No4 Mk1 bolt face question

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elvis3006

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While firing my Long Branch No4 Mk1 I noticed one time it fired differently. It still went bang loudly but this time it was a little different. I inspected the spent casing and noticed the primer strike was more pronounced and deep, I also inspected the bolt head and noticed the firing pin hole no longer looked circular like a portion of the surface was missing. My questions are, what caused this/how do I fix it, is it safe to shoot still with this bolt head and should I replace the bolt head ? I am thinking the bolt head is pooched. Thank you.
 
elvis3006: What does the tip of the striker look like? Perhaps it is damaged in addition to the bolt-head which could explain the pierced primer. The tip of the striker can be reshaped to the proper profile by stoning but if this were mine I would also replace the bolt-head. You'll need to find one that has near identical critical dimensions to maintain headspace while also giving proper overturn, etc. A trivial matter if you can find a local collector/ gunsmith that has an inventory of bolt-heads to try. To simply try to purchase a single bolt-head without being able to try it in your bolt is not highly likely to work. Try to post a photo of the tip of your striker.

milsurpo
 
Bolt head is fine to use.

Unscrew it and look at the tip of the firing pin. It should be round. Sometimes a piece breaks off and makes it a spike.

If it is round, carry on shooting.

Stuff happens.
 
Thanks for the help fellas. Here are two pictures of the striker and one of the cocking piece showing where the firing pin/striker is set at. Also it is a number 1 size bolt head and I have several same sized spares.
 
how about a picture showing fireing pin protrusion. Going from memory its 0.050" max.

the other pictures look OK, perhaps a little cleaning up of the fireing pin.

and S&B Ammo may be part of the problem
 
woodchopper said:
how about a picture showing fireing pin protrusion. Going from memory its 0.050" max.

the other pictures look OK, perhaps a little cleaning up of the fireing pin.

and S&B Ammo may be part of the problem
Click to expand...

Here you go, first one shows the protrusion of the original number 1 bolt head I experienced the issue and the next pic shows the protrusion on the replacement number 1 bolt head.
 
Max/min specs on FP protrusion in the No4 are .50/.40.

The firing pin tip should be smoothed up to eliminate the burrs which can cause the primer to be punctured the way it is. It's not a good idea to shoot any rifle when you are experiencing pierced primers.
 
Looks like it may be a little long.

use the depth gauge on your calipers (if you have calipers) to measure the protrusion

thanks Purple for confirming that my brain in not total mush and that I did remember that 0.050" was max :)



and I had another thought. While you have your calipers out measure your bolt head.

there are some that have been altered by stoning the face down. I have a No2 marked bolt head that is shorter then the spec for a No0 :(
 
OK so the firing pin hole on bolt face is still ok despite the gas cuts and safe to use ? Where do you measure bolt head ? And smooth up firing pin and measure its protrusion. Thank you
 
That pin looks good. Buff it up and you are good to go.

With military primers I have used protrusions as long as 75 thou, but 50 is a good number, assuming the bold head is the correct size.

Can you get your hands on a 0 bolt head and see if it will close on a case?
 
Ganderite said:
That pin looks good. Buff it up and you are good to go.

With military primers I have used protrusions as long as 75 thou, but 50 is a good number, assuming the bold head is the correct size.

Can you get your hands on a 0 bolt head and see if it will close on a case?
Click to expand...

Yup I got one will give it a try.
 
The 0 bolt head will not screw on to the bolt body all the way and I am not comfortable trying to force it. The best way to ensure it is the proper bolt head size would be to get a 303 headspace no go gauge right ? And I buffed up the firing pin she looks cleaner/smoother.
 
Best way to check headspace is to use gauges.
There are other methods that can give you a pretty good idea.
One way is to fire a primed case. The primer will be backed out of the case. Determine the measurement from the front of the rim to the face of the primer.
Or you can use shims on a case head. Measure thickness of the rim and the thickness of the shims.
 
Thanks for the info everyone I appreciate it. Where can you buy 303 headspace gauges here in Canada ? Or perhaps someone here would be kind enough to lend me theirs ?
 
The quick and dirty way i check head space is start a primer into the pocket. Then put the round in the chamber and close the bolt on it, the bolt will push the primer in also holding the rim into the chamber. Then after closing bolt i open it and take the case out and see how far primer is still sticking out

Some bolt heads dont work with some bolts. The have to thread all the way on and not clock past the lug on the bolt by 8*

although there may be dirt causing it not to thread on if its not going tight to the bolt face before lining up.
 
I’ve had the odd pierced primer with S&B .303 Brit, you could definitely hear the difference when they fired. Likely that was th case, I had two in one box and nothing since. None with any other brand of .303 ammo I’ve put through my no4.
 
The rounds must have been made on a Friday afternoon before closing lol. As Ganderite said I will just carry on thank you for the help everyone.
 
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