I'm having two Chinese M14 bolts tested. Hardness results came in for the second Chinese bolt. Here's an abridged version of my preliminary report to date. Crystalline structure examinations for the two bolts are still pending. The fnal report will be made available later on in .pdf format. It will include photos of Chinese M14 Bolt # 1. Note that these are bolts exported to the United States in the early 1990s.
Chinese M14 Bolt # 1
###X ######XX (Schaumburg, IL) purchased a Norinco M14 Sporter rifle in 1991. He shot 15,000 rounds through it by March 2010. He decided at that point to have a M14 gunsmith install a USGI bolt in his Norinco M14 Sporter. He sent the original bolt to me for research purposes. I received it on March 20, 2010. ###X wrote a note stating that he bought this unmarked Norinco new in 1991 and now had 15,000 rounds down the barrel. As an unmarked Norinco receiver, it was likely imported by Century Arms International (then St. Albans, VT).
The Chinese bolt is electropenciled 77121 on the bottom center rear and 37406 on the bottom left rear. I was able to install and remove USGI bolt guts (firing pin, ejector and spring, and extractor assembly) with no trouble. The USGI extractor stem did not protrude below the bottom plane. The Norinco bolt fit inside the receiver of Poly Technologies M-14/S serial number 00074 without issue. It easily passed the tilt test. However, it would not close on a 1.630 “ head space gage. The bolt roller was undamaged and properly lubricated with grease. It rotated freely by hand. The bolt electropenciled 77121 on the bottom almost closed on a 1.6405 “ headspace gauge in the Norinco M14 Sporter rifle.
I took photographs of the bolt before hardness testing. The Norinco bolt was photographed alongside an unfired Poly Technologies bolt and a used USGI Winchester bolt. Compared to the unfired Poly Technologies bolt, the Norinco bolt did have minor peening and wear. These areas appeared to be peened: 1) rear end outer edge at 9:00 o’clock 2) front edge of the bottom side of the left locking lug and 3) rear inboard corner of the right locking lug. These areas appeared to have loss of metal due to wear: 1) bottom and outboard vertical surfaces of the safety (left rear) lug and 2) rear edge of the top side of the left locking lug. About one-third of the finish was worn off from normal use. Visually, there was no pitting on the bolt face or enlargement of the firing pin hole.
Chinese M14 bolts are made of equivalent AISI 4135 alloy steel. The bolt was tested for surface and core hardness at a metal heat treating company that has a fully equipped metals testing laboratory on site. The results obtained on 04/23/10 were as follows:
1) rear end vertical surface – 49.9/45.0/47.8/47.0/47.5 Average 47.44
2) top surface – 35.0/23.5/37.9/37.7/23.6 Average 31.54
3) left side lug core – 35.6/40.4/37.3/38.8/37.8 Average 37.98
4) right side lug core – 40.4/38.1/38.4/41.7/36.8 Average 39.08
Here's a few of the photos I took before the bolt was cut apart for testing:
http://www.imageseek.com/m1a/gallery/al bums/civilian/Norc15K_front.sized.jpg
http://www.imageseek.com/m1a/gallery/albums/civilian/WinleftNorc15KctrPolyunfiredright_c.sized.jpg
http://www.imageseek.com/m1a/gallery/albums/civilian/PolyunfiredleftNorc15KctrWinright_b.sized.jpg
Chinese M14 Bolt # 2
###XX ###### (Las Vegas, NV) purchased Federal Ordnance M14SA serial number 60164 in the early 1990s. It was built into a complete rifle at Federal Ordnance, Inc. (South El Monte, CA) using Chinese parts and a U. S. made receiver and stock. He had put about 500 rounds through the rifle by 2010. On 04/18/10, I traded ###XX a M14 related item for the Chinese bolt in his Federal Ordnance M14SA rifle.
The bolt was tested for surface and core hardness at the same company as the first Chinese bolt. Hardness was tested in the same areas as Chinese M14 Bolt # 1 above. The results obtained were as follows:
1) rear end vertical surface – 34.3/35.1/33.80/34.6/33.0 Average 34.16
2) top surface – 34.3/32.7/34.4/34.3/33.7 Average 33.88
3) left side lug core – 31.1/31.8/32.1/31.1/30.5 Average 31.32
4) right side lug core – 30.0/30.2/29.4/30.9/29.6 Average 30.02
Conclusion
The Chinese M14 Bolt # 1 overall average hardness was 39.01 HRC. Its average hardness varied from 31.54 at the top center to 47.44 at the rear end vertical surface. Even though the contact points were substantially harder than the middle portion of the bolt, there was still peening of contact points with a moderate amount of firing cycles.
The Chinese M14 Bolt # 2 overall average hardness measured 32.35 HRC. The middle portion of both bolts was comparable. Hardness was much more consistent throughout than Chinese M14 Bolt # 1. However, the locking lug and rear end contact surfaces were substantially softer. This bolt had 500 firing cycles with no evidence of peening.
Based on the information above, I recommend checking headspace on M14 rifles assembled with Chinese M14 bolts every 500 rounds. The Chinese M14 bolt should be examined for signs of peening each time the rifle is field stripped. Results of microstructure examinations for these two bolts will follow later on.
Chinese M14 Bolt # 1
###X ######XX (Schaumburg, IL) purchased a Norinco M14 Sporter rifle in 1991. He shot 15,000 rounds through it by March 2010. He decided at that point to have a M14 gunsmith install a USGI bolt in his Norinco M14 Sporter. He sent the original bolt to me for research purposes. I received it on March 20, 2010. ###X wrote a note stating that he bought this unmarked Norinco new in 1991 and now had 15,000 rounds down the barrel. As an unmarked Norinco receiver, it was likely imported by Century Arms International (then St. Albans, VT).
The Chinese bolt is electropenciled 77121 on the bottom center rear and 37406 on the bottom left rear. I was able to install and remove USGI bolt guts (firing pin, ejector and spring, and extractor assembly) with no trouble. The USGI extractor stem did not protrude below the bottom plane. The Norinco bolt fit inside the receiver of Poly Technologies M-14/S serial number 00074 without issue. It easily passed the tilt test. However, it would not close on a 1.630 “ head space gage. The bolt roller was undamaged and properly lubricated with grease. It rotated freely by hand. The bolt electropenciled 77121 on the bottom almost closed on a 1.6405 “ headspace gauge in the Norinco M14 Sporter rifle.
I took photographs of the bolt before hardness testing. The Norinco bolt was photographed alongside an unfired Poly Technologies bolt and a used USGI Winchester bolt. Compared to the unfired Poly Technologies bolt, the Norinco bolt did have minor peening and wear. These areas appeared to be peened: 1) rear end outer edge at 9:00 o’clock 2) front edge of the bottom side of the left locking lug and 3) rear inboard corner of the right locking lug. These areas appeared to have loss of metal due to wear: 1) bottom and outboard vertical surfaces of the safety (left rear) lug and 2) rear edge of the top side of the left locking lug. About one-third of the finish was worn off from normal use. Visually, there was no pitting on the bolt face or enlargement of the firing pin hole.
Chinese M14 bolts are made of equivalent AISI 4135 alloy steel. The bolt was tested for surface and core hardness at a metal heat treating company that has a fully equipped metals testing laboratory on site. The results obtained on 04/23/10 were as follows:
1) rear end vertical surface – 49.9/45.0/47.8/47.0/47.5 Average 47.44
2) top surface – 35.0/23.5/37.9/37.7/23.6 Average 31.54
3) left side lug core – 35.6/40.4/37.3/38.8/37.8 Average 37.98
4) right side lug core – 40.4/38.1/38.4/41.7/36.8 Average 39.08
Here's a few of the photos I took before the bolt was cut apart for testing:
http://www.imageseek.com/m1a/gallery/al bums/civilian/Norc15K_front.sized.jpg
http://www.imageseek.com/m1a/gallery/albums/civilian/WinleftNorc15KctrPolyunfiredright_c.sized.jpg
http://www.imageseek.com/m1a/gallery/albums/civilian/PolyunfiredleftNorc15KctrWinright_b.sized.jpg
Chinese M14 Bolt # 2
###XX ###### (Las Vegas, NV) purchased Federal Ordnance M14SA serial number 60164 in the early 1990s. It was built into a complete rifle at Federal Ordnance, Inc. (South El Monte, CA) using Chinese parts and a U. S. made receiver and stock. He had put about 500 rounds through the rifle by 2010. On 04/18/10, I traded ###XX a M14 related item for the Chinese bolt in his Federal Ordnance M14SA rifle.
The bolt was tested for surface and core hardness at the same company as the first Chinese bolt. Hardness was tested in the same areas as Chinese M14 Bolt # 1 above. The results obtained were as follows:
1) rear end vertical surface – 34.3/35.1/33.80/34.6/33.0 Average 34.16
2) top surface – 34.3/32.7/34.4/34.3/33.7 Average 33.88
3) left side lug core – 31.1/31.8/32.1/31.1/30.5 Average 31.32
4) right side lug core – 30.0/30.2/29.4/30.9/29.6 Average 30.02
Conclusion
The Chinese M14 Bolt # 1 overall average hardness was 39.01 HRC. Its average hardness varied from 31.54 at the top center to 47.44 at the rear end vertical surface. Even though the contact points were substantially harder than the middle portion of the bolt, there was still peening of contact points with a moderate amount of firing cycles.
The Chinese M14 Bolt # 2 overall average hardness measured 32.35 HRC. The middle portion of both bolts was comparable. Hardness was much more consistent throughout than Chinese M14 Bolt # 1. However, the locking lug and rear end contact surfaces were substantially softer. This bolt had 500 firing cycles with no evidence of peening.
Based on the information above, I recommend checking headspace on M14 rifles assembled with Chinese M14 bolts every 500 rounds. The Chinese M14 bolt should be examined for signs of peening each time the rifle is field stripped. Results of microstructure examinations for these two bolts will follow later on.
