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

Gewehr43 04-09-2020 09:30 PM

Quote:

Originally Posted by Beeks (Post 1927946)
I didnít take a course. I just read a book. I donít 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 itís 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...Ö.

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

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.


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