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-   -   AR Service rifle? (http://forums.thecmp.org/showthread.php?t=261519)

Beeks 04-07-2020 06:30 PM

AR Service rifle?
 
The rules clearly state that adjustable gas blocks are not permitted. What about adjustable gas tubes or an adjustable gas key? My AR is over gassed. I’m looking for options.

Gewehr43 04-07-2020 11:05 PM

I'm of the approach that when I shoot competitions I don't any sort of equipment challenges...…. that said...……. I wouldn't use those either.

Why don't you fix the root problem here and sort out why your rifle is over gassed?

la Fiere 04-08-2020 12:42 AM

Heavier buffer?

Beeks 04-08-2020 06:10 PM

I’ve shot this rifle two seasons now. After the first season the rubber stopper on the buffer was completely destroyed. I replaced it with an H2 buffer. Very minimal improvement there. The brass gets sooty.

So how do I figure out why my rifle is over gassed?

The barrel is a Bushmaster DCM that was purchased new at Camp Perry a few years ago. I verified that the buffer spring is correct.

Gewehr43 04-08-2020 07:32 PM

You bought just the barrel there or?
What I'm getting at is there a way the rifle is still under a warranty and simply send it back to the maker?

cranehunter 04-08-2020 08:24 PM

Look at your ammo first.

Beeks 04-09-2020 01:17 PM

I built the rifle myself. Just the barrel was purchased from Perry. A few people I shoot with are using the same barrels with good results. I’ve tried a variety of handloads as well as complete ammo including Federal Gold Medal Match. I have not noticed any difference with ammo selection.

Gewehr43 04-09-2020 03:51 PM

Ok... you built it yourself...…
Which Armorers course did you take prior to the build?
Where did you get the other parts for the build?

With the factory ammo what exacting happens and how did you figure out what/how the damage occurred?
What I'm asking is a detailed explanation as to what happened...

Beeks 04-09-2020 05:27 PM

I didn’t take a course. I just read a book. I don’t recall the name any more. The other parts were all purchased new from a variety of places. PSA bcg, la rue quad rail, Ergo f93 stock, Geissel trigger, etc.

The rifle throws brass twice as far as the rifles I shoot against. The brass comes out sooty like it’s being extracted before the pressure in the barrel is completely gone. After the first season I stripped down the rifle and found the rubber end of the buffer destroyed.

4gun-drill 04-09-2020 08:32 PM

What’s does it headspace at?

Gewehr43 04-09-2020 09:30 PM

Quote:

Originally Posted by Beeks (Post 1927946)
I didn’t take a course. I just read a book. I don’t recall the name any more. The other parts were all purchased new from a variety of places. PSA bcg, la rue quad rail, Ergo f93 stock, Geissel trigger, etc.

The rifle throws brass twice as far as the rifles I shoot against. The brass comes out sooty like it’s being extracted before the pressure in the barrel is completely gone. After the first season I stripped down the rifle and found the rubber end of the buffer destroyed.

Ok..... this is just my 2% because you have so much different stuff going on there.
Ok so you replaced the buffer since it was gone, did you replace the buffer spring as well??
The problem here is just by your description you are describing opposite things:
-I've never seen a buffer end gone like that but you have a misc part grouping so the quality may not have been there.
-Depending on what you mean by "soot" on the case, that usually indicates LOW chamber pressure.
-Where the cases are ejected is more what people discuss, not how far.... but I can see why it's concerning...….

Is there a local AR Gunsmith you trust to look at it???
There seems to be multiple issues going on maybe...….

And this happens with FACTORY ammo?

canes7 04-10-2020 07:22 AM

The interesting part to me is the destroyed rubber on the original buffer. Makes me call into question the spring and buffer type (i.e. - rifle vs. carbine) and quality of the spring. I have a hard time believing that with standard HP loads and factory ammo being fired thru a rifle with a standard gas system would be overgassed.

Gewehr43 04-10-2020 11:41 AM

Quote:

Originally Posted by canes7 (Post 1928027)
The interesting part to me is the destroyed rubber on the original buffer. Makes me call into question the spring and buffer type (i.e. - rifle vs. carbine) and quality of the spring. I have a hard time believing that with standard HP loads and factory ammo being fired thru a rifle with a standard gas system would be overgassed.

Yes.... which is why I asked about the source of the rifle/parts.

Even with full-auto I've not seen that before.

Beeks 04-10-2020 03:12 PM

Headspace is good. I had a gunsmith check it.

Beeks 04-10-2020 03:20 PM

Yes, all ammo. I have not replaced the buffer spring. It measures 10 1/4 long which I believe is appropriate for a carbine length buffer tube.

Gewehr43 04-10-2020 03:36 PM

Quote:

Originally Posted by Beeks (Post 1928155)
Yes, all ammo. I have not replaced the buffer spring. It measures 10 1/4 long which I believe is appropriate for a carbine length buffer tube.

Ok, my suggestion is this:
-Replace the buffer spring with a KNOWN good one, one from a reputable source.
-I'd have a good known AR gunsmith to look at your rifle and tune it.
You have a lot going on there and it really needs to be looked at in person.

Beeks 04-11-2020 09:16 AM

And if the gunsmith would want to add an adjustable gas tube or key, would it be service rifle legal?

7.62 Nitro Express 04-11-2020 09:46 AM

Quote:

Originally Posted by Beeks (Post 1928155)
Yes, all ammo. I have not replaced the buffer spring. It measures 10 1/4 long .......

So what? That does not mean it is providing the correct force when compressed. F = kX

If I were you I'd approach it logically and based on the ease of effort.

Do you have a spare, known good BCG available or can you borrow one? Swap it out and see if anything changes. Don't just assume it is good because you bought it new.

Next thing would be to swap out whatever buffer and spring you currently have for a set that is known to be good. See what happens. This is cheap and easy, even if you have to buy new.

If that does not work, remove the front sight tower/gas block and measure the port hole size in the barrel. If it is too big you have some decisions to make.

I'm not a fan of custom goofiness (adj gas block) to compensate for out of spec components.

A new ready to install bbl from White Oak is about $210.

My experience has been that "early" extraction results in cases that remain in the chamber after being torn through the rim.

Gewehr43 04-11-2020 10:42 AM

Quote:

Originally Posted by Beeks (Post 1928323)
And if the gunsmith would want to add an adjustable gas tube or key, would it be service rifle legal?

Sir:
What I am suggesting to you is you have a messed up rifle.
It needs to be fixed by a gunsmith who knows what they are doing.

And no by my reading of the rules, they are not legal.

https://thecmp.org/wp-content/upload...RifleRules.pdf

WindLogik 04-11-2020 11:44 AM

Unfortuneately, this is a common problem while running a 20" AR service rifle barrel on a carbine buffer system (I'm assuming you're using that). You should be running a slower powder like Varget or RE15. The gas port on a SR barrel for a FL gas system is typically in the neighborhood of .095". Best you can do is match the standard A2 buffer at 5.2 OZ. This translates to an H3 carbine buffer. Use this with a standard carbine spring (same stiffness as an A2 spring). This should fix your problem assuming you are using a proper SR load (77 grain bullet with correct powder) and your gas port is properly sized. The other thing you can do to add weight is use an M16 style bolt carrier, this will ad a bit more weight.

This issue cropped up with the switch to optics/carbine buffer systems. Companies like WOA and CLE have done a good job controlling their port diameters for SR match builds. If you have a grossly oversized port, you will be SOL. The easy button is to buy a complete upper from WOA.

Gewehr43 04-11-2020 01:00 PM

Quote:

Originally Posted by WindLogik (Post 1928362)
Unfortuneately, this is a common problem while running a 20" AR service rifle barrel on a carbine buffer system (I'm assuming you're using that). You should be running a slower powder like Varget or RE15. The gas port on a SR barrel for a FL gas system is typically in the neighborhood of .095". Best you can do is match the standard A2 buffer at 5.2 OZ. This translates to an H3 carbine buffer. Use this with a standard carbine spring (same stiffness as an A2 spring). This should fix your problem assuming you are using a proper SR load (77 grain bullet with correct powder) and your gas port is properly sized. The other thing you can do to add weight is use an M16 style bolt carrier, this will ad a bit more weight.

This issue cropped up with the switch to optics/carbine buffer systems. Companies like WOA and CLE have done a good job controlling their port diameters for SR match builds. If you have a grossly oversized port, you will be SOL. The easy button is to buy a complete upper from WOA.

You've seen as a common problem that the rubber end of a buffer has been "destroyed" in shooting it?
Or are you referring to the general issues he's having?

WindLogik 04-11-2020 01:26 PM

Quote:

Originally Posted by Gewehr43 (Post 1928381)
You've seen as a common problem that the rubber end of a buffer has been "destroyed" in shooting it?
Or are you referring to the general issues he's having?

I have not seen that. But, I'd expect that most folks would start to troubleshoot before that became an issue. I don't think that a new shooter would have any idea what the recoil should feel like. You'd really have to do it a lot to beat up that urethane. Maybe he's using some kind of crap buffer with a bumper that is cheap, who knows. When I first started tinkering with the "new" rules, I put my 20" A2 upper on a carbine lower with a standard carbine buffer. Shooting my usual 77 grain SR load, the system was so out-of-time that it was bending the rims on the cases. In otherwords, because of the lack of mass, it was extracting cases way, way too early and with way, way too much force. Matching the buffer weight to that of an A2 immediately fixed the problem. This was with a barrel having a proper port for that load, though.

Even in the A2 days, guys would piece together rifles with incorrect gas port diameters. It's something that folks generally don't know about. They slam something together and it doesn't work right. If the OP's port diameter is in the right range, there is no reason he shouldn't be able to run a typical SR load with an H3 buffer.

We tell new folks, time and time again when they start shooting HP, not to buy anything. Invariably, they run out and buy what looks like a HP kit, but literally every component is wrong. From the upper to the sling to the mat to the spotting scope to the trigger to the bullets. I just don't know why new shooters do that. This sounds like that kind of a case. If the shooter is in a local HP community, he should be asking his peers for guidance. Literally, that is one of the purposes of the distinguished program and CMP competitions.

Gewehr43 04-11-2020 04:38 PM

Quote:

Originally Posted by WindLogik (Post 1928392)
I have not seen that. But, I'd expect that most folks would start to troubleshoot before that became an issue. I don't think that a new shooter would have any idea what the recoil should feel like. You'd really have to do it a lot to beat up that urethane. Maybe he's using some kind of crap buffer with a bumper that is cheap, who knows. When I first started tinkering with the "new" rules, I put my 20" A2 upper on a carbine lower with a standard carbine buffer. Shooting my usual 77 grain SR load, the system was so out-of-time that it was bending the rims on the cases. In otherwords, because of the lack of mass, it was extracting cases way, way too early and with way, way too much force. Matching the buffer weight to that of an A2 immediately fixed the problem. This was with a barrel having a proper port for that load, though.

Even in the A2 days, guys would piece together rifles with incorrect gas port diameters. It's something that folks generally don't know about. They slam something together and it doesn't work right. If the OP's port diameter is in the right range, there is no reason he shouldn't be able to run a typical SR load with an H3 buffer.

We tell new folks, time and time again when they start shooting HP, not to buy anything. Invariably, they run out and buy what looks like a HP kit, but literally every component is wrong. From the upper to the sling to the mat to the spotting scope to the trigger to the bullets. I just don't know why new shooters do that. This sounds like that kind of a case. If the shooter is in a local HP community, he should be asking his peers for guidance. Literally, that is one of the purposes of the distinguished program and CMP competitions.

Ok.... we have the same experiences.
I was wondering about the beat up buffer..... that is a new one.
That is why (my thoughts and your comments) I asked the OP about the source of the parts/build...…

Beeks 04-11-2020 07:37 PM

Quote:

Originally Posted by WindLogik (Post 1928392)

We tell new folks, time and time again when they start shooting HP, not to buy anything. Invariably, they run out and buy what looks like a HP kit, but literally every component is wrong. From the upper to the sling to the mat to the spotting scope to the trigger to the bullets. I just don't know why new shooters do that. This sounds like that kind of a case. If the shooter is in a local HP community, he should be asking his peers for guidance. Literally, that is one of the purposes of the distinguished program and CMP competitions.

There may be a little truth to this in regards to some of the components I used. I did use a M1 in competition for a number of years before starting to build this AR. I did get a lot of advice from the other shooters. They even brought the barrel back from Perry for me. They did push a fixed stock but I thought adjustable would be better for my kids.

I found my old buffer. It doesn’t have any manufacturer markings.

hebes405 04-19-2020 09:48 AM

Quote:

Originally Posted by WindLogik (Post 1928362)
Unfortuneately, this is a common problem while running a 20" AR service rifle barrel on a carbine buffer system (I'm assuming you're using that). You should be running a slower powder like Varget or RE15. The gas port on a SR barrel for a FL gas system is typically in the neighborhood of .095". Best you can do is match the standard A2 buffer at 5.2 OZ. This translates to an H3 carbine buffer. Use this with a standard carbine spring (same stiffness as an A2 spring). This should fix your problem assuming you are using a proper SR load (77 grain bullet with correct powder) and your gas port is properly sized. The other thing you can do to add weight is use an M16 style bolt carrier, this will ad a bit more weight.

This issue cropped up with the switch to optics/carbine buffer systems. Companies like WOA and CLE have done a good job controlling their port diameters for SR match builds. If you have a grossly oversized port, you will be SOL. The easy button is to buy a complete upper from WOA.

I was thinking about the exact same thing. I would add, take the advice of your local shooters and switch to a fixed stock with all correct rifle length components. However if length of pull is a concern, put on an A1 stock. That 3/4" makes a bigger difference than you would think.

Hope you get it figured out.


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