A5 Buffer Setup with a 15.5" rifle gassed carbine?

For fun, I picked up the Brownells 15.5" rifle gassed barrel and snapped together a pseudo Colt 605. Pinned and welded a Griffin Arms linear comp for California compliance. Also hoping the linear comp can add a little dwell time and pressure to the system. Running a DD BCG and a standard rifle extension. I have not verified, but the port is supposedly 0.1015.

So far this summer, in upper 80oF temps, I've run PMC bronze and Federal XM193. The PMC has not stalled the gun yet, but its border line and kick cases back at 4~4:30. Tosses them about 2'. The two FTF's I've had were 10/20 Pmag related issues.

I was debating going to an A5 set up. Done a fair bit of digging and I've found the buffer weights, but am wondering which buffer most directly mimics a standard rifle weight, 5.1oz, as that appears to work now. With the shorter tube, I know it's not apples to apples.

I figured I could start there and then work a little lighter to see if that can speed things up a little and give me a little kick towards maintaining reliability. It's a 1-12 twist barrel and will spend it's life shooting PMC Bronze and various XM193 types I pick up (Federal, PMC Xtac, etc).

I've read some of the built 605's with cut down 20" barrels are running 0.110 ports. I'd like to see if I can keep this carbine happy without opening it up any further.

https://i.imgur.com/CwbcC8A.jpg

If you like the rifle stock and are just looking for lighter buffer options, modifying the rifle buffer is relatively easy.

For example, replacing 2 steel weights with an aluminum spacer drops the weight down ~1 oz.


A .101 port seems pretty lightly gassed.

I'm not married to the fixed stock. I like the A1 length, but am willing to shift over to an A5 or carbine extension.

Fix the easiest and most obvious problem first. Replace the extractor spring with either a Colt or Sprinco M4 spring. I know- it's a DD BCG, but are you certain it isn't the extractor spring? At the very least, installing a Colt/Sprinco M4 extractor spring is a known standard that works. If you go chasing buffers & springs but the extractor spring isn't up to snuff, you'll be continuously chasing and never catching your tail. I know from personal experience.

What tells me that it could be the extractor spring? Short ejection distance. If the extractor spring is weak or marginal, it will not hold the case against the bolt face to firmly compress the ejector. This robs the ejector of its power. If the Colt/Sprinco spring is installed and ejection is still weak, you will know a variable has been eliminated and can confidently look elsewhere.

Before getting caught up in swapping buffer weights, place a single round in a mag known to work and perform a lockback check. If the AR locks back consistently, it's not undergassed.

Don't worry much about angle. Sometimes, an AR can be dialed in and ejection angle still not fit the pie.

Taking my boy to the range on Thursday one more time before he heads off to college. I'm going to try to film things while he shoots it and see what we see. I'm not sure if the 2' throw is due to tension or how it's coming off the deflector. I replaced the extractor spring when I chucked the DD installed o-ring. I know these cut down rifles are a finicky piece. This was built strictly as a range toy, but even toys are more fun when they always work.

Quote:

---

Originally Posted by mrbieler

With the shorter tube, I know it's not apples to apples.

---

It actually is apples to apples. Same spring, same travel... the shorter tube is matched by the shorter buffer. So the same weight is traveling against the same spring... the rifle spring.

Quote:

---

Originally Posted by markm

It actually is apples to apples. Same spring, same travel... the shorter tube is matched by the shorter buffer. So the same weight is traveling against the same spring... the rifle spring.

---

The A5 system does place more preload on the rifle spring in battery. Its 3/8” difference, if I recall correctly. I don’t know whether thats enough to matter.

Quote:

---

Originally Posted by mrbieler

Taking my boy to the range on Thursday one more time before he heads off to college. I'm going to try to film things while he shoots it and see what we see. I'm not sure if the 2' throw is due to tension or how it's coming off the deflector. I replaced the extractor spring when I chucked the DD installed o-ring.

---

Gotcha!

Quote:

---

I know these cut down rifles are a finicky piece. This was built strictly as a range toy, but even toys are more fun when they always work.

---

Is the AR giving you any kind of trouble?

The rifle has not given me any trouble, but with under 400 rounds I'm still playing with things. Folks so far seem to think the Brownells 15.5" barrel does well provided you use XM193, but I'm a pessimist by nature and keep waiting for a shoe to drop... I also have about 5k of PMC bronze I don't want to have to shelve when I shoot this one.

I was not aware of the travel distance similarity. Good to know. Wondering if an A5 tube with a H0 light weight buffer might be a good way to help ensure reliability.

Have you shot it with the PMC yet?