The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools Search this Thread
Old February 6, 2015, 03:11 PM   #51
Tinbucket
Senior Member
 
Join Date: January 17, 2015
Posts: 355
Need some advice from handloaders for .308

Kind of a diverent thread but for slam fires in Garand and M16 or AR15.
There are or were Titanium firing pins available for the M16. I haven't ordered on since I've not had the problem. It might take a bit of a search for them, if still available. Lither firn pins help with slam fires.
I have a Garrand and ran across mention of a spring loaded firing pin.
I didn't book makr it but others I'm sure know a lot more about these two subjects.
Tinbucket is offline  
Old February 6, 2015, 05:36 PM   #52
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
Quote:
Thanks for that info. I do understand why it happens (now), but did not know about that ammo. It was the Superperformance ammo. I do have an adjustable gas block on it now and will try again. I completely understand the whole chain of events causing the swiped head and all that, however,..... The bulges caused by the ejection holes still have me a little confused. I understand the timing and that the bolt is trying to pull the case out before it has shrunken back down to size, but those two ejector port hole bulges must be caused at the very moment the round is fired. That's the only point where the pressure is that high and the bolt is not turning yet, which pushed the soft hot brass in to those two holes. I don't see how closing off the gas port can have any effect at all on the initial pressure and those two dimples/bumps???? With the adjustable gas block and the timing being corrected, I can see how it will no longer swipe those two bumps off, but they would most likely still be there correct? The gas block is not changing the pressure that the round creates, it's just changing how much of it comes back (and when) to the bolt. Does that all make sense? Anyway, thanks for that link. Luckily I only had a few shots before I realized that this was happening. Hopefully the gas block corrects it all. Thanks again.
No problems. As to the amount of pressure verses the ammount of gas, those are two important concepts to understand. The "initial pressure" needs to be in a mechanically locked environment. Superformance ammo reaches peak pressure sooner, and stays there longer, than normal ammunition. Weird stuff happens when you get early bolt unlocking. Superformance doesn't produce more pressure, it just produces more gas to get more performance. So you get more pressure both earlier and later, with the same peak maximum pressure where it should be.

I don't know if I have the words to explain why you have two dimples, but I'll try.

But, what I expect the two dimples are is one from the bolt pushing the cartridge into the chamber on loading, and the other on early extraction. I think the brass is catching in the chamber before the bolt rotates into the locked position. As your ejector spring weakens with time and the chamber dimensions grow, expect one of the dimples to start fading away.

Hope this helps,
Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old February 6, 2015, 05:50 PM   #53
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
There's one section of extruded brass back from the case head normal flat surface for each cutout in the bolt face that lets brass extrude back into it.

Look at the bolt face and its cutouts will be a mirror image of the case heads.

Would be good to see pictures of both bolt face and case head for the most extruded case for all to see and compare.
Bart B. is offline  
Old February 7, 2015, 02:48 PM   #54
rboyer224
Junior Member
 
Join Date: February 2, 2015
Posts: 5
So are you saying it's normal for the brass head to extrude back in to the bolt face holes? Is it going to continue to do this even when the gas block is adjusted correctly? I hope not. That kind of ruins my reloading brass!! Here's a picture of the bolt.
Attached Images
File Type: jpg 20150207_134035 (800x450).jpg (136.7 KB, 12 views)
rboyer224 is offline  
Old February 7, 2015, 02:57 PM   #55
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
You have twin ejectors, so twin ejector marks are to be expected with high pressure signs. I was wrong in my previous assessment.

But during normal firing the brass will push back into the bolt face. Under normal pressure this will not prevent your brass from being reloadable. Properly adjusted, you shouldn't be ruining brass.

Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old February 7, 2015, 03:10 PM   #56
rboyer224
Junior Member
 
Join Date: February 2, 2015
Posts: 5
Very good. Thanks Jimro. I was hoping that would be the case.
rboyer224 is offline  
Old February 7, 2015, 07:04 PM   #57
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
Cartridge brass starts extruding into bolt face holes at about 65,000 cup or 75,000 psi. Pressure in those cases is way too high for safety. Cut the charge 5 grains then try again.

I've shot .308 proof loads that didn't have anything like those cases do.
Bart B. is offline  
Old February 7, 2015, 08:20 PM   #58
rboyer224
Junior Member
 
Join Date: February 2, 2015
Posts: 5
Bart B

Thanks sir, but if you look back, that ammo is factory Hornady ammo. That's why I've been asking the questions. If it were my handloads I would assume full ownership and of course reduce the charge.
rboyer224 is offline  
Old February 7, 2015, 10:29 PM   #59
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
I forgot about it being factory ammo.

Now I think the barrel is bad. Have someone measure chamber, bore and groove dimensions. Something is way too small.

My first guess is the chamber is too short from bolt face to chamber mouth. The firing pin drives the case mouth hard into the chamber mouth crimping it into the bullet. That raises pressure. Fire an empty primed case in it then see if the case mouth is crimped in.

Last edited by Bart B.; February 7, 2015 at 10:35 PM.
Bart B. is offline  
Old February 8, 2015, 09:14 AM   #60
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 7,097
Bart B.

The ammo in question is Hornady Superformance, which has a different pressure curve than standard ammunition.

The adjustable gas block should fix the problem, which is that the sooner than expected peak pressure is causing earlier unlocking while the cartridge is still under significant pressure. It may turn out that the lot of Superformance being used is just unsuitable to that rifle, although I think the adjustable gas plug will work. But a potentially bad lot of ammo isn't out of the realm of possibilities either.

We used to see this when people would try to run "Hornady Light Magnum" loads through Garands and M1As without adjustable gas plugs and they'd ruin the op rods.

Jimro
__________________
Machine guns are awesome until you have to carry one.
Jimro is offline  
Old February 8, 2015, 09:11 PM   #61
gman3
Senior Member
 
Join Date: December 19, 2008
Posts: 408
As someone already said before, try some Federal GMM in the rifle and see how it shoots with that. If it shoots good with that, then work on your loads. If not, then think about what may be wrong with the rifle.
gman3 is offline  
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 04:24 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.07725 seconds with 11 queries