Pennsylvania Firearm Owners Association
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  1. #1
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    Default My SBR Build Adventure

    My AR platform SBR build has been dragging out over many years. It all started decades ago when I picked up a Bushmaster 10" 1/9 HBAR barrel on eBay. This was purely an impulse buy, I had no idea what to do with it, and was questioning if I could even legally possess it, but I was young and it was cool! Years went on, and I went back and forth on if I wanted to extend the barrel and make a rifle, or if I wanted to try and build a pistol. One day, after moving to Pennsylvania, I heard about this whole NFA deal, which I am fairly certain would have been prohibited by laws in my home state. I was like, "What? The same jack-booted thug ATF that burnt down the Waco compound was going to let me build and own such a weapon?" It was then I finally figured out what I wanted to do, and how I had to do it. BTW, I discovered along the way that ATF agents are not the jack-booted thugs I once feared, and were actually quite reasonable people doing a difficult job. I was finally on my way! Purchased all my parts and pieces, researched, sought advice on how to navigate the process, and after years of dreaming, I got my Tax Stamp a few years back. Legally, I'm ready. Functionally, well that's a whole other story.

    I'll get into it for a little, throw some things together, hit the range, then I'll put it down for a while. Needless to say, even the most simple of tasks can turn into a year-long endeavor. My issue is in the cycling. Some rounds it will fail to feed, others will fail to extract. Two different issues, handled from opposite ends of the rifle. Barrel is stamped 5.56, and I have a mixture of .223 and 5.56 that I have been firing thinking (incorrectly) they were the same thing. I quickly realized this was my first task, to isolate the ammo and clarify the issue.

    Swung by Walmart on my way to the range and picked up two fresh boxes of economy ammo: Winchester 5.56 and American Eagle .223 (this was before I understood the difference). When firing Winchester 5.56, it fails to extract. When firing the American Eagle .223, it fails to feed. If I am not incorrect, 5.56 should have higher pressures, which I would assume would mean faster cyclic rate, resulting in failure to feed. Also, the failure to extract might result from not enough gas making it back to effectively cycle the bolt and carrier, likely from either low pressure ammo, or an overly restrictive gas port in the barrel.

    Opting to go the most simple route, I was pleasantly surprised to find that French Creek Outfitters carries a stock of common AR parts and pieces, to include an H1 buffer. I know it is not uncommon to find accessories, but I was quite excited to find parts and pieces in a brick and mortar store! This last point was actually the thing I initially intended to post on, but thought perhaps my experience is not new to many enthusiasts on here, and might even be of interest to somebody attempting their first build.

    I will update after I make it back to the range and try out my new buffer.

  2. #2
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    Default Re: My SBR Build Adventure

    You are on the right track with a different buffer. A different bolt may be in order as well. Since we don't live to far apart maybe I could loan you a few different buffers and bolts. Swapping in and out some parts may help you dial in on the problem.
    Aggies Coach Really ??? Take off the tin foil bro.

  3. #3
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    Default Re: My SBR Build Adventure

    Does your extractor have an o-ring? Had similar issues and that $.50 fixed it.

  4. #4
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    Default Re: My SBR Build Adventure

    Daycrawler, I never considered the bolt. Would you be referring to the bolt only, or the carrier as well?

    Esh, not sure about the o-ring, unless you are referring to the small rubber piece under the extractor spring? My extractor does effectively grip the rim, just does not seem to cycle back far enough to eject. It appears I misspoke in my original post above...

  5. #5
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    Default Re: My SBR Build Adventure

    Quote Originally Posted by marstev View Post
    Daycrawler, I never considered the bolt. Would you be referring to the bolt only, or the carrier as well?

    Esh, not sure about the o-ring, unless you are referring to the small rubber piece under the extractor spring? My extractor does effectively grip the rim, just does not seem to cycle back far enough to eject. It appears I misspoke in my original post above...
    The bolt and bolt carrier along with the buffer and spring. I have several that could be tried out. I am in the 19512.
    Aggies Coach Really ??? Take off the tin foil bro.

  6. #6
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    Default Re: My SBR Build Adventure

    A heavier buffer is not going to make the carrier travel back further.

  7. #7
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    Default Re: My SBR Build Adventure

    Quote Originally Posted by marstev View Post
    Daycrawler, I never considered the bolt. Would you be referring to the bolt only, or the carrier as well?

    Esh, not sure about the o-ring, unless you are referring to the small rubber piece under the extractor spring? My extractor does effectively grip the rim, just does not seem to cycle back far enough to eject. It appears I misspoke in my original post above...
    I believe we are on the same page: https://www.bravocompanyusa.com/BCM-...exspring-1.htm

    Though AAC says to not use the heavier spring with the o-ring:

    EXTRACTOR SPRINGS
    We have 5.56mm test data for the Bushmaster ‘4 coil’ extractor spring with a blue insert and an o-ring. Four uppers
    completed a 12,000 round test with no extractor spring related failures. Two uppers completed an 18,000 round test
    with no extractor spring related failures.
    We do not recommend using extra-power extractor springs because they are under higher stress and will likely
    break sooner. The included o-ring adds the desired extra extractor force without requiring a spring which would
    have more force and hence more stress. Also, extra-power springs, when combined with an o-ring, may make the
    extractor harder to snap over the case rim and may lead to function problems. If you do use such a spring, please
    don’t use an o-ring and change the spring every 1500 rounds for mission-critical use.
    Note that, again per our spring discussion, Chrome Silicon springs do not resist taking a set better than ASTM A228
    certified music wire when used at temperatures below 250 degrees F.


    Taken from https://www.advanced-armament.com/Manuals_ep_45-1.html
    300 BO AAC Upper manual.pdf

    It's tough to diagnose. There might be a chance the extractor is just slipping before reaching the point of ejection. I had this issue and most people said gas and buffers. One person mentioned the o-ring. I bought that kit and tried the o-ring and the heavier spring (but not both). Both worked, but the AAC article convinced me to use the o-ring.. May not be your issue, but cheap enough to try.

  8. #8
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    Default Re: My SBR Build Adventure

    Quote Originally Posted by marinville View Post
    A heavier buffer is not going to make the carrier travel back further.
    I even tried a buffer with all the weights removed and most still said it was a gas problem. After the o-ring/peg upgrade I could run with any buffer weight.

  9. #9
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    Default Re: My SBR Build Adventure

    Quote Originally Posted by marinville View Post
    A heavier buffer is not going to make the carrier travel back further.
    The buffer will not affect the distance of travel, but heavier buffers will slow the cyclic rate. I have been told that if it is too fast, then it may not allow the next round to be picked up from the magazine.

    On the flip side, I could also have a gas issue that might require removing the gas block and reaming the hole in the barrel.

    I have both feeding and ejecting failures, depending on the ammo.

    Hope to make it out to the range this weekend so I can at least try out my buffer. If I can at least get one kind of ammo to work, it will be a start, and I can have some fun! I was quite impressed that firing single shot, I was still able to keep it on the paper at 100yds. Not bad for a 10" barrel.

    Daycrawler, I might take you up on that offer one weekend. Thank you!

  10. #10
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    Default Re: My SBR Build Adventure

    Quote Originally Posted by marstev View Post
    The buffer will not affect the distance of travel, but heavier buffers will slow the cyclic rate. I have been told that if it is too fast, then it may not allow the next round to be picked up from the magazine.

    On the flip side, I could also have a gas issue that might require removing the gas block and reaming the hole in the barrel.

    I have both feeding and ejecting failures, depending on the ammo.

    Hope to make it out to the range this weekend so I can at least try out my buffer. If I can at least get one kind of ammo to work, it will be a start, and I can have some fun! I was quite impressed that firing single shot, I was still able to keep it on the paper at 100yds. Not bad for a 10" barrel.

    Daycrawler, I might take you up on that offer one weekend. Thank you!
    Take note of your ejection pattern, when it does eject. That should give you a clue about how much gas you're getting.

    What length gas system does your barrel use?

    ETA: I still don't think you're overgassed. An overgassed rifle should not have ejection problems with any ammo.
    Last edited by marinville; October 12th, 2018 at 09:05 AM.

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