Velocity and short stroking

Discussion in 'Small Stuff--22s, 20s, and 17s' started by Chasin Beaver, Mar 18, 2020.

  1. Chasin Beaver

    Chasin Beaver

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    I have dealt with short stroking with my service rifles ARs before, but this is a little different I think. Before it seemed to have more to do with powder selection. My current issue is with a Les Baer match in .223. It seems to short stroke everything I make for it. Manual says factory loads only, and recommends Federal Gold Medal. The Federal GM won’t short stroke, but I ain’t gonna only put factory ammo through it. I put my tried and true service rifle loads through it. All short stroke. Since Les Baer has 24” inch barrel, I reduced charge until chrony said was shooting at same speed as other ARs, still short stroking. The factory federal was shooting around 2600 I think. Most of my other loads were around 2800fps. I dropped a charge of reloder 15 all way down to 23.2 grains (with Sierra 77) and it finally cycled. Would a heavier buffer maybe remedy this? I don’t consider any of the loads hot loads that I been trying. I don’t want to shoot anemic loads though at 300 and 600. I have tried Varget, 8208, Reloder 15, n135, 4895, ar comp, and probably a few others I am forgetting.

    ps. I call short stroking when bolt overrides mag latch and sometimes carrier gets stuck on it, or bolt/carrier don’t stay back at all.
     
  2. GaryL1959

    GaryL1959

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    To me, it almost sounds like ike the bolt is outrunning the magazine, if that makes any sense. Happens when the the bolt returns before the magazine pushes the round up.
    First, try different mags, see if this helps.
    Second, load a function test, start with the book minimum charge for whatever bullet and piwder.
    Only load 1 round in the mag, starting with the lightest charge. See where in the test loads that the bolt locks open, and then try the next higher charge.
    A heavier buffer may help to slow the cycle down, or an adjustable gas block may be in order.
    I have a long barreled 6.5 Grendel that had to have the gas almost completely shut off to stop this from happening for a few hundred rounds until it was broken in and loosened up a bit.
     
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  3. Chasin Beaver

    Chasin Beaver

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    I think that “outrunning” magazine may be a possibility since it seems to work with slower federal loads. I have tried different mags and bobsled. No change. I guess I kinda did backwards as you described. I kept reducing charge until it locked back, but the charge/speed was lower than I would want to use. This is my first match barrel, all my others are service length. Seeing you also had issue with a long barrel, maybe I should look into a adjustable block. New territory for me. Have never used match length barrel or adjustable block before.
     
  4. rsmithsr50

    rsmithsr50

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    I doubt it is the bbl.
    gas port.buffer something
     
  5. Sniper338

    Sniper338

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    Buffer spring
     
  6. searcher

    searcher Gold $$ Contributor

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    Go to Wolff spring company and order an underweight buffer spring. I have had so many short-stroke and bolt hold-back issues shooting light weight varmint loads in all my A/R's - that I install one of these springs when the rifle is built. You can also run into a short stroke when using a lighter load and having just put a new bolt assembly on the rifle with new gas rings which can be extra tight. My bet is the Buffer spring.
     
  7. Rustytigwire

    Rustytigwire

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    Maybe cut some coils? Watch Tubb spring youtube video first.
     
  8. thatguyshm

    thatguyshm

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    Where is it throwing your brass? If your brass is being thrown forward you are over gassed. That would be my guess since most bulk 223/556 is pretty anemic, so company's started opening up the gas port to cycle reliably. Any time I hand load for a service rifle, I always like to have an adjustable gas block on the rifle just for this reason. An H2/3 buffer would slow you down but your cam pin is still going to take a beating. I'd lessen the amount of gas going into your rifle and it will smooth out.

    I don't want to sound like a know it all, but if you are trying to Google this, a short stroke is actually a totally different problem. It's when the bolt doesn't have the power to go all the way back in battery to pick up the next round , sometimes resulting in the spent brass never being thrown clear of the receiver. This would be solved the opposite, by going with a lighter buffer or more powerful ammo.
     
  9. Zero333

    Zero333

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    Did you try different magazines ???
     
  10. dellet

    dellet Gold $$ Contributor

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    Without a real fast video camera, you’re left to trial and error to figure out if the carrier is not going back far enough, or traveling too fast.

    First thing to stop wondering about is velocity. It means nothing in a gas operated system, it’s all about gas pressure, volume and time/distance traveled. It’s entirely possible to have more velocity and less gas to operate the system.

    If this barrel has a longer gas tube, that may be part of the problem with your loads. It sounds like the rifle was tuned to the Federal ammo. Which will have a certain pressure and volume at the port and muzzle. Most likely your loads being hotter, will have less of both, but this will depend on powder choice.

    This is where’s it gets hard to tell and it becomes trial and error.

    A hot load can hyper cycle, too fast for the magazine to feed. It can also burn up all the powder and drop port and muzzle pressure enough where there is not enough gas to cycle the action.

    Dropping your powder charge can cure both problems. When you drop the charge, you effectively change the burn rate of the powder. It slows down. That means less peak pressure, more muzzle pressure. That gives more gas to cycle the action.

    If the gas system is longer, or has a smaller port, this extra pressure can be critical.

    Since you seem to be having problems with multiple powders, I would lean toward the hyper cycling, but be aware of the possible load issues.

    Easiest way to check is to change buffers. If more weight cures it, your over gassed. If it gets worse, your under gassed and try a lighter buffer. Or it could just be really tight bolt and carrier group.
     
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  11. Chasin Beaver

    Chasin Beaver

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    I just noticed the long message I typed the other night never posted? Deleted, bad internet connection at time, I don’t know. Anyway, thanks again for all the info. Have few things I plan on checking once get some motivation. Between virus and sick family member, haven’t been motivated to tear into it.
     
  12. 243winxb

    243winxb

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    High pressure may stick the brass in the 223 chamber. Slow extraction.

    Is there any rim damage to the fired brass, from the extractor? A sign of high pressure.

    I hate to bring this up, but 5.56 Nato should not be shot in a 223 match chamber. Its a pressure issue. (SAAMI)

    Screenshot_20200323-200208.jpg
     
    Last edited: Mar 23, 2020
  13. Rsadams

    Rsadams

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    Instead of cutting springs take a look at sprinco springs... The guy is nice and he will tell you what you need plus he sells buffer kits so you can customize your buffer... A heavier buffer will make short stroking worse... Short stroking meens just that , it is normally found in guns that aren't over gassed and weak ammo.... It's why manufacturers started over gassing guns...
     
  14. Fast14riot

    Fast14riot Silver $$ Contributor

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    Measure your gas port, should be about 0.095" for a 24" rifle gassed barrel. An adjustable gas block may be what you need. Also, check your bolt stop for free and proper functioning. Different mags, too. Another possibility could be magazine catch, I've seen a couple lower/magazine combos that left the magazine too high and caused the carrier to drag.
     
  15. Fast14riot

    Fast14riot Silver $$ Contributor

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    Btw, here is what classic short stroking looks like. This one one of my 24" 6.8spcII upper right after I built it.

     
  16. searcher

    searcher Gold $$ Contributor

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    Those Les Baer varmint A/R's are nice. Two of my buddies have them. Short stroking is brought about by an insufficient amount of gas through the gas tube to push the buffer spring rearward far enough to clear the back of the magazine. Either you have insufficient gas because of a misaligned gas block or insufficient hole size in the barrel under the gas block (unlikely coming from Baer), or using a powder that does not generate the energy needed to provide the gas - usually an underpowered load. The lighter the bullets used - the more prevalent this is due to cycle action inertia. While I earlier said installing a lighter buffer spring will likely fix it (it will), I also think part of your problem is your gas rings are not broken in. They usually take about 500 rounds to do so, though you can do it manually by simply pulling the bolt carrier out of the rifle, pull the firing pin retaining pin and firing pin out, then applying cutting oil to the gas rings and inside the bolt carrier recess where they ride - and pull and push the bolt in and out a few hundred times. I have owned and dialed in countless A/R's over the years and never needed an adjustable gas block. Might have been nice a few times - but springs are cheaper and faster to change out for light/heavy load changes. If all of a sudden, your rifle starts shooting lighter loads and is cycling - it is more likely your rings are breaking in.
     
  17. Oso

    Oso

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    Common causes:
    1. Gas Block misalignment
    2. Gas Port hole to small or partially blocked by bur
    3. Buffer Spring too weak
    4. Buffer weight too light

    Problematic / Unusual Issues
    1. Nonconcentric bore in Upper Receiver causing binding of BCG - usually evidenced by unusual wear/rubbing along the BCG
    2. Misalignment of Upper and Lower receiver - usually evidenced by wear or gouging along buffer tube threads on Lower receiver
    3. Hardware Part issue that is causing upward force on the BCG effectively creating friction that slows down or retards BCG
    - Trigger pins driller too high causing hammer to push upward on bottom of BCG... manufacturing failure
    - Bolt Assist Device that is too heavy causing constant upward pressure on BCG causing it to rub against tip of Upper Receiver... think of it like riding the brakes
     
    Last edited: Mar 28, 2020
  18. TheOtherZilla

    TheOtherZilla Gold $$ Contributor

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    My Bud had failures to cycle.. Turned out his gas block was loose
     
  19. Oso

    Oso

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    The easiest way to eliminate some of the variables is by testing the upper. Simply swap the upper onto another lower receiver and see if it continues to short stroke. If it clears up and runs fine then you know it isn't the gas block / gas hole or issue within upper receiver.

    While you are at it put the good gun's upper receiver on the lower receiver of bad gun and see if it has any issues running.
     

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