AR bolt carrier question

[Rittmeister]

My first AR was a Rock River rifle. I've modded it significantly in the time I've owned it - changed out the fore-end for a lighter unit, and a few other things.

My question concerns the bolt carrier group and accuracy. The BCG is what is known as "semi-auto" and I'm interested in changing it out for a full-auto bolt group for longevity; I'm also interested in the nickle-boron finish I'm seeing, for ease of cleaning. I also just like to tinker, if I'm honest

Anyway, what I don't know is how the bolt is matched to the chamber, so to speak, from the factory. The rifle is quite accurate (better than I am) as it is and I don't want to affect that.

Can I swap out the whole BCG for a different unit, or will I potentially ruin the rifle's precision?

Thanks!

 

[Hurricane]

I can't speak for precision, although I can't imagine it making a huge difference. But as far as swapping, it shouldn't be an issue. Unless you got one for a different caliber on accident.

Edited: oh sorry. I see now that your main concern was precision. Sorry. It's early.

 

[MistWolf]

You can swap out the carrier without changing the original bolt.

However, unless the carrier you have lacks a shroud around the rear of the firing pin, there's no reason to change the carrier. Search the internet for photos showing the difference between a carrier with a shrouded firing pin and a carrier without.

Don't pay extra for a NiB coated carrier. The fancy coatings make no practical difference in function, reliability or durability. If you want to tinker, polish the guide rails and the sides of the gas key on your existing carrier for smoother operation. You can search the internet for instructions where to polish the carrier

 

[Sam1911]

There really won't be much of a way to tell, except to try it out.

Historically, changing bolts on a rifle would be very likely to cause headspace problems and even be dangerous. The amazing world of precision mass machining, and the "Lego" nature of ARs means that this is now rarely a problem with those guns. Still pays to re-check headspace if you're going to switch bolts, but problems are unusual.

I'd say that your Rock River is probably unlikely to have been built to produce the level of truly exceptional accuracy that would make it so you're able to see the differences in precision caused by a bolt swap, if there are any. It was probably capable of something around 1 moa with good ammo when you got it, and it will likely still be capable of that with a new bolt that fits properly.

If you've got a rifle that shoots groups down around 3/8" +/- at 100 yards...maybe I wouldn't change ANYTHING.




Personally, I'm of the "if it ain't broke don't fix it" camp and wouldn't go get another BCG just because of a theoretical "longevity" claim. But some guys really love that sort of thing.

If you run it hard in high-round-count classes or matches, you might want to keep a spare bolt and small parts (don't know about the carrier, too...maybe), but I wouldn't swap out your known good setup just because.

 

[Jeff White]

The BCG is what is known as "semi-auto" and I'm interested in changing it out for a full-auto bolt group for longevity;

I think any difference in longevity between a semi auto bolt carrier and a full auto bolt carrier is going to depend on who made the carriers, what steel they were made from and how the steel was treated.

I've run Colt ARs with semi-auto bolt carriers hard for years. I've got Colt full auto bolt carriers in a couple ARs that I built and I have seem no difference in longevity.

If you start with a bolt carrier of good quality and you don't need the extra mass of the full auto carrier to make your hybrid gas system home built rifle run it should make no difference if you have a full or semi bolt carrier.