DPMS and AR10 bolt differences?

[TryLikeHell]

A friend brought out a built .308 gas rifle and his BCG gets stuck shut. His lugs on the bolt are actually a trapezoid shape instead of symmetrically square. His friends bolt is symmetrically square as well and the lug widths are narrower on the square ones. I've read many manufacturers are listing DPMS LR308s as AR10 (armalite) when they actually aren't. My to the point question is, are the symmetrically square thinner lug bolts AR10 or DPMS?
Then I see AR308. Confusing as hell.

 

[msgriff]

The biggest difference between an ArmaLite and DPMS pattern bolt is the depth of the bolt face (typ. 0.004"-0.005" difference). The trapezoid shaped lugs sounds like a Sharps Relia-Bolt, which is DPMS pattern, and their carriers are marked "SRC".

 

[BCP]

A friend brought out a built .308 gas rifle and his BCG gets stuck shut.

Stuck with a cartridge? Could be headspace.

 

[TryLikeHell]

This is sticking with no cartridge.

 

[Charger442]

This is sticking with no cartridge.

how far does the gas tube protrude into the upper?

is the cam bolt able to rotate easily with the BCG out?

 

[TryLikeHell]

how far does the gas tube protrude into the upper?

is the cam bolt able to rotate easily with the BCG out?

I'll have to check his gas tube.
The bolt moves in and out freely with the carrier out. Here's a crude drawing of the visual bolt difference. Wish I had taken pictures early yesterday at the range. I'll try to get exact measurements today. The width is definitely wider with his on the left.

 

[BCP]

If it's something he built it's hard to say without knowing his parts list.

 

[TryLikeHell]

If it's something he built it's hard to say without knowing his parts list.

Definitely understand, Im new to the 308 gas guns so I was guessing it was one bolt or another, but often there's many. He might have to physically take it to a gunshop for accurate info.
I thank everyone for your replies.

 

[x248716x]

A friend brought out a built .308 gas rifle and his BCG gets stuck shut. His lugs on the bolt are actually a trapezoid shape instead of symmetrically square. His friends bolt is symmetrically square as well and the lug widths are narrower on the square ones. I've read many manufacturers are listing DPMS LR308s as AR10 (armalite) when they actually aren't. My to the point question is, are the symmetrically square thinner lug bolts AR10 or DPMS?
Then I see AR308. Confusing as hell.

could be a couple of things. first and foremost, is his barrel extension lined up correctly? a quick check for that is the barrel extension feed ramps blend nicely with the upper receiver feed ramps.

i'm hinting at the clocking of the bolt lugs is not dis-engaging the barrel extension lugs correctly. could also be due to an out-of-spec, poor clocking, poor machining of the barrel extension itself. or cam-pin slot off-axis.

also, if the bolt carrier is nickel-boron coated, could be the application of the coating inside the carrier bore is thicker at the bottom, causing the bolt to get stuck, wedged in the carrier bore, binding.

in addition to the previous listed gas key, gas tube. could be any number of things. especially if first-timer-AR-308 assembled.

 

[longshot2000]

Definitely understand, Im new to the 308 gas guns so I was guessing it was one bolt or another, but often there's many. He might have to physically take it to a gunshop for accurate info.
I thank everyone for your replies.

Sorry to make you the poster child, but if you are not an armorer, or technical user with lots of experience with different .308 gas guns, building a mix and match is very hard to do. I am not even sure what some brands sell BCGs, as most BCGs are specific to a receiver and/or barrel receiver.

There are, what I would call families, of rifles and parts. They fall into the .308AR with DPMS standards, the AR10 with traditional standards, and the SR25. The Armalite AR10 is not very reliable, as they have A and B parts, so there are few original AR10 designed parts. The DPMS standard is 80% okay, but then you get the manufacturer who makes a special geometry with their bolt carrier. SR25 is pretty reliable, but there are only three brands that can be trusted: LMT, LaRue and Knights. Most of each of those brands have interchangeable parts, with the exception of the barrels.