1. Announcement:
    Contributing Member Plan Available !
    Badger ‎(Administrator)
    10-29-2006
    Views:
    252,819
+ Post New Thread
Page 1 of 175 1 2 3 11 51 101 ... LastLast
Threads 1 to 20 of 3487

Forum: M1903/1903A3/A4 Springfield Rifle

Forum for discussions about the M1903/1903A3/A4 Springfield Rifle

» Sticky Threads

  1. Sticky Thread Firearms photography

    (I don't know if I ran this on the old CSP forum or not. In view of the fact that there has been a lot of discussion about posting pictures, I...

    Started by Rick the Librarian‎, 03-07-2009 08:43 AM
    4 Pages •
    1 2 3 ... 4
    firearms, photography 4 Attachment(s)
    • Replies: 34
    • Views: 66,419
    Flying10uk
    11-09-2019, 08:27 PM Go to last post

  2. Sticky Thread How to clean a Warner & Swasey Musket Sight

    To start the whole story, I took off all W&S Musket Sights from the rifles I have them with, I took all of the spare ones I had around (including the...

    Started by Promo‎, 01-02-2013 11:18 AM
    2 Pages •
    1 2
    clean, musket, sight, swasey, warner 17 Attachment(s)
    • Replies: 10
    • Views: 33,746
    ChrisW
    06-12-2017, 05:07 PM Go to last post

  3. Post Sticky Thread Remington 1903A3 (displaying original configuration and finish)

    The question of what the original parts and finish of a Remington 1903A3 comes up very often, as most 1903A3's were refinished during arsenal...

    Started by Harlan (Deceased)‎, 02-05-2010 11:25 AM
    configuration, displaying, finish, original, remington 26 Attachment(s)
    • Replies: 1
    • Views: 55,207
    Harlan (Deceased)
    01-05-2011, 07:42 AM Go to last post

  4. Post Sticky Thread Model 1903 and Mauser Patent Infringments

    Here is the little write up on the Mauser patents. The original article from The 1915 Outers publication was posted by Michael Petrov on the old CSP...

    Started by JGaynor‎, 11-01-2010 07:20 AM
    1903, infringments, mauser, model, patent
    • Replies: 0
    • Views: 17,547
    JGaynor
    11-01-2010, 07:20 AM Go to last post

  5. Arrow Sticky Thread The Guns at Springfield (DOD Video)

    An interesting video for Springfield collectors ... :thup:

    Started by Badger‎, 08-31-2010 10:29 AM
    dod, guns, springfield, video
    • Replies: 0
    • Views: 14,726
    Badger
    08-31-2010, 10:29 AM Go to last post

  6. Post Sticky Thread United States Rifle, Cal .30, Model 1903 Manual

    United States Rifle, Cal .30, Model 1903 Manual Washington Printing Office Pamphlet No. 1923 Revised October 17th, 1911 Format: 72 pages with two...

    Started by Badger‎, 04-13-2010 12:45 PM
    1903, cal, manual, model, rifle, states, united
    • Replies: 0
    • Views: 41,133
    Badger
    04-13-2010, 12:45 PM Go to last post

  7. Post Sticky Thread TM 9-1270 U.S. Rifles, Cal .30, M1903, M1903A1, M1903A3, M1903A4 Sniper

    TM 9-1270 U.S. Rifles, Cal .30, M1903, M1903A1, M1903A3, M1903A4 Sniper Ordnance Maintenance Manual War Department Format: 116 pages with multiple...

    Started by Badger‎, 04-13-2010 12:43 PM
    cal, m1903, rifles, sniper
    • Replies: 0
    • Views: 26,881
    Badger
    04-13-2010, 12:43 PM Go to last post

  8. Post Sticky Thread M1903 - Individual Instruction in Rifle Practice (A.E.F No. 1418 G-5) (1918)

    M1903 - Individual Instruction in Rifle Practice (A.E.F No. 1418 G-5) (1918) Author: Colonel A.J. Macnab Jr (United States Army) Reprinted November...

    Started by Badger‎, 04-13-2010 12:41 PM
    1418, 1918, aef, individual, instruction, m1903, practice, rifle
    • Replies: 0
    • Views: 15,538
    Badger
    04-13-2010, 12:41 PM Go to last post

  9. Post Sticky Thread M1903 Private's Manual (1918)

    M1903 Private's Manual (1918) Author: Colonel Jas. A. Moss (United States Army) Format: 43 pages Note: After you click on images to ENLARGE...

    Started by Badger‎, 04-13-2010 12:40 PM
    1918, m1903, manual, private
    • Replies: 0
    • Views: 18,135
    Badger
    04-13-2010, 12:40 PM Go to last post

  10. Post Sticky Thread The Remington Society of America (Remington 03, 03A3, 03-A4 Serial Numbers)

    http://www.remingtonsociety.com/rsa/questions/barrelcodes

    Started by Badger‎, 01-28-2010 06:44 PM
    03a3, 03a4, america, numbers, remington, serial, society
    • Replies: 0
    • Views: 44,514
    Badger
    01-28-2010, 06:44 PM Go to last post

  11. Post Sticky Thread U.S. Military Dates of Manufacture (OldGuns.Net)

    Caveat: The Oldguns table does have some problems with the production dates for Remington M1903 and M1903A3 rifles. M1903s are listed as ALL...

    Started by Badger‎, 01-01-2010 08:51 AM
    dates, manufacture, military, oldgunsnet
    • Replies: 0
    • Views: 23,184
    Badger
    01-01-2010, 08:51 AM Go to last post

  12. Post Sticky Thread Vi Shooter's Web Pages - Extensive Information on M1903 & Variants

    http://www.vishooter.net/m1903.html

    Submitted by Badger‎, 11-24-2009 09:27 AM
    extensive, information, m1903, pages, shooter, variants, web
    •  
    •  
    Badger
    11-24-2009 09:27 AM Go to last post

  13. Post Sticky Thread Fundamentals of Small Arms Weapons (WWII U.S. Training Films)

    Fundamentals of Small Arms Weapons (WWII U.S. Training Films) These combined videos demonstrate the mechanics of pistols, rifles and machine guns....

    Started by Badger‎, 11-04-2009 12:47 PM
    arms, films, fundamentals, small, training, weapons, wwii
    • Replies: 0
    • Views: 14,115
    Badger
    11-04-2009, 12:47 PM Go to last post

  14. Post Sticky Thread TM-43-0001-27 - Army Ammunition Data Sheets (1994)

    TM-43-0001-27 - Army Ammunition Data Sheets (1994) DISTRIBUTION STATEMENT: Approved for public release: distribution is unlimited....

    Started by Badger‎, 11-04-2009 10:38 AM
    1994, ammunition, army, data, sheets, tm27
    • Replies: 0
    • Views: 20,032
    Badger
    11-04-2009, 10:38 AM Go to last post

  15. Post Sticky Thread TM9-270 U.S. Rifle, Cal. .30, M1903a4 (Sniper's) Characteristics and Operation

    TM9-270 U.S. RIFLE, CAL. .30, M1903A4 (SNIPER'S) CHARACTERISTICS AND OPERATION Published by War Department (Sept 28, 1943 - 30 Pages) ...

    Started by Badger‎, 10-14-2009 10:41 AM
    cal, characteristics, operation, rifle, sniper
    • Replies: 0
    • Views: 14,264
    Badger
    10-14-2009, 10:41 AM Go to last post

  16. Post Sticky Thread Infantry Weapons and their Effects (WWII and Korean era U.S. Training Films)

    Infantry Weapons and their Effects (WWII U.S. Training Film) "Infantry Weapons and Their Effects" is an official WWII era training film which...

    Started by Badger‎, 10-11-2009 04:29 PM
    effects, era, films, infantry, korean, training, weapons, wwii
    • Replies: 0
    • Views: 14,215
    Badger
    10-11-2009, 04:29 PM Go to last post

  17. Post Sticky Thread Small Arms Instructors Manual (1918)

    Small Arms Instructors Manual (1918) Compiled by the Small Arms Instruction Corps Format: 234 pages - E.P. Dutton @ Company, New York (1918) ...

    Started by Badger‎, 09-28-2009 02:44 PM
    1918, arms, instructors, manual, small
    • Replies: 0
    • Views: 13,000
    Badger
    09-28-2009, 02:44 PM Go to last post

  18. Post Sticky Thread United States Rifles and Machine Guns (1917)

    United States Rifles and Machine Guns (1917) Authors: Fred H. Colvin and Ethan Viall Associate Editors American Machinist Members Society American...

    Started by Badger‎, 09-21-2009 01:49 PM
    1917, guns, machine, rifles, states, united
    • Replies: 0
    • Views: 13,165
    Badger
    09-21-2009, 01:49 PM Go to last post

  19. Post Sticky Thread Red Star Remington Model 1903's

    Extracted from "United States - Milsurp Knowledge Library" Red Star Remington Model 1903's (Click PIC to Enlarge)(Click PIC to Enlarge) ...

    Started by Badger‎, 09-14-2009 09:06 AM
    1903, model, red, remington, star
    • Replies: 0
    • Views: 38,612
    Badger
    09-14-2009, 09:06 AM Go to last post

  20. Post Sticky Thread Victory Is Our Business (1942)

    Victory Is Our Business (1942) A patriotic motivational film for World War II industrial workers film, located with thanks to member "PBI". It...

    Started by Badger‎, 09-09-2009 02:42 PM
    1942, business, victory
    • Replies: 0
    • Views: 12,439
    Badger
    09-09-2009, 02:42 PM Go to last post

  21. Post Sticky Thread Basic Manual of Military Small Arms by W.H.B. Smith

    Basic Manual of Military Small Arms by W.H.B. Smith (Expired Copyright 1943) Observations: by Badger How to load, operate, disassemble,...

    Started by Badger‎, 09-09-2009 12:51 PM
    arms, basic, manual, military, small, smith, whb
    • Replies: 0
    • Views: 13,476
    Badger
    09-09-2009, 12:51 PM Go to last post

  22. Post Sticky Thread Springfield 03A3 Rear Sight Removal and Replacement

    Springfield 03A3 Rear Sight Removal and Replacement by "Bob S" Note: After you click on images to ENLARGE them, you may find they...

    Started by Badger‎, 09-09-2009 12:31 PM
    03a3, rear, removal, replacement, sight, springfield
    • Replies: 0
    • Views: 23,497
    Badger
    09-09-2009, 12:31 PM Go to last post

  23. Post Sticky Thread 640 Yard Shooting (1943 1903a3 Rifle)

    640 Yard Shooting (1943 1903a3 Rifle) (Videos by YouTube member Ernest "mag30th") Ernest "mag30th" kindly gave us permission to put his two...

    Started by Badger‎, 09-09-2009 11:03 AM
    1943, 640, rifle, shooting, yard
    • Replies: 0
    • Views: 17,584
    Badger
    09-09-2009, 11:03 AM Go to last post

  24. Question Global Thread Help: How do I upload pictures to my posts for storage on milsurps.com?

    The following tutorial was created for the benefit of our members by Milsurps Moderator Harlan (deceased). On behalf of all of our membership, I'd...

    Started by Badger‎, 02-06-2011 03:38 PM
    2 Pages •
    1 2
    5 Attachment(s)
    • Replies: 10
    • Views: 65,770
    Badger
    04-22-2020 08:08 AM Go to last post

  25. Question Global Thread Help: How do I find threads with questions that have never been answered?

    Other than someone who fails to say thank you when they get an answer to a question they’ve posted, I don’t think there’s anything more frustrating...

    Started by Badger‎, 02-26-2016 09:16 AM
    • Replies: 4
    • Views: 67,882
    Badger
    03-28-2020 06:39 AM Go to last post

  26. Question Global Thread Help: What is the Advisory Panel Review & Validation Service?

    <center><img src="images/advisory_panel_reviewed_medium.png" alt="This item has been reviewed by members of the Milsurps Advisory Panel."><img...

    Started by Badger‎, 02-19-2014 10:18 AM
    2 Pages •
    1 2
    • Replies: 11
    • Views: 230,952
    Mrshimm
    02-06-2020 10:23 AM Go to last post

  27. Question Global Thread Help: How safe from viruses and hackers am I when using the Milsurps.Com web site?

    Today’s Internet exposes computer users and the web sites they access, to a wide range of malicious pieces of infectious software code, designed to...

    Started by Badger‎, 03-03-2016 07:20 AM
    2 Pages •
    1 2
    23 Attachment(s)
    • Replies: 14
    • Views: 255,665
    Badger
    12-07-2018 03:55 PM Go to last post

  28. Question Global Thread Help: Where can I discuss politics and gun legislation issues?

    Why have a separate Social Groups area? Over the last 10 years, we’ve received many requests to permit broader public discussions amongst members,...

    Started by Badger‎, 08-08-2016 10:35 AM
    • Replies: 7
    • Views: 78,445
    Sylvano
    12-04-2018 05:53 AM Go to last post

  29. Question Global Thread Help: What is good forum etiquette and how do I deal with other members who make me angry?

    Hello folks … :) I'd like to remind everyone to re-read our Forum Rules & Site User Agreement (click here), particularly the section which covers...

    Started by Badger‎, 01-02-2017 01:32 PM
    • Replies: 1
    • Views: 62,145
    WASATCH CHARLIE
    01-10-2017 01:04 AM Go to last post

  30. Question Global Thread Help: Why am I having a problem uploading pics to attach to my posts?

    There are some members who seem to experience site time-outs, or other problems when uploading pics as attachments to their threads and posts. It...

    Started by Badger‎, 04-26-2016 05:25 AM
    • Replies: 3
    • Views: 65,264
    Badger
    04-27-2016 08:10 AM Go to last post

  31. Question Global Thread Help: How do I use the classifieds system to buy and sell items?

    We understand you may be impatient to get on with placing your advertisement, but we would ask that you please read this post carefully, in order to...

    Started by Badger‎, 11-15-2012 07:16 AM
    • Replies: 0
    • Views: 91,050
    Badger
    11-15-2012 07:16 AM Go to last post

  32. Question Global Thread Help: Why are my images from Photobucket, ImageShack etc. copied to milsurps.com?

    Answer: For your own protection and to help preserve them for future research by all members ... :thup: The reason we capture and store all...

    Started by Badger‎, 03-01-2011 09:52 AM
    2 Pages •
    1 2
    • Replies: 10
    • Views: 167,534
    Badger
    03-03-2011 02:21 PM Go to last post

  33. Question Global Thread Help: How do I show pics from Photobucket, Flickr, ImageShack etc. on milsurps.com?

    The following tutorial was created for the benefit of our members by Milsurps Moderator cafdfw (Harlan). On behalf of all of our membership, I'd...

    Started by Badger‎, 02-12-2011 12:10 PM
    • Replies: 0
    • Views: 61,505
    Badger
    02-12-2011 12:10 PM Go to last post

  34. Question Global Thread Help: Can I access the milsurps.com site from dial-up, cell phone, iPhone or Blackberry?

    The answer is YES … :beerchug: With the evolution of technology, many of our very active members want to keep current viewing our forums using...

    Started by Badger‎, 02-04-2011 08:34 PM
    • Replies: 0
    • Views: 39,878
    Badger
    02-04-2011 08:34 PM Go to last post

  35. Question Global Thread Help: My screen is too dark!! How do I change my colour scheme on the milsurps.com site?

    A lot of members don't realize that our site supports multiple interfaces, often referred to as Forum Skins. Fundamentally, there are three...

    Started by Badger‎, 02-02-2011 12:38 PM
    • Replies: 0
    • Views: 34,397
    Badger
    02-02-2011 12:38 PM Go to last post
» Normal Threads

  1. M1903a3 Authentication Assistance

    I am interested in thoughts as to the authenticity of a 1903a3 Remington. I have attached pictures. This is the description: 30.06; 95%...

    Started by Amasoero@aol.com‎, 06-02-2020 01:45 PM
    assistance, authentication 7 Attachment(s)
    • Replies: 2
    • Views: 148
    John Beard
    06-02-2020, 08:01 PM Go to last post

  2. Receiver stamp 1903/A3?

    My buddy inherited a 1903/A3 with an RA barrel 12-43 but the receiver just has U.S. and the serial number 48xxxx. I am trying to help ID the...

    Started by Robinsom‎, 05-26-2020 12:36 AM
    2 Pages •
    1 2
    1903 or a3, receiver, stamp 25 Attachment(s)
    • Replies: 11
    • Views: 378
    John Beard
    06-02-2020, 07:55 PM Go to last post

  3. Authentication Assistance re: m1903a3

    Hello! I am considering the purchase of a m1903a3 that is being represented as part of an elder gentleman’s estate. I am attaching some...

    Started by Amasoero@aol.com‎, 06-01-2020 09:11 AM
    assistance, authentication 10 Attachment(s)
    • Replies: 1
    • Views: 80
    bml
    06-01-2020, 03:25 PM Go to last post

  4. Rock Island 1903, possible NM rifle?

    Greetings! I've used a few threads here for answers, but I seem to be in a unique situation so I thought I would ask around here first. I recently...

    Started by damienslc‎, 12-04-2019 08:44 PM
    4 Pages •
    1 2 3 ... 4
    1903, island, rifle, rock 11 Attachment(s)
    • Replies: 34
    • Views: 3,652
    Promo
    05-29-2020, 03:14 AM Go to last post

  5. 1903 mark one ???

    This rifle was given to me as payment for helping a friend clean out the attic of his sporting goods store. That was about 15 years ago and the...

    Started by John O‎, 05-22-2020 10:03 PM
    1903, mark 4 Attachment(s)
    • Replies: 6
    • Views: 193
    John O
    05-26-2020, 02:11 PM Go to last post

  6. 1903 mark1 what do I have

    This rifle was given to me by a Friend several years ago for spending a lot of hours helping him clean out the attic of his sporting goods store...

    Started by John O‎, 05-22-2020 10:38 PM
    1903, mark1 4 Attachment(s)
    • Replies: 2
    • Views: 184
    twh
    05-23-2020, 09:29 AM Go to last post

  7. Another project 1903

    Stopped off at a local pawn shop today to see what they had. A Kongsberg 1911 that was too much, a 1903A3 that I had see before, also too much. ...

    Started by Hal O'Peridol‎, 05-21-2020 05:28 AM
    1903, project 6 Attachment(s)
    • Replies: 1
    • Views: 145
    browningautorifle
    05-21-2020, 12:57 PM Go to last post

  8. What can you tell me about my new 1903

    I recently picked up my first 1903 on Gunbroker that dates to 1915 with what appears to be original barrel. Inspector stamp is consistent with date....

    Started by Dknight‎, 04-12-2020 04:15 PM
    2 Pages •
    1 2
    1903 10 Attachment(s)
    • Replies: 13
    • Views: 1,054
    Herschel
    05-14-2020, 03:15 PM Go to last post

  9. I finally got my own

    Copy of Brophy's book, the 1903 Springfield. Been eyeing one for years, but seeing them priced on eBay and Amazon between $200-300 dollars, I said...

    Started by sgtgeorge‎, 05-10-2020 06:23 PM
    finally
    • Replies: 3
    • Views: 153
    ArtPahl
    05-11-2020, 10:49 AM Go to last post

  10. I think I have excess headspace

    Hey guys. I just received new Clymer Go and No Go (SAAMI) gauges in the mail. Here’s my problem...my 1903 bolt closes on Go AND on the No Go gauge. I...

    Started by Dknight‎, 04-27-2020 09:41 PM
    excess, headspace 1 Attachment(s)
    • Replies: 7
    • Views: 340
    pocketshaver
    05-10-2020, 11:35 PM Go to last post

  11. Information on 1903A3 Springfield Armory rebuild

    I have a Remington 03A3 manufactured in January 43, with a 2-43 barrel date, that was apparently rebuilt at Springfield Armory. The stock cartouche...

    Started by Digger459‎, 05-10-2020 01:36 PM
    armory, information, rebuild, springfield
    • Replies: 0
    • Views: 88
    Digger459
    05-10-2020, 01:36 PM Go to last post

  12. I Shot My 101 Year Old Rock Island Today

    Serial #347176. I have owned it since 2008. It was sporterized many years ago and nicely done. The stock work is first rate with expertly executed...

    Started by ArtPahl‎, 05-01-2020 11:14 PM
    101, island, rock, shot, today, year
    • Replies: 4
    • Views: 296
    El Woodman
    05-09-2020, 03:15 AM Go to last post

  13. Remington firing pins

    I have a spare bolt that is blued and has a blued firing pin and a spare parkerized firing pin. Both are remington. Was there a time line for the...

    Started by jamie5070‎, 05-03-2020 11:09 PM
    firing, pins, remington
    • Replies: 2
    • Views: 203
    jamie5070
    05-05-2020, 08:30 PM Go to last post

  14. This 1903 is no longer a bubba gun

    This is the rifle I bought from an auction a while back. Because of where it is in the SRS list I thought it was a target rifle but I didn't know if...

    Started by GUTS‎, 04-13-2020 04:45 PM
    2 Pages •
    1 2
    1903, bubba, gun, longer 8 Attachment(s)
    • Replies: 18
    • Views: 1,076
    GUTS
    05-01-2020, 10:49 PM Go to last post

  15. Another trigger guard question, sorry

    Looked until my eyes bleed and couldn't find the answer here or on the web with any clarity. Here goes, I need to know if Remington or a...

    Started by Hateca‎, 04-28-2020 04:22 PM
    guard, question, trigger
    • Replies: 4
    • Views: 211
    Hateca
    04-30-2020, 06:40 PM Go to last post

  16. Is This Spare Parts Container an Original?

    Evening guys. I posted a couple days ago about a new 1915 ‘03 I acquired recently. I have yet to receive any replies, but I wonder if this isn’t more...

    Started by Dknight‎, 04-14-2020 08:15 PM
    1903, 1903 springfield, container, original, parts, spare, spare parts container 5 Attachment(s)
    • Replies: 6
    • Views: 499
    Dknight
    04-23-2020, 11:52 AM Go to last post

  17. Bolt ID

    The bolt on my '03, serial # 1374814, has a what appears to be a #6 or #9 on the bottom of the bolt handle. A "US" on the forward side of the safety...

    Started by jamie5070‎, 04-11-2020 12:11 PM
    bolt
    • Replies: 3
    • Views: 291
    Rick the Librarian
    04-23-2020, 10:13 AM Go to last post

  18. Correct Bolt for Model 1903 N.B.A. Sporter

    Hello, I'm new to the forums and looking for some clarification on my Model 1903 N.B.A. Sporter. My father originally purchased this rifle in...

    Started by Lt.AldoRaine‎, 04-09-2020 08:48 PM
    2 Pages •
    1 2
    1903, bolt, correct, model, nba, sporter
    • Replies: 16
    • Views: 879
    mark1
    04-22-2020, 04:24 PM Go to last post

  19. Anyone recognize this barrel stamp?

    I have this M1903 rifle. Serial number and Feb 1918 barrel date appear to be consistent. The rifle is in unusually clean condition for its age, the...

    Started by AustinWiseguy‎, 04-20-2020 10:58 AM
    barrel, recognize, stamp 12 Attachment(s)
    • Replies: 9
    • Views: 270
    John Beard
    04-20-2020, 11:47 PM Go to last post

  20. SC 1903A3 Rebuild Barrel Markings O.B.S.3

    I have searched a bit and found no like rebuild codes I found while cleaning my new acquisition SC 1903A serial #3622813. I place this receiver in...

    Started by Winch61‎, 03-08-2018 08:27 PM
    2 Pages •
    1 2
    barrel, markings, obs3, rebuild 2 Attachment(s)
    • Replies: 11
    • Views: 3,522
    Winch61
    04-15-2020, 12:17 PM Go to last post
+ Post New Thread
Page 1 of 175 1 2 3 11 51 101 ... LastLast

Forum Information and Options

Thread Display Options

Use this control to limit the display of threads to those newer than the specified time frame.

Allows you to choose the data by which the thread list will be sorted.

Order threads in...

Note: when sorting by date, 'descending order' will show the newest results first.

Icon Legend

Contains unread posts
Contains unread posts
Contains no unread posts
Contains no unread posts
More than 15 replies or 150 views
Hot thread with unread posts
More than 15 replies or 150 views
Hot thread with no unread posts
Closed Thread
Thread is closed
Thread Contains a Message Written By You
You have posted in this thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Forum Rules & Site User Agreement

All times are GMT -4. The time now is 10:26 AM.
Powered by vBulletin™
Copyright © 2020 vBulletin Solutions, Inc. All rights reserved.
Image resizer by SevenSkins

Profile Hover, vB Optimise, vBMail, Username Change, Thread / Post Bookmarking - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©2006 - 2020 by MILSURPS.COM - All Rights Reserved
Your IP Address: 3.235.172.213  |  OS: unknown  |  Browser: unknown unknown