If I have a barreled MKX action. Can I swap the bolt out? Provided the distance from the rear of the locking lugs to the bolt face MICs the same?

I would use a headspace gauge myself.....

quote:

I would use a headspace gauge myself.....

In a perfect world I'd agree with you 100%. But some of us use those DARN wildcats with no gauges.

But in theory if the measured the same in my case the replacement is about .0002 shorter. So SHOULD have a tighter headspace. Or is there a flaw in my theory?

Your theory is correct; headspace on two bolts with the same face to rear lug distance, will be the same.

quote:

Originally posted by ramrod340:

quote:

I would use a headspace gauge myself.....

In a perfect world I'd agree with you 100%. But some of us use those DARN wildcats with no gauges.

But in theory if the measured the same in my case the replacement is about .0002 shorter. So SHOULD have a tighter headspace. Or is there a flaw in my theory?

Your mic'ing over the lug? .0002" in which direction? Is it shorter towards the bolt face? Mic'ing the lugs really means nothing. It is the relationship between the bolt face and the REAR face of the bolt lugs.

When I want to swap bolts on an existing firearm I set up the bolt in a v block so the rear of the bolt lugs are on the face of the block. Then I zero an indicator on the bolt face. Then I swap bolts and measure from the bolt face.

I am a bit eccentric, in that I do not like using indicators to measure. I won't get into the issues with that... but usually I will make up a stack of gauge blocks as reference. Then I have a comparator with a known measurement.

quote:

Your mic'ing over the lug? .0002" in which direction? Is it shorter towards the bolt face? Mic'ing the lugs really means nothing. It is the relationship between the bolt face and the REAR face of the bolt lugs.

The distance from the rear of the lug to the bolt face differed by .0002. As it is I found the parts to make the original bolt work so really ended as a theoretical exercise.

Ram measured the critical dimension, correctly.

I would love to learn how you mic from the back of the bolt lug to the bolt face? That is not sarcasm, I mean it genuinely.

I'll send you a photo of such a measuring tool. You m ay post it here if you want

quote:

I would love to learn how you mic from the back of the bolt lug to the bolt face

Well first I got out my wooden yard stick.

You are correct trying to mic the distance directly would be difficult or impossible due to the angle.

What I did in my test was use a rare earth magnet that was thicker than the distance from the outside bolt edge to the face. Then laid a piece of bar stock I had checked for uniform thickness on the magnet. Then mic'd from the back of the lug to top of the bar. Took the measurement from both lugs. Turned the magnet and bar around just in case and the measurements matched. Repeated on the other bolt.

In this case I had a no/go. With the bolt that came with the rifle the bolt closed to around 4 o'clock. The second bolt which measure said should be a tighter head space didn't close as far. It was totally visual. I didn't try to measure it.

What I have learned from all this is that what many of you already knew all parts are interchangeable. Swapping from Military, to FN to modern commercial like the MKX just adds to the flux.

As to swapping bolt. Yes ideally use a set of gauges to be sure. For my own use in one of my wildcats I would have no issue with swapping a bolt measured the way I did that matched. I adjust my dies to the chamber anyway.

People talk about the bolt matching the action. I checked 5 MKX actions I have and the number on the bolt doesn't match any part of the action number. Should they match or am I missing a number on the action?

I never need to do it, but I have a round gauge block that is machined to fit into the bolt face, and comes out so you can measure from the lug rear surfaces to the block. then subtract the height of the block. Can use it on a height gauge too.
If I fit a bolt to an action, I am also fitting a barrel, so that measurement doesn't matter anyway.

Forgot to add; the MKX bolts are not numbered to the rifle serial number; that is an assembly number which is usually found stamped in the cocking piece notch in the receiver tang.
I think they added the actual rifle serial number on the right side of the receiver ring after build.

quote:

Forgot to add; the MKX bolts are not numbered to the rifle serial number; that is an assembly number which is usually found stamped in the cocking piece notch in the receiver tang.

Well another good day since I learned something. Yep just checked the rifle I had been working on the bolt matched a stamping in the tang. However the FN action had no stamping on the bolt that I was. But the way my day is going I wouldn't bet anything on it.

Like dpcd said.

Cut a squared plug in the machine that will sit on the bolt face. Rest the lug tightly against a piece of precision ground material. Measure from the top of the plug to the ground stock. Subtract the length of the plug from the measurement that you took.

If the two measurements are +-.001 inch of each other you are more than good to go. You can measure both lugs if you wish and split the difference if you think the lugs are not square.

headspace bolt by Rod Henrickson, on Flickr

Hey you stole my gauge. I am filing a cross border international complaint through the embassy; or something like that; I ain't a lawyer or anything else. Maybe I will just yell across the 49th parallel. If I knew where it was.

Oh, Ram, that is because the MK10s were made in Yugo, and the Fns, in Belgium. Fns are numbered under the bolt handle and will match the receiver SN.

d feeling about this. The action is no doubt FN Is stamped as such with a 4 digit serial #.

However this is the bolt that is in it.

There is no number stamped on the bolt.

To add insult photobucket isn't posting the edited photos.

That is the shape of the FN handle,, it should have a proof mark on the outside at the top, and the back of the shank. If it works, use it.

Yep proof mark back top of shank. With it laying next to the MKX bolt all afternoon I started wondering if I had a Belgium/Yugo cross. Now I feel better.

Thanks

quote:

Originally posted by dpcd:
Hey you stole my gauge. I am filing a cross border international complaint through the embassy; or something like that; I ain't a lawyer or anything else. Maybe I will just yell across the 49th parallel. If I knew where it was.

So, don't leave the windows unlocked anymore and you won't have nocturnal visitors pilfering your tools!

OH, by the way, yer outta beer ! ! You weren't. But you are now. he he he

I thought it was a skunk in my yard last week, but now I see it was you.

Don't feel bad. A lot of other people have made the same mistake. I tend to make funny farting noises when I scuttle around and scare the shit out of the dog. I also smell much the same !

he he