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weagle Offline OP
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I recently purchased an older Zastava commercial 98 in .375 H&H. It's a beautiful rifle, but a previous owner had installed a military style bolt shroud and trigger.

I have installed a timney trigger and the bolt from my Interarms Mark X 7mm mag feeds loaded ammo perfectly.

If the swapped out bolt passes a no-go gauge test can I safely assume the headspace is good to go?

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As long as it goes on the go and doesn't go on the no go, you're fine, given that all obvious parameters are met.

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weagle Offline OP
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Thanks. Do I really need the go-gauge if the bolt closes easily on a factory round?

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The gauges test only to the belt and factory brass is very erratic. It is quit possible some factory ammo will not fit. A simple chamber cast is simple, quick, easy, and cheap.

But in general the answer is no.


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I hate to ask the obvious, but why don't you just swap the shrouds and internals? No muss no fuss. You may have to lap the threads in with valve grinding compound if it doesn't want to screw on easily. Rarely, and I mean very rarely, a mauser shroud won't index, but even those are usually very easy to fit.


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weagle Offline OP
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Originally Posted by sbrmike
I hate to ask the obvious, but why don't you just swap the shrouds and internals? No muss no fuss. You may have to lap the threads in with valve grinding compound if it doesn't want to screw on easily. Rarely, and I mean very rarely, a mauser shroud won't index, but even those are usually very easy to fit.


There is something odd about the bolt that came in the rifle. I put a commercial style shroud and striker in it, but the cocking surface on the bolt is shorter than a standard Interarms MK X. The result is when I close the bolt there is about an 1/8 inch of "cock on close" that draws the striker all the way back once the striker contacts the trigger. Never encountered one like it. Perhaps it's a modified military bolt? as it worked correctly with the military shroud and striker and trigger.

In these pics you can see the difference in the bolt bodies. The one with the non blued shroud is the one that came with the gun. The one with the blued shroud is from my Interarms MK X 7mm mag. The last pic you can see how much further back the striker is on the Interarms assembly.

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]


Last edited by weagle; 05/25/20.
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The one with the silver shroud is speed locked. Hence, what looks like a two step cocking cam on the bolt. The correct cocking piece is flat bottomed and has a shorter nose. If you are experiencing hard to lift bolt after firing, put the flat bottom P back in. Using the factory adjustable trigger with a standard cocking piece can cause hard bolt lift.

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Well I would invest in headspace gauges and swap the bolts. The long mauser throw may not be optimal for benchrest accuracy; it is designed for posiitive ignition. That is part of the beauty of the design. I would want that one in my 375 H&H. To be honest I would chuck that speedlock bolt, but that is just me.


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Provided they both pass the go / no-go test... AND both chamber rounds without resistance.

Something you can check after that...

1) actual headspace to the chamber collar (belt) - With each bolt...

Put a piece of scotch tape on the back of the go gauge, trim it with a exacto knife so it doesn’t extend past the edge and chamber it... if it goes (chambers with no resistance) Add a second piece of tape, and repeat until you can’t chamber it... know you know how much room (headspace) you have with each bolt based on a known increment of thickness. If you have a micrometer you can check the thickness of the tape.

This will tell you how the bolts compare inside the go/ no-go range.


2). Fire a couple of rounds with each bolt (same brass lot).. and use a hornady headspace gauge to compare how far the shoulder moves forward with each bolt, when comparing the results it should be close or match the results from above because it mirrors bolt face to shoulder..

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weagle Offline OP
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Originally Posted by z1r
The one with the silver shroud is speed locked. Hence, what looks like a two step cocking cam on the bolt. The correct cocking piece is flat bottomed and has a shorter nose. If you are experiencing hard to lift bolt after firing, put the flat bottom P back in. Using the factory adjustable trigger with a standard cocking piece can cause hard bolt lift.


10-4, Thanks.

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weagle Offline OP
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Originally Posted by z1r
The one with the silver shroud is speed locked. Hence, what looks like a two step cocking cam on the bolt. The correct cocking piece is flat bottomed and has a shorter nose. If you are experiencing hard to lift bolt after firing, put the flat bottom P back in. Using the factory adjustable trigger with a standard cocking piece can cause hard bolt lift.


Thank you again. I looked through my stuff and found a cocking piece that matched your description and bingo; works perfect now.

[Linked Image from i.imgur.com]


Bolt is smooth as silk and it cocks smooth also. Timney trigger breaks nice at a little over 3 lbs.

The Campfire comes through again.


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