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+--- Thread: Bolt catching on bolt catch . (/showthread.php?tid=21806)
Bolt catching on bolt catch . - bigdaddyjak - 08-09-2020
New build only a few rounds thru it . 20 barrel rifle length gas. Low pro non adjustable gas block ,Mil-spec carbine buffer , spring and adjustable stock . Lubed well, gas block, gas key , everything is lined up . Has been checked , swapped out gas tube and block , swapped lowers . Tried 3 different magazines , still same problem. First shot, then it short cycles . It will eject the spent casing but wont fully engage, causing a misfire . If I just load one round , instead of bolt locking back on extractor face, bolt catch is holding bolt back , therefore extractor is actually hanging over empty magazine . Only think I can come up with is that it is under gassed. Gas port seems to b 3/32 ( thats what size bit fits hole). Thanks for your time !
Bolt catching on bolt catch . - montana - 08-10-2020
The bolt catch should not touch your extractor..The bolt catch will catch the lower two bolt lugs.. Your barrel is .0938 and Lilja 20" barrel specs out at .093, so your gas port seems just right. I would check your gas key, gas block, etc for gas leakage.. What bolt carrier group do you have?? All bolt carriers are not made the same. The bolt tail vs the firing pin chamber dimensions can create gas leakage, if the differences in diameters are great..Did you check your gas tube button with a gauge?? Is the gas tube cracked?? There could be friction "binding" in the lower receiver buffer tube, off center barrel extension, leaking gas block, gas key, under power ammunition,ruff or short chamber or throat, etc..
Bolt catching on bolt catch . - montana - 08-10-2020
You should also check your gas rings..
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
Sorry, let me rephrase that . What I meant by extractor face is lower 2 lugs . And as long as I manually cycle it with an empty mag this is where it stops every time just like its supposed to . During operation, with only 2 rounds in magazine it , the bolt catch is catching the bolt itself , behind the extractor . I swapped out different gas tubes and blocks , and everything else in between , no change . Aero precision bolt . Gas rings look fine to the eye . Have maybe 40 rounds thru this rifle . Everything is new . Thanks for the info !
Bolt catching on bolt catch . - montana - 08-10-2020
bigdaddyjak Wrote:Sorry, let me rephrase that . What I meant by extractor face is lower 2 lugs . And as long as I manually cycle it with an empty mag this is where it stops every time just like its supposed to . During operation, with only 2 rounds in magazine it , the bolt catch is catching the bolt itself , behind the extractor . I swapped out different gas tubes and blocks , and everything else in between , no change . Aero precision bolt . Gas rings look fine to the eye . Have maybe 40 rounds thru this rifle . Everything is new . Thanks for the info !
Did you do the common gas ring test by extending the bolt from the carrier and setting it on a flat surface to make sure the gas rings hold the bolt up?? Drilling out a gas port is the last thing I would do.. There are so many other variables to check, "before I would increase the gas port size" especially when your gas port seems to have specked out perfectly.... Gas keys can leak, "with no outward sign" until they are removed.. The gas tube and gas block fit can leak excessively..Gas tube button and gas key I.D. can be excessive, creating less gas efficiency..Gas block may not be mated to the gas port 100% by being too far forward, too far back or cocked sideways.. The 3 bolt carrier well "chamber" sizes can be extreme, causing gas inefficacy.. The combination of many factors can cause under gassing, that can be fixed relatively easier than drilling out the gas port.. Adjustable gas blocks, "can only lower the gas pressure" of the drilled gas port, not increase them..
Bolt catching on bolt catch . - A5BLASTER - 08-10-2020
bigdaddyjak Wrote:New build only a few rounds thru it . 20 barrel rifle length gas. Low pro non adjustable gas block ,Mil-spec carbine buffer , spring and adjustable stock . Lubed well, gas block, gas key , everything is lined up . Has been checked , swapped out gas tube and block , swapped lowers . Tried 3 different magazines , still same problem. First shot, then it short cycles . It will eject the spent casing but wont fully engage, causing a misfire . If I just load one round , instead of bolt locking back on extractor face, bolt catch is holding bolt back , therefore extractor is actually hanging over empty magazine . Only think I can come up with is that it is under gassed. Gas port seems to b 3/32 ( thats what size bit fits hole). Thanks for your time !
Undergassed and overgassed can have the same effects.
How does the gun react during recoil? Is it harse feeling and does it sling the case out hard? Where does the case land? And how far away?
At first blush it sounds undergassed but it could be overgassed as well.
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
Recoil seems typical . I have been so focused on the issue that I havnt look rad at the ejection path . Im not an expert or anything even close . But I have built about 30 Ar15 and 10s and this is the first problem I havnt been able to figure out . Im confident that the bcg is not cycling back completely, that Im %100 sure of . I have 4 other AR15s here to compare and work from . I personally would have no use for an adjustable gas block , only reason I would consider one is if I need to adjust gas down , if for some reason its to high (perhaps gas port to big) after much collaboration Ive come to the not so obvious conclusion . Manufacturer has sent rifle buffer spring with carbine buffer kit . I actually have 2 that I just got ( stock and complete buffer kit) and I tried both springs in this rifle and just could not fathom that both springs would b wrong , hence the only logical thing is a gas issue (lack of) . But after taking another rifle apart it hit my like a ton of bricks as soon as I seen the buffer spring !! Thanks for your help gentleman , issue defeated !! Lesson learned !
Bolt catching on bolt catch . - Klem - 08-10-2020
big,
Are you saying you had a rifle length spring in a carbine length buffer tube?
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
Thats the only thing I can conclude . As the spring is longer than another AR I took apart to check . The strange thing is , I have never purchased, ordered or ever thought of using a rifle length buffer setup of any kind . I order only carabine buffer parts . And I buy them in a set with buffer tube and adjustable stock , how could I have to long of buffer spring ??? Unless it was sent with the carbine setup . Thats the only way it could have happened !!
Bolt catching on bolt catch . - VASCAR2 - 08-10-2020
Id measure the length and number coils on the spring. You can only use carbine buffer spring in carbine buffer tube and only rifle length spring in rifle length buffer tube. If you have the correct length spring and buffer the next thing to check is the size of the gas port hole. You didnt mention the manufacturer of the barrel but undersized gas ports have slipped out with several manufacturers. The size have seen reported for 6.5 Grendel 20 barrel is .0935 (same size as 5.56/223). If the port is smaller than this youll probably need to drill out the port.
If the port is much larger than .0935 you are probably over gassed and getting bolt bounce. I bet the gas port is undersized if the gas block is centered over the port. Ballistic Advantage has a habit of shipping 6.5 Grendel barrels with small gas ports.
I copied this but this should match up to your spring.
While most rifle and carbine springs have exactly the same diameter, they come in different lengths. ... A standard carbine spring will measure about 10.5 and have 37 to 39 coils, but a standard rifle spring has a typical length of 12.75 and boasts 41 to 42 coils.
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
Yes, I know that carbine springs go in carbine buffer tides and vise versa ! What Im saying is I ordered carbine buffer tube and springs , and didnt think much of it . Installed and having issues !!! Well when compared to another AR spring it is longer . So evidently, they sent the wrong springs with the buffer tube . Gu. Runs fine when I switched it out . I have NEVER, purchased a rifle length extension or spring , so I dont know how it could have happened ! Hence, why I assumed it was a gas issue ??
Bolt catching on bolt catch . - VASCAR2 - 08-10-2020
Your probably right and someone sent the wrong spring. Sorry I didnt see where the upper functioned once you switched the spring. Glad you got it sorted out.
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
Its crazy, like I said Ive built a lot of them !! Im not saying I know it all, but typically I can figure it out !! This really stumped me . I had 2 bran new buffer kits(carbine) from the same co !!! Thats why I was sure it had to b a gas issue . I had swapped both of those springs in and got the same results !!! But as soon as I pulled the buffer spring out of another AR, it was very obvious!!! Lesson learned !! I order a few new springs. For the time being snip s few could off of this one ! Thanks for helping out guys !
Bolt catching on bolt catch . - montana - 08-10-2020
Take the upper off the lower and put the BCG in the buffer tube. Push the BCG all the way back into the buffer tube until it stops. There should be a minimum space between the gas key and the lower receiver two American quarters thickness.. I have never seen a spec for the space between the mag catch and bolt face when the BCG is in full cycle all the way back, but there should be at least .120-.125 minimum space or better in my experience.. Out of spec buffer tubes, poor installation, weak or using the wrong recoil spring will show after doing this test common test..
Bolt catching on bolt catch . - bigdaddyjak - 08-10-2020
I know the problem is the buffer spring, in fact 2 brand new buffer springs ! That were shipped inside a carbine buffer tube and stock kit ! I just dont understand how it happened . As I stated previously, when compared to one out of another one of my rifles, its easy to c that both of the new ones are longer , hence the short cycle problem ! Not enough room for the bolt to retract as much as its required to !
Bolt catching on bolt catch . - Klem - 08-10-2020
big,
Someone made a mistake at the warehouse - wrong spring, wrong package.
Bolt catching on bolt catch . - Lastrites - 08-11-2020
montana Wrote: I have never seen a spec for the space between the mag catch and bolt face when the BCG is in full cycle all the way back, but there should be at least .120-.125 minimum space or better in my experience.. Out of spec buffer tubes, poor installation, weak or using the wrong recoil spring will show after doing this test common test..
Bolt face on most ar's are supposed to 1/8" to 1/4" in front of the back edge of the ejection port, if it disappears beyond the back of the port all sorts of wonky malfunctions may occur. On 9mm uppers the bolt face is supposed to stop a 1/4" past the bolt catch.
Bolt catching on bolt catch . - montana - 08-11-2020
Lastrites Wrote:Bolt face on most ar's are supposed to 1/8" to 1/4" in front of the back edge of the ejection port, if it disappears beyond the back of the port all sorts of wonky malfunctions may occur. On 9mm uppers the bolt face is supposed to stop a 1/4" past the bolt catch.
Thanks for the info, I have never seen an official spec for this measurement. If there is one out there, I would love to see it. SureFire,"designed by Jim Sullivan himself" Optimized Bolt Carrier Group, cut the gas key on their BCG, shortened the buffer and elongated the cam groove.. This allows more recoil travel and dwell time, creating more energy to strip the round from the magazine.. https://www.youtube.com/watch?v=BBVtx8zUcF8
Bolt catching on bolt catch . - bigdaddyjak - 08-11-2020
Thanks for the info !!