I recently picked up one from S&W, for the same reason. Well, hog hunting with a can at night. I'll never shoot a deer with it. I have too many other rifles for that duty.

 

Congrats. I love my 300blk. I can't wait to try it on a hog.

 

from the beginning except the bolt didn't lock back after the last rounds were ejected.

Having simular problem with a stock Ruger AR 556 lower and my upper specked the same as yours.

I suspect because of the pistol length gas system I may go to a adjustable gas block,I'm sure it's over gassed as to failure to lock back on one round in magazine test. It also appears like bolt carrier bounce back. SJ 40

 

I bought a Spike's T2 heavy buffer for the rifle. I think the new rifle is overgassed shooting only supersonic ammunition. I found a brass smear in the chamber and the bolt doesn't lock back after firing the last round.

 

Try a standard carbine weight buffer..not a H2 or H.

 

I started with a standard carbine buffer. I haven't tried anything else yet. The brass smear ring in the chamber is leading me to think it is unlocking too early but I'm not sure. I'm going to check some other factors tonight. Any insight on my problem is appreciated.

 

Try an H2 buffer.
My first 300blk was a 10.5" PSA upper and it ran fine with supersonic and subsonic. Bolt locked back.

My AAC PDW (9" 300blk) pistol came from the factory with an H2 buffer. I SBR'd that sucker real quick. It's awesome.

 

I received the Spikes T2 buffer I ordered and installed it tonight. It is a nice looking and quiet buffer! I also cleaned, inspected and thoroughly lubed the bolt carrier group. I looked for other potential problems (found none) and cycled the bolt many times. I'm looking forward to shooting it tomorrow to see if it is overgassed or undergassed or was just not broken in and adequately lubed.

The rifle looks great. I hope it will lock the bolt back after the last round this time.

 

Well phooey. The Spike's ST2 buffer didn't help and made the rifle even less reliable at locking back the bolt after firing ejecting the last round. I put in the original buffer and the bolt locked back about 1/3 of the time. It will feed reliably but not lock back the bolt. I can't find anything wrong with the bolt or bolt catch assembly. Trying different magazines didn't make a difference. The only thing I can guess at this point is the gas block isn't lined up with the hole in the barrel quite right. I'm going to try a different lower that has proven reliable tomorrow to eliminate the bolt catch assembly being the problem.

On a positive note, the accuracy of the PSA 300 BLK upper is excellent!

 

I was able to take the PSA 300 BlK upper to the range this afternoon for more troubleshooting and testing.

I used a different proven lower, 3 different popular quality magazines and switched out buffers. The bolt still wouldn't lock back reliably after firing the last round 80% of the time. The heavier Spike's ST2 buffer made it worse. So, my conclusion after shooting 56 rounds is the upper is definitely undergassed. The only other possibility is the Rem/UMC 120 gr supersonic ammo is underpowered. I don't have any other inexpensive range ammo to use. The Remington ammo seems plenty potent.

I also used a proven 5.56 upper on the lower I bought for the 300 BLK upper and the lower and magazines worked 100% reliably. It's definitely not the lower/bolt catch.

I'll call PSA soon to find out my options. It is a very nice upper and very accurate. I'm very pleased with it other than the undergassed issue. I suspect it is a misaligned gas block and will be easy to correct. I am recording my experience to hopefully help others who may have a similar problem in the future. I tried different searches but couldn't find much information about this problem.

 

So I've since read and learned that being under gassed is a problem with 300 BLK rifles and Remington/UMC 300 BLK ammo is thought to be a little weak. So, I am going to look into lightening the recoil system.

 

So I've since read and learned that being under gassed is a problem with 300 BLK rifles and Remington/UMC 300 BLK ammo is thought to be a little weak. So, I am going to look into lightening the recoil system.

That is the same brand,weight ammunition in my 300 I was having a similar problem you are experiencing .
Would you mind linking what you have read on said problem,as with the pistol length gas system I was thinking over gassed rather than under now I don't know what to think. SJ 40

 

:needspics:

 

SJ 40:

I just did a search on Duck Duck Go using the terms...
overgassed 300 blk
over gassed 300 blackout

There were several helpful links that came up. It seems to be a common problem with manufacturers' drilling small gas holes in barrels. The 300 BLK might be used in 4 different configurations each providing a different level of gas. An owner of a 300 BLK will probably have to do some tinkering to get the gas system working right for his or her intended use.

The least expensive step to try would be a reduced power Wolff recoil buffer spring. The next step might be a lighter semi auto bolt carrier rather than the heavier full auto carrier.

I'm no AR or 300 BLK expert. This is just a summary of what I've gleaned on the internet.

 

SJ 40:

I just did a search on Duck Duck Go using the terms...
overgassed 300 blk
over gassed 300 blackout

There were several helpful links that came up. It seems to be a common problem with manufacturers' drilling small gas holes in barrels. The 300 BLK might be used in 4 different configurations each providing a different level of gas. An owner of a 300 BLK will probably have to do some tinkering to get the gas system working right for his or her intended use.

The least expensive step to try would be a reduced power Wolff recoil buffer spring. The next step might be a lighter semi auto bolt carrier rather than the heavier full auto carrier.

I'm no AR or 300 BLK expert. This is just a summary of what I've gleaned on the internet.

Shane

Thanks as I'm experiencing the same as you,I'll give the search tirms a whirl and see what can bee gleamed,Thanks. SJ 40

 

In my search I did come across this, Nemo
.300 Blackout Custom Carbine Buffer Spring

http://store.nemoarms.com/300-blackout-custom-carbine-buffer-spring/

For 15.99 it may be worth a try other than enlarging the gas port. SJ 40

 

Thank you for the video. It was helpful and the steps make sense. I think the lighter Nemo spring is my next step. Mine is close to cycling properly since it locks back on an empty mag 20% of the time. The lighter spring may be all I need.

 

I'm trying the same and it's a lot less work/risk than enlarging the gas port. SJ 40

 

Got nothing to add on the bolt not locking back. I put a PSA lower and upper together in 300blk but in a pistol and it runs like a sewing machine. All the ammo that has gone thru (granted not a lot at 200rds) has come from Ozark Ammo. I liked it so much, I bought some JHP from them as well. It's all supersonic ammo.

 

From what I have read it all depends on what the barrel manufacturer decides to drill the gas port diameter at seems to vary between .87 to 1.25 at pistol length gas system and of course subject to subsonic or supersonic ammunition. SJ 40

 

I called PSA this morning and they want to check it out. They emailed a UPS shipping label to me. I hate to send it back but don't want to spend more money on it. It is a really nice upper. I'm sure it will be great after they repair it and send it back to me.

If it is just undergassed, I will try the reduced buffer spring and maybe a semi auto bolt carrier to lighten the resistance.

 

In the case of my Ruger lower It does use the semi auto carrier in the upper.
Took out the buffer and spring yesterday and the spring is hell for stout,ordered the Nemo Blk Out buffer spring this morning from Brownells going to get to the bottom of this. SJ 40

 

Please let me know what you learn. I may need it later.

Shane

Installed the Nemo 300 Blk. buffer spring and took 6 different manufactures magazines and 3 different factory loads and 3 different handloads to the range yesterday.

Barrel is 16" with pistol gas length with .110 gas port on a Ruger AR556 lower.

The rifle with the Nemo spring installed would lock back on 1 round loaded and fired from all 6 manufactures magazines.
Next step load 3 rounds in all 6 magazines and repeat,all locked back on last round save for a Brownells 5 round hunting magazine.

Loaded of 20 rounds in all magazines,all 20 rounds fired from 5 magazines save the Brownells 5 round hunting magazine without a stutter

That Brownells magazine has a very stout spring in it and is going to require trouble shooting or will be returned.

My overall take away in the case of my 300Blk. was the Nemo buffer spring so far looks to solve the short stroking problem I was suffering. SJ 40

 

SJ 40:

Thank you for the very helpful report. Very good to know! I can't wait to get mine back from PSA and see what they did and say. I will get the Nemo spring if I continue to have issues. Glad your situation is pretty well worked out. I think the 300 BLK is such a cool cartridge.

Shane




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SJ 40:

Thank you for the very helpful report. Very good to know! I can't wait to get mine back from PSA and see what they did and say. I will get the Nemo spring if I continue to have issues. Glad your situation is pretty well worked out. I think the 300 BLK is such a cool cartridge.

Shane

"I think the 300 BLK is such a cool cartridge."

Shane so does a friend of mine who went along to the range with me yesterday,he said that's the ticket in the Vermont deer woods. SJ 40




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Just got my 300 BLK upper back from PSA! A nice letter said it was my PSA bolt carrier group that was causing the problem and they replaced it. I didn't see any problem with the BCG. They stated that it was shot 10 times without a problem. I can't wait to see how it runs runs now. I guess I'll head to the range and sight it back in.

I am very pleased in the 10 day turnaround and with the very professional letter with an explanation. I only wish they had sent me a shipping notice. I was lucky I was home to receive it.

I bet the 300 would be perfect for the dense Vermont deer woods.

I'll post a range report. Now I am wondering what kind of buffer it needs?

 

I tested the 300 BLK upper briefly and checked the zero this afternoon. Worked flawlessly. Definitely had more gas and the BCG locked back on the empty mag every time.

The Aimpoint PRO and mount kept its zero when I remounted it. The group was just a ragged hole from the beginning.

I will test the upper more and experiment with different weight buffers to fine tune it. I bet the Spikes ST-T2 buffer will be perfect. I used a carbine buffer to test it earlier.

I'm sitting in my blind hunting hogs with it this evening even as I post.

 

Good to hear that PSA took care of it for you,keep us updated on your testing and results. SJ 40

 

I shot the 300 BLK PSA rifle again this evening. I had installed the Spike's Tactical ST-2 buffer to try. The newly replaced BCG was well lubed.

I shot 20 rounds of Remington 120 gr OT and 19 rounds of Federal AE 150 FMJ using a 20rd PMAG. The 300 BLK upper started out great with the Remington ammo but began to not lock the bolt back after the last round. I switched to the Federal ammo and it locked back every time. The pistol length gas system and recoil seemed to be plenty strong.

The common denominator with the failure to lock the bolt back malfunctions is the Remington/UMC ammo. The Federal ammo ran flawlessly. I think the Remington ammo is underpowered or inconsistently charged and runs down the ragged edge of reliable function. I've read where others report Remington 300 BLK ammunition to be weak. It is surprising since the brass is marked Berger and the ammo may be made by them. Perhaps if I went to a plain H (heavy) or carbine buffer the Remington ammo would cycle more reliably.

I really like the 300 BLK concept and can't wait to do more shooting with and reloading for it. It will become my deer and hog hunting rifle.


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I came across some interesting information of a AR barrel manufacturer regarding their 300 Blk. barrels with what they think works best.

>Do I need an adjustable gas tube with your 300 whisper barrel?

Yes, If you want to use both ends of the performance range the whisper offers.
No, if you want to stick with one or two specific loads, we can taylor your gas port to match them.
The adjustable gas tube is a nice accessory because you can then run a larger gas port in the barrel and adjust the gas flow to your specific loads. Normal AR barrels are drilled 0.089" and most 223 loads with the proper powders will work the action just fine. In the whisper, I have found the same size works fine with near max loads using light to medium weight bullets. I recommend that we drill the gas port 0.120" and use an adjustable gas block or tube to fine tune functioning. The standard gas tube measures 0.120" on the inside, so a gas port in the barrel any larger than that is a waste. Ideally, you want just enough gas to function the gun, but not so much that you beat up the brass and buffer. If you want the front sight on the barrel, you have to go to an adjustable gas tube. If you do not need a front sight, there are adjustable gas blocks that use a standard gas tube.

>Do your 300 whisper barrels require special length gas tubes?

Yes and No...
It really depends on what you want to do with your barrel.
If you are ordering a 1:8" twist barrel, I usually use a pistol length gas tube for shooting subsonic heavy bullets.
If you are ordering a 1:10" twist barrel, I use a carbine length tube as the 10" twist will not stabilize the really heavy bullets used in subsonic loads.

SJ 40

 

Can somebody explain why failing to lock back would be a symptom of over-gassing? Everything listed sounds exactly like undergassing, to include the solutions (lighter buffer, lighter buffer spring, larger gas port). Are some folks just using the wrong terminology?

My .308 is overgassed with the block adjusted wide open, and with full-power loads it will toss brass 15-20 feet from a standing position and ding them up pretty good against the brass deflector. On the other hand, when doing "work-downs," failing to luck back is always the first indicator of reliability issues as I get down to, for example, a 110gr bullet below 1900fps or so.

 

Are some golks just using the wrong terminology?

I think that may be the case. SJ 40