use slower powders. It would/will pierce primers with loads using 4227 or H110 and still not cycle(125gr jktd with max load of H110 will now cycle that bolt/upper reciever have broken in)
(18.0gr H110. 16.5gr with 155gr Lee ptgc won't lock back, occasionally pierces primers...)

With the Lee 155gr PTGC over compressed loads of Rl7, 5744, or max published load of 1680, it will cycle and lock back. Velocities are 1,850-2,000fps. Accuracy is all you can ask for (2moa).
It also feeds the Lee 150gr FNGC. (All sized .311"). I plan to hunt deer/pigs with it next season.
LT30 might also work but haven't run across any. Some old H4198 I have wouldn't lock back bolt, but might now that reciever/bolt have worn in.
btw, it recoils 2-3x what a .223 does. A LOT of power from a small package.
Also, using worn out, recycled . 223 cases. Occasionally, one won't hold a primer. That's when they get tossed!

[OilyPablo]

We need more information.

What Gas length do you have? Carbine or Pistol. I've never seen a rifle length gas system on a 300BO.

What reloads are you shooting? Need details.

What weight buffer are you using?

Have you cleaned it? Any corrosion, heavy grease, etc?

How does it cycle manually? Gritty? Smooth? Difficult?

What type of gas block does it have? How is it attached?


Answer these first!

Don't drill or cut anything yet.

Always make sure your bolt (BCG) is free moving and super smooth (most aren't!!) An over gassed rifle won't really care that's why most people never notice how lousy the bolt moves. Yes, make sure the key is well sealed.

Assume your AR is undergassed and go from there, but start with the easy stuff first. Don't cut the spring, get this one:

http://www.davidtubb.com/ar15-tubb-parts/ar15-buffer-spring-stainless

I can show you how to polish all the correct BCG parts to make is super slick and feel like a precision rifle.

For sure make sure there are no burrs in the bolt carrier, hone with light polishing compound, then go with a one piece gas ring. Polish the cam pin and cam way.

I have more tips, but answer the basic questions.

[Moonie]

I've got a carbine length gas 16" barrel, never had a problem with 155gr boolits on top of 15gr W296/H110. I have had problems with W296/H110 over subs in it. I now use RL7 and AA1680 (just purchased) with heavies to shoot subsonic through my new can. I use a standard carbine buffer and spring.

We really do need to know load data to be able to help with issues. If the loads are appropriate I would suggest the port isn't lined up properly.

[Boolit_Head]

If you have a free float hand guard check that the gas block has about .025 to .030 space from the rear to the shoulder. If not your gas block is not lined up with the hole. They are designed to have the plate that holds the front of a standard hand guard in there. Pictures might help.

[bigjake]

We need more information.

What Gas length do you have? Carbine or Pistol. I've never seen a rifle length gas system on a 300BO.

What reloads are you shooting? Need details.

What weight buffer are you using?

Have you cleaned it? Any corrosion, heavy grease, etc?

How does it cycle manually? Gritty? Smooth? Difficult?

What type of gas block does it have? How is it attached?

Its a carbine system -

im loading 130 gr. and 150 gr speer HP with max load of 296/H110

Cleaned it like someone with OCD

Not sure of the weight of the buffer

I noticed the chamber is a little rough- the brass looks like it was sanded with 240 grit after shooting.

I ordered the light nemo spring

The gas hole is .093

I used LC 5.56 cases cut and trimmed to book specs. used RCBS 300 blk T/C SB dies

the gas block has a small scope/light rail on top. that's the only way I can describe it.

[Boolit_Head]

Any gas system longer than a pistol is more finicky. You did not mention if you have a gap between the gas block and the shoulder of the barrel. I am betting your gas block is not lined up. Pictures would help.

[popper]

0.093 is right for gas hole. Chamber shouldn't be rough - check it with dental pick or such. Chamber a single round and check for lock back and where the brass goes when ejected. Load 2 in the mag and make sure both get picked up & chambered. If 2nd doesn't chamber, check nose for jam or BCG over-run.

[bigjake]

I want to use this mold for the 300 blk.

Lee 2-Cavity Bullet Mold CTL312-160-2R

anyone use this in their 300 blk out?

[Boolit_Head]

I'm having good results with the 312-155-2R mold, it's just not the tumble lube version. By the time I PC and gas check they are weighing in at 160 grains.

[bigjake]

I'm having good results with the 312-155-2R mold, it's just not the tumble lube version. By the time I PC and gas check they are weighing in at 160 grains.

Do you load the 312 dia boolit right out of the mold or do you size it down?

[Boolit_Head]

I am sizing to .309 after PC and seating the gas check at the same time. Reportedly from several sources the gas check makes a big difference in accuracy.

But I'd worry more about posting a picture of your gas block so we can see if it is fitted correctly. If not your gas port could be blocked and that could be the source of your issues with your upper. Carbine length would be more picky about alignment. You should be seeing a .025 gap to account for the unused hand guard cap if you have a free floated hand guard.

[Gunnut 45/454]

Well obviously his gas port is not blocked. As he is getting BCG movement. I would really want to know what ammo he shot? If as he said max load of W296 that points to buffer- which should be a Carbine buffer ! With a normal length/tension spring . Hell my Carbine gassed 300 AR cycles everything subs and suppers just fine with this setup. Also may want to look at the gas key on BCG it may be loose or have a broken screw. Gas tube not cracked? Sounds like you may have bought a home built upper. Maybe the builder didn't know what he was doing!

[Boolit_Head]

Not necessarily, he could not be getting full gas pressure if the port is partially blocked. That could cause his issues. Forgetting the gap is a common mistake and will misalign the gas port causing insufficient gas. A max load of 296 with 150 or 160 grain bullets is more than enough gas to cycle any system.

[bigjake]

I understand about the gas block alignment and the .025" gap. Im going to look at the buffer weight. im probably going to open the gas hole from .093 to .099. or .096 not decided. I'm going with that nemo buffer spring. I also traded bolt carrier group with my son, the bottom of the one I got has more material(steel) on it. his is more open, hence lighter.

[popper]

Chamber shouldn't be rough this will increase friction when cycling and cause short stroking. You also didn't state (or check) for short stroking vs over-run. Run the BCG really WET.

[BK7saum]

You stated that the gas port was 0.093". Was this confirmed by removing the gas block and measuring or what it was spec'd to be? if you did removed the gas block, was there a black carbon ring completely around the gas port in the barrel? If so, then the gas block was properly aligned. Proceed with changing out parts per your pocketbook.

If you didn't confirm gas port size and didn't verify that the port was aligned with the gas block by observation of the carbon ring, please do so before proceeding further. I reread all of your posts to this point and did not see where you confirmed that the gas block was properly aligned. If I missed it, my apologies. Just want to cover first things first.

Brad

[Pumpkinheaver]

I would not drill the port bigger. That is a last resort, at least to me.

[adanymous]

I make a very good living specifically off of the AR-15 rifle, and I own a company devoted to selling parts and accessories for them. A real company, with employees and stuff. Which is to say, I kinda know a bit about them. And as a guy who has been through this same thing at least 1000 times. Id check your gas block alignment like everyone has said. Secondarily, if aligned properly, and aluminum. Id swap it for a US made steel part. Most of the aluminum blocks I see are chinese made and Ive seen several where the gas passages did not connect inside, and many more with flashing partially blocking the passages. 3rd step for me would be to drill the gas port. Lots of 300 barrels have 223 ports. Its nothing to be concerned about if you have a drill press.Next would be gas key check. If its secure and going on the tube youre good. After that, a lighter buffer and lastly a weaker spring. Weak springs can cause issues stiripping the next cartridge from the magazine and can cause failures to go into battery. Weaker springs are kind of like putting a band aid on a broken arm in my opinion. Yeah, its a treatment, but not likely one getting to the root of the problem. If everything lines up and is in functional condition. Its likely an ammo problem.

I dont know what you do for a living, but I bet youre great at it. And if I needed advice about it Id likely take yours. I only say that cause most people dont listen when I tell them stuff about their AR.

[6622729]

You should be seeing a .025 gap to account for the unused hand guard cap if you have a free floated hand guard.

Are you saying that in the upper build with a free floating hand guard, the gas block should not be slid all the way back against the shoulder? There should be a .025" gap between the gas block and the shoulder?

[Boolit_Head]

That is correct since the free floated hand guard does not use the hand guard cap so it is not installed. You have to have the gap to account for the thickness of the missing metal.

[Green Frog]

I dont know what you do for a living, but I bet youre great at it. And if I needed advice about it Id likely take yours. I only say that cause most people dont listen when I tell them stuff about their AR.

If I were having the problem you are having, OP, I would carefully read and follow the advice in post #29 from adanymous One additional point I would make is that after I made sure the gas port in the barrel for my build was to spec, I used an adjustable steel gas block, and had this part of upper assembled by a professional. I took the attitude that this cartridge is used in so many iterations that adjustability in the gas system can be a real asset.

I'm a Biologist, and I agree with adanymous both about the Band-Aid on a broken arm and about listening to professionals about their areas of expertise.

JMHO,YMMV,
Froggie

[bigjake]

The gas port is .093 now. what do you think I should open it up to? The block is steel. What would be a good weight for the buffer? The cases look scuffed after shooting, how do you recommend I polish out the chamber to smooth it a bit? I don't have a large enough lathe to chuck up the barrel.
Thanks for your advice.



I make a very good living specifically off of the AR-15 rifle, and I own a company devoted to selling parts and accessories for them. A real company, with employees and stuff. Which is to say, I kinda know a bit about them. And as a guy who has been through this same thing at least 1000 times. Id check your gas block alignment like everyone has said. Secondarily, if aligned properly, and aluminum. Id swap it for a US made steel part. Most of the aluminum blocks I see are chinese made and Ive seen several where the gas passages did not connect inside, and many more with flashing partially blocking the passages. 3rd step for me would be to drill the gas port. Lots of 300 barrels have 223 ports. Its nothing to be concerned about if you have a drill press.Next would be gas key check. If its secure and going on the tube youre good. After that, a lighter buffer and lastly a weaker spring. Weak springs can cause issues stiripping the next cartridge from the magazine and can cause failures to go into battery. Weaker springs are kind of like putting a band aid on a broken arm in my opinion. Yeah, its a treatment, but not likely one getting to the root of the problem. If everything lines up and is in functional condition. Its likely an ammo problem.

I dont know what you do for a living, but I bet youre great at it. And if I needed advice about it Id likely take yours. I only say that cause most people dont listen when I tell them stuff about their AR.

[OilyPablo]

How rough are we talking? Are there burrs? (yikes) Is it uneven?

If the chamber has some surface roughness just get some super fine metal polish and a nylon bore/chamber brush. Don't get too aggressive.

[Pumpkinheaver]

Is your chamber/barrel chrome lined? I don't like the sounds of it. Could be some or all of the cause of your issue depending upon how rough we are talking.

[6622729]

That is correct since the free floated hand guard does not use the hand guard cap so it is not installed. You have to have the gap to account for the thickness of the missing metal.

Are you sure about this? I haven't measured a low profile gas block hole but it sure doesn't make sense to me that they'd make a low profile gas block designed to be used with a free float handguard with the hole drilled so that the builder would have to shim the gas block out .025" from the barrel shoulder. No Youtube video I have ever watched of AR builds have done this either. I am not saying you are wrong, just asking for a confirmation from someone else.

[Boolit_Head]

The gas blocks are not specific to the type of hand guard hence the need to have the gap when you remove the hand guard cap to install a free float guard.

Do I really have to mention that you tube videos may not be accurate? The instructions I received from Syrac mentioned this, and if you take a set screw type and flip it over you will probably find the rear screw is in line with the gas port. Placing this upside down against the shoulder will show the misalignment.

[6622729]

The gas blocks are not specific to the type of hand guard hence the need to have the gap when you remove the hand guard cap to install a free float guard.

Do I really have to mention that you tube videos may not be accurate? The instructions I received from Syrac mentioned this, and if you take a set screw type and flip it over you will probably find the rear screw is in line with the gas port. Placing this upside down against the shoulder will show the misalignment.

I've built several uppers now (all free flaoting) and don't have any issues but I'm going to take my 300AAC upper apart and see if I'm misaligned a bit. It doesn't always hold the last shot bolt open but I contribute that to a soft load. Now you have me wondering. Lol.

[popper]

Got 3 uppers with Syrac adj. (both clamp & dimple) on them. The blocks I took off had oversized holes to accommodate some misalignment. Gas tube I.D. is only 0.125 so going much larger than 0.093 will run you into the lands, probably. Only one I enlarged was 0.082 which I took out to 093 (slowly!!) with a elec. hand drill & dowel in the barrel. Just use a pencil and calipers to get it aligned right.
See post #34.

[6622729]

The gas blocks are not specific to the type of hand guard hence the need to have the gap when you remove the hand guard cap to install a free float guard.

Do I really have to mention that you tube videos may not be accurate? The instructions I received from Syrac mentioned this, and if you take a set screw type and flip it over you will probably find the rear screw is in line with the gas port. Placing this upside down against the shoulder will show the misalignment.

To report back, I took two uppers apart last night to confirm that .025" gap needed between the end of the gas block and the shoulder of the barrel. I had never heard of this before.

#1 upper is a 16" Voodoo 5.45 barrel with Mas Defense melonited low profile gas block. The holes line up perfectly when the block is slid up against the shoulder of the barrel.

#2 is a Mas Defense 20" .223 Wylde barrel and Mas Defense lightweight, low profile gas block. The holes also align perfectly centered when the gas block is slid up against the shoulder of the barrel.

If I had put the .025 gap in either of these builds, the holes might have caught the edges of one another and worked but clearly this is not what was intended. No gap for my builds.

[rnelson11]

When I first got my 300 blk I loaded 20 bullets, 10 with IMR 4227 and 10 with IMR 4198. The bullets loaded with IMR 4227 would not cycle the rifle but the IMR 4198 worked great. If I were you I'd try some different powders.

[6622729]

When I first got my 300 blk I loaded 20 bullets, 10 with IMR 4227 and 10 with IMR 4198. The bullets loaded with IMR 4227 would not cycle the rifle but the IMR 4198 worked great. If I were you I'd try some different powders.

I agree. Different powders generate different volumes and speeds of gas. I'm using W296 which seems very popular in 300AAC supersonic. I am nowhere near max load so I'm satisfied that as I continue to dial up my load a pinch more, last round bolt hold open will be consistent.

[Boolit_Head]

With mine a minimum load of 296 under a 150 to 160 grain bullet functioned fine and held back with a lighter carbine buffer. But I have a pistol length gas system. Strangely enough both the Syrac and DPMS low profile blocks I used on my two AR's needed the .025 gap to align properly.

[OilyPablo]

No doubt about it, my 10mm AR runs way way better with hot slow powder like Longshot and Accurate #9

[6622729]

With mine a minimum load of 296 under a 150 to 160 grain bullet functioned fine and held back with a lighter carbine buffer. But I have a pistol length gas system. Strangely enough both the Syrac and DPMS low profile blocks I used on my two AR's needed the .025 gap to align properly.

That's also an option, a slightly lighter buffer spring. I don't really want to mess with the gun too much because my 300aac has been great straight from the build and right from the start with the Lee 312-155-2R. I'm only at 15.3 on W296 right now. I'll have to look up Syrac, I have never heard of that brand.

[Boolit_Head]

Syrac makes adjustable gas blocks. I use one on my 223 instead of using a heavier buffer. Heavier buffers and stronger/lighter springs are a fix for a problem, you don't go there first or you cause yourself headaches. Start off with what the gun is designed for such as a standard spring and normal carbine buffer to get the gun functioning. You may not need the rest.

Since my 223 is more of a paper puncher/varmint/gamer gun than something I would use in Iraq I preferred to cut down recoil by limiting the gas rather than adding reciprocal weight. At some point I may go to a lighter carrier to reduce the reciprocating mass further but for now I am happy with it. As it is set up with the m4-72 comp, mid length gas, and the adjustable gas block there is no movement of the barrel upon recoil. Cases eject to about 4 clock which is about perfect and it's 100% reliable.

Now my blackout is a different story it's a work in progress. Since it is soon to be a sbr and is currently a 7.5 inch pistol and will mainly be used for hunting/suppressor host I went with a straight gas block and standard weight spring and buffer. It's wearing a KAK flash can to direct the gas forward away from me. It jumps like a mule for a AR but that is mostly a function of the bullet weight and lack of a stock. As it changes I will probably add a adjustable gas block when the suppressor gets built. It's also been 100% reliable so far.

Both are set up for different purposes and are wearing some big scopes so I can wring them out. The 223 is looking like a 1/2 MOA gun while the blackout is around a 1 1/2 MOA gun so far but there is a vast difference in the barrel manufacturers. Maybe someday the 300 will get a better barrel.

163298

[PULSARNC]

Bubba had his way with the at my son bought. Same prob not cycling. He moved the gas block to make the hand guards not rattle .remounted gas block in correct position and works fine

[Quiettime]

When I first got my 300 blk I loaded 20 bullets, 10 with IMR 4227 and 10 with IMR 4198. The bullets loaded with IMR 4227 would not cycle the rifle but the IMR 4198 worked great. If I were you I'd try some different powders.

THIS. I solved all my problems cycling with A1680 powder.

Try one of these powders:
A1680
H4198
A5744
Reloder7

[Faret]

I drilled out my gas port to .125 as big as you can go. I can now shoot super and subs. Before I was limited to supers only. H110 for the supers and Rel 7 is your best bet for the subs other that 1680 if you can find it. I read somewhere you can not over gas a carbine length .300 but take it with a grain or 2 of salt.

[bigjake]

I drilled the hole out from .093 to .103, polished up the rough chamber, installed a weaker spring (didn't need the weak spring after all) Something that I think did help was, my son and I took apart 3 other ar's and compared bolt carriers, turns out, one of the carriers was made with less steel. I cant describe what I mean but it was lighter. we installed that also. Now that sucker runs with anything I feed her.

Thanks everyone for your help!

[hicard]

I stopped having such problems when I switched to AA1680 powder. Try it, works great with the 300 BO.

[adanymous]

Sorry I was slow to reply, I was sick and then busy trying to catch up after. Most 300 bbls are .096-.098 I would recommend going to .096 off the bat and stepping up a size at a time until it runs right. I am at .1 ish on a mid length system on mine and it runs like a top. I didnt measure mine,that is a finished project from 3 or 4 years ago. But if memory serves Im in that neighborhood. Also I have adjustable blocks on both of my nice ARs, I find they were both a waste of $100. I run em both wide open all the time. Put it in a drill press correctly and drill slowly and youll be fine. Use a new or freshly sharpened bit and you wont have much of a burr. Run a brass brush through your bore a few times and shoot it! You arent talented enough to break it I assure you. I have tons of breaking stuff talent and I havent broken one yet.