The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: Semi-automatics

Reply
 
Thread Tools Search this Thread
Old January 20, 2020, 08:37 PM   #251
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
I do intend on breaking out a separate thread for it--this isn't the place for it as this should be for 350 Legend related stuff--though it is my thread so I can break the rules every now and then.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 21, 2020, 12:42 PM   #252
9x19
Senior Member
 
Join Date: October 15, 1998
Location: Sherman, TX USA
Posts: 3,547
Maybe change the title then: .350 Legend Madness

__________________
Make mine lean, mean, and 9x19!
9x19 is online now  
Old January 21, 2020, 09:08 PM   #253
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
Quote:
....350 Legend Madness....
to be sure....

(you don't have to be mad... but it helps)
mehavey is offline  
Old January 22, 2020, 01:53 AM   #254
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
heya mehavey--I'm still very curious about what the "no-go" headspace measurement is for your CMMG AR in 350 legend--I'm almost certain the reason for the failure I experienced and the near failure you had was due to excessive headspace that allowed for the head of the case to be unsupported while fired. The tolerance for the ptg gage is 1.714 and that is what the savage axis tolerance is made to--but my Faxon set-up went with the default SAAMI spec max of 1.72 which is what allowed the area above the web in the starline case to be unsupported IMO.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; January 22, 2020 at 02:01 AM.
stagpanther is offline  
Old January 22, 2020, 07:02 AM   #255
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
Stag, it's where the excess headspace (if any) might be.

- If the boltface-to-chamber threshhold is outside of spec/too long*, then a thin web floor can statistically expose the case wall.
- If, on the other hand the bolt-to-chamber distance is OK, the remaining distance to case mouth is no big deal.

How does one measure that critical bolt-chamber distance ?



* e.g., chamfer too deep/long
mehavey is offline  
Old January 22, 2020, 10:31 AM   #256
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
Quote:
How does one measure that critical bolt-chamber distance ?
It's pretty easy really. You can either use a no-go gage like ptg makes--or take a piece of sized brass and add thin spacers to the rim face until you you can't get the bolt to close without significant force--record what that measurement is. You should remove the ejector and extractor to get a precise measurement. As I've said, if that total space can conceivably exceed case support and still be within SAAMI max spec (which in the case of my Faxon AR set-up it could with starline brass)--toss of the dice whether your cartridge has necessary head support.

The thing is--the ptg no-go gage is set to not close at 1.714--so AR's and other auto-loaders might be compliant with SAAMI specs and still close on the 1.714 no-go gage. Not good.

I've already decided I'm going to use nothing but Hornady brass since it's the only brass that comes at a max length of 1.71. I wish I had known that before I ordered the 1,000 or so starline and winchester cases.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; January 22, 2020 at 10:42 AM.
stagpanther is offline  
Old January 22, 2020, 06:07 PM   #257
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
Overall case length isn't the problem.
The problem is overly-long Bolt face-to-Chamber distance, combined w/ thin case web floor.

mehavey is offline  
Old January 22, 2020, 09:19 PM   #258
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
Nicely done--your illustration does get to the heart of the unsupported case head issue. However--what's important to note is that it is because the SAAMI spec inherently allows a max 1.72 headspace as compliant the delta between that and the 1.714 of the ptg no-go gage is what allows the head area of brass like starline's to be potentially unsupported if the case backs all the bolt breech face upon firing. Using the ptg gage a user might be unaware of that since it could close on an autoloader--which is the case with my Faxon barrel and carrier. I suspect ptg's 1.714 no-go is what the SAAMI specs will eventually settle on.

Doing a cast should get you very close to the actual chamber dimensions, I think it would then be a matter of getting your total headspace and subtract the chamber case support area from the headspace and then take that result and then subtract the distance of the case rim face to the top of the case web. If the result is negative--then I think that would mean it's supported by the chamber. If that result is positive--that would mean part of case above the head could be unsupported potentially if the case rim face was backed all the way to the bolt breech face upon firing. That's what I think is going on with the loads I did using starline.

Why do I think hornady's brass is better being closer to the full 1.71? Again, just pure conjecture on my part, but the timing of the peak pressure and gas cycle in an autoloader with the 350 legend is a tricky thing--in part because of it being such a long strait wall cartridge. I know at least in the case of my Faxon barrel that's why they chose the short carbine gas length to reliably cycle in an 18" barrel. What I found was that depending upon when that peak pressure was achieved--and how fast the case sealed to the chamber--that had a pretty significant effect on gas leakage which in turn effects consistency. Of all the boxes of factory ammo I tested hornady's whitetail showed the least signs of gas leakage and usually the best consistence and SD numbers.They are powder wizards--so maybe that was one reason I got better results--but they also have significantly longer brass than the other guys. I think it does make a difference--but can't exactly empirically prove it.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; January 22, 2020 at 10:09 PM.
stagpanther is offline  
Old January 24, 2020, 08:36 PM   #259
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
A Legend is [re]born

Being a glutton for punishment, I decided to make another go--but this time I used a cheap Anderson upper which I lapped the receiver face. I then canibalized one of the three 224 valks I built for the rest of the parts

Attached Images
File Type: jpg IMG_2656.jpg (84.3 KB, 52 views)
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 24, 2020, 08:50 PM   #260
9x19
Senior Member
 
Join Date: October 15, 1998
Location: Sherman, TX USA
Posts: 3,547
Well... it looks good!

Maybe the AR deities will treat you better on this go.

__________________
Make mine lean, mean, and 9x19!
9x19 is online now  
Old January 25, 2020, 12:14 AM   #261
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
I hope so too ; )
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 25, 2020, 02:46 PM   #262
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
I fired the new build and it shot very well, quite accurately. Then, while firing the hornady American whitetail ammo the last cartridge did not eject--after mortaring the case came out--bulged at the head. It passed both the go and no-go gage tests--though the no-go passing was meaningless since the headspace is well beyond the ptg gage's 1.714. I had added spacers to the gage and it stopped closing at about 1.718

I can take a hint, time to call it a day with this one.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 25, 2020, 04:05 PM   #263
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
Stag . . .
Can U Spell "Snakebit" ?
mehavey is offline  
Old January 26, 2020, 09:58 AM   #264
9x19
Senior Member
 
Join Date: October 15, 1998
Location: Sherman, TX USA
Posts: 3,547
Wow... I was hoping (though not really expecting) things would turn out different as I still like the idea of that cartridge.
__________________
Make mine lean, mean, and 9x19!
9x19 is online now  
Old January 26, 2020, 10:34 AM   #265
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
The cartridge ain't the problem... no more/no less than any of the AR straightwalls like the 450 BushMstr or the 50 BeoWooof.

Somehow we're getting the critical Bolt-to-Chamberwall-Start dimension wrong in the builds, and it's getting rolled into the much simpler term/overall cartridge length "headspace"




With all the 556 ARs being built -- operating at that same pressure/with that same critical distance -- it ought to be a no-brainer. But again, I don't know how to measure it.
mehavey is offline  
Old January 26, 2020, 05:21 PM   #266
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
It's not a mystery--SAAMI specs as submitted by winchester specify a max headspace of 1.720. If the top of your case head will not be supported by the chamber--you are tossing the dice.
Quote:
Wow... I was hoping (though not really expecting) things would turn out different as I still like the idea of that cartridge.
I'm guessing this problem has already been accounted for by most gun manufacturers--but as with other intros there might still be some components out there that fall to the max end of specs.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 26, 2020, 05:57 PM   #267
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
Quote:
It's not a mystery--SAAMI specs as submitted by winchester specify a max headspace of 1.720.
If the top of your case head will not be supported by the chamber--you are tossing the dice.
Apples vs Oranges.

A. AR straightwall headspace is simply bolt-face-to-case-mouth stop. SAAMI: 1.710-1.720"
B. The problem is bolt face distance to chamber transition/start SAAMI: 0.200" ... two different measurements.

As long as the bolt face forces the cartridge in far enough to have the web floor safely/fully clear the chamfer cutout, everything's fine. (case length/headspace is irrelevant)
When the web floor is left hanging out there, however (B. above > 0.200"),* then you gotta problem no matter what.

Two ways that can happen:
- Bolt face is too far back from chamfer/chamber transition
- Chamfer is cut too deeply into the chamber

I'm beginning to think that the chamfer cut is the problem.




* Or.... the case head thickness (base-to-web-floor) is << 0.200"

Last edited by mehavey; January 26, 2020 at 06:47 PM.
mehavey is offline  
Old January 26, 2020, 07:14 PM   #268
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
Quote:
I'm beginning to think that the chamfer cut is the problem.
I consider case support exclusive of the chamfer/radius in the chamber face.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 26, 2020, 11:12 PM   #269
P Flados
Member
 
Join Date: January 8, 2017
Location: Wilmington NC
Posts: 90
Stag, I understood what Mehavey has been talking about since the beginning, but did not focus on it as we were trying to understand the cause of the overpressure.

First, lets assume that the bolt has the correct depth for a recess. A bolt problem big enough to matter would be gross and obvious.

For an AR, inadequate case wall support is caused by the way the barrel is cut, a bad barrel extension, how much chamfer/rounding was done or a combination of the above. The associated dimensions and tolerances are generic to all AR-15 platforms that use a standard bolt and barrel extension (including the 223, 5.56, 300 BO, etc.). There is nothing about this that would be different for a 350L.

I have cut and threaded a couple of AR barrels. The distance from the working face of the barrel extension locking lugs to the back surface of the barrel needs to be just enough for a bolt to rotate into the locked up position. With a barrel out of the upper, insert a bolt and rotate it into the locked up position. It should have very little free play forward and backward. I took a spare barrel and the free play was about the thickness two layers of card stock.

Next there is any chamfer and/or rounding at the chamber entrance. The removed metal for a chamfer and/or rounding increase the effective distance from the bolt face to the back of the chamber.

If there was no free play and no chamfer/rounding, the only portion of the case not fully enclosed by the chamber would be the portion extending into the bolt face recess.

If your free play of an engaged bolt is more than it should be, you could have a problem even with a normal chamfer / rounding at the chamber entrance. If your chamfer / rounding is excessive you can be in trouble even with normal free play. If both are "on the long side" it could be the combination that causes the problem.

Excessive free play is just bad machining by the guy that cut the barrel (most likely) or by the maker of the barrel extension (less likely).

Limits on the chamfer / rounding may not be as explicit and/or may be harder to measure/control. With all of the "my gun does not feed" complaints that the 350L had early on, cutting too much chamfer / rounding could have been intentional by someone that did not fully appreciate the downside of what they were doing.

Last edited by P Flados; January 26, 2020 at 11:40 PM.
P Flados is offline  
Old January 26, 2020, 11:34 PM   #270
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
No disagreement to what you and mehavey are saying--his illustration shows the problem perfectly. What I am pointing out--is that you could have ammo or component manufacturers staying within specs and still have a potential for problem. I mentioned to mehavey earlier the issue of the depth of the radius chamfer cut to the chamber face as being a contributor to the problem. Again, I believe that if the AR set-up I have complied with ptg's default for 1.714 on the no-go (I'm guessing ptg also makes the chamber and bore reamers many manufacturers are using) most likely there would be no issues even with the AR I have.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 26, 2020, 11:58 PM   #271
P Flados
Member
 
Join Date: January 8, 2017
Location: Wilmington NC
Posts: 90
An AR chamber is usually cut after the barrel extension is installed so that they can get the headspace just right.

If they cut the length of the threaded shank on your barrel too short, they could still have set up the correct headspace.

If they cut the length of the threaded shank on your barrel too short, you have a "bad barrel" with excessive bolt engagement free play. If this is your problem, the maker should be replacing your barrel at no cost to you or otherwise making things right.

Too much chamfer / rounding is still a "bad barrel" but it would be harder to make a case that they made an outright mistake.

Last edited by P Flados; January 27, 2020 at 12:06 AM.
P Flados is offline  
Old January 27, 2020, 08:19 AM   #272
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,515
The only other reasonably plausible cause of "Mag Belt Syndrome" would opening too early.
Just a thought.






So far, after 300 rounds or so, no strange CMMG issues -- and it feeds
high-pressure 200-240gr cast very reliably. (2,000/1,800 fps respectively)
(and of course, now I've jinxed it)
mehavey is offline  
Old January 27, 2020, 09:09 AM   #273
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
Quote:
The only other reasonably plausible cause of "Mag Belt Syndrome" would opening too early.
Just a thought.
In my particular barrel timing of peak pressure would be an issue IMO because of the very short gas system. However, as long as the head is supported I don't think there would be anything to worry about (unless you really did have an over-pressured cartridge for other reasons).
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 27, 2020, 09:55 AM   #274
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 6,793
In the recent overpressure with the hornady factory ammo there was a rather interesting side effect I noticed on the bolt carrier--the extractor was slightly bent in and down (definitely happened after the firing of the particular cartridge). I've noticed in other bulged and failed cases that there was a bending down of the rim in the area of the extractor (as I had mentioned before). I'm now thinking the cartridge possibly went into battery with the rim in front of the extractor.
__________________
If you’re ever hiking in the woods and you get lost, just look up and find the brightest star in the sky and you’ll know which way space is.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Old January 27, 2020, 11:14 AM   #275
MarkCO
Senior Member
 
Join Date: October 21, 1998
Location: Colorado, USA
Posts: 2,727
Curiously watching this thread stag. Enjoy your work and I really like the idea of the .350L. Ready to ditch my .450BM and .450Corvette to switch to the L, but I will be patient. I jumped on the .224V too soon and frankly, it really does not do much more than my 5.56Nato pressure loaded match ammo from the 223Wylde chambered guns. Sold my original and will be unloading the JP barrel kit instead of building one up.
__________________
Good Shooting, MarkCO
www.CarbonArms.us
MarkCO is online now  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 10:19 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2018 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.10390 seconds with 11 queries