Question for the AR gurus

flying_scotsman

flying_scotsman

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I have a never-been-used Bushmaster AR here, and having just disassembled the lower receiver for the first time, have noticed that while the trigger and hammer pins are .154", the hammer itself is sized for a .170" pin...

My question is will the mismatch create problems once the gun gets out to the range on a regular basis? I would hazard a guess that it can't be good in the long run.
 
Just wondering why you disassembled the lower receiver. Thats not part of regular maintenance. Thats something thats not needed right off the bat considering your rifle is new.
 
That can't be good. My memory must be really bad, because I just had mine apart last night to install a RRA 2 stage trigger and I can't picture all the details, but by having play in the hammer, wouldn't that create inconsistent engagement of the machined surfaces that form the sear and disconnect? Can't wait to hear from the experts on this one.
 
Medic:

You're right, I don't normally pull my ARs apart like that. I took it apart to take pictures of the relationship between the hammer, trigger and disconnector for another member. While I had it apart, I noticed the oversized hammer pin hole.

Grizzlypeg:

That's the jist of what I was thinking too.

Demon:

The rifle has been a safe queen for several years. I'm not worried about voiding any warranty. Frankly I'm glad to have found the potential problem before it had the chance to manifest itself in a malfunction that may have been more expensive to repair beyond the cost of a replacement hammer.
 
Okey Dokey...

Hammer pin: just under .154"
IMG_4376q.jpg


Hammer pin hole: just under.172"
IMG_4379q.jpg


I see the light!
IMG_4380q.jpg
 
flying_scotsman said:
Demon:

The rifle has been a safe queen for several years. I'm not worried about voiding any warranty. Frankly I'm glad to have found the potential problem before it had the chance to manifest itself in a malfunction that may have been more expensive to repair beyond the cost of a replacement hammer.
Click to expand...

Was just joking around. Like how you always find a tag on (electronic) devices or machines reminding you that if you open the casing or remove a part the warranty becomes void. :rolleyes:

Guess I didn't give an obvious enough indication of the sarcastic humor... my bad.

Anyway, out of seriousness, it is good that you found the deficiency of your firearm prior to firing. Some would call that luck (or good intuition). Though it sux you got a bum rifle. Suppose it depends on how you see the situation.
 
Looks like a good excuse to upgrade to a match-type trigger group... The RRA 2 stage is fairly low cost and will drop in...with the proper fitment...
 
What you have there is a Colt hammer. They made them, for awhile, with larger pin holes so we evil gun owners couldn't put full auto parts in them. I can't figure out why your non colt rifle has one but perhaps you rifle started out as a parts gun?

Scott
 
flying_scotsman said:
I have a never-been-used Bushmaster AR here, and having just disassembled the lower receiver for the first time, have noticed that while the trigger and hammer pins are .154", the hammer itself is sized for a .170" pin...

My question is will the mismatch create problems once the gun gets out to the range on a regular basis? I would hazard a guess that it can't be good in the long run.
Click to expand...

You have no choice but to change the hammer.

Just wondering, did you buy it brand new from a dealer or from somebody else? Looks to me that it is not an original hammer.

:cheers: Kazimier
 
m39a2/Armafix:
The rifle was purchased from a dealer. It is a used 11.5” upper on a new lower. I don’t know if the LPK was assembled into the lower by Bushmaster or the dealer.

KevinB:
That was my initial reaction as well; I just wanted to filter the situation past those here who have a greater depth of knowledge than I do. The hammer in question has been removed to the parts bin, in the event it’s ever needed for my 6920. I’ve contacted the vendor for his reaction.
 
M39A2 has it right. From the Midway \Bushmaster site:http://www.midwayusa.com/viewProduct/?productNumber=482695

AR-15 Hammer and Trigger Pin Dimensions:

Some Colt® AR type rifles have been manufactured with hammer and trigger pins and holes which are approximately .176" in diameter. These are referred to as "large pin" Colts. This was done to eliminate the chances of someone putting M16 fire control parts into an AR receiver. This is not found in all Colt models, just some.
All other AR type rifle manufacturers have stayed with the .156" diameter hammer and trigger pins and holes, or "small pin" which is the same spec used in all military M16 rifles.
Measure your pins or the holes in your lower receiver to determine if you have a "small" or "large" hole Colt® AR
Click to expand...
 
Just out of curiosity, what could have happened down the road as the round count rose, if I hadn't noticed the problem? Would I have been looking at a ruined receiver, or worse?
 
flying_scotsman said:
Just out of curiosity, what could have happened down the road as the round count rose, if I hadn't noticed the problem? Would I have been looking at a ruined receiver, or worse?
Click to expand...

As you know the AR15 action is not gentle at all, it is rather violent. Due to this a sloppy hammer like yours will not engage the sear and disconnector consistantly as it should, but will do it at random angles and amounts of sear engagement. As the result the trigger system will wear in unpredictable way and pretty soon will become negative and the gun will be very unsafe. It may be unsafe already. Don't shoot it, change the hammer asap. If you don't do it and keep shooting, your receiver will not get ruined but you know what an unsafe gun can do, don't you?

:cheers: Kazimier
 
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