Need help on M79 Barrel Proof Marks

[Rekraps]

Gentlemen, after hours and hours of "Google" searching, reviewing TM manuals etc. I can find no references at all to manufacturer proof marks on M79 barrels. Mine has a Capital letter "P" with the letters TAP inside the P, and the number "2" under the curve of the "P".  Anyone have solid info on what this means?

[Rekraps]

Hard to believe nobody out there has a clue as to what this is.... ?

[Rekraps]

Ugh.  Come on! 

[Frank Iannamico]

On 12/8/2022 at 7:17 PM, Rekraps said:

Ugh.  Come on! 

PM sent

[Rekraps]

Okay fellow forum members. M79 barrels with marking such as the one pictured above, have been "proofed" that is to say had overcharged rounds fired through it to test the barrel strength. In the case of mine, an overcharged round rated "2" was fired and the barrel came through just fine. My source for this information indicated that earlier barrels listed the "charge rating" using a number and that he/she has seen such ratings from 1 to 6. Later barrels, all government issued/used just sported a "P" with no numerical rating.

No clue as to the meaning of "TAP". Commercial barrels had/have no proof marks like this.

So, my gun is a C&R Kanaar receiver with what appears to be an original era/matching barrel. That's the take-a-way.

[inertord]

All USGI M79 Launches and USGI 79 Replacement Barrels were proofed with a USGI XM385 Series 40x46mm Proof Round. There were no charge ratings or variations in the proof cartridge or proofing requirements.

[Rekraps]

Which would then brings us around and back to my original post and question.

Does anyone know what the proof mark means? Does anyone else have the "P" stamp? Perhaps some were pulled out and extra pressure tested for quality control? Those stamps had to come from somewhere. I think it does have something to do with quality control or testing as my source implied.

[Rekraps]

So, after much thought I'm going to run with this explanation:

The P "Tap" stamps on the Vietnam Era M79 Military barrels (which seems to be the ones with the stamp) indicate a quality check of some type, separate from test firing as described by Inertord above. The nature of the quality check could have been dimensional, finish or otherwise, however the best source I've spoken with so far believes it to be a strength test stamp, where an "over-pressure" load was imparted on the barrel to validate quality. The actual marking could mean "Pressure Tested", "Passed" or just be code assigned to that process. The "TAP" and the number, in this case "2" could likewise mean anything. My source says he/she has in the past seen Military barrels of the type pictured with identical "P TAP" marks, but with different numbers ranging from 1 to 6. So, the numbers might indicate mfg location, or inspector, or perhaps pressure load rating. Who knows.

 

I'm just glad the stamp is not "666". Ha.

 

 

[Rekraps]

Another source has confirmed that the "P" proof marks mean... "The P proof mark means that the USGI barrel was proof tested for strength using the XM385 40x46 proof round. 

Mystery solved. USGI barrels are the only ones to have the "P" proof mark.

[Rekraps]

And being the "old" man that I am, my eyes sometimes do me a bit off. Just today I was working on the M79 and sure as heck, I noticed another "P" proof mark on the barrel. This on is on the top, by the raised ribs that hold the barrel locking lug. 

So my USGI barrel has two "P" proof marks, the "P TAP 2" mark on the bottom and the "P" on the top. 

[Rekraps]

On 12/27/2022 at 3:52 PM, Rekraps said:

And being the "old" man that I am, my eyes sometimes do me a bit off. Just today I was working on the M79 and sure as heck, I noticed another "P" proof mark on the barrel. This on is on the top, by the raised ribs that hold the barrel locking lug. 

So my USGI barrel has two "P" proof marks, the "P TAP 2" mark on the bottom and the "P" on the top. 

I found yet another. See pic. So my unit has two USGI "P" proof marks on the barrel, one under and one on top (see photo earlier in this thread & pic attached) and one on the receiver top just in front of the locking lever.