Gun store Shooting Locations It is currently Thu Mar 28, 2024 2:25 pm



Rules WGO Chat Room Gear Rent Me Shield NRA SAF CCKRBA
Calendar




Reply to topic  [ 36 posts ]  Go to page 1, 2, 3  Next
 Bolt Carrier Locking On Mag Catch 
Author Message
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
We've got two 6.8's in the house and both have been doing the same thing. I didn't notice the first one doing it until I built the second one and was doing a more thorough function check on it. So here's what going on. Both rifles lock back on an empty magazine but, they lock on the carrier and mag catch. Not the bolt and mag catch. I'm clocking 95gr projectiles at over 2800fps.
Carbine buffer and carbine springs. Mid length gas system. I even took a deer last year with one of them and it doesn't suffer any apparent losses in accuracy.
So here's what I've tried so far:

Lubed buffer spring and buffer extension
Checked gas rings
Checked gas block alignment
Ported gas tube to match diameter of gas block.
Checked gas port in barrel.
Sealed the gas tube to the block and gas block to the barrel with gasket sealer.
Changed buffer weight down to 2.2oz
Swapped bolt carrier from a known working firearm

None of that made a difference.

So I took one of the 6.8 uppers and put it on my 300blk lower. The same firearm that was the donor bolt carrier for test. I even left the carbine buffer in it. BANG. Lock on bolt! :bigsmile:
OK so WhAT is your major malfuction???

I'm out of ideas and internet searches aren't giving me any insight. The only thing I can think of now to try is, turning the buffer tube back out a turn or two.

Anyone got any ideas?


EDIT: I just went to back out the buffer extension by one turn and the buffer retainer was free to come out. So that's not going to work either.

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Sun Apr 23, 2017 6:57 pm
Profile WWW
Online
Site Admin
User avatar
Site Admin

Location: Olympia, WA
Joined: Fri Mar 11, 2011
Posts: 38291
Real Name: Dan
What happens when you slowly manually cycle the carrier on an empty mag? Is the mag not seated high enough to push the catch up all the way? Do you have anything on the catch, like a BAD lever etc that could be causing resistance?


Mon Apr 24, 2017 5:52 am
Profile WWW
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
No BAD lever. The catch works when you manually cycle the bolt carrier group. It also works when you drop the mag after the last shot. But it's caught on the carrier not the lugs of the bolt.

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Mon Apr 24, 2017 7:17 am
Profile WWW
Site Supporter
User avatar
Site Supporter

Location: East Renton Plateau
Joined: Tue Jul 5, 2011
Posts: 909
Is the BCG able to travel back as far in the 6.8 lower as it does in the 300blk lower?
Could the BCG be outrunning the mag spring in the 6.8 mags?
Have you compared spring and buffer lengths?

Sent from my SM-G935T using Tapatalk


Mon Apr 24, 2017 9:16 am
Profile
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
1811GNR wrote:
Is the BCG able to travel back as far in the 6.8 lower as it does in the 300blk lower?
Could the BCG be outrunning the mag spring in the 6.8 mags?
Have you compared spring and buffer lengths?

Sent from my SM-G935T using Tapatalk



Yes. It will function as it should when it is cycled by hand. I can pull the charging handle back and the bolt lugs are caught by the catch. It does that in both lowers.

Yes, I compared the springs and buffer lengths last night after the original post.
The 6.8:
Spring is 10.25"
Tube is 7.125"

The 300blk:
Spring is 10.5"
Tube is 7.25"

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Mon Apr 24, 2017 9:44 am
Profile WWW
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
Thinking about physics....I would need a helper to shoot video in slo-mo to verify but, what if it's not short stroking at all? What if the follower spring is too slow (not enough tension) and the buffer spring is ahead of (faster than) the follower spring. It could be that the follower is not coming up fast enough for the bolt to catch.

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Mon Apr 24, 2017 9:53 am
Profile WWW
Site Supporter
User avatar
Site Supporter

Location: East Renton Plateau
Joined: Tue Jul 5, 2011
Posts: 909
dreadi wrote:
Thinking about physics....I would need a helper to shoot video in slo-mo to verify but, what if it's not short stroking at all? What if the follower spring is too slow (not enough tension) and the buffer spring is ahead of (faster than) the follower spring. It could be that the follower is not coming up fast enough for the bolt to catch.

That is what I was trying to say with: "Could the BCG be outrunning the mag spring in the 6.8 mags?" Wasn't very clear was it.

Sent from my SM-G935T using Tapatalk


Mon Apr 24, 2017 2:58 pm
Profile
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
1811GNR wrote:
dreadi wrote:
Thinking about physics....I would need a helper to shoot video in slo-mo to verify but, what if it's not short stroking at all? What if the follower spring is too slow (not enough tension) and the buffer spring is ahead of (faster than) the follower spring. It could be that the follower is not coming up fast enough for the bolt to catch.

That is what I was trying to say with: "Could the BCG be outrunning the mag spring in the 6.8 mags?" Wasn't very clear was it.

Sent from my SM-G935T using Tapatalk



Earlier today I couldn't figure out where I got that idea from. Didn't mean to steal your thunder. Thank you.

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Mon Apr 24, 2017 6:45 pm
Profile WWW
Site Supporter
User avatar
Site Supporter

Location: Everson, WA
Joined: Sun Jan 6, 2013
Posts: 28149
Real Name: Ace Winky
dreadi wrote:
So I took one of the 6.8 uppers and put it on my 300blk lower. The same firearm that was the donor bolt carrier for test. I even left the carbine buffer in it. BANG. Lock on bolt! :bigsmile:


I was going to guess a nasty bolt rough bolt, so that kills that idea.

Never had a lower give me any trouble so I am in guess land right now.

What trigger and hammer group are you using? I mean it's possible but not very probable the hammer (spring) is using up a bunch of the energy.

_________________
Why does the Penguin in Batman sound like a duck?

Because the eagle sounds like a hawk.


Mon Apr 24, 2017 7:18 pm
Profile
Site Supporter
User avatar
Site Supporter

Location: Everson, WA
Joined: Sun Jan 6, 2013
Posts: 28149
Real Name: Ace Winky
Or somehow the bolt carrier is illicitly contacting the inside of the tube, or the buffer is. Some kind of lower misalignment.

A real clue is they both do it. I think comparing them to a running AR would be wise.

_________________
Why does the Penguin in Batman sound like a duck?

Because the eagle sounds like a hawk.


Mon Apr 24, 2017 8:10 pm
Profile
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
Compare in what ways? Oh you mean to another 6.8.

Trigger and LPK are BCM

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Mon Apr 24, 2017 10:01 pm
Profile WWW
Site Supporter
User avatar
Site Supporter

Location: Everson, WA
Joined: Sun Jan 6, 2013
Posts: 28149
Real Name: Ace Winky
dreadi wrote:
Compare in what ways? Oh you mean to another 6.8.

Trigger and LPK are BCM


What is different about the two lowers that don't work and your .300 that does work?

Do your 6.8 lowers work with your 5.56 and .300 uppers?

_________________
Why does the Penguin in Batman sound like a duck?

Because the eagle sounds like a hawk.


Tue Apr 25, 2017 3:13 am
Profile
Site Supporter / FFL Dealer
User avatar
Site Supporter / FFL Dealer

Location: Tacoma, Washington
Joined: Fri Nov 21, 2014
Posts: 8328
The 6.8 lower works with the 5.56 upper.

I can't put the 300blk upper on any other lower because it creates an SBR.

_________________
BLACK HAMMER ARMS
Buy A Suppressor http://www.silencershop.com/blackhammerarms
Type 7 Class 2 SOT NFA Dealer
1911 Pistolsmithing
Firearm Refinishing
GLOCK Certified Armorer
CMMG Authorized Dealer
NEMO Arms Authorized Dealer
http://www.blackhammerarms.com
http://www.facebook.com/blackhammerarms
https://www.instagram.com/blackhammerarms/


Tue Apr 25, 2017 7:14 am
Profile WWW
Site Supporter
User avatar
Site Supporter

Location: Everson, WA
Joined: Sun Jan 6, 2013
Posts: 28149
Real Name: Ace Winky
dreadi wrote:
The 6.8 lower works with the 5.56 upper.



So there is some interference in just your 6.8 combos. Interesting. Just side by side compare to your 5.56 with mics and calipers all sliding and contact areas. Sherlock eyeballs on. Something is hanging, the tips above about mag fits and such could be spot on.

_________________
Why does the Penguin in Batman sound like a duck?

Because the eagle sounds like a hawk.


Tue Apr 25, 2017 7:30 am
Profile
Site Supporter
User avatar
Site Supporter

Location: Bellingham Canada
Joined: Thu Jan 3, 2013
Posts: 4998
Real Name: Josheewa
What a drag. :cussing:
Have you tried multiple mags from different manufacturers?

_________________
It must be frustrating always being the smartest person in the room.-Jagerbomber35


Divided we fall.


Tue Apr 25, 2017 7:52 am
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 36 posts ]  Go to page 1, 2, 3  Next

Who is online

Users browsing this forum: No registered users and 20 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum



Rules WGO Chat Room Gear Rent Me NRA SAF CCKRBA
Calendar


Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF.
[ Time : 2.310s | 19 Queries | GZIP : Off ]