2 uppers using the same lower

[lmmmmm]

Do I need each upper to have their own BCG???

[GONIF]

It would be better in the long run .:D

[RetreatHell]

Bolt carrier? No.

Bolt? Yes, definitely.

I'm just rehashing info here that was given to me by USMC03 when I asked him a similar question 6 or so months ago.

If I were you I'd go ahead and just buy a complete F/A bolt carrier group from BCM, as changing out the bolt each time would just be a pain in the ass. That way all you have to do when swapping out uppers on your lower is pull pins, swap upper, push pins back in.

-Paul

[SWATcop556]

Having a BCG with every upper is the way to go. Then throw down some change and grab a spare bolt to keep on hand.

I just keep a spare BCG in the range bag.

[m4fun]

Just to reemphasize and reinforce what has been said, have a dedicated BCG for each separate upper.

Lets hope no headspace issues, etc but ARs are simple enough that once you get it working with good quality parts, only a catastrophic failure should make you need to change out.

[bkb0000]

i'm gonna have to drop a big disagree on the bolt vs BCG statement... it's not just the interface between bolt and barrel extension that "mates." the cam-pin/bolt relationship is also really important- cam-pin play is the main reason for bolt breakage at the pin hole.

the carrier and receiver also mate, as do the cam pin and receiver.. how much interaction there is varies, and how important the mating process is with these parts i don't know- but when you can have a great BCG for $130, why push your luck?

dont be cheap- get a dedicated BCG for every upper. it'll take less effort to place the order than engaging in this thread

[RetreatHell]

bkb,

Out of curiosity, how do you know when to replace the cam pin?

Do you just use it until it breaks or what?

-Paul


i'm gonna have to drop a big disagree on the bolt vs BCG statement... it's not just the interface between bolt and barrel extension that "mates." the cam-pin/bolt relationship is also really important- cam-pin play is the main reason for bolt breakage at the pin hole.

the carrier and receiver also mate, as do the cam pin and receiver.. how much interaction there is varies, and how important the mating process is with these parts i don't know- but when you can have a great BCG for $130, why push your luck?

dont be cheap- get a dedicated BCG for every upper. it'll take less effort to place the order than engaging in this thread

[bkb0000]

bkb,

Out of curiosity, how do you know when to replace the cam pin?

Do you just use it until it breaks or what?

-Paul

definately not not till it breaks- the bolt will break before the cam pin does, but if you replace the pin before its so worn that it starts to bend the bolt, you can, in theory, extend the life of the bolt. keeping in mind that parts breakage blame is usually a compilation of varying shit, rather than just one thing.

there's no great consensus on when to replace anything.. two guys from the same school will tell you two different round counts varying by thousands. i think most guys around here will just got with the "if it looks ****ed up, replace it. so check regularily" philosophy.

the more play between the pin and the bolt, the more slamming and torquing agains the cam hole. there was a thread some time ago where bill alexander talked about watching for bright spots at the top and bottom of the hole, indicating there was enough play to torque on the hole... personally, i'll replace at about half the bolt's expected life- 2,500-3,000 rounds, regardless of how it looks. sometimes sooner, if it's a gun that eats cam pins faster, for whatever reason.

recently, there was a thread that touched on indexing cam pins.. i don't recall it getting very in-depth on the topic, but it got me to thinking about that.. if you index the pin, so it mates consistently on both sides, then flip it around at a given round count, you can probably make the pin/bolt relationship last longer by tightening up the play between bolt and pin... just a theory, and i've done nothing to experiment. its literally just as easy to replace.

[Fringe]

This is interesting about the cam pin. It never occurred to me that the thing would not last as long as the bolt. I for sure thought it would last longer, or better than, the 2500 to 3000 mark. Should I be concerned about marks on the pin where it is leaving "smile" type marks from hitting each end of the BCG?

[6933]

If I remember correctly, IG recommends dedicated BCG's with each upper for a variety of reasons. Maybe he can chime in and give us his thoughts.

Paul- Good advice on getting set up for the EAG Carbine course. All recommendations worked well.

[blade_68]

My thought, I've got no dog in this fight but I'd say go with BCG for each upper and maybe think about a spare BCG or bolt assm. I have 2 spare BCG and at least 2 bolts and spare parts cam pins, LPGs. when I have a parts failure hammer, sear. ect.. change out the part(s) drive on bolts wear in and take a set?? I've changed out buffer detent due to showing wear.

[variablebinary]

Makes life easier if the uppers are complete

[Argus]

I can't see a reason not to have both uppers complete, especially now that the BCM BCG's are readily available.

Of course, I'm not sure how you've resisted the urge to buy/build another lower to have two complete rifles. Complete AR's have a tendency to grow out of spare parts.