WHY????? Mag feed vs. Hand feed

[Thumper580]

I've been shooting AR's for 30 years, have built a ton of them. My target AR15 (223) shoots 3/8", 100 yard groups pretty easily and consistently from the magazine.
Built another AR10 308 with top tier products... because I'm pigheaded and won't give up.
Matched AERO upper and lower
Nightforce ATACR 7-35 F1 Mil C
ARC M Brace mount
Midwest industries FF handguard
SLR adjustable gas block, 9 oz. buffer
Triggertech Diamond trigger
Craddock Precision custom Bartlien heavy 18" barrel
Rubber City Armory bolt carrier with JP high pressure bolt headspaced to the barrel.
Handloading using Sierra, Berger 168, 169 and 175 hpbt, Lapua brass, etc. etc.
Probably pounded 5-6 hundred dollars of components into the berm......
All Magazine fed...because that's how it's supposed to shoot.
Every group always looks like the one on the LEFT.....
TODAY out of frustration I had 5 rounds left exactly like the ones in the left target......and for some unknown reason I decided to single feed them. I pushed a round into the chamber and dropped the bolt release for each one.
Single feed is on the right!!!!!! WTF. Seriously. 0.142" 5 shot group.
Why the difference? Is it a result of the violent forces of the BCG slamming back and forth? Sort of depressing since it's a semi auto......
What is happening during the BCG cycling process that's introducing so much inaccuracy?

 

[DemonicLemming]

Not enough neck tension on the brass and changing CBTO on bolt close? Sharp edges on the barrel extension chewing up bullet jackets?

 

[roostercogburn98]

This has been discussed on here quite a bit if I remember correctly. Some say BCG settles differently when using semi auto vs bolt release vs racking the charging handle and letting that send the BCG forward. I believe the consensus is the BCG is resting at slightly different positions for each style and shows up on target.


Someone will be along shortly to correct me

 

[Thumper580]

Not enough neck tension on the brass and changing CBTO on bolt close? Sharp edges on the barrel extension chewing up bullet jackets?

I've tested different neck tensions with SAC bushings and expander mandrels from loose to tight. Makes no difference. The brass comes out like it was shot out of a bolt gun. Barely even feel or see anything on the case rim.

 

[Jdowns0415]

when you chamber a round from the magazine, run the charging handle and eject the round, is the bullet all scratched up from chambering? mine were getting tore up pretty bad. Polishing the feed ramps helped it out and tightened the groups back up.

 

[Thumper580]

when you chamber a round from the magazine, run the charging handle and eject the round, is the bullet all scratched up from chambering? mine were getting tore up pretty bad. Polishing the feed ramps helped it out and tightened the groups back up.

I'll check....but I'd hope that for $760.00 Craddock Precision would have done this.... but I'll check.

 

[TonyAngel]

I'll check....but I'd hope that for $760.00 Craddock Precision would have done this.... but I'll check.

Shoot, if Craddock put it together, give them a call.

My knee jerk is that rounds are getting buggered up during cycling. Chamber a round and check it before shooting it. Have you tried a different magazine?

 

[Earnhardt]

It is my opinion that any round with a “longer” bullet sticking out the front of the brass, has more negative impact on the bullet’s seating as it is extracted from the mag, and is ran up the barrel extension/feed ramps.

The bullet gets slammed forward into the feed ramp(s), and “hopefully” the round is aligned as best as possible as it is chambered.
-when you single feed rounds you can slide them in nice and easy and not effect how the bullet is seated

Here’s a test…if you have a Concentricity Tool (I have a Hornady brand), set some rounds up that are perfectly concentric.
Then just run them thorugh the mag/feed cycle, without shooting them, by just pulling the charging handle back…running several rounds through.

Then check to see if the concentricity changes.

As mentioned, you could always use a smaller bushing to increase the neck tension on your brass when reloading.

-In a 6.5 CM, I would assume the 140 ELD will be more affected by the feeding cycle than let’s say a 123 ELD would.

My 2 cents

 

[hlee]

Shoot a 5x5 from the mag, then another single feeding.

Do this for 4 or 5 different seating depths and 4 or 5 neck tensions.

By the time you have enough data to figure it out, it’ll be time to call up Craddock for another barrel.

Or… accept that sub moa (which the left group appears to be) is exceptional for any semi auto.

 

[Ernest 5.56]

Yes a 5x5 single feed!

 

[Thumper580]

Shoot, if Craddock put it together, give them a call.

My knee jerk is that rounds are getting buggered up during cycling. Chamber a round and check it before shooting it. Have you tried a different magazine?

Yep.... Magpul and a $90.00 Larue... No difference.

 

[Thumper580]

Shoot a 5x5 from the mag, then another single feeding.

Do this for 4 or 5 different seating depths and 4 or 5 neck tensions.

By the time you have enough data to figure it out, it’ll be time to call up Craddock for another barrel.

Or… accept that sub moa (which the left group appears to be) is exceptional for any semi auto.

Already sent the barrel back.... No issues found. Can't see it's anything with the barrel since it shot a 0.147" group single feeding it. I have to conclude that the rifle is accurate, my loads are accurate and I can shoot it accurately.... But something is happening during the BCG cycling that is screwing up something.... What that something is I have no idea......
Just to check out if my handloads are the issue.... I've fired factory FGGM and Federal T308T..... No difference when magazine fed. I have two different BCG's and nothing changes....

 

[Thumper580]

Shoot, if Craddock put it together, give them a call.

My knee jerk is that rounds are getting buggered up during cycling. Chamber a round and check it before shooting it. Have you tried a different magazine?

Craddock just made the barrel and headspaced the JP bolt to it.

 

[AZLong]

Did you bed the barrel? Easy fix.

Amazon.com

 

[hlee]

Another alternative is to grab a “Bob sled” and embrace the single feeding glory…

https://www.creedmoorsports.com/search.php?search_query=Bob+sled

 

[Thumper580]

Did you bed the barrel? Easy fix.

Amazon.com

It's glued in, per Craddocks direction.

 

[TonyAngel]

Just spit balling here, but have you checked the mag height in the magwell? Long shot, but could be your mag catch is holding the mag too low causing too steep of a feed angle. Once an empty mag is seated and the mag catch is engaged, how much up and down play is there?

 

[TonyAngel]

Another spit ball, but did you confirm that the feed ramps on the barrel extension do not extend beyond the feed ramps in the receiver? Assuming that your receiver has feed ramps.

 

[stanley_white]

This will be a movie scene someday…

Our hero realizes that his target is so small and so far away that he needs more accuracy. He turns to his teammate and says “Hold my magazine, Johnny, I got to single load for this one.”

-Stan