Walking AR trigger pins - Tilted Forum Project Discussion Community

Walt · 06-11-2010, 03:55 PM

I've been having a problem with my trigger and hammer pins walking on both of my AR's recently. I've never had the problem before I started firing 77 gr. SMK's loaded a nun's cunt hair below the maximum rec'd charge. In fact, I went through roughly 600 rounds of HOT 60 gr Noslers with no problems. Didn't get more than 6 rounds out with the 77 gr loads before the pins walked out.

1) Anyone ever had this problem before?
2) How did you go about sorting it out? I'm thinking of investing in the JP anti-walk pins, though don't know if the walking pins is indicative of a bigger problem.

Plan9 · 06-11-2010, 08:59 PM

Answer: Stop shooting .22-250 out of your AR.

And: I see baggy holes! Heh. No clue. I'm sure a SME at Some Other Board has the answer. The hot ammo is obviously a part of it but probably not the whole story.

I was a unit armorer for a minute and I never saw pins walk out on a gov't gun that hadn't been fucked with extensively by the operator. Most pin problems stem from people taking the steel FCG outta the old aluminum gun a zillion times for some lame promotion board inspection. Solution? Plan A was to use superglue, Plan B was to deadline. Plan C was me trying to come up with an effective way of telling my 1SG boss that total disassembly plus a bath in Simple Green was really not the best way to clean a M4.

And why the hell are you hotrodding ammo outta a M4? You're livin' on the edge!

The_Dunedan · 06-12-2010, 06:41 AM

Dude. You said the other day you were pushing those 77s at close to 3K. That takes some pretty serious juice if you're actually hitting those velocities (or even anywhere close) out of a carbine-length bbl, and those walking pins would seem to be a result of this. Consider that the "Original Recepie" for 5.56mm was 55gr at 3,000fps from a 20" bbl. You're running 77gr out of a much shorter tube and approaching the same velocity. Consider the loads that's putting on your rifle, man. Hot 60gr and hot 77gr is two different animals: it's all in the percentages.

Walt · 06-12-2010, 08:25 AM

So....you're telling me that I should weld the pins in place?

I just rechecked the Sierra manual and my numbers were way off. I was getting (an advertised) 2750 fps with 24.0 grs of TAC from my SPR with the 77 gr SMKs. From the 14.5" barrel, I figure the velocity should be somewhere around 2500 fps with the same load (using Gale McMillian's math). Still too much?

Hektore · 06-12-2010, 09:16 AM

Quote:

Originally Posted by Walt

So....you're telling me that I should weld the pins in place?

I just rechecked the Sierra manual and my numbers were way off. I was getting (an advertised) 2750 fps with 24.0 grs of TAC from my SPR with the 77 gr SMKs. From the 14.5" barrel, I figure the velocity should be somewhere around 2500 fps with the same load (using Gale McMillian's math). Still too much?

I think he may have been joking, he also may have meant literally superglue (or the smallest manageable dot of JB weld)...but if he wasn't...

Before you go welding them, on drilling equipment we take a punch tool and 'mushroom' the heads on pins, makes them an SOB to get out, but it's better than welding something that may have to come apart again at some point in the future.

Walt · 06-12-2010, 09:32 AM

The welding bit was a lame attempt at humor. Instead of mushrooming the heads out, I'm just going to go with the anti-walk pins. Much easier to get in and out.

Plan9 · 06-12-2010, 09:32 AM

A little pinhead of cyanoacrylate is perfect for keeping pins where they need to be. I recommend the gel, myself.

...

Damnit, you posted the same time I did. And fine, go for the silly anti-walk pins.

It doesn't mean you can throw .470 Nitro Express rounds out of your friggin' AR.

...ya psycho.

Walt · 06-23-2010, 07:34 AM

Eh. I finally got around to mic'ing the pin holes. They are all about 0.001" bigger than they should be. This is probably due to me using the slightly oversized JP pins to begin with and then moving back to the conventional ones.

Went back to the JP pins; problem solved. Now I can get back to shooting loads that bring a bit more ass.

Plan9 · 06-23-2010, 08:02 AM

Hah, I knew it. Gnarly. Keep us informed. If the JP pins start walking out... you know you've really outdone yourself.

06-11-2010, 08:59 PM	#2 (permalink)
Plan9 I Confess a Shiver	Answer: Stop shooting .22-250 out of your AR. And: *I see baggy holes!* Heh. No clue. I'm sure a SME at Some Other Board has the answer. The hot ammo is obviously a part of it but probably not the whole story. I was a unit armorer for a minute and I never saw pins walk out on a gov't gun that hadn't been fucked with extensively by the operator. Most pin problems stem from people taking the steel FCG outta the old aluminum gun a zillion times for some lame promotion board inspection. Solution? Plan A was to use superglue, Plan B was to deadline. Plan C was me trying to come up with an effective way of telling my 1SG boss that total disassembly plus a bath in Simple Green was really not the best way to clean a M4. And why the hell are you hotrodding ammo outta a M4? You're livin' on the edge! __________________ *Whatever you can carry.* "You should not drink... and bake." Last edited by Plan9; 06-11-2010 at 09:09 PM..

06-12-2010, 08:25 AM	#4 (permalink)
Walt I'm calmer than you are, dude Location: North Carolina	So....you're telling me that I should weld the pins in place? I just rechecked the Sierra manual and my numbers were way off. I was getting (an advertised) 2750 fps with 24.0 grs of TAC from my SPR with the 77 gr SMKs. From the 14.5" barrel, I figure the velocity should be somewhere around 2500 fps with the same load (using Gale McMillian's math). Still too much? __________________ Calmer than you are... Last edited by Walt; 06-12-2010 at 08:27 AM..

06-12-2010, 09:32 AM	#6 (permalink)
Walt I'm calmer than you are, dude Location: North Carolina	The welding bit was a lame attempt at humor. Instead of mushrooming the heads out, I'm just going to go with the anti-walk pins. Much easier to get in and out. __________________ Calmer than you are...

06-12-2010, 09:32 AM	#7 (permalink)
Plan9 I Confess a Shiver	A little pinhead of cyanoacrylate is perfect for keeping pins where they need to be. I recommend the gel, myself. ... Damnit, you posted the same time I did. And fine, go for the silly anti-walk pins. It doesn't mean you can throw .470 Nitro Express rounds out of your friggin' AR. ...ya psycho. __________________ *Whatever you can carry.* "You should not drink... and bake." Last edited by Plan9; 06-12-2010 at 09:36 AM..

06-23-2010, 07:34 AM	#8 (permalink)
Walt I'm calmer than you are, dude Location: North Carolina	Eh. I finally got around to mic'ing the pin holes. They are all about 0.001" bigger than they should be. This is probably due to me using the slightly oversized JP pins to begin with and then moving back to the conventional ones. Went back to the JP pins; problem solved. Now I can get back to shooting loads that bring a bit more ass. __________________ Calmer than you are...

06-12-2010, 06:41 AM	#3 (permalink)
The_Dunedan Junkie	Dude. You said the other day you were pushing those 77s at close to 3K. That takes some pretty serious juice if you're actually hitting those velocities (or even anywhere close) out of a carbine-length bbl, and those walking pins would seem to be a result of this. Consider that the "Original Recepie" for 5.56mm was 55gr at 3,000fps from a 20" bbl. You're running 77gr out of a much shorter tube and approaching the same velocity. Consider the loads that's putting on your rifle, man. Hot 60gr and hot 77gr is two different animals: it's all in the percentages.

06-23-2010, 08:02 AM	#9 (permalink)
Plan9 I Confess a Shiver	Hah, I knew it. Gnarly. Keep us informed. If the JP pins start walking out... you know you've really outdone yourself. __________________ *Whatever you can carry.* "You should not drink... and bake."