Finding bore center through action?

[wbrco]

I have a Ishapore 2A that I sporterized some time back. At the time I had it drilled and tapped and put one of the Parker Hale scope mounts on.

Well, that mount design just won't stay tight due to the cast aluminum against the stripper clip bridge and the bridge gouging into the aluminum.

I want to try to make my own mount out of flat steel and some creativity. My question is how do I find the center of the bore along the length of the action? I know the bridge is at a different height than the front of the receiver, and want to account for this difference.

I thought about a 36" piece of 1/4" threaded rod and some tapered rubber faucet washers and a couple of nuts. Then I can use the depth gauge on my calipers to obtain a reference.

How do "real" 'smiths do this for a custom mount?

[samari46]

There was a rather lengthy thread regarding using common angle iron (no I'm not kidding) on the #4 series of Lee Enfields. However if I'm not mistaken the Ishapore 2A and 2A1 series of rifles were based on the #1MKIII series and as such have a round type receiver rather than the flat sidewalls of the #4. About the only commercial mount I'm aware of would be those made by Williams Gunsight company. Not an expert but may I suggest using the top of the front receiver ring as your starting point?. I have seen exactly one #1MKIII drilled and tapped using weaver scope bases. One on the front receiver ring and the other on the charger bridge. Hope this helps. Frank

[wbrco]

There was a rather lengthy thread regarding using common angle iron (no I'm not kidding) on the #4 series of Lee Enfields. However if I'm not mistaken the Ishapore 2A and 2A1 series of rifles were based on the #1MKIII series and as such have a round type receiver rather than the flat sidewalls of the #4. About the only commercial mount I'm aware of would be those made by Williams Gunsight company. Not an expert but may I suggest using the top of the front receiver ring as your starting point?. I have seen exactly one #1MKIII drilled and tapped using weaver scope bases. One on the front receiver ring and the other on the charger bridge. Hope this helps. Frank

Yes, but the length of the action is just different enough that the 1mk3 mounts won't work. And I have custom stock work so the mount that wraps around the front of the rx is not something I want to consider.

[John Boy]

How do "real" 'smiths do this for a custom mount?
Finding bore center through action?

Certified plug gages - insert in muzzle and then take half the diameter ... yields bore center every time

[pietro]

I have a Ishapore 2A that I sporterized some time back.

I want to try to make my own mount out of flat steel and some creativity.

My question is how do I find the center of the bore along the length of the action ?

I know the bridge is at a different height than the front of the receiver, and want to account for this difference.

Both the front & the rear end of the firing pin by definition align with the bore C/L of any CF rifle, so - using the K.I.S.S. principle - install the bolt and measure the distance from the center of the rear end of the FP, up to wherever.


.

[flintlocke]

Lacking plug gauges, I have made some custom mounts, mostly for Mannlichers by sacrificing a cheap Harbor Freight transfer punch turned on a lathe or drill press to slip fit bore diameter. In my experience any flat reference place on the action may not exactly correspond with bore centerline. Then level your action and barrel, I mean LEVEL, Starrett level, fore and aft, side to side. Forget vee blocks, use a leather padded vise. Tight. Fabricate your base and temporarily fasten it in approximate location. Take a piece of cold rolled roundstock 1" dia., about the length of a scope tube,( or you can use the intended scope with the adjustments centered) drill it DEAD center with a 1/4" to 5/16" drill, yes you can drill from both ends. Install your rings temporarily on your base with the 1" "peep sight" you just made. Recheck level, hang a plumb line in the other end of your shop so it optically bisects the bore, check your "peep sight" image, adjust your rings and or base to get exact center for windage with the plumb line. Your elevation should be ok if the bore is level with your "peep sight". You can bias your mount if you now wish, ever so slightly to give a couple minutes of elevation so the scope will be in its mechanical center when sighted in at say a hundred or so yards. Very carefully mark and index everything for final drilling and tapping. Sounds more complicated than it is, do not be intimidated. Do not get hung up on my suggestions. Machine work is the art of the possible, not any more or any less than solving the problem at hand with the tools you have. good luck

[wbrco]

Both the front & the rear end of the firing pin by definition align with the bore C/L of any CF rifle, so - using the K.I.S.S. principle - install the bolt and measure the distance from the center of the rear end of the FP, up to wherever.


.

Ohh, I like that idea! Gives me a crude but close enough measurement. Technically, I could use the bolt body itself to get my height offset.

[Nobade]

I hold the barrel in V blocks, those clamped in the mill vise. Indicate off the edge of the V block and move to center. Most barrels have the hole close enough to the center that this works every time.

-Nobade

[Ballistics in Scotland]

What kind of method of finding the centre depends on what you want to do with it once found, and that I am not entirely clear about. But do you have a 6.5mm. rifle? If you get one of the laser boresighters which are in the form of a cartridge case? The neck should be a close fit in the muzzle, but a little tape on a .270 one should do. Then shine the laser through the flash-hole of an unloaded case in the chamber.

[richmanpoorman]

Or you could just buy an SK scope mount which work great.

[Sur-shot]

I had to bookmark that S&K scope mount page. That Mini-14 scope mount is like the Wichita, no longer made, and they work great.
Ed

[country gent]

I would clamp a piece of flat steel on the tallest part of the receiver. and then use shim stock to get the dimension. Or apiece of flat stock clamped to the lower ring and just inside the higher then mike down to the ring with depth mikes. Subtract the thickness of the stock and you have the offset. It might be easier to go to a scout type mount forward with a extended or long eye relief scope. This woul give several benefits, 1 You will maintain the use of stripper clips, The rifle may balance better, and it makes it easier to carry the rifle carrying over the receiver magazine area

[Ballistics in Scotland]

Ah, the benefits of a dry climate! I much prefer to carry with the eyepiece lens under my armpit to keep the rain off.