6.5 Grendel build issues.

[usmcm16a2]

Folks,


Took my Grendel build to the range today. The build itself, 18 inch Dead Shot barrel mid length. Micro gas block, mid length gas tube, Aero Precision M4E1 upper with a Aero Precision 12 free float handguard. Bolt carrier is chrome plated with a type one bolt headspaced to the barrel.
Ammo was my hand loads. 29.5gr CFE-223, virgin PPU brass, 123gr Amax, Federal GMM primers. COAL was 2.238 inches.
I had problems out the starting gate, first round stove piped, subsequent rounds would not feed. I thought that maybe lower which has an M4 buffer and spring was not allowing the bolt to go back far enough. I shortened the spring about 1.5 inches. Problem still persists.
The only thing I noticed was that there was some carbon beginning to build up where gas tube comes out the gas block and heads back toward the bolt. I came home, tore the rifle down, popped the pin from the gas block. And checked all of the alignments of the tube, in the gas block and the block to the gas port. At the bottom of the gas block, I removed the Allen heads, and made sure the back screw matched the dimple. Applied a bit of red loctite 271 tightned the screws.
I cleaned the bolt and barrel, oiled it and will another range trip. The magazines I used were AA 10 rounders. Any feedback would be greatly appreciated. A2

[montana]

Did you try firing one round to see if you had enough gas for your bolt catch to work? You should not shorten your buffer spring, ever.

[usmcm16a2]

Montana,


The bolt did go back and the bolt catch did function. I can get a replacement spring in the morning. A2

[m796rider]

Mid length gas on an 18" barrel? I'm guessing your setup is way overgassed, which is completely throwing off your action's timing. Shortening the buffer spring just made it worse.

I'd get either a Sprinco RED spring or a H2/H3 buffer and try again. If neither of these work, you may need an adjustable gas block. Also, try some factory Hornady ammo to rule out your handloads as a contributing factor.

[montana]

I use adjustable gas blocks on all of my Grendels. I start out by shooting one round out of my mag and continue to turn "open" my gas block till the bolt carrier catch holds the bolt carrier back . I'll then turn another couple clicks on the adj gas block for reliable gas pressure . Then I'll shoot three rounds out of my magazine and then fill the mag testing for malfunctions. If a mag fails it will usually be on the last few rounds indicating a weak spring or sticky follower. If your rifle has enough gas to engage the bolt carrier catch with one round repeatedly you may have a magazine problem or extractor, ejector issues. Have you tried shooting factory ammo eliminating a problem with your reloads?

[usmcm16a2]

Montana,



The rifle would stove pipe, the shell would partially extract and the bolt would start to feed the next round. When I took the upper off and played with the gas system at the range I could get it to fire 3-4 rounds but the last shell would stay in the rifle and the bolt would be held back by the latch. I looked at some of the brass and the primers are showing pressure sign. 29.5gr of CFE223. A2

[Variable]

Mid length gas on an 18" barrel? I'm guessing your setup is way overgassed, which is completely throwing off your action's timing. Shortening the buffer spring just made it worse.

I'd get either a Sprinco RED spring or a H2/H3 buffer and try again. If neither of these work, you may need an adjustable gas block. Also, try some factory Hornady ammo to rule out your handloads as a contributing factor.

^^^^^^ I'm leaning toward all of this.

Sounds like heavily overgassed to me.


Also
Re: carbon marks behind the gas block--- Fairly common occurence. Not a big deal most of the time. It usually builds a little carbon fouling up in the tiny gap, and then stops leaking. If you are already overgassed, it sure isn't hurting you that some is leaking out.

[montana]

Montana,



The rifle would stove pipe, the shell would partially extract and the bolt would start to feed the next round. When I took the upper off and played with the gas system at the range I could get it to fire 3-4 rounds but the last shell would stay in the rifle and the bolt would be held back by the latch. I looked at some of the brass and the primers are showing pressure sign. 29.5gr of CFE223. A2

What do you mean by played with the gas system? M796rider is correct about messing up the rifles action when over gassed. If your rifle is over gassed it is an easy fix with an adjustable gas block. The heavier buffers are another plus for reliable cycling. I would also try one with Hornady factory ammo to eliminate any other problems. You may have another problem but I think M796rider's recommendation is the correct way to start.

[usmcm16a2]

Round II,


Purchased a new spring and a Spikes Tactical type 2 heavy buffer. It cured about 80% of the problem. I am still having problems with stove piping, the last shell not bring eject. Per Montanas instructions, I tried Hornady 123gr Amax, and my reloads. Same story for both. At powder loads above 28.5gr CFE-223 I am getting pressure sign. Above 28.5 flattened primers, the shells are being tossed at the 1 o'clock position, and a small portion of the brass is getting mangled. I have contacted the barrel maker. I am going to look at a new adjustable gas system. I should have just spent the money on an already built upper. A2

[montana]

Round II,


Purchased a new spring and a Spikes Tactical type 2 heavy buffer. It cured about 80% of the problem. I am still having problems with stove piping, the last shell not bring eject. Per Montanas instructions, I tried Hornady 123gr Amax, and my reloads. Same story for both. At powder loads above 28.5gr CFE-223 I am getting pressure sign. Above 28.5 flattened primers, the shells are being tossed at the 1 o'clock position, and a small portion of the brass is getting mangled. I have contacted the barrel maker. I am going to look at a new adjustable gas system. I should have just spent the money on an already built upper. A2

Sounds like it is over gassed. I had an 18" AA barrel that was over gassed. My barrel wouldn't eject any cases , they would just stay in the chamber and jam. The good thing about an adjustable gas system is you can fine tune your loads for low recoil and reliability to a specific load if needed. You could have spent your money on a factory upper but you are now becoming a reluctant expert on the AR rifle system like many of us on the forum have become out of necessity LOL.

[rabiddawg]

Round II,


Purchased a new spring and a Spikes Tactical type 2 heavy buffer. It cured about 80% of the problem. I am still having problems with stove piping, the last shell not bring eject. Per Montanas instructions, I tried Hornady 123gr Amax, and my reloads. Same story for both. At powder loads above 28.5gr CFE-223 I am getting pressure sign. Above 28.5 flattened primers, the shells are being tossed at the 1 o'clock position, and a small portion of the brass is getting mangled. I have contacted the barrel maker. I am going to look at a new adjustable gas system. I should have just spent the money on an already built upper. A2

Don't beat yourself up. Store bought guns have troubles too.

Back when I farmed I told an old farmer he needed some green equipment. He said "son, I ain't seen a dealership yet that didn't have a service dept in the back".

[tackdriver]

If this is way off course then I am sure someone will be quick to say so. It seems to me that 28.5 great of cfe is a very mild charge (most all here are running over 30).
I purchased an upper from a member here that was running g a type 2 bolt in a type 1 chamber. The result was case head seperate on from excessive head space. You mentioned you were shooting a type 1 bolt, are you 100% sure this is correct? If you had a type one bolt in a barrel that required a type 2 I am thinking "if" the bolt would close it could be jamming the bullets into the lands and giving a higher chamber pressure.

Again, I'm no gunsmith just been head scratching a bit. Hope you get the kinks worked out, I know they can be frustrating but this is an awsome round in the ar15 platform.

[montana]

If this is way off course then I am sure someone will be quick to say so. It seems to me that 28.5 great of cfe is a very mild charge (most all here are running over 30).
I purchased an upper from a member here that was running g a type 2 bolt in a type 1 chamber. The result was case head seperate on from excessive head space. You mentioned you were shooting a type 1 bolt, are you 100% sure this is correct? If you had a type one bolt in a barrel that required a type 2 I am thinking "if" the bolt would close it could be jamming the bullets into the lands and giving a higher chamber pressure.

Again, I'm no gunsmith just been head scratching a bit. Hope you get the kinks worked out, I know they can be frustrating but this is an awsome round in the ar15 platform.

That is not way off at all. In the end it is up to the individual to know his own barrel and bolt for correct head space. It is also the individuals responsibility to know the type of chamber and ammunition they are using. If a barrel and bolt are purchased separately the barrel should always have the head space checked. I know there have been factory uppers marked 5.56 which are actually 223 chambers. This will cause pressure problems when using 5.56 spec ammo. It is wise to always check your head space after any rifle build or purchase of used firearms, bolts and barrels. It is not a bad idea to check factory built firearms chambers either. Most gun smiths will do this for free or charge a minimal fee for checking head space.

Good catch and reminder to all.

[LRRPF52]

First thing I noticed as well is that 28.5gr of CFE223 under a 123gr A-MAX is a mild load. If that is generating pressure signs, something is wrong with the chamber most likely, or the COL.

[am4966]

Dead shot barrels use 264lbc reamers