View Full Version : Tuning issue
So, I built myself what amounts to basically a DPMS Tactical 16. 16" bull barrel with a 20" gas system. I have an SA chrome BCG, A2 stock and rifle buffer. Shoots fine and ejects to about 3-4 o'clock. However, it often fails to lock open on the last round. Looking for ideas to fix this. Thinking of either changing to a carbine buffer (maybe an H2?), or lightening the rifle length buffer. Thoughts?
So you've got a 16" barrel with a rifle length gas system? What is the port size?
.113 inch according to DPMS. I really think the issue is on the back end, considering the only failure is failure to lock open on the last round, but I'm still pretty new at this.
Range reloads mostly, which I figure will probably be the weakest ammo I'll run which is what I think should be the minimum test for functioning.
.113 inch according to DPMS. I really think the issue is on the back end, considering the only failure is failure to lock open on the last round, but I'm still pretty new at this.
All diagnostic issues start at the gas port. The buffer changes required to make it run are just treating the symptoms. With that said, the port size is what it is, so you have no choice but to try a different buffer. The A5 system with a -1 buffer may work.
ETA: I'd also like to know what ammo you're using. The gas system set up you have is going to be sensitive to lower pressure ammo.
Range reloads mostly, which I figure will probably be the weakest ammo I'll run which is what I think should be the minimum test for functioning.
Unless you loaded them, they are not going to be a reliable indicator at all. You need to try it with a known good factory load, even if it is relatively weak like PMC.
I know I am going to regret asking this... But why would anyone create such an abomination?
DPMS parts have enough trouble the way it is. doing something like this seems like it would only increase the issues. Also what buffer/spring are being used?
Also what buffer/spring are being used?
I have an SA chrome BCG, A2 stock and rifle buffer.
Here is what he stated in OP.
I know I am going to regret asking this... But why would anyone create such an abomination?
DPMS parts have enough trouble the way it is. doing something like this seems like it would only increase the issues. Also what buffer/spring are being used?
He's using a rifle buffer and spring, which is usually very forgiving. I suspect that the barrel doesn't have enough dwell time to function properly.
I know I am going to regret asking this... But why would anyone create such an abomination?
DPMS parts have enough trouble the way it is. doing something like this seems like it would only increase the issues. Also what buffer/spring are being used?
I got the barrel before I really knew about DPMS. DPMS sells it as a complete rifle. Before someone ask, DPMS hasn't bothered to answer my inquiries. Its a mil-spec rifle buffer/spring (as was stated in the op).
Sorry I completely missed that.
Hmmm. I will be curious to see what comes of this.
If it's short stroking or not locking back on an empty mag, then you need to do two things.
1) try better / more consistent ammo
2) if #1 fails to resolve the issue, you're going to have to try a lighter buffer.
In your case, a lighter buffer also means a carbine or A5 receiver extension and the appropriate action spring.
If it's short stroking or not locking back on an empty mag, then you need to do two things.
1) try better / more consistent ammo
2) if #1 fails to resolve the issue, you're going to have to try a lighter buffer.
In your case, a lighter buffer also means a carbine or A5 receiver extension and the appropriate action spring.Why would I need a receiver extension? I don't understand.
Sorry I completely missed that.
Hmmm. I will be curious to see what comes of this.
No worries.
Why would I need a receiver extension? I don't understand.
Because you can't get a lighter weight rifle buffer.
He's using a rifle buffer and spring, which is usually very forgiving. I suspect that the barrel doesn't have enough dwell time to function properly.Would switching to a FA BCG help or hinder or not have any effect?
Because you can't get a lighter weight rifle buffer.
Couldn't I either run a carbine buffer or remove some weight from the rifle buffer?
TacticalMark
11-13-13, 21:29
Would switching to a FA BCG help or hinder or not have any effect?
No effect
Couldn't I either run a carbine buffer or remove some weight from the rifle buffer?
To run a carbine buffer, you need a carbine receiver extension. You could try and remove some weight but i don't think it's worth the effort.
I would shoot another 250-500rds of 5.56 through it and then try again with weak ammo like PMC Bronze
Heavy Metal
11-13-13, 21:40
If you put a carbine buffer in a rifle extension, you will damage your rifle. The buffers are a different length. You want the motion of the BCG arrested by the rear end of the buffer on the bottom of the tube. If the buffer is too short, the ass-end of your gas key will violently impact the bridge on the reciever ring of the lower and damage it.
If your rifle won't cycle on a rifle buffer and rifle spring in a rifle extension, you have issues that need resolving and going lighter on ANY buffer ain't going to cure them.
You CAN lighten a rifle buffer.
The stock rifle buffer contains 5 steel weights and an aluminum spacer that is the same length as 2 steel weights and a rubber disk.
Just replace some steel weights with another aluminum spacer.
That said, the 16" rifle configuration is not one of the more reliable ones.
The gas port is just about as large as possible, so opening it up would not do much.
Ensure everything with the gas block and tube is lined up.
Lube it up well, try again with factory loads and see how it goes.
ColtSeavers
11-13-13, 22:37
First: USE BETTER AMMO! I am always amazed when I read about people actually buying and shooting hillbilly reloads from the local range monkeys, Darryl, his brother Darryl and his other brother Darryl.
Second: if somehow the problem persists using quality (and more powerful) ammo and you don't feel like messing with your rifle buffer (don't have enough spare parts for instance) there's this;
http://www.jprifles.com/buy.php?item=JPLMB
I have a suggestion that you won't like, but nonetheless it is prudent. I doubt that this particular set up is going to be reliable. That port is huge. For a perspective on this, a 16" carbine (Colt is .063 and the rifle is .093). Take that barrel off, throw it in the trash and then put a QUALITY barrel on it. Then get a new bolt to replace the DPMS one. You should be fine for the most part.
Unless I'm missing something, I'm still confused about the a 16" bull barrel with a 20" gas system.
Unless I'm missing something, I'm still confused about the a 16" bull barrel with a 20" gas system.
You are not the only one. Leave it to DPMS.....
First: USE BETTER AMMO! I am always amazed when I read about people actually buying and shooting hillbilly reloads from the local range monkeys, Darryl, his brother Darryl and his other brother Darryl.Well, I was hoping to make it reliable with whatever I put in the chamber kind of gun. Like I said, I started it before I really knew much about it.
Second: if somehow the problem persists using quality (and more powerful) ammo and you don't feel like messing with your rifle buffer (don't have enough spare parts for instance) there's this;
http://www.jprifles.com/buy.php?item=JPLMBYes! This is the kind of solution I was thinking of. Well, this or some kind of spacer for a carbine buffer.
I have a suggestion that you won't like, but nonetheless it is prudent. I doubt that this particular set up is going to be reliable. That port is huge. For a perspective on this, a 16" carbine (Colt is .063 and the rifle is .093). Take that barrel off, throw it in the trash and then put a QUALITY barrel on it. Then get a new bolt to replace the DPMS one. You should be fine for the most part.Well, actually I was hoping for a quick fix to make it more reliable before I sell it. Take what I learned and build the next one that will be more suitable for me.
Unless I'm missing something, I'm still confused about the a 16" bull barrel with a 20" gas system.Meh, I was hoping it would tun out to be basically a shortened version of an A2, which I'm very familiar with. Cest la vie.
Well, I was hoping to make it reliable with whatever I put in the chamber kind of gun. Like I said, I started it before I really knew much about it.
Not going to happen with that barrel & gas system.
Not going to happen with that barrel & gas system.
Yeah, I get that now. Not to mention its heavy as a brick and about as accurate.
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