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No4MK2 bolt is sometimes hard to open after firing

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Tommyt View Drop Down
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    Posted: October 08 2018 at 2:28pm
he!!o Everyone,
I have a NO4 MK2 that I had not used in a while.  I took it out to use and noticed that sometimes the bolt was a bit difficult to open when the bolt was turned up.  Once the bolt was turned up it was easy to pull the bolt to the rear.

I was using prvi 150 grain ammo at the time.

I took the rifle home and cleaned it out.  I used a copper solvent to remove all the copper fouling (there did seem to be a lot) and I used Kroil and JB paste to follow up.  This seems to have removed a lot of fouling.

I took the rifle out again after cleaning and the first 20 rounds of the same prvi 150 grain fired wihtout issue.

Then I tried some of the surplus MEN 174 grain I recently bought from SG ammo and the hard to open bolt issue came back.  I then switched to ppu 174 grain fmj and had no issues.

I checked the headspace with a coin gauge and the bolt  does not close on  a field gauge.

Does anyone have any idea why sometimes the cases seem to stick?  The chamber is smooth and the bore is also smooth with no pitting I can see.
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Shamu View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 09 2018 at 6:44am
Lifting the bolt causes the cams to rotate & pull back very slightly, breaking any bond with the chamber walls. Its called "Primary extraction".
Its more noticeable on cock on closing actions as there's nothing else going on. Its normal as long as its not excessive in which case start looking at higher pressures in some rounds causing the issue.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 09 2018 at 7:06am
Did the MEN ammo have noticeably more recoil?  I agree with Shamu, some resistance to bolt opening is OK, but it should not be "excessive".  Hard to define what excessive here means, but my reloads which are about equal to service round pressures, show very little resistance to primary extraction, perhaps no more than a few pounds of force to open the bolt.  If you have to pull hard to open the bolt, those cartridges are hot and I don't think I'd use them in the rifle.  How to the spent primers look?  Also, be sure to use a bronze brush on the bore to make sure there is no caked on fouling.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 09 2018 at 9:04am
Ok. This is what happened to my Enfield Mk2, not what the other gentleman's issues that turned out to be the safety. Try removing the magazine and cycling. I found the magazine left front ear was catching the bolt head.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 09 2018 at 10:21am
The OP indicates it is sensitive to the ammo used.  But, I would try as Honkytonk suggested, is there any resistance to opening the bolt on an empty chamber with mag in vs mag out?   
 
Another thing to try, take a fired case from the MEN ammo and see if there is resistance on re-chambering the empty.  If it was a hot load, it may have stretched the case enough to feel resistance to close the bolt fully on the empty (the last bit of rotation). 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tommyt Quote  Post ReplyReply Direct Link To This Post Posted: October 09 2018 at 3:35pm
Thanks everyone.
I wouldn’t say that the bolt lift is excessive but it stops you from cycling the bolt while the rifle is on your shoulder. Some of these rounds show flattened primers. After a cleaning the flattened primers went away.
And yes they stick a bit on extraction if the empties are rechambered.

Here are two videos where the guys have a similar issue during a mad minute. I found others as well so I think this happens....you can see in the videos where the heavier bolt lift slows them down.


https://m.youtube.com/watch?v=hibb5eX58hI

https://m.youtube.com/watch?v=NA6kX8AH1co
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