$50 borescope (Read 700 times)

ren

Re: $50 borescope
« Reply #20 on: November 07, 2019, 09:19:25 AM »
another use for the borescope - seating bullets to the lands
From James Tate at Nationalmatch.us


Accurately measuring bullet contact with the lands for calculating jump has always been a problem for me. I was able to use the borescope to tell when an SMK 80 is touching the lands.

1) Insert borescope, without mirror, into the barrel from the crown end.

2) Insert bullet held by the Hornady OAL gauge.

3) Carefully slide the borescope until you can see the bullet. It needs to be clear enough to detect bullet rotation.

4) Gently push the bullet into the lands until you feel contact.

5) Watching through the borescope, rotate the OAL gauge. The bullet should rotate with the OAL gauge. If not, back out the bullet until it does.

6) Gently push the bullet in. Look for rotation. Push in gently until rotation stops.

7) Remove the bullet. If you are just touching the lands the bullet should come out without any force.

8 ) Measure the OAL.

In the one try I could see that at 2.495 the 80 SMK rotated. At 2.497 it would not rotate but easily came out with the OAL tool. At 2.500 the bullet was jammed and had to be pushed out.

This video is large but should stream easily. Not much to see but interesting. The first 10 seconds the bullet is seated at 2.495. You can see the bullet rotate freely when I rotate the COL tool. Second half, I adjusted the COL tool in and now the bullet will not rotate freely but you can see the bullet move as I rotate the OAL tool. Bullet did stay in the COL tool on extraction. This measured 2.497. Not in the video is the last step I made by pushing the bullet hard into the lands. That measured 2.450 on extraction. Extraction required a push from a cleaning rod.

In this case I would use 2.497 as the starting point to calculate any jump.

https://drive.google.com/open?id=1TvtAAU_jzfIZEdqBpeobnZwYtALhDBXC

esk808

Re: $50 borescope
« Reply #21 on: November 07, 2019, 09:36:02 AM »

Ren,

You started this conversation..........   :D

Don't you want one?    Don't you need one ?

ren

Re: $50 borescope
« Reply #22 on: November 07, 2019, 12:40:48 PM »
Ren,

You started this conversation..........   :D

Don't you want one?    Don't you need one ?

Contemplating one but I'm in a holding pattern as far as rifle shooting goes.
Working on interior plantation shutters, home improvement stuff got me occupied as well as work related mandatory stuff....