Strange AR jam

[abunaitoo]

This happened last weekend, but found out what the problem was on Sunday.
Guy was shooting an AR, and it stopped cycling.
Checked everything, and it seemed to be fine.
Just not cycling.
Bolt not even moving.
Swapped the bolt with another, and all was fine.
Guy took it home and found.......................
A primer had blown out of the case, and somehow went into the gas port on the bolt!!!!!!!!!!!
No gas going through to unlock the locking lugs.
It is stuck.
Anyone have this happen to them????
First I've heard of it.

[Moonie]

I have heard of it happening, never seen it myself though.

[3leggedturtle]

Saw that twice last year.. Washer on barrel was in wrong position, reduced head space and was blowing primers til i looked at it and figured it out. Came that way from factory disremember what brand it was. Todd/3leg

[popper]

Had a primer get stuck in the cam hole last week. Lots of fun getting the bolt to move. Check those PP when loading.

[tomme boy]

Saw that twice last year.. Washer on barrel was in wrong position, reduced head space and was blowing primers til i looked at it and figured it out. Came that way from factory disremember what brand it was. Todd/3leg

Care to explain this a little better? There should be NO washer on the barrel extension for head space.

The only washers I have ever seen are used for timing the handguard. They dont effect the head space in any way.

[phonejack]

Many years ago I was advised not to load federal cases with federal match primers. Well, I did and 60+ Rounds into a match the rifle jammed. Hammer was blocked. I found about 7 spent primers in the trigger assembly. 2 had jammed the hammer.

[Lloyd Smale]

ive had hammers blocked by primers a few times. Mostly caused by being to cheap to toss brass when the primer pockets were getting loose
Many years ago I was advised not to load federal cases with federal match primers. Well, I did and 60+ Rounds into a match the rifle jammed. Hammer was blocked. I found about 7 spent primers in the trigger assembly. 2 had jammed the hammer.

[Sig556r]

Not even remotely likely but possible, as the bolt retracts there's a minute fraction of a second the bolt gas port separates from the gas tube while the blown primer found its way between them before bolt springs back...

[popper]

There should be NO washer on the barrel extension for head space. Actually yes, shims to increase HS. Decreasing HS is a lot more work.

[country gent]

That doesn't sound right here. The barrel extension and bolt set headspace thru the locking lugs interlock inside the extension. washers or shims on the outside would only move that joint forward more but it would remain the same. washers or shims would need to be between the extension face barrel shoulder to change headspace and this would also change to location of the alignment pin in the extension and the timing of the barrel. Shiming the shoulder on the extension dosnt affect the interlocking surfaces of the bolt barrel extension other than moving the forward. But headspace will remain the same as set with or without the shims only it will be moved forward or back

[M-Tecs]

Shims work to increase headspace on barrels that are not indexed. AR barrels are indexed so shims would change the indexing. Since the pitch is 16 the barrel will move .0625" per complete rotation. In other words a shim .006" will rotate the barrel 36 degrees out of indexed. A shim that is not between the barrel and the extension will not effect headspace.

Federal primers are the most sensitive in rifles like the M1 and M-14 they have the greatest potential for a slam fire. It a lesser problem for AR but Federal does make a AR specific primer. http://bulletin.accurateshooter.com/2011/09/new-federal-gold-medal-match-primers-for-ars/ Either Federal primer will not fall out unless the primer pocket is loose and that is not the fault of the primer.

[country gent]

I have seen the front edge of the barrel extension "rolled" to move it forward and change the lock up point and increase headspace by .003-.006 thousandths, this increases the distance from the locking lugs to the chambers shoulder. It also changes the timing of the alignment pin to its locking socket in the barrel by about 1 hour.
A shim between the shoulder on the outside of the extension and upper receiver moves the barrel and extension forward as one unit not changing the locking lugs interface to shoulder distance.

[M-Tecs]

I have seen the front edge of the barrel extension "rolled" to move it forward and change the lock up point and increase headspace by .003-.006 thousandths, this increases the distance from the locking lugs to the chambers shoulder. It also changes the timing of the alignment pin to its locking socket in the barrel by about 1 hour.
A shim between the shoulder on the outside of the extension and upper receiver moves the barrel and extension forward as one unit not changing the locking lugs interface to shoulder distance.

Rolling a barrel is somewhat common on M1 and M14. This is done to tighten the fit not to change headspace. Once in a while new barrels are loose but it mostly is for swapping used barrels between receivers. M1's and M14 threads are timed so they all start at the same spot within the specified tolerance.

Rolling an extension would be more of a challenge than doing the barrel since extensions mostly are 8620 that is case hardened or 4140 that is heat treated significantly harder than the barrel. Either way one hour rotation is 360 degrees divided by 12 equals 30 degrees. If you use a 24 hour cloak it's still 15 degrees. The gas port would need to be slotted. That should work. I was given a Krieger AR barrel that was chambered way to deep. I had to set it back 3 full rotations so I slotted the barrel gas port 3/16 of an inch for .094" depth and width. It didn't create any function issues.

[Lloyd Smale]

im confused. Maybe its a terminology thing but why and how would you index an ar barrel. they are put on using a barrel nut not by rotating the barrel
Shims work to increase headspace on barrels that are not indexed. AR barrels are indexed so shims would change the indexing. Since the pitch is 16 the barrel will move .0625" per complete rotation. In other words a shim .006" will rotate the barrel 36 degrees out of indexed. A shim that is not between the barrel and the extension will not effect headspace.

Federal primers are the most sensitive in rifles like the M1 and M-14 they have the greatest potential for a slam fire. It a lesser problem for AR but Federal does make a AR specific primer. http://bulletin.accurateshooter.com/2011/09/new-federal-gold-medal-match-primers-for-ars/ Either Federal primer will not fall out unless the primer pocket is loose and that is not the fault of the primer.

[popper]

I was responding to 3leggedturtle comment, causing some confusion, sorry. M-Tek is correct but I have seen washers put on the extension as the upper was not deep enough for the extension - an assembly fix. On an AR, shims go between extension and barrel and should be done before pining and porting.

[M-Tecs]

im confused. Maybe its a terminology thing but why and how would you index an ar barrel. they are put on using a barrel nut not by rotating the barrel

Lloyd when you chamber the barrel you install the extension. This is when and how the headspace is established. Unless you are drilling the gas port after chambering the barrel extension must be indexed so the alignment pin and the gas port are both at top dead center. Note on Krieger fully contoured unchambered barrels the barrel will have a witness mark that matches a witness mark on the extension so indexing is easy.

Shims if used are between the barrel extension and the upper receiver. This is done to maintain torques specs verse alignment of the barrel nut/gas tube.


https://www.youtube.com/watch?v=QZe5cQ5Ir5E

[M-Tecs]

This shows chambering a Remington 700 barrel for an AR. They will drill the gas port after chambering. When most people order a AR barrel they order it fully chambered so the extension/gas port and headspace it not an issue. On the other hand a lot of builders/owner want more control of specific dimensions so they start with an uncontoured barrel blank or fully contoured unchambered barrel. On the fully contoured unchambered barrels most come with the gas port drilled and the extension fitted so the only thing required is the actual chambering. Krieger barrels have the gas port entirely in a groove as do some other barrel makers. When chambering a barrel that already has the gas port drilled but not threaded for the barrel extension indexing is an issue.


https://www.youtube.com/watch?v=Ru-ZiaEQNMs

[Lloyd Smale]

I guess that's where my confusion came from. Ive always bought barrels already chambered that could only be put on aligned.
This shows chambering a Remington 700 barrel for an AR. They will drill the gas port after chambering. When most people order a AR barrel they order it fully chambered so the extension/gas port and headspace it not an issue. On the other hand a lot of builders/owner want more control of specific dimensions so they start with an uncontoured barrel blank or fully contoured unchambered barrel. On the fully contoured unchambered barrels most come with the gas port drilled and the extension fitted so the only thing required is the actual chambering. Krieger barrels have the gas port entirely in a groove as do some other barrel makers. When chambering a barrel that already has the gas port drilled but not threaded for the barrel extension indexing is an issue.


https://www.youtube.com/watch?v=Ru-ZiaEQNMs