M47C sportster recovery to T status?

[Roger Payne]

I would concur with surpmil - I use an old butt that I've cut off flush with the semi-pistol grip at the front & I wrap sand paper round it. It seems to work well, but you do need to proceed with care or you risk having a sloppy fit at the front (as he explains).

ATB

[Surpmil]

Mind you don't rock it left or right as you slide it backwards and forwards or that will muck it up as well. Short travel and moderate pressure is the ticket, that and clean, sharp sandpaper.

[ArtioZen]

Being a Gen X “space head”, I wanted to use a bore laser to indicate my rifles barrel axis to compare to the centered scope reticule (with the subject repro scope bracket to assess its geometry). The following saga kept me active, engaged and off the streets…

Expected errors in this test:
The laser beam eccentricity to its body cylinder – with the battery cap finger tight, I added an index mark with a sharpie and always oriented this “up” in the chamber – with the bolt “safe closed” and snugged up to provide a light pressure to the back of the laser body (do not close the bolt on the laser – the extractor claw will do bad things).

I used my vernier caliper to visually estimate the X and Y location of the respective centers – hoping to achieve a window of 0.020 – 0.040 error! The inch lines on the target are about 0.020” for slop-estimating…. When the calcs are run this window effects the results minimally as the measurements are made at the target face which is feet away (orders of magnitude greater).

The laser body is smaller in diameter than the chamber and “lays down” so Y axis position and attitude (effecting elevation readings) will not at all reflect the centerline of the bore (so this test will gain insights and potential adjustments for the X axis – windage location of the scope bracket).

Test Series 1 I set up an orange bull’s-eye on 1” squared target and added 1/8” increment lines to the X and Y axies passing through dead center. I had the rifle clamped in a workmate with lots of padding (an old vinyl faced, blanket backed table cloth folded to four thicknesses).

The first test used a target at 14’ from the scope objective lens and then a second target distance of 28’ (all distances are measured from the center of the rifles rear scope mount)

For each distance I positioned the center the laser dot at the center of the upper orange star. Then went to the rifle and scope and settled in to view the POA. When happy I read off the POA through the scope, added a mark to the target and reconfirmed its center back at the scope. – Doing this for both distances I produced the upper black dots in the photograph and the following positions:

At a target distance of 14’ the sight POA 1.85” high and .320 right
At a target distance of 28’ the sight POA 1.85” high and .690 right
I wanted to go to distances 42’ and beyond but it was snowing here and I would have had to leave doors open and the target outside (making Mrs Breakdown very unhappy and loud

Calc 1 - Trigonometry time! Hopefully you remember SOH CAH TOA – the TOA applies in this case – Cotangent of the Angle times the Opposite side length (readings on the targets X axis) divided by the Adjacent side length (distance to target). With this I could calc the angle of error between the laser POI and sight POA. The calcs yielded an angle of 0.00190 degrees at 14’ and 0.00205 degrees at 28’ – this aftermarket sight bracket is close – but no banana!


Calc 2 - To determine the magnitude of the bracket difference to the H&H scope mounts – and provide a number to create a working adjustment (shim first – machined adjustment of bracket later):

I assume the scope bracket is pivoting at the rear mount and any shim I can add would act of the front mount which is 3.6” forward (treated as another Adjacent side measurement in the Trig)

Now knowing an angle (a range of angles to cover measurement error) I could use the Tan of this angle times the Adjacent side length (3.6”) to get a calculated shim width (Opposite side in the Trig) to push the POA back to center above the laser indication of the bore. At the angle calculated for the 14’ target distance this is a 0.006857” shim and using the 28’ target distance values this is a 0.007390” shim. So for now I want to use a 0.0007” shim at the front scope mount to move the POA left in relation to the laser indication of the bore.

So, giving that the H&H mounts are god and a zero datum: the Chinese bracket has a bore axis aligned off to the right by 0.007” at the front pad when assuming the rear pad location is its zero.

Impact of Chinese Scope Mount on H&H Brackets - Extrapolating the angle involved this bracket error could have given a 7” error (POA to the right) at 100 yards, and with the calc indicating the need for a 0.007” correction at the front pad, this supports the old marksman’s rule of thumb that a .001” error at the rear sight is an inch of POI at a hundred yards. I could have consumed 7 minutes of scope windage to create an artificial zero at 100 yards and the bullet will still be heading away from POA at greater ranges….

Test Series 2 -Having sourced specimens of a suitable shim which is 0.003” thick and fits over the front mount spigot, and within the bracket counter bore to act on the datum face to move the sights X axis left, it was time for trial #2

This time the sight crosshairs were set on the upper target center and the laser POI colored with a felt marker to indicate its shape and position so its center can be discerned (and a vernier caliper again used for approximation).

The first test (small pink dot with a + mark in the photo) was without any shims at 14’ and produced a laser POI slightly to the left of POA.

The second test (large pink dot with a + mark in the photo) was without shims at 36’ 5” and produced a laser POI 0.800” left and 1.79” low.

The third test at 36’ 5” (large green dot with a + mark in the photo) added a single 0.003 shim to the front bracket (a little under half the estimated adjustment) and it found the laser POI 0.34” left and 1.5” low.

The fourth test at 36’ 5” (large blue dot with a + mark in the photo) added two 0.003 shims (0.006” total) to the front bracket (a little less than the estimated adjustment) and found the laser POI 0.080” right and 1.54” low.

A fifth test took the target face back as far as possible at 72’ 6” – almost 25 yards (large orange dot – in the lower target star!) with the 0.006” shim pack still in place and found the laser POI 0.56” left and 5.71” low!

Laser Test Conclusion - So the Chinese scope bracket with the 0.006” shim is now slightly off to the left near the maximum reach of the laser (very nearly at 25 yards) – An ideal shim would seem to be as calculated at 0.007”. The bracket also seems to be pointing way high (will consume about ¾ of the scopes depression adjustment to create a 200yd zero – this will leave lots of elevation available!) but this is confounded by the laydown and attitude of the laser body in the chamber.

The next step is to prove any of this on paper with the shim and the scope still at its centered setting. I expect the 0.006” shim to be close for the windage value with live fire and actually get a real and improved read on the elevation magnitude. These tests and shim adjustments my have saved me 20 odd rounds of ammo to tame windage and at least one trip to the range. To be continued!....

Rehabilitation of a Chinese Scope Bracket - To make a permanent adjustment for this bracket to collimate to this rifle, I would propose to have the scope bracket surface ground at the requisite angle to remove 0.007” of material from the upper surface of its angled rear mount – this should eliminate the need for the shim at the front mount and also go some ways to lower the elevation setting when remounted – experts please advise!

Still saving for a real or modern authentic production of the scope bracket – will also test the fit in a similar fashion against this rifle and its H&H brackets..LMK if any interest in those results and similar excruciating detail etc. I am interested to learn more of the H&H measuring techniques, measuring tools used and their effective accuracy / precision also.

[Roger Payne]

Wow! I wouldn't dream of arguing with that..........even if I understood it!

[Ridolpho]

I1A1: Not to be critical but in your "trig" section you calculate angles of around 0.002 (two thou) of a degree. I think that's off a wee bit. I hope you've read Mr. Laidlers 4 part series on assembling a replica 4T as it addresses all your issues as dealt with during new pad installation. You want to achieve the same via modification on the bracket and I hope Peter or others might comment on how a replacement new or used bracket was installed on a rifle that already had pads (but had lost its bracket?). I've just finished an ad-hoc job of this on my replica and I think I could have done it better.

Ridolpho

[ArtioZen]

Hi Roger = Welcome back =LoL sorry for letting my thoughts out of my head - I tried (and failed) to get them all organized!

Ridolpho - thx - you are right, I read off the "Tan of the angle" readings by mistake from my spreadsheet not the angle. These should read:

Target at 14' (no shims) 0.109 degrees
Taregt at 28' (no shims) 0.117 degrees

I calculated the angle and shims required for the target at 36' 5" (no shims) as 0.104 degrees and 0.00658 shim to correct.

I am happy that the numbers are trending with range (with the various errors) and the shims when applied correct the POA - the 0.007" adustment is still my minimum target but only currently have 0.006 shims.

I have have indeed read and re-read Mr Laidlers instructions especially on the scope mounting. I am not going to alter my rifles pads in any way and will strive to adjust the bracket to suit! First the chinese exampe as practice and then one of Rogers as funds allow.. The only place I can use a distant object (as per the instructions) for bore sighting is my club range (I dont want to be pointing my rifle around neighborhood!). I will be off to the range at the first opportunity!

Let's hear more about you replica and tuning etc - we can cheer each other on! Yes I would love to hear from the experts how a replacement bracket was matched to existing H&H mounts (hopefuly without starting all over with pads!).

[Ridolpho]

I1a1: I was going to put in a post after I get out to the range. The scope is, apparently, from Taiwan and was one of half a dozen a friend imported. It's a Mk1 replica and accurately replicates the Mk1 adjustment procedures. After finishing with the bracket I tested the scopes adjustment with an original chart from "Canadian Army EME Manual.......17 Jun 55" and the thing appears to be well calibrated (for distance and lateral adjustment). The rifle is a '42 Savage with original 2 goove barrel and I have already tested it (and bracket) with a Weaver K3 and it seems to be quite accurate. The pads were installed by a previous owner and seem to be solidly attached although crude in comparison to a real H&H job. Will post once I've shot it with the new scope.

Ridolpho

[Peter Laidler]

There's a real Mk2 telescope on 'that' auction site as we speak - under Lee Enfield I believe

[bearrowland]

I agree and what a beautiful weapon. I'm a huge Lee Enfield fan too!

[Ridolpho]

Peter: That's a nice looking scope for sale on e-bay. I see it's up to $1123 (USD) as of a minute ago. Do you know anything about the "Peter" that's selling it?

Ridolpho