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  #1  
Old 02-05-2022, 03:15 PM
littlefield littlefield is offline
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Default Bolt assembly/receiver fit

New MP15 5.56. The bolt assembly is a snug fit in the last ~1/2 of travel. If I slowly release the bolt it will stop short of its full travel. If I release it quickly it closes all the way. Is this normal?
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  #2  
Old 02-05-2022, 03:30 PM
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mckenney99 mckenney99 is offline
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Yes, let the bolt go forward under the full power of the spring, don't baby it.
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Old 02-05-2022, 03:34 PM
jbtrucker jbtrucker is offline
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Yes normal , like a pistol slide the bolt needs to be quickly released to go into battery
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Old 02-05-2022, 04:14 PM
mscampbell2734 mscampbell2734 is offline
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Instead of telling you what to do I'll try to explain why.

During the last half inch of BOLT CARRIER GROUP travel the bolt comes into contact with the inner rear face of the barrel extension. The inertia of the BOLT CARRIER causes it to continue forward, which in turn because of the cam pin and cam pin cut causes the BOLT to rotate and lock into the barrel extension.

What your doing is removing the inertia of the BOLT CARRIER
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Old 02-06-2022, 04:34 AM
Oldsalt66 Oldsalt66 is offline
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Don't ride the charging handle.
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Old 02-06-2022, 09:23 AM
bamashooter bamashooter is offline
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However, if the parts were near-perfectly spec'd and lightly lubed, you could walk the bcg forward. But most guns are as you describe thus the recommendation to let it fly. Just another reason for a side-charger model.
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Old 02-07-2022, 07:52 PM
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Tiribulus Tiribulus is offline
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Flip open your rifle and put the muzzle on the floor holding it upright in your hand.


Pull the charging handle up with the other hand and you'll get some resistance until the bolt lugs come out of the barrel extension. Then it will come up easily.


Let it back down slow until it stops. Shine a flashlight down where the bolt goes into the extension and push slowly on the carrier. You'll see the lugs rotate as they go back into battery.



That's what's responsible for that resistance you're talking about.

Last edited by Tiribulus; 02-07-2022 at 07:53 PM.
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Old 02-08-2022, 01:55 AM
Racer X Racer X is online now
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Quote:
Originally Posted by bamashooter View Post
However, if the parts were near-perfectly spec'd and lightly lubed, you could walk the bcg forward. But most guns are as you describe thus the recommendation to let it fly. Just another reason for a side-charger model.
2 of my 3 uppers are side chargers (not S&W obviously)

But a brass catcher and a side charger have their own issues.
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Old 02-08-2022, 09:39 AM
bamashooter bamashooter is offline
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Quote:
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2 of my 3 uppers are side chargers (not S&W obviously)

But a brass catcher and a side charger have their own issues.
I have no brass catchers and no issues, whatsoever, with my one Gibbz side charger.
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Old 02-08-2022, 12:22 PM
ggibson511960 ggibson511960 is offline
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Default Completely Normal

Quote:
Originally Posted by littlefield View Post
New MP15 5.56. The bolt assembly is a snug fit in the last ~1/2 of travel. If I slowly release the bolt it will stop short of its full travel. If I release it quickly it closes all the way. Is this normal?
Every semi-automatic, locked breach firearm I own, and there are many, encounters resistance as bolt lugs are cammed into place. Many can be "hung up" short of battery by carefully lowering the bolt carrier group. It has nothing to do with bolt carrier-receiver fit or the charging handle and everything to do with the sudden encounter with camming surfaces or locking recesses. That's why continued use will "slick up" a gun by self-polishing the surfaces. You won't fix it by changing to a side charger, but lubrication and shooting will.
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