Need advice - ar 308 buffer tube

[NATEWA]

I picked up an ar 308 build the other day. I think I have the issues figured out but want to make sure. Seller informed me the bcg hit the lower receiver where the buffer tube screws in (see pic).

I started doing some research and found out that should not be physically possible. I ordered a new carbine buffer, tube and spring from fulton armory. I also read about the "quarter method." That is simply a quarter or quarters being dropped in the buffer tube to restrict how far the buffer and bcg go back.

If I install the new parts and use the quarter method, I'm thinking it's all good? I also plan to install an adjustable gas block. I'm not sure what happened to the old buffer tube and threads (see pic). The old buffer tube looked as if it slanted up from the lower.

Thanks

[NATEWA]

Pic of buffer tube threads

[kcstott]

most likely the previous own installed AR15 parts in an AR308 lower.

with the proper parts installed you should not need to quarter method anything. the weapon should work.

Verify all parts are correct then try again.

[NATEWA]

most likely the previous own installed AR15 parts in an AR308 lower.

with the proper parts installed you should not need to quarter method anything. the weapon should work.

Verify all parts are correct then try again.

Thanks - I purchased a carbine 308 buffer, spring (top) and mil spec buffer tube (to use with b5 adjustable stock).

http://www.fulton-armory.com/FAR-308-Lower-Parts.aspx

Will update this weekend when parts are installed.

[NATEWA]

Installed new parts and placed one quarter back there just to make sure it doesn't hit. I'll test fire soon and install an adjustable gas block to tame the recoil. I know the spring he had in there was a 308 spring and fairly certain the buffer is for a 308. I think the buffer tube was the issue - maybe it wasn't installed correctly or bottoming out with too much force, causing the alignment and threads to be off?

[kcstott]

1 quarters worth of preload is not going to keep the bolt from bottoming out if you don't have the correct parts.

[NATEWA]

1 quarters worth of preload is not going to keep the bolt from bottoming out if you don't have the correct parts.

Ok - I'll take it out

I just don't want it hitting. I have the correct parts. All new from Fulton Armory. Maybe I'll take a pic of the gap between the bcg and threads of the lower receiver to make sure it's good.

[NATEWA]

Another pic. It's close! My other ar 308 build with a rifle buffer tube and buffer has more of a gap.

[kcstott]

that looks about right. very similar to my Mk11

[sleepur606]

The threads on the buffer tube look like it was cross threaded when installed. In all my builds, I've never seen anodizing or any coating removed from the threads on the receiver or the buffer tube.

Even if the buffer tube were cross threaded, I can't see it causing the damage to the lower receiver. Maybe someone with more knowledge will have better insight.

[kcstott]

The threads on the buffer tube look like it was cross threaded when installed. In all my builds, I've never seen anodizing or any coating removed from the threads on the receiver or the buffer tube.

Even if the buffer tube were cross threaded, I can't see it causing the damage to the lower receiver. Maybe someone with more knowledge will have better insight.

Thats because the tube didn't cause the damage to the lower. The bolt carrier did by inpacting the lower. More then likely it was out of spec parts or incorrect parts that caused this. Bad or incorrect spring, or incorrect buffer.

[ar15barrels]

Another pic. It's close! My other ar 308 build with a rifle buffer tube and buffer has more of a gap.

The rubber snubber on the tail of the buffer can compress 1/8" or more so you want at least 1/8" of gap behind the bolt carrier rails so they won't strike the threads.
Higher quality 308 lowers have those threads machined out to make more room for the carrier so it won't strike the buffer tower threads.

[NATEWA]

Thanks will measure to see if there is an 1/8" gap.

If no, a quarter or two? Maybe this?

http://www.opticsplanet.com/anderson-manufacturing-308-buffer-tube-spacer-disc.html

Took it to the range today and ran 15 rounds though it without any issues.

[kcstott]

Thanks will measure to see if there is an 1/8" gap.

If no, a quarter or two? Maybe this?

http://www.opticsplanet.com/anderson-manufacturing-308-buffer-tube-spacer-disc.html

Took it to the range today and ran 15 rounds though it without any issues.

Will you quit trying to fix something that ain't broke... put mil spec parts in it an call it good. and leave it the hell alone.

[sleepur606]

Thats because the tube didn't cause the damage to the lower. The bolt carrier did by inpacting the lower. More then likely it was out of spec parts or incorrect parts that caused this. Bad or incorrect spring, or incorrect buffer.

I was thinking of misalignment due to cross-threading moving the centerline of the bolt carrier and allowing contact, but even that seemed extremely far fetched. You would need some serious cant/misalignment to allow for the kind of contact the OP posted and by that point it would be obvious.

But, like you say, put mil-spec parts in it and call it good. Always worked for me.