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Posted: 1/22/2006 9:05:41 AM EDT
[Last Edit: 1/29/2006 8:30:55 AM EDT by Wolf_Warrior]
My RRA 16" is throwing spent cases with marks on the cartridge rim face that concern me. The marks dig into the brass slightly in a straight line across the lower 1/4 of the rim face. Some actually result in small points of brass extending out from the edge (caused by the brass being dug out). The point of brass is generally in the same line as the rim face mark.

I don't have a camera with enough resolution to show them to you.

No other problems -- seems to shoot fine and otherwise extract correctly.

I am using an MGI buffer with a standard carbine spring.

Any assistance would be appreciated.

WW
Link Posted: 1/22/2006 10:36:58 AM EDT
Sounds like extractor problems to me. When's the last time you took apart and really cleaned your bolt (not BCG, actual bolt)?
Link Posted: 1/22/2006 10:58:00 AM EDT

Originally Posted By caneau:
Sounds like extractor problems to me. When's the last time you took apart and really cleaned your bolt (not BCG, actual bolt)?



It has been a while. I put one of those MGI D-rings on about 6 months ago. I can't point to it as a factor because I just noticed the problem a few weeks ago.

What kind of problem are you thinking of? Extractor too tight? Too loose?
Link Posted: 1/22/2006 12:15:31 PM EDT
Are you saying that there is a line marking across the base of the cartridge case or on the side of the case? If the marking is on the case base, you are probably looking at pressure related marks. If it's on the side, the extractor claw is probably the cause.
Link Posted: 1/22/2006 1:54:30 PM EDT
[Last Edit: 1/22/2006 3:17:04 PM EDT by Wolf_Warrior]

Originally Posted By wrecktech:
Are you saying that there is a line marking across the base of the cartridge case or on the side of the case? If the marking is on the case base, you are probably looking at pressure related marks. If it's on the side, the extractor claw is probably the cause.



It is on the base (the face of the rim -- primer side). Looks like the extractor claw is digging in to the base and mortising the brass. I just removed the MGI D-ring thinking that it was putting too much downward (inward) pressure on the extractor claw -- resisting too much.
Link Posted: 1/22/2006 5:52:59 PM EDT
Some brands of ammo have soft brass, commerical Federal and Winchester comes to mind. Unless it is damaging the brass to the point you feel you couldn't reuse it for reloading, I wouldn't worry about it.
Link Posted: 1/22/2006 6:17:22 PM EDT

Originally Posted By jason_h:
Some brands of ammo have soft brass, commerical Federal and Winchester comes to mind. Unless it is damaging the brass to the point you feel you couldn't reuse it for reloading, I wouldn't worry about it.



Seems to be happening to all brands. The degree varies but I can't attribute it to brand. It is enough to leave a burr sticking out of the rim. I guess you could reload it without a problem but I don't reload so I don't know.
Link Posted: 1/22/2006 11:58:45 PM EDT

Originally Posted By jason_h:
Some brands of ammo have soft brass, commerical Federal and Winchester comes to mind. Unless it is damaging the brass to the point you feel you couldn't reuse it for reloading, I wouldn't worry about it.



I hate to call BS on someone, and I know jason_h knows his stuff, but this is potentially BS. If this problem gets worse and you actually manage to pierce your brass because of the extractor, the results might be dangerous. Your extractor is probably causing this mark at one of two points, either at the moment the bolt strips the round from the mag and sort of clicks it into the extractor, or when it the bolt opens back up after the round is fired and the extractor flings the round out. Of course, if the problem is happening during extraction of the round, then jason_h is absolutely right, it's nothing to worry about. Obviously if it's happening after the bolt locks in, bad things may occur.

What I was thinking actually is that you may have carbon build-up on the extractor or somewhere inside your bolt. The military cleaning guide does say to drive out the extractor pin and clean both inside the bolt and the extractor itself for a reason.

If all else fails, RRA does have that lifetime warranty on their guns. Might be worth saving yourself the hassle, giving them a call, and having them send you a new bolt.
Link Posted: 1/23/2006 12:04:40 AM EDT
[Last Edit: 1/23/2006 12:09:51 AM EDT by Randall_Rausch]
Link Posted: 1/23/2006 11:08:59 AM EDT

Originally Posted By Randall_Rausch:

Originally Posted By Wolf_Warrior:
My RRA 16" is throwing spent cases with marks on the cartridge rim face that concern me. The marks dig into the brass slightly in a straight line across the lower 1/4 of the rim face. Some actually result in small points of brass extending out from the edge (caused by the brass being dug out). The point of brass is generally in the same line as the rim face mark.

I don't have a camera with enough resolution to show them to you.

No other problems -- seems to shoot fine and otherwise extract correctly.

I am using an MGI buffer with a standard carbine spring.



Your upper is probably over-gassed.
I'll assume since you have an extra heavy buffer and defender that you should not otherwise need that you probably had FTE's in the past.



Actually, no. I did not previously -- to my knowledge -- have extraction problems. I got the RRB to reduce the recoil and the "d" thing came with it.

I have taken the bolt apart and cleaned it well. I have also removed the "d" thing. The extractor works much more freely now. Hopefully, I can get it out the range this weekend and see if it did any good.

I think that since the brass is frequently getting mortised with a short burr sticking out from the rim, that it is ocurring on the ejection cycle.

That is not to say that I might not have a gas problem. I've noticed what appears to be some erosion at a small place on the FSB. Perhaps that is normal...

Link Posted: 1/23/2006 11:21:17 AM EDT
Link Posted: 1/23/2006 5:31:43 PM EDT

Originally Posted By Randall_Rausch:

Originally Posted By Wolf_Warrior:
Actually, no. I did not previously -- to my knowledge -- have extraction problems. I got the RRB to reduce the recoil and the "d" thing came with it.

I have taken the bolt apart and cleaned it well. I have also removed the "d" thing. The extractor works much more freely now. Hopefully, I can get it out the range this weekend and see if it did any good.

I think that since the brass is frequently getting mortised with a short burr sticking out from the rim, that it is ocurring on the ejection cycle.

That is not to say that I might not have a gas problem. I've noticed what appears to be some erosion at a small place on the FSB. Perhaps that is normal...





MGI also makes a very good adjustable gas tube.
If it turns out that you are getting marks from the extractor pulling on the rim, that is a sure sign of excessive gas.
Excessive gas is also why it recoils so much.
Tap less gas into the action and everything gets better.



Tell me how...I'm still learning.

Why don't you have your shop in Austin? Come on, you need to be in Texas.
Link Posted: 1/23/2006 9:47:56 PM EDT
[Last Edit: 1/23/2006 10:24:21 PM EDT by Randall_Rausch]
Link Posted: 1/24/2006 2:02:27 AM EDT

Originally Posted By Randall_Rausch:

Originally Posted By Wolf_Warrior:
Tell me how...I'm still learning.



YOU ASKED FOR IT...
...so here it is.

Hope it all sinks in and you can benefit from it.



OUTSTANDING!
thank you!!!
Link Posted: 1/24/2006 6:25:36 AM EDT
I just learned a few things.

Thank You!!
Link Posted: 1/24/2006 8:44:04 AM EDT
Very cool, Ranall. That's probably one of the most useful things ever posted on ARFCOM.
Link Posted: 1/24/2006 6:14:50 PM EDT
[Last Edit: 1/24/2006 6:24:10 PM EDT by jason_h]
No prob with your reply caneau. Without a pic, it is really hard for me to visualize what is going on with the rim. If it is doing it with LC brass, I guess I would be a bit more worried about it.

From what I can tell, based on your description it could be hard extraction which Randall has described in detail above. Still even if this is the case, if you are not experiencing any issues with reliability, and you don't reuse the brass, I guess I would not be too worried about it.

Still, I understand the desire to want to get it fixed if possible. Randall's suggestions would work if it is hard extraction that you are dealing with. However, it may just be something as simple as a extractor with some mean looking burrs on it. Judicial application of a file may be all you need.

Edited to add: Just re-read you description of marks on the case head. Sounds to me like maybe your extractor or possibly even the bolt is out of spec. If the back face of the extractor groove is sitting above the bolt face, it would put a nice mortised notch into the back of the case head when the round is fired and the pressure in the case forces the cased head around the rear of the extractor groove. May want to replace the extractor or the whole bolt group and see if the same problems still exist.
Link Posted: 1/24/2006 7:03:12 PM EDT
Ok, I have too much time on my hands tonight so I took a couple pics. Compare and contrast.





Link Posted: 1/25/2006 12:08:58 PM EDT

Originally Posted By jason_h:
Ok, I have too much time on my hands tonight so I took a couple pics. Compare and contrast.

img86.imageshack.us/img86/6158/img0488c8cq.th.jpg

img86.imageshack.us/img86/2264/img0489c6gb.th.jpg




I'll check tonight and will also see if I can figure a way to get a reasonable close up of the bolt and the case. Just from memory, my bolt/extractor looks like the top picture.

I guess that I ought to chamber a round and extract (without firing) to see if there are any marks.
Link Posted: 1/25/2006 4:16:26 PM EDT
[Last Edit: 1/25/2006 4:18:13 PM EDT by Wolf_Warrior]
With my current digital cameral equipment, this is the best I can do.






1. This was before I removed the D-Fender.

2. This effect was not consistent. In other words there is a lot of brass in my ziplock that doesn't have these marks.

Thanks.
Link Posted: 1/25/2006 6:48:00 PM EDT
Is the rim bent at all? If it is bent towards the rear, I would guess it's a hard extraction issue.

It is kind of hard to tell from my pictures, but the rear of the extractor groove should be recessed below the bolt face. It should not come in contact with the rim at all. It looks to me, best that I can tell, that you either have a burr on the inside of the extractor groove that is biting into your case or that the case is making contact with the rear of groove.

If you don't already, you should get a spare bolt group. It may allow you to isolate the problem and its good to have a spare on hand. I would recommend a MPI'd CMT bolt or Colt if you want to spend the extra. This guy is pretty standup guy, is a site sponsor, and he has good prices: www.bravocompanyusa.com/

I wouldn't worry about headspace issues if you are just switching out bolt for a few rounds. Putting a new bolt in an used rifle should only decrease the headspace, not increase it.
Link Posted: 1/27/2006 6:18:23 PM EDT
[Last Edit: 1/27/2006 6:21:54 PM EDT by Wolf_Warrior]
Ok. I ordered a new bolt but I STILL want to know what is happening...so I took the carrier/bolt apart again and looked hard at the extractor -- looking for burrs, as suggested. What I discovered was what appeared to be a torqued extractor. How the heck can that happen? Anyway, here are some pictures -- which although not very clear, show that one side of the extractor is bent/torqued. If you look at the bolt picture above, you can see it there also. I didn't notice it before. I still suspect a potential pressure problem but I'll have to wait till after I get a chance to run a few rounds through the new bolt...which will probably be next weekend.







The "Ripper" claw extractor.
Link Posted: 1/28/2006 6:31:44 AM EDT
[Last Edit: 1/28/2006 6:33:56 AM EDT by Wolf_Warrior]
Although I think I have discovered why the marks look the way they do -- twisted/torqued extractor claw digging deeper on one side of the rim face than the other -- I'm still not understanding WHY they are appearing at all.

The rim is not bent at all nor are there any other "pull" marks on the upper case, so high pressure is not obviously a factor. I'm not experiencing any FTF.

It is like the bolt/extractor claw is striking the case face too hard as it is seating itself around the rim. I've tried to duplicate the effect by hand-cyling rounds but I am not seeing any marks at all.

The only things that I can think of that would cause this, then, would be:

1. The "torqued" extractor claw is actually bent forward a bit (toward the muzzle). I can't tell for sure with a visual inspection but it is possible. How the extractor claw could get bent/toruqued like that is another question.

2. The MGI buffer is thowing the bolt carrier forward too hard (harder than a manual cycling) on subsequent rounds. Of course, this might mean too much gas, right? I mean, if there is too much gas, it will throw the carrier back too far which would naturally make the MGI RRB throw the carrier back too hard? If this is a clue -- before I replaced the stock buffer with the MGI, I was getting marks from the carrier on the buffer face. I think your post suggests that might be a sign of too much pressure?

3. Somehow the bolt is striking the rim head twice before final extraction. I don't see how this would be physically possible after reading your post above.

4. A combination of the above.

I have ordered a new bolt/extractor and, if the problem disappears, I'll get a new extractor claw for this bolt.

If the problem is too much gas, would it be prudent to first replace the MGI with a regular carbine buffer?

Anyway, thanks to all of you for your assistance.

By the way, great write up, Randall. Now that I have digested it, I've got a much better understanding of what to look for in the future.
Link Posted: 1/28/2006 10:22:34 AM EDT

There is one more possibility --

I have an "enhanced" bolt carrier and a standard spring.

Perhaps the bolt is not fully engaging the cartridge rim when the cartridge is pushed into the chamber by the carrier lip. If so, when it fires, the bolt is being driven onto the rim with the force of the gas in the carrier and the cartridge pushing back out of the chamber. Although the extractor is finally grabbing the rim, it is being done with such instantaneous force that it scores the rim face.

The first thing, then, that comes to mind is that I need a new, more powerful, buffer spring. However, since I can't replicate the results by manually charging the cartridge, wouldn't that suggest that the spring tension is correct?

If that is so, then what? The gas pressure is not driving the bolt carrier back far enough to rebound enough for the extractor to grab the rim?

The inverse logic is driving me crazy!

Link Posted: 1/28/2006 1:01:18 PM EDT
Primer ignites and the barrel pressure goes to 50,000 psi plus. Bullet passes the gas port, and starts the action cycling (carrier movement). Before the bolt unlocks, the bullet has exited the barrel and the barrel pressure has dropped down to 20,000 psi and falling.

Now your problem could be that you have a 223 chamber, yet trying to shoot Nato ammo in it. (Read over pressure, and the spent case unbinding from the chamber walls during the bolt cycle extraction pull). Correct ammo will solve this problem.

You have a new/rough/tight chamber, and again there is more case bound tension to the chamber sidewalls than needed during extraction. Allowing the chamber to self-polish out threw live fire will solve the problem.

Soft case ammo. Again ammo selection will solve this problem.

The gas port was drilled too large and over cycling. If the rifle is new, then allowing the rifle to break in will loosen up the tolerances (read more gas blow by to slow/lengthen the unlock dwell time), or increasing the buffer mass such as a MGI buffer will slow the action down during unlock and allow the barrel pressure to drop down father before the extractor starts the case pull from the chamber walls (read less tension).

Before you really do anything to the rifle, my suggestion would be to break the rifle in with a few hundred rounds, and while you're at it, try a few different brands of ammo to see it the problem is only selective ammo related (high pressure/softer cases).

Or, if you would like one of use to break the rifle in for you, I'm sure we can find a RLL and a few C mags to do so in a very short time (read the barrel will be tension relieved when it’s all said and done).
Link Posted: 1/29/2006 6:11:54 AM EDT
[Last Edit: 1/29/2006 6:17:41 AM EDT by Wolf_Warrior]

Originally Posted By Dano523:
Primer ignites and the barrel pressure goes to 50,000 psi plus. Bullet passes the gas port, and starts the action cycling (carrier movement). Before the bolt unlocks, the bullet has exited the barrel and the barrel pressure has dropped down to 20,000 psi and falling.

Now your problem could be that you have a 223 chamber, yet trying to shoot Nato ammo in it. (Read over pressure, and the spent case unbinding from the chamber walls during the bolt cycle extraction pull). Correct ammo will solve this problem.

You have a new/rough/tight chamber, and again there is more case bound tension to the chamber sidewalls than needed during extraction. Allowing the chamber to self-polish out threw live fire will solve the problem.

Soft case ammo. Again ammo selection will solve this problem.

The gas port was drilled too large and over cycling. If the rifle is new, then allowing the rifle to break in will loosen up the tolerances (read more gas blow by to slow/lengthen the unlock dwell time), or increasing the buffer mass such as a MGI buffer will slow the action down during unlock and allow the barrel pressure to drop down father before the extractor starts the case pull from the chamber walls (read less tension).

Before you really do anything to the rifle, my suggestion would be to break the rifle in with a few hundred rounds, and while you're at it, try a few different brands of ammo to see it the problem is only selective ammo related (high pressure/softer cases).

Or, if you would like one of use to break the rifle in for you, I'm sure we can find a RLL and a few C mags to do so in a very short time (read the barrel will be tension relieved when it’s all said and done).



Its an RRA 5.56 upper from ADCO

I've probably got over 2000 rounds through her now.

I've used several different brands of ammo. I had "short stroking" problems with Wolf but I think that was partially due to a broken gas key screw (which has been replaced and re-staked).
Link Posted: 1/29/2006 7:23:07 AM EDT
At 2000 rounds, the chamber is about as polished as it's going to get in the carbine rifle.

If all ammo types has the bent rim marks when shot threw the rifle, your options are either send the barrel back for replacement (gas port too large) or changing out the buffer/spring to get more mass/tension to help lengthen the unlock dwell time (allows the barrel residual pressure to drop down father before the bolt unlocks and the pressure bound case is stripped off the chamber walls).

The wolf extra power spring goes for around $10, and either an H buffer or 9mm buffer goes for around $30.
Link Posted: 1/29/2006 8:06:58 AM EDT

Originally Posted By Dano523:
At 2000 rounds, the chamber is about as polished as it's going to get in the carbine rifle.

If all ammo types has the bent rim marks when shot threw the rifle, your options are either send the barrel back for replacement (gas port too large) or changing out the buffer/spring to get more mass/tension to help lengthen the unlock dwell time (allows the barrel residual pressure to drop down father before the bolt unlocks and the pressure bound case is stripped off the chamber walls).

The wolf extra power spring goes for around $10, and either an H buffer or 9mm buffer goes for around $30.



Yeah. That's what I was just going to do. I have the MGI Rate Reducing Buffer so I think I'll order the piano wire spring that MGI sells.

By the way, the rim is not bent. The rim face is being scored/marked by the ejector. I had a D-fender on it which I have now taken off. I have not shot it since I took it off so I haven't been able to see if that changes anything.

My thinking was that the D-Fender was putting too much resistance on the ejector causing it to score the rim as it grabbed the cartridge. The only problem with that theory is that there doesn't appear to be any "sliding" marks which I would expect if that were the case. However, it is clearly an impact created mark...the ejector is hitting the rim face hard enough to score the brass before it grabs the rim.

If that is truly the situation, then it wouldn't seem to be caused by pulling the case out. It is the reverse. The problem is happening when the cartridge is being seated in the chamber.
Link Posted: 1/29/2006 8:26:28 AM EDT
Although I've got a midlength gas system and this Armalite article is about carbine gas issues, I'd be interested to know more about this:

The faster movement of the carrier group in carbines also creates an interesting and largely unknown problem with the extractor. During extraction, the extractor opens for a very short period, and then recovers to complete extraction. The faster movement of the carbine bolt increase the time that the extractor is open. This tends to decrease extractor efficiency and increase extraction trouble.
www.armalite.com/library/techNotes/tnote48.htm (just beyond half-way down the page).

What do they mean "the extractor opens for a very short period, and then recovers to complete extraction"? Could that have anything to do with the problem?
Link Posted: 1/29/2006 8:28:16 AM EDT
If you are running the MGI buffer, then you shouldn't need a stronger spring.

Have you tried to run the rig with a standard buffer and not the added D ring?

Also, is this Winchester white box or Q-3131 ammo. The Wcc white box ammo does have softer brass, and it alone could be causing the problems.

P.S. If you in the DFW area, we can hook up and I take good look at the spent cases and rifle.
Link Posted: 1/29/2006 8:38:30 AM EDT
[Last Edit: 1/29/2006 8:39:27 AM EDT by Dano523]

Originally Posted By Wolf_Warrior:
Although I've got a midlength gas system and this Armalite article is about carbine gas issues, I'd be interested to know more about this:

The faster movement of the carrier group in carbines also creates an interesting and largely unknown problem with the extractor. During extraction, the extractor opens for a very short period, and then recovers to complete extraction. The faster movement of the carbine bolt increase the time that the extractor is open. This tends to decrease extractor efficiency and increase extraction trouble.
www.armalite.com/library/techNotes/tnote48.htm (just beyond half-way down the page).

What do they mean "the extractor opens for a very short period, and then recovers to complete extraction"? Could that have anything to do with the problem?



Not sure what point they are making.

Normal unlock is the bullet passes the gas port, and gas system gets charged at 50,000, then drops down to around 20,000 (falling) as the bolt spins (case still pressure bound to the chamber side walls), then extractor pull as the bolt lugs clear the extension lugs (carrier moving back and the cam at the front of the slot).

Only recovery that comes to mind is the extractor rotation/slip during bolt rotation, and unless the rim is oblonged, it should track the rim at all times (chamber is sealed off by the fire formed round so there should be no gas pressure applying to the extractor).
Link Posted: 1/29/2006 8:52:03 AM EDT
In looking through other Armalite Tech Notes, I found this:

--------------------
TECHNICAL NOTE 17: MARRING OF CARTRIDGE CASES
GENERAL: Cartridges fired in AR-10 and M16 family firearms bear characteristic scratches and marks which shooters sometimes think indicate defects.

5. Circular mark on edge of base, with shiny brass or shaved brass in evidence. Caused by case being pressed into ejector hole, with some burnishing or cutting as the bolt rotates.
---------------------

The marks on the rim face are consistent with bolt/extractor rotation. In other words, the scoring starts small then digs in -- if that makes any sense. I've already discovered what appears to be a malformed extractor head (see above).

There may still be gas/spring issues but this might be the most obvious cause of the scoring.

Link Posted: 1/29/2006 12:17:27 PM EDT

Originally Posted By Wolf_Warrior:
In looking through other Armalite Tech Notes, I found this:

--------------------
TECHNICAL NOTE 17: MARRING OF CARTRIDGE CASES
GENERAL: Cartridges fired in AR-10 and M16 family firearms bear characteristic scratches and marks which shooters sometimes think indicate defects.

5. Circular mark on edge of base, with shiny brass or shaved brass in evidence. Caused by case being pressed into ejector hole, with some burnishing or cutting as the bolt rotates.
---------------------

The marks on the rim face are consistent with bolt/extractor rotation. In other words, the scoring starts small then digs in -- if that makes any sense. I've already discovered what appears to be a malformed extractor head (see above).

There may still be gas/spring issues but this might be the most obvious cause of the scoring.



Be careful about confusing the ejector, and the extractor. This note is refering to the ejector. Randall_Rausch talks about this issue in his "how it works" post.


My thinking was that the D-Fender was putting too much resistance on the ejector causing it to score the rim as it grabbed the cartridge. The only problem with that theory is that there doesn't appear to be any "sliding" marks which I would expect if that were the case. However, it is clearly an impact created mark...the ejector is hitting the rim face hard enough to score the brass before it grabs the rim.

Again, some confusion here. The D-Fender works on the extractor, not the ejector.


I think Dano has a good point. Have you tried it without the D-Fender and with a standard buffer?



Link Posted: 1/29/2006 12:31:38 PM EDT

Originally Posted By Dano523:
If you are running the MGI buffer, then you shouldn't need a stronger spring.



ok



Have you tried to run the rig with a standard buffer and not the added D ring?



I took the D ring off but haven't had a chance to shoot it since then.




Also, is this Winchester white box or Q-3131 ammo. The Wcc white box ammo does have softer brass, and it alone could be causing the problems.




It is Winchester 3131 from Academy.




P.S. If you in the DFW area, we can hook up and I take good look at the spent cases and rifle.



Thanks for the offer but I'm in Austin. If I can't figure it out, maybe I can find a camera with better pictures. I first need to try some of the things we've talked about here and pay closer attention to what does what and when -- a little more diligent troubleshooting process.
Link Posted: 1/29/2006 12:37:36 PM EDT

Originally Posted By Triple_D:

Be careful about confusing the ejector, and the extractor. This note is refering to the ejector. Randall_Rausch talks about this issue in his "how it works" post.



Good catch. It is pretty clear to me, however, that the extractor is causing the scoring and that the turning bolt is causing the score pattern...for whatever that is worth.

There is some ejector "branding" also which might indicate a pressure issue...but I think it is within tolerances. The main thing that bothers me is the relatively severe scoring by the extractor. As I pointed out earlier, I think that the extractor is torqued/twisted. I have ordered a new bolt and will try that next weekend -- hopefully.

Link Posted: 1/29/2006 12:44:27 PM EDT
BTW...I have a carbine that leaves very similar marks on Q3131 brass from Academy. Maybe it's just damn high pressure ammo, combined with soft brass. Frankly, I don't worry about it since my rifle works fine. Next time I go to the range, I'll save a few pieces for comparison.
Link Posted: 1/29/2006 12:49:46 PM EDT

Originally Posted By Triple_D:
BTW...I have a carbine that leaves very similar marks on Q3131 brass from Academy. Maybe it's just damn high pressure ammo, combined with soft brass. Frankly, I don't worry about it since my rifle works fine. Next time I go to the range, I'll save a few pieces for comparison.



I'd just like to figure out what is happening. Maybe it is the soft brass. I need to pay close attention to other brands (esp. .223). I really wouldn't think much of it except that the scoring on serveral is pretty deep (it is not consistent) and I found one extractor mark that went over the primer. I apparently didn't cause premature ignition but....
Link Posted: 1/29/2006 3:41:19 PM EDT
Link Posted: 1/29/2006 4:15:23 PM EDT

Originally Posted By Randall_Rausch:
I tend to agree with soft brass and high pressures and maybe it's combined with too much gas as well.
The only way you get marks such as you are is for the brass to yield (flow) back into the ejector (round plunger) or extractor (square cut) receesses of the bolt face.
The bolt unlocking while the case is still holding on to the chamber walls is what gives you the wipe marks as the bolt smears or swages the brass back into place while unlocking.

As Dano already said, try some different ammo.



Wipe marks. Very descriptive and exactly what it is...almost like a tiny windshield wiper that digs deeper as it wipes. At the end of the swipe, it builds a small ridge of brass with -- sometimes a small pointed burr of excess brass extending away and in a direct line from the ridge.

So it is the bolt turning during the UNLOCK phase and not the "SEATING" phase? That makes much more sense. There would likely be much more force during extraction than there would be during "seating," right?

Of course, if the extractor claw is uneven (bent or torqued slightly), it would magnify the effect. Since the ejector is polishing the brass slightly, pressure is, as you say, probably involved. This is Q3131 so greater (but normal) pressure is to be expected, eh?

Thanks for your patience and information.

I'll try out the new bolt on Saturday and see if it repeats itself. If it does, I'll try some .223 stuff. If I've still got the marks...well, I'll post what I find anyway.
Link Posted: 1/29/2006 4:37:03 PM EDT

Originally Posted By Wolf_Warrior:
So it is the bolt turning during the UNLOCK phase and not the "SEATING" phase?



Correct. When the round is fired, the pressure forces brass from the case head to flow into, or to be extruded into, the ejector hole/extractor recess. Then, as the bolt rotates during the unlocking phase, this "extruded" brass is wiped or shaved off.
Link Posted: 1/29/2006 4:54:31 PM EDT
Some of the bolts I have that were shaving brass had a slight ridge running around the ejector hole. I could slide a small flat blade across it and it would catch the ridge. Guess they did not get it off in the manufacturing process. I was able to get it off and it reduced the shaving almost completely.
Link Posted: 1/29/2006 5:48:08 PM EDT
[Last Edit: 1/29/2006 5:48:54 PM EDT by Wolf_Warrior]

Originally Posted By Triple_D:

Originally Posted By Wolf_Warrior:
So it is the bolt turning during the UNLOCK phase and not the "SEATING" phase?



Correct. When the round is fired, the pressure forces brass from the case head to flow into, or to be extruded into, the ejector hole/extractor recess. Then, as the bolt rotates during the unlocking phase, this "extruded" brass is wiped or shaved off.



When I looked at one of the Armalite Tech Notes, it indicated that during the "seating" phase, the bolt turned clockwise. The scoring pattern on the rim face of the subject brass would indicate counter-clockwise movement of the extractor -- supporting the theory (or fact, for you experts) that the scoring was done during the unlocking phase.

I still don't know why I had one round with an extractor mark across the primer area. Oh well, one variable at a time.
Link Posted: 1/29/2006 5:51:56 PM EDT

Originally Posted By j3_:
Some of the bolts I have that were shaving brass had a slight ridge running around the ejector hole. I could slide a small flat blade across it and it would catch the ridge. Guess they did not get it off in the manufacturing process. I was able to get it off and it reduced the shaving almost completely.



Thanks.

I'll check that too but these are mostly extractor marks. I have some ejector "imprinting" but it doesn't appear to be significant...just polishing...no digging or malformed rims.
Link Posted: 1/29/2006 6:42:48 PM EDT

Originally Posted By Wolf_Warrior:
When I looked at one of the Armalite Tech Notes, it indicated that during the "seating" phase, the bolt turned clockwise.



That is incorrect. The bolt rotates counter-clockwise when it locks, and clockwise when it unlocks....assuming you are looking down the barrel, the way you would when normally holding the rifle.
Link Posted: 1/30/2006 5:57:44 AM EDT

Originally Posted By Triple_D:

Originally Posted By Wolf_Warrior:
When I looked at one of the Armalite Tech Notes, it indicated that during the "seating" phase, the bolt turned clockwise.



That is incorrect. The bolt rotates counter-clockwise when it locks, and clockwise when it unlocks....assuming you are looking down the barrel, the way you would when normally holding the rifle.



It is helpful to have a reference point, isn't it? Thanks for pointing that out. I was looking at the bolt from the bolt face. So...let me restate...

The mark on the rim is the result of a clockwise rotation of the bolt (looking down the barrel). Therefore, the scoring must be occuring at the unlock phase.
Link Posted: 1/30/2006 7:34:15 AM EDT
[Last Edit: 1/30/2006 7:35:40 AM EDT by Dano523]
Since you can use the reference points of the bolt face (ejector mark verses the extractor mark), you should be able to see if the marring is happening during ignition (bolt locked), or during the pull when the bolt is unlocked.

If the rim is not being bent, then my guess is that you are getting case flow at ignition, and if one side of the extractor case rim relief section (channel below the claw) is protruding above the face of the bolt, This could be causing the mark.

Or, the extractor is loose in the bolt, it could be that with the added retention of the extractor to the case rim (d-fender), as the bolt goes to make the spin, the extractor is being canted while is allowing the protruding edge (past the bolt face) to dig into the back of the case.

If it is the latter, then you may want to check the claw face and the ends of the rim relief channel on the extractor. A protruding milling bur at one of these areas will dig into the case and not allow the extractor to cleanly slip as the bolt goes to unlock.

------------------
Now so we are all on the same page and don’t get to the point that we are strapping band-aid on other band-aid, we really need to know if the rifle will cycle correctly without the use of the MGI buffer, and the D-ring.

If the original problem with rifle is the gas port was drilled to large, and using the D-fender for more extractor tension, and the MGI buffer to slow/lengthen the unlock dwell time to solve the problem, then the mar’g may be just a part of life you will have to live with if sending the barrel back is not a option to be taken.

Hell, truth be told on military rifles, no consideration is even thought of how the brass is treated once it is fired and being ejected from the rifle. To take it one step further, there are HK shooters out there that are just rolling there eyes since normal damage to the spent case coming out of a delayed blow back action with a fluted chamber verse the minor problems you’re having is night and day apart.

So to conclude, if cleaning up the extractor burs helps, this problem is single ammo type related, and/or the end product of band aiding added (D-ring and MGI buffer), we could take this 6 pages and still be going round and round trying out different band-aids of the week as each new introduced band-aid causes yet another side effect. Where the side effects to other products like Vaigra are cardiac Death (no shit, and listed in the warning sheets), the minor case base mar'g should be very doable (especially if you never intend to reload the cases).
Link Posted: 1/30/2006 6:34:56 PM EDT
1. I don't think that the barrel is the problem...at least not yet.
2. I will eliminate the variables -- hopefully -- this weekend.
3. Viagra is GOOD and is worth the risk.
Link Posted: 1/30/2006 8:01:01 PM EDT
The more you describe what is going on, the more I am convinced you just have an out-of-spec extractor. RRA is not perfect, they do send out substandard parts every so often. Fire the rifle with the new bolt and extractor and see what happens. If the marks go away, then try to isolate if it is the old extractor or old bolt that is the problem by switching around parts.

At this point, I don't really see the problem being an issue with pressure, timing, or the recoil spring/buffer. I could be wrong, but I wouldn't worry about these things until you have ruled out the old extractor/bolt being the culprit.
Link Posted: 1/31/2006 3:41:29 AM EDT

Originally Posted By jason_h:
The more you describe what is going on, the more I am convinced you just have an out-of-spec extractor. RRA is not perfect, they do send out substandard parts every so often. Fire the rifle with the new bolt and extractor and see what happens. If the marks go away, then try to isolate if it is the old extractor or old bolt that is the problem by switching around parts.

At this point, I don't really see the problem being an issue with pressure, timing, or the recoil spring/buffer. I could be wrong, but I wouldn't worry about these things until you have ruled out the old extractor/bolt being the culprit.



That's pretty much where I've gotten to. Step one will be firing with the new bolt (no other changes). If that doens't work, I'll try different (lower pressure) ammo. If that doesn't work, then...well, I'll be back for more advice...probably a stronger spring.

Thanks a TON for all of your thoughts. I'll let you know how it works out.

I'm in DC this week on business so hopefully I can sneak out of the house long enough to work this through on Saturday.
Link Posted: 2/1/2006 12:00:23 PM EDT
Look familar?

Link Posted: 2/2/2006 6:00:14 PM EDT
[Last Edit: 2/2/2006 6:01:12 PM EDT by Wolf_Warrior]

Originally Posted By Triple_D:
Look familar?

images.snapfish.com/345%3B%3A62%3B2%7Ffp338%3Enu%3D3256%3E%3B87%3­E338%3EWSNRCG%3D32334%3A5262389nu0mrj



Where'd you get my brass? Actually, your ejector marks are a quite a bit brighter than mine and my extractor marks might be a bit deeper on the edge but ... all in all...that's it.
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