UPDATE: AR-15 Buffer and Spring Help Needed

[pdhntr]

So I got the 20 Practical barrel shortened and plumbed. Shoots well, but I am having a problem.



I have a SA adjustable gas block and it runs fine with the M4 adjustable stock. When I switch to the A2 stock no matter how I adjust the gas block, I can't make the bolt run all the way back to lock on empty mag or reliably pick up another round.

I need this to run with the A2 stock as I have it set up with the battery for the thermal.

I don't have any experience with the springs and buffer, and I am sure someone has done this before and knows exactly what I should do with either the spring length or buffer weight to make this run.

Thanks.

Jim

 

[6ShotsOr5?]

So I got the 20 Practical barrel shortened and plumbed. Shoots well, but I am having a problem.

View attachment 1283000

I have a SA adjustable gas block and it runs fine with the M4 adjustable stock. When I switch to the A2 stock no matter how I adjust the gas block, I can't make the bolt run all the way back to lock on empty mag or reliably pick up another round.

I need this to run with the A2 stock as I have it set up with the battery for the thermal.

I don't have any experience with the springs and buffer, and I am sure someone has done this before and knows exactly what I should do with either the spring length or buffer weight to make this run.

Thanks.

Jim

I recommend you talk to Clint Butler at Heavy Buffers. He helped me with different buffer and spring recommendations that have run well with three different stocks on ARs in 5 different calibers, although none were A2 stocks. I have had very good luck following his recommendations.

 

[Mark M.]

Flat wire buffer spring by Superior, I believe Brownells still carries them

 

[Ggmac]

install a spacer . Make it out of a wood dowel . Measure the lenght difference between the two and install . Spacer , spring and carbine buffer in rifle butt .
No coffee yet , hope this makes sense . Ive done it a couple of times .

 

[VA_XTC_Shooter]

Sounds like the A2 "rifle length" buffer setup, typically something like 5.1 oz, is too heavy for your load/gas port/gas block combo. Decrease the buffer weight. You can take off the rubber bump stop and remove a weight or two to test. If that works, roll with it with some filler material so the weights aren't bouncing around.
The above spacer idea and swap in a carbine buffer and spring would work too. I'd still recommend adjusting the internal weights of the buffer to tune the rifle.

 

[pdhntr]

install a spacer . Make it out of a wood dowel . Measure the lenght difference between the two and install . Spacer , spring and carbine buffer in rifle butt .
No coffee yet , hope this makes sense . Ive done it a couple of times .

Sounds like the A2 "rifle length" buffer setup, typically something like 5.1 oz, is too heavy for your load/gas port/gas block combo. Decrease the buffer weight. You can take off the rubber bump stop and remove a weight or two to test. If that works, roll with it with some filler material so the weights aren't bouncing around.
The above spacer idea and swap in a carbine buffer and spring would work too. I'd still recommend adjusting the internal weights of the buffer to tune the rifle.

agshooter,

I didn't know there were weights inside the buffer. I will check that out.

Thanks.

Ggmac,

Yes it makes perfect sense. If I can't get it to run with agshooter's suggestion, I will try making a filler block and use the carbine buffer. Thanks.

Jim

I recommend you talk to Clint Butler at Heavy Buffers. He helped me with different buffer and spring recommendations that have run well with three different stocks on ARs in 5 different calibers, although none were A2 stocks. I have had very good luck following his recommendations.

If none of the above fixes work out, I will contact Heavy Buffers. Thank you.

Jim

 

[Pawnee Bill]

Get JPRifles Silent Capture Buffer system. No more guess work and mainly no more BOING BOING......

 

[VA_XTC_Shooter]

Get JPRifles Silent Capture Buffer system. No more guess work and mainly no more BOING BOING......

I have to disagree. The silent capture springs don’t do anything a properly tuned buffer a d spring can’t do. Other than noise, I’ll give ya that

 

[Pawnee Bill]

I have to disagree. The silent capture springs don’t do anything a properly tuned buffer a d spring can’t do. In fact, I think they are worse. I’ve seen the lock up more than one gun

To each his own.

 

[Ggmac]

Abuffer is generally needed . The bolt goes back , recoiling with the buffer , the weights in the buffer are now in the foward position. As it hits the springs full compression, the weights inside the buffer are still moving , now the weights are moved to the rear position. As the bolt and buffer go foward the weights are still at the rear . The bolt closes buffer behind it , foward momentum stops but the weights give a second hit now sliding to the foward position and the cycle starts over . This timing and weight cycle can and does have an important part of cycling in the AR .
Just going from memory , I think

 

[itchyTF]

How about opening up the gas port a little? I had to have that done on a 20P.

 

[pdhntr]

Thanks for all the help. You guys have offered just what I was looking for, as I haven't had to deal with this problem in the past.

I am working on it, and this is my plan.

1. Remove buffer weights to see if I can get it to run with the rifle length buffer and spring. If that doesn't work...
2. Measure and make a spacer to try to fit the shorter (carbine length) spring and buffer into the A2 stock. If that doesn't work...
3. Get a replacement long spring and start cutting it down to shorter lengths and use the A2 buffer and adjust weights and length of spring. If that doesn't work...
4. Get another bottle of whiskey and consider opening the gas hole, although I believe it is at .090 already.

I really don't think I need the JP stuff, as I can usually figure things out on my own if I have a little guidance, and the cost is more than I really want to spend.

It runs with the M4 stock, spring and buffer, so I really think Ggmac has the answer. I just don't want to overlook the possibility that working with the A2 buffer weights might get it running.

Thanks again guys. Very helpful.

Jim

 

[jelenko]

If the gas tube is rifle length, the ports for barrels in XTC generally start at .093 and go to .1.

 

[VA_XTC_Shooter]

Weigh the carbine buffer it works with and compare that weight to the A2 buffer. Make the A2 buffer the same weight, or close, and I bet it works.

 

[itchyTF]

I think I got my 20P barrel from WOA. Don't remember what the original gas port diameter was but it was short stroking using H4198. I think they opened it up to .093 and that solved it.

 

[pdhntr]

If the gas tube is rifle length, the ports for barrels in XTC generally start at .093 and go to .1.

It is a mid-length now, with a total of 17 inches of barrel and a 9 inch suppressor. I cut down and rechambered a 24" 20 practical barrel from Krieger that I got many years ago for a bench AR.

If I have to, I will fumble my way through that process.

Thanks for the information, good to know.

Jim

 

[pdhntr]

Weigh the carbine buffer it works with and compare that weight to the A2 buffer. Make the A2 buffer the same weight, or close, and I bet it works.

That is my plan for the morning.

Jim

 

[Ggmac]

modified my post aboout using a wood plug : if you use wood make sure its as large as the spring or use a piece of PVC tubing . After thinking about it I think the last one I modified, I used a piece of PVC . Its lighter and fits better. Wood will work but it may need to be turned on a lathe .

 

[jelenko]

It is a mid-length now, with a total of 17 inches of barrel and a 9 inch suppressor. I cut down and rechambered a 24" 20 practical barrel from Krieger that I got many years ago for a bench AR.

If I have to, I will fumble my way through that process.

Thanks for the information, good to know.

Jim

Turns out it's easier than you might think. It's best to go one drill size at a time; use 'through hole' reamers - i.e., not drill bits, and put a wooden or plastic dowel in the bore so when the reamer goes through the port it runs into the dowel. No problem using a hand drill - the reamer will just follow the hole. But, go slow, let the bit do the work.

That said, I think the port diameter tends to be smaller for shorter, thinner barrels.
Here's a sample from Builders Guide to AR 15 Gas systems

• 11.5" Barrel (0.625") Port: 0.081" to 0.089"
• 11.5" Barrel (0.750") Port: 0.086" to 0.094"
• 14.5" Barrel (0.625") Port: 0.063" to 0.078"
• 14.5" Barrel (0.750") Port: 0.070" to 0.086"
• 16" Barrel (0.625") Port: 0.063" to 0.078"
• 16" Barrel (0.750") Port: 0.070" to 0.086"
• 20" Barrel (0.625") Port: 0.086" to 0.093"
• 20" Barrel (0.750") Port: 0.093" to 0.096"
• 24" Barrel (0.825") Port: 0.089"

I can say that the gas port on my 24", .936 gas blocks is more than 0.089

 

[pdhntr]

Well I got it running just fine and want to apologize to everyone for wasting your time.

When I put it together, I put on a SA adjustable gas block and glanced over the instructions for settings and anything that might be helpful. The instructions say in a couple places to start with the gas block open 4.5 turns or 18 clicks. Like a moron I dialed in that setting and figured I would adjust as needed.

I should have followed my gut, and turned the gas block all the way off, and then opened it up until it ran properly, which is just what I did a little while ago.

It is running properly at just 5 clicks. I was way overgassed and probably sliding right past the bolt stop, etc.

Again, sorry for wasting your time. All of you guys offered great information.

Thanks.

Jim