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Headspace and bolt heads

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mausernut View Drop Down
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    Posted: July 21 2018 at 7:11pm
Recently came across No. 4 Mk 1 supposedly for parts, however there wasn't much needed to make it shoot. Have some gauges and 2 other No 4 Mk 1 rifles here. 

So I decided to see which bolt head I needed. The bolt with the No 1 bolt head (measuring .637) does not close on the no-go gauge in all three rifles. The bolt with the No 3 bolt head (measuring .640). 
In the rifle it belongs to it will almost close on the no-go and in the new rifle it will close on the field gauge. Bow I'm not sure what bolt head to buy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: July 22 2018 at 5:41am
I might not have understood this right. Your saying that the No. 1 Bolt Head works fine in the new rifle (does not close on the No Go gage) but a No. 3 Bolt Head closes on the field gage? And the No. 3 Bolt Head measures longer than the No. 1 (as it should)? Your not changing bolts between rifles, right?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mausernut Quote  Post ReplyReply Direct Link To This Post Posted: July 22 2018 at 5:46am
Since the new rifle came without a bolt, yes I was just changing bolts between rifles to figure out which bolt head I need. Apparently it matters what bolt body you have.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: July 22 2018 at 8:40am
It matters immensely. You cannot simply swap in a different bolt then what was in it from the factory. The variations in where the lugs on the bolt mate to the channels in the receiver can be immense. So much so that you can experience what you just described. The other thing would be a lack of contact between the lugs,one or both,and the receiver channels the lugs engage when the bolt us fully closed, preventing lockup. There is a procedure done with hand lapping a new bolt into the receiver body. Another gentleman will arrive shortly and explain the process to you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: July 22 2018 at 8:59am
Yes, absolutely. One of the biggest aims of the various bolt heads was to deal quickly & cheaply with manufacturing tolerances in things like bolt bodies.
Also you will need to check for things like over clocking out to 15 degrees & locking lug engagement. Fixing locking engagement may alter headspace as well!
Definitely not a fully interchangeable plug & play part.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mausernut Quote  Post ReplyReply Direct Link To This Post Posted: July 22 2018 at 12:01pm
First thing I need to do is get another bolt for the one gun and go from there.
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