Author Topic: Bad Bolt Carrier  (Read 7531 times)

alfsauve

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Bad Bolt Carrier
« on: June 12, 2015, 10:46:08 AM »
I had this one BCG that keep bending the gas rings.  It would work for a while and then all of a sudden a ring would jump out of the groove and jam the bolt.

I have been pouring over on-line drawings trying to figure out which dimension was off and how to measure it without a depth gauge micrometer.   Finally finally figured out how to prove what was wrong and which dimension it is.

Both bolts are slowly lowered into the carrier until they are held in place by the rings just before the rings are squeeze into their "cylinder".   Uh - oh.  There's a significant difference in how far down the "cylinder" starts.



That difference means that when the bolt is full forward (out of battery) the rings are not fully inside their cylinder.  The one on the left is too far down into the carrier.  And as the bolt is locked, pushed back, the rings must re-engage that space.   You could feel them if you operated the bolt with your fingers.

Here's a crude drawing of what I was trying to measure. (Don't laugh too hard at my drawing.)  It represents the interior of the forward half of the bolt carrier.  The slight, very slight, decrease in diameter  A-B is the area the rings should travel in and never leave.  Mine were coming just out side the bevel area.  The B-C dimension is what's too long and what I was trying to figure out.  But the simple comparison in the picture above shows the problem quite handily even if I don't know the exact dimension.



For those who don't remember here is what a ring looks like if it catches and gets wedge between bolt and bolt carrier.




Ah the joys of DIY, especially when you're buying parts helter-skelter.  I'll test the next BCG I get, because I now know what this feels like.  But then it'll be something else.    The glass is neither half-full nor half-empty in my world.  It's just twice as big as it needs to be.   Unless it's a wine glass, then it can never be too big.

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Big Frank

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Re: Bad Bolt Carrier
« Reply #1 on: June 12, 2015, 12:51:59 PM »
Thanks Alf. If I ever have bent bolt rings I'll know what to check.
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tombogan03884

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Re: Bad Bolt Carrier
« Reply #2 on: June 12, 2015, 12:55:56 PM »
Buy a pair of dial calipers with a tailstock (Bit that sticks out the end when you are measuring) that allows you to take depth measurements.

http://www.harborfreight.com/hand-tools.html?CatPath=All%2BProducts%252F%252F%252F%252FHand%2BTools%2F%2F%2F%2FMeasuring+Tools&RequestData=CA_CategoryExpand

alfsauve

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Re: Bad Bolt Carrier
« Reply #3 on: June 12, 2015, 02:18:14 PM »
Buy a pair of dial calipers with a tailstock.


I knew that.   I knew that.   DUH.  And mine has one.   Double Duh. 

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PegLeg45

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Re: Bad Bolt Carrier
« Reply #4 on: June 12, 2015, 08:21:05 PM »

I knew that.   I knew that.   DUH.  And mine has one.   Double Duh.

Revelation!!   ;)
"I expect perdition, I always have. I keep this building at my back, and several guns handy, in case perdition arrives in a form that's susceptible to bullets. I expect it will come in the disease form, though. I'm susceptible to diseases, and you can't shoot a damned disease." ~ Judge Roy Bean, Streets of Laredo

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Re: Bad Bolt Carrier
« Reply #5 on: Today at 01:11:51 PM »

alfsauve

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Re: Bad Bolt Carrier
« Reply #5 on: June 15, 2015, 07:28:00 AM »
Using my electronic calipers with a tailstock, <cough, cough>, I determined the difference in my bad bolt and my good bolts is 0.05".    Difficult to measure on that very slight shoulder, but taking the measurement by feel and doing it 10 times, averaging the distance gave me that number.  I compared it against two bolts that work.  Also compared the distance difference the bolt was loosely seated in the BC for comparison and found it about the same. 

This is a lesson in buying no-name, inexpensive parts from a no-name one-table dealer at a show. 

Have new BCG on order.  Decided just to get a whole new one and keep the bolt from the old one as spare.
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tombogan03884

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Re: Bad Bolt Carrier
« Reply #6 on: June 15, 2015, 09:43:09 AM »
Standard tolerance for 3 place decimals is seldom more than .01. usually more like .003 -.005 range.

alfsauve

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Re: Bad Bolt Carrier
« Reply #7 on: June 15, 2015, 08:26:32 PM »
Picture of my setup to measure.  This particular try 1.243"   My other bolts are all under 1.200"



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alfsauve

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Re: Bad Bolt Carrier
« Reply #8 on: June 18, 2015, 08:20:16 PM »
The new one's here.  The new one's here.

Feel good.  Measures right.    AND GUESS WHAT?  Sunday is Father's day, so my boys (3) and I will  spend a couple of hours at the range.  This year it's going to be "rifle day"   Let's see, 4 ARs, 2 308s,  a 30/30, a sporterized Mosin and a hyper accurate 10/22.  That should keep us busy you think?

 
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USAF MAC 437th MAW 1968-1972

tombogan03884

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Re: Bad Bolt Carrier
« Reply #9 on: June 19, 2015, 06:17:20 AM »

 

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