Bolt Catch locking on carrier, not bolt face

[Reaper 31]

Racking my brain and losing sleep.... not new to gas guns but I just built an Aero M5 with a rifle length buffer system, RCA BCG, and it appears the bolt catch is locking on the carrier vrs bolt face. I've tried swapping buffer springs starting with a Sprinco Green, JP, then standard DPMS buffer spring and I'm using a standard weight 308 rifle buffer . I'm using an EXPO A2 buffer tube and a Luth-AR MBA-1 stock. I've read the bolt catch could be a problem but it's the Aero M5 catch. I will look at the plunger tomorrow if need but wanted suggestions on where to start?
Thanks

 

[bigjake83]

If it's doing it with all different buffer combinations then it sounds like you need more gas, If you're running an adjustable gas block back it out a couple clicks If not check to make sure your gas block is properly aligned and not leaking.

 

[Reaper 31]

Thing is it's locking the bolt carrier not being fired, just locking bolt back pulling the charging handle.

 

[Powder_Burns]

Measure your tube and buffer. There are dimensional differences between AR-10 and LR-308 buffer systems.

 

[Ravenworks]

How much room is there from the bolt face to the catch when you pull the changing handle all the way back?

 

[Jigstick]

Almost sounds like the buffer tube or plug arent the proper lengths. So it’s locking back on the face of the carrier ?

 

[Reaper 31]

How much room is there from the bolt face to the catch when you pull the changing handle all the way back?

I wish I could post a picture but I'm away from home all day. I would say the bolt face is about 1/4 inch from locking on the face ( this is where the catch is locking on the carrier). I can pull back harder on the charging handle and it will clear the bolt face but not catch...

 

[hitman]

If you cannot lock it back to the rear manually then you need the 308 buffer, since it is shorter than a regular buffer. You can only use a standard ar buffer with the longer buffer tubes, like LMT and Vltor A5 etc...

 

[bigjake83]

So it's either your charging handle hitting your cheek rest or that buffer tube is out of spec or incorrect.

 

[Reaper 31]

It is a308 buffer, I made that mistake buying the longer ar15 before. Would the buffer tube being too forward against the retainer be a potential issue? It should be an A2 that the MBA requires

 

[Reaper 31]

Is there a difference between the A2 buffer tube and an LR308 tube?

 

[Powder_Burns]

Shouldn’t be for an A2 tube but the spring lengths and buffer lengths are different. Measure your spring and buffer to ensure they are the right length.

 

[Reaper 31]

Just got home and here is a picture of what I'm speaking of...

 

[Powder_Burns]

Looks like your bcg ran out of leg room in the buffer, measure the buffer and spring. Buffer should be 5.2-5.25”, spring should be around 13.75”. Anything longer and its wrong.

 

[Reaper 31]

Here's what I got. Tried two different springs also

 

[Powder_Burns]

Top spring looks like a ar-15 a2 spring to me, bottom looks more like the ar-10 rifle length spring. When compressed the top spring would be almost 3/4” too long so your buffer would bottom out in the tube before the bcg clears the catch. Buffer looks correct.

 

[Reaper 31]

The original spring I tried was the springco green. And it's longer

 

[Reaper 31]

Also the buffer tube and the little screw

 

[Powder_Burns]

The green one is for a 5.56 tube. Try a .308 carbine spring if you can find one. Willing to bet it solves your problem.

 

[Reaper 31]

I thought the green spring was for any rifle length buffer tube/A2 style? I have the carbine length springs laying around I'll try but I thought that was for only carbine length tube?

 

[Powder_Burns]

Number of coils, when fully compressed the spring will be longer than one for a .308. A .308 carbine spring will be the same as the .308 rifle spring, the difference is the buffer and tube lengths.

 

[6.5SH]

The shiny silver spring on top looks closest to being correct, the other two have too many coils. But that doesn't solve your problem if it occurs with all three.

Some info that may help:

Slash's Heavy Buffers | Reference

 

[Reaper 31]

I borrowed my father in law lower. Also an m5 with a rifle leftmost length tube and spring, and the bolt will lock on the face. I took out the same combo buffer and spring and put on the lower in working on and it doesn't lock back on the bolt face

 

[Powder_Burns]

Are the carriers the same length too?

 

[Reaper 31]

Yes sir compared 3, 308 style bolt carriers
Toolcraft, JP, and the RCA on this build

 

[6.5SH]

Measure the internal depth of both buffer tubes?

 

[Powder_Burns]

Something isn’t adding up. Look inside your buffer tube and check to see there isn’t something in there preventing the buffer from going all the way back. If your bcg is the right length, the spring is correct, and the buffer is correct, and the tube is the right length then it should work. Are the charging handles the same length too?

 

[Reaper 31]

Going to try swapping the buffer tubes....

 

[XLR308]

Is there a bolt running through the back of the buffer tube retaining the stock ?

 

[Precision Underground]

Just got home and here is a picture of what I'm speaking of... View attachment 7400307

Is this pic showing you pulling the charging handle all the way back or just the bolt catch on the carrier? What happens if you pull past here? The bolt catch will hit the back side of the bolt and stop the carrier if you are pressing hard to engage the bolt catch. Either way if the pic shows the bolt as far back as you can pull it something is stopping it. Find that something. Cheek riser, buffer tube length or obstruction , buffer/spring length, or the bolt catch hitting the back side of the bolt. It pretty much has to be one of those.

 

[Reaper 31]

I think I found the problem. The darn buffer tube appears to been out of spec. The bolt is closing now now problem

 

[Reaper 31]

darn thing it measures the same length as the one I borrowed off father's rifle

 

[bigjake83]

 

[bfoosh006]

I'm sorry, you did say you can manually lock the BCG back , correct ?

Will it lock back on a single mag fed , and loaded round ?

Are you running an Adj. GB ?

It might be running fast enough to "out run" the bolt catch.

 

[Ravenworks]

I think I found the problem. The darn buffer tube appears to been out of spec. The bolt is closing now now problem

Sorry I didn't get back to you sooner but looks like you had plenty of help.
Remember,on these 308 gas guns it's REALLY easy to get things out of wack.

Next time to save you the headache always look where the bolt is in relationship to the catch

 

[Ravenworks]

I'm sorry, you did say you can manually lock the BCG back , correct ?

Will it lock back on a single mag fed , and loaded round ?

Are you running an Adj. GB ?

It might be running fast enough to "out run" the bolt catch.

No not the problem,wrong tube

 

[Reaper 31]

I appreciate everyone's help, I know if it's not one thing is another with these gas guns. I've been through several builds and each one was different. But this one had me for two days. Going to the range if all possible tomorrow....
Thanks again

 

[Scottmilk9]

You sure you don' t have an AR15 bolt catch in an AR10?

 

[Reaper 31]

its an Aero m5 catch. I took rifle to the range today and it ran with no problems. Went through a box of 147gr and 175 and experienced no problems. Thanks again to the forum!

 

[Isaac_ws]

its an Aero m5 catch. I took rifle to the range today and it ran with no problems. Went through a box of 147gr and 175 and experienced no problems. Thanks again to the forum!

I am having the exact same issue you were having with your gun on my aero m5. What buffer tube did you end up going with? Hoping just swapping the buffer tube fixes my issue