Changing upper from 16" mid-length to 11.5" - 2 questions

[--Terry--]

Hi,

I have an RRA 16" mid-length AR-15, and have just purchased a 11.5" upper. I heard somebody mentioned that with a shorter barrel and a shorter gas tube, the bolt could open too early and could cause FTE.

And the solution would be either a smaller gas port on the barrel or a heavier buffer.

I don't know whether the 11.5" barrel on the new upper has the smaller gas port. It is one of those "key hole" uppers.

Could anybody tell me whether I will need a heavier buffer?

By the way, I have not test-fired the new upper yet. Just got it in today.

Thanks for any info.

(Added 11/16: This new upper does not come with bolt and bolt carrier. I will have to use my existing BCG from my RRA. A friend reminded me about checking head space. Could anybody tell me whether I should worry about head space?

(And are there any Poco Range members who has the .223 Rem head space gauges that I could borrow and try? I don't have those myself.

(THANKS again for your help.)

 

[Scarecrow]

Unless you have experienced stopages its not worth trying to diagnose non-existant problems. When you have problems, then you fix them.

 

[--Terry--]

Good point.

I will test fire in the weekend first and see whether it works.

 

[darko]

I use the same lower for my 11.5, 14.5, and 24" uppers... no problems of any kind.

 

[OneBarfly]

If you have a problem, I'd look at the extractor spring first - The cheapest fix for common shorty problems (solved mine x2).

 

[dangertree]

Unless you have experienced stopages its not worth trying to diagnose non-existant problems. When you have problems, then you fix them.

Sound advice. The carbine buffer and gas system was used in the 11.5 commando for what, 35 years?

Good luck with it.

PS: (the upper receiver keyhole forge mark isn't related to the barrel manufacturer, or the receiver manufacturer, just the raw forging, everyone uses Cerro forgings at some point).

 

[Mondo]

I switch between my 14.5 and 10.5 all the time and no problems so far.

 

[--Terry--]

Added 11/16: This new upper does not come with bolt and bolt carrier. I will have to use my existing BCG from my 16" RRA. A friend reminded me about checking head space. Could anybody tell me whether I should worry about head space?

And are there any Poco Range members who has the .223 Rem head space gauges that I could borrow and try? I don't have those myself.

THANKS again for your help.

 

[KevinB]

FWIW - it is a bad idea to keep swapping bolts in between uppers - as they wear differently - kinda like a cluth on a manual transmission - different drivers using one will wear it out quicker (all else being equal)

 

[--Terry--]

Hmm......

So I should take it to a gunsmith who also sells bolts and bolt carriers?

 

[contact148]

Hmm......

So I should take it to a gunsmith who also sells bolts and bolt carriers?

no just buy a bolt and carrier for each upper

 

[--Terry--]

But I'm still worried about the head space issue.

 

[koalorka]

But I'm still worried about the head space issue.

Headspace is not an issue with the AR15.

 

[Scarecrow]

But I'm still worried about the head space issue.

1 new upper + 1 new bolt = no issues.
1 new upper + 1 old bolt = maybe issues

If you want to know the make of your upper you might be able to find a marking on the barrel.

 

[--Terry--]

No, there is no markings at all on the light barrel. But it is a chrome moly, so I believe it is a Wilson.

The upper has a forging mark that looks like a key hole. Anybody knows who makes this one?

 

[Scarecrow]

The upper has a forging mark that looks like a key hole. Anybody knows who makes this one?

refer back to;

PS: (the upper receiver keyhole forge mark isn't related to the barrel manufacturer, or the receiver manufacturer, just the raw forging, everyone uses Cerro forgings at some point).

 

[dangertree]

The barrel was headspaced when the barrel extension was installed. You're fine (but X2 on the bolt).