Another Cycling saga…

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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Ptrk99
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Another Cycling saga…

Post by Ptrk99 »

Hi group,
First post for me after spending a lot of time reading and diagnosing. I am new to the 300Blk round and this is my third AR platform.

The goal: a 300Blk bag gun that I keep suppressed most of the time (still in the waiting period for the Banish 30 suppressor).

The equipment: https://shieldarms.com/sa-15-stripped-lower
and
https://palmettostatearmory.com/psa-7-3 ... l-kit.html

The problem: weapon will not lock back the BCG or strip next round while shooting subsonic ammo (I’ve only tried 3 types; Fiocchi Range Dynamics 220gn 1020fps, Fort Scott 190gr 960fps, and Hornady Sub-X 190gn 1050fps). In a recent range test it did cycle and lock back using Wolf 145gn 1985fps ammo.

Background: Bought this build recently and put it all together with no known issues. Took it to a local outdoor range on a butt-ass cold day to test her out and it was a complete fail. First round would not even fire. Jammed in the chamber and took a little fiddling to get it out. Tried a second round and it fired but stovepiped. Third round jammed in the chamber again. Called it a day and went home.

When I got back to the house I broke it all down and thoroughly cleaned and lubed everything and was able to get a round to fall into the chamber as one might expect. It was still tight but considering that it is new I guess that is to be expected. I then went over to a buddy’s house just to shoot a couple of rounds to figure out where I was and shooting the Fiocchi it fired nicely, ejected the round (I don’t know clock code) but would not lock back or strip next round. So, it was boom, click, cycle charging handle, boom, click, etc….

That’s when I started reading various sources to diagnose the problem. Eventually I landed here and have learned boat loads of info so far but no Ah-Ha!! moment that solved my issue. I could write a whole post about all the things I didn’t know when I started but I’ll spare you all that. In an effort to test the upper setup I did switch it to the lower on one of my 6.8SPC builds and the results were didn’t lock back a single shot and stovepiped the brass.

At this point I started investigating buffer weight. The buffer in the SA-15 is specific to that lower since it is a folding lower and needs an extension on the end to bridge the gap between a typical upper BCG and a typical buffer. The PSA kit included a spring and buffer with the brace. The buffer that came with the brace weighed 2.98 oz and the buffer included with the SA-15 is longer and weighed 4.45 oz. “Ah-ha, that’s got to be it” I thought. I disassembled the buffer and removed the included single weight which brought it down to 3.21 oz. Put it all back together and same result. No lock back/no stripped round.

More reading, more cleaning more inspecting now thinking maybe a misalignment of the gas block or a blockage in the gas system somewhere? Back to the range for a quick session where I ran half a box of the Wolf 145gn supersonic through it and it cycled fine. Brass was heading mostly south out of the gun at about 5:00. Now I’m thinking it’s got to be a gas system problem. Went back home and back to the bench and tore the upper down more and discovered…..nothing telling. No blockage that I could find. Barrel is dimpled (one dimple) in the right spot and all lines up. The gas port is .094”, using the drill bit test I read on here, and the port in the gas block and in the tube of the gas system are both .124”. I cannot lighten the buffer any more unless I modify it, which is probably possible but I’d think I could fix this without going that route. I’d like to resort to opening the gas port in the barrel last since, as someone on here said “you can’t put the metal back”. I did check spring compression lengths and distance between the BCG and the hold back when I pull the charging handle fully back and it’s about 3/8” which I think I read on here is enough room for both lock back and stripping the next round. I’m thinking lighter weight spring maybe? I would like the option to shoot supers and subs, at least right now, which might mean adjustable gas block? The odd thing is that reviews of the upper kit have comments about running sub and super just fine so I’m wondering if it has something to do with the SA-15!folding lower? I’ve not found a lot of info about that lower out just yet.

Ok, that’s my saga… I turn it over to the experts in the field and appreciate any and all deductions and suggestions.
BJK
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Re: Another Cycling saga…

Post by BJK »

I'm not the best person to diagnose, but here goes.

Does the BCG lock back where it should manually? Could it be a rifle spring rather than a carbine spring? I was going to ask if it cycles supersonic but I reread and got my answer. So it's probably not a spring issue. Moving on...

Pistol length gas, that's good. 6" barrel might be part of the issue.

OK, assuming the right spring, I HATE factory subsonic ammo. I only tried one brand, Fiocchi (sp?) and decided that was the one and only factory subsonic I was going to try. I had similar issues that you describe. I was going to reload anyway and I tailor my loads to my gun which is set up as generically as possible to allow it to cycle the generic subsonic load. Yeah, right! Generic subsonic load, HAH!

OK, factory subsonics... What barrel length are they designed for? If pistol length gas and a 16" barrel I suspect that would be easy to load for. But a 6" barrel requires really fast powder I would think to get the port pressure and enough gas to make it work. Before buying more ammo I would discuss your build with the ammo manufacturers to see if they think theirs will cycle the gun. That's exactly why I went with a 10" barrel to reduce my problems and I still had factory ammo issues as I already explained.

Do you reload? If you don't reload maybe start? Or keep trying factory ammo and maybe you'll find one that has the right port pressure to make it work. But with reloads and the right powder it's easy.

No doubt someone here has better news for you.
Ptrk99
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Re: Another Cycling saga…

Post by Ptrk99 »

Thanks for weighing in. Yes, it does lock back manually when the magazine is in place. According to the build sheet it came with “SBA3 Adjustable Pistol Brace, castle nut, latch plate, carbine buffer spring, 5 positioning mil-spec buffer tube, and standard carbine buffer.”

Yes, pistol length and it’s a 7” barrel with a 6” M-Lok hand guard. Good idea talking with the ammo guys to see what their thoughts are. I will reload at some point but don’t currently have the capability. One day though…

Thanks again for your thoughts.
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dellet
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Re: Another Cycling saga…

Post by dellet »

I’m assuming you were shooting without the suppressor, it will make a difference.

First in theory, it should work fine with the info you provided. Pistol gas, H2 buffer weight, FA carrier. Port is on the small side, but should work with factory ammo.

First thing I would question is the lube. Is it rated to at least 30* less than the temp you were shooting?
Lubes like Frog lube will stop an AR in its tracks in cold weather.

Next is how many rounds through the rifle, if it’s less than 2-300, either go shoot that many supers, or hand cycle it. I prefer live fire.

You need to have a rock solid shoulder mount. Like limp writing a pistol, allowing the rifle to move instead of the buffer will cause light loads to not cycle.

Leave drilling the port as a last resort. When you pulled it apart to check, there should have been a perfect carbon circle centered around the port. If there was not a circle, there is a leak. Also a good way to check if the block is aligned properly.

You might try some Remington UMC subs. If they won’t cycle those, it’s not an ammo issue.

I wouldn’t change anything drastic until you have the suppressor in hand.
300 Blackout, not just for sub-sonics.
Ptrk99
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Posts: 10
Joined: Thu Dec 29, 2022 11:57 am

Re: Another Cycling saga…

Post by Ptrk99 »

Hey dellet, thanks for weighing in. Yes, no suppressor yet so all info is sans suppressor at this point.

Yeah, from what I had read I thought the same about the setup running fine with the buffer weights I have. As for lube, I’m running Beretta gun oil that came with a gun I bought. I have a few options but would expect this would be good enough to let it cycle as it should.

Way less than 2-300 rounds at this point. More like 20-30, maybe. I wondered if break-in could be the issue or a combo of break-in and crappy ammo. But, I’d think the Hornady would cycle but that is just because I’ve always had good luck with their ammo.

Shooting shoulder is good but that is something to watch. I checked the gas port and it looks like there is a carbon ring around the gas port. Just a thin faint burned area all the way around. The is a more visible charred circle around the gas port hole in the gas tube but it does not extend to the back side of the tube. No charring or discoloration on the inside of the gas block at all.

I’ll get some of those Remington rounds and report back. In the meantime I’ll put more super rounds through it and see what changes. I’m with you on the not changing too much at this point but would like to get this going with subs without a suppressor first since the suppressor is several months away.

If I want to run subs and supers through it should I be thinking adjustable gas block? If I put a lighter weight spring (wouldn’t know which one at this point) in it to facilitate the subs will the supers beat it to death?

The fun thing about this project is it’s taken me further into this AR than I’ve been before with either of my other two. I love the learning part and I guess I wouldn’t have that if it had worked right out of the box. Thanks again for everyone’s help. This is a great forum!!
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dellet
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Re: Another Cycling saga…

Post by dellet »

Rule of thumb is that if it will cycle subs, it’s will be over gassed for supers. That’s why you want the smallest port possible. It’s a bit tougher with factory ammo, unless you decide on one or two loads that are always available.

Here’s where people get in trouble with the cartridge. Not picking on you, but showing the hill climb you have. This is also why the cartridge has a reputation of being hard to work with.

Your rifle is completely out of the design specs as is half your ammo. Think about that.

The system was designed for barrels no shorter than 9”, bullets over 200 grains, preferably 220 for subs. Supers pretty much anything goes.

That makes you the design engineer. Lots of people have done what you are doing and it’s no big deal, but consider that off the shelf ammo is expected to work for your out of spec build as well as somebody else’s idea of how it should have been built and loaded for.

It’s a wonder some of the configurations people post work at all.

I wouldn’t do a thing until it has at least another 100 rounds through it. One thing I look for is that I can take out the BCG and stand it on the bolt face extended. The carrier should freely collapse.
300 Blackout, not just for sub-sonics.
Ptrk99
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Posts: 10
Joined: Thu Dec 29, 2022 11:57 am

Re: Another Cycling saga…

Post by Ptrk99 »

No worries at all about any info passed. I don’t feel picked on at all, quite the opposite. I’m grateful for the input.

I completely see your point on design vs reality. I’m sure the race for a unique ammo creates some interesting bed fellows, as they say. I gravitated towards the 190gn because I wanted to use the Hornady offering to hunt with if I get the chance. So I thought I’d start there and see how it went. Guess I got my answer…lol.

I will start my break-in process tomorrow. The advice about the collapsing carrier caught me by surprise. I just the other day watched a Brownells tech video discussing gas systems and they said that same scenario meant the seals in the BCG needed to be changed (I hope I am saying that right). I’m probably confusing something.

Ok, step one… shoot lots of ammo!!
BJK
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Re: Another Cycling saga…

Post by BJK »

It's not absolutely one OR the other. You can both cycle it by hand and then when you get to it shoot lots of ammo. You're not going to hurt it. But when cycling it by hand you might want to hold the latch on the charging handle back to prevent premature cosmetic wear on the area of the upper that the latch rubs on as it closes.

Just to check, there are 2 holes in the dished out flat section of the BCG that can be seen with the dust cover open. They lead to places in the BCG that get oiled, each one gets a drop or 2 of oil. I was told that was plenty in those holes, but in the link below he suggests that more can be used.

https://thearmsguide.com/9511/lubricate-ar15/

One thing we definitely were taught was that if we were having malfunctions with our M16A1s was to just pour CLP lube into the action, lotsa lube. The gent in the above link does that first, sorta. I wear eyeglasses and I hate having lube spray onto them so I'm a bit more sparing with the lube than he is, but I still run it wet.

edit: The seals you refer to are 3 rings in a mil spec design, think of them as the rings in the cylinder of your internal combustion engine in your car, just smaller. Some rings are now one continuous ring that take the place of the 3 separate rings. Those rings shouldn't be aligned but I've run across folks who deliberately aligned them as a test and had no problems.
Ptrk99
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Joined: Thu Dec 29, 2022 11:57 am

Re: Another Cycling saga…

Post by Ptrk99 »

Thanks BJK. That is very helpful and an area I had neglected. I will lube that up as well and run it shooting or hand cycling. I do need to buy more super ammo. I have the Remington UMC on the way for a baseline test to see where we are once I address some of these other issues. Thanks again for all the help and info.
Ptrk99
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Posts: 10
Joined: Thu Dec 29, 2022 11:57 am

Re: Another Cycling saga…

Post by Ptrk99 »

The latest update to the cycling saga follows: I ordered the Remington UMC 220gn subs that were recommended and they arrived from an outfit in TX pretty quickly. I saved a few bucks going with them which was nice considering this experiment is costing me about $1/boom right now 😂. I also bought some boxes of Winchester 125gn supers running at 2185 fps at the muzzle. We had a chilly morning shooting at a buddy’s outdoor range that consisted of lots of steel targets and paper so a plethora of things to aim at. I only wish I had some optics on this weapon at this point because it’s a fun place to shoot. At this point, between subs and supers I have put about 150 rounds through her and still no lock back with subs. The supers cycled like dream and even piled the brass into a small little pile that couldn’t have been more than 10” in diameter. That makes collecting brass awfully nice. After each box of Winchester supers and or the Wolf steel cased ammo I would clean her up and relubricate liberally. I could tell some things in the BCG were moving a little more smoothly which made me realize I need to give some love to my 6.8SPC ARs as well. Then, I’d take one round of the Remington UMC and fire it to test for lock-back and nothing ☹️.

My buddy has quite a few AR platforms in various varieties and so we decided to play Franken-gun smith and put my upper on one of his lowers to see if that produced a different outcome. The thinking was that if this Shield Arms folding lower with its proprietary buffer is the problem then that might be an ah-ha moment. He runs .556 through his weapon normally so does not have any subsonic experience with that lower. But, no change in outcome. Same Remington UMC ammo and no lock-back. He also had a folding kit on one of his weapons (Sylvan Arms) and it came with a “heavier” and “lighter” spring option that he ended up not using. We put the lighter option in the tube of my brace (I have no way to quantify lightness here especially in relationship to the spring that came with my brace) to see if it made a difference and no change. Shots the subs fine, plops the brass close to the same area as the super brass but still no lock-back.

So, now I’m really scratching my head about the folks on PSA that reviews this upper saying it cycled subs and supers just fine. The only difference between my setup and theirs’ is the lower and buffer which is only 0.3oz difference in weight so I can’t imagine that is the lim-fac for success.

Ok, I open it up to you guys once again. At least now I’m starting my brass collection so I can load my own. Guess I’ll be asking for primer/powder/load data recommendations next…😂

As usual, thanks for all your help with my project.
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