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

 

[hlee]

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

Very common in NRA high power…

 

[Potsy]

Now I gotta single feed my AR next range trip so I can have something else in my life to be pissed off about.

That said; some good info here on feeding….

 

[ironpony52]

IMO which is worth less than free.............

The one on the left is dead the one on the right is really dead. It is a semi auto which again IMO is not a precision gun. Yes they can be super accurate but it really is not what they were made for.

 

[OpticsNerd]

I saw something similar, but with an extra twist. Full mag would always stack the first two rounds in the same hole but eventually give 1.5” groups, single feeding by throwing a round in the chamber and dropping the bolt would give 0.7” groups. Suspected rounds getting messed up on feeding but couldn’t measure a setback or anything else on chambered then extracted rounds. Tried single feeding from the mag (pushed the round into the empty mag, then dropped the bolt) and got… 0.7” groups.

Clearly whatever was going on was from having the rounds *riding in the mag*. I was loading to just under mag length and I suspect the bullet tips were hitting/dragging on the inside of the front of the mag. I tried seating bullets 0.050” deeper and got consistent 0.7-0.8” groups from the mag.

Edit: this was in 6.5CM, Aero receivers, bedded Proof barrel, JP high pressure bolt, PMAGs. Was consistent across loads using Hornady and Alpha brass, 142 and 140 SMKs.

 

[MikeMiller]

Lots of great info here. I will add on my AR types I polish feed ramp/barrel extension like it was a 1911 pistol. My magazine groups are more consistent after doing this

 

[6.5SH]

From another older thread here the theory was the alternating left-right pressure on the bolt carrier from the rounds in the magazine.

 

[Earnhardt]

Thumper580, what powder(s) are you using in your loads?

The reason I ask, is that in the past, I've used temp sensitive powders before min an AR load...

And by the time I got to the 3rd and 4th shots, the chamber had gotten so hot from the previous rounds, the temp powder in the brass/round was increasing, and the velocities climbed dramatically....greatly effecting the grouping of any shots after 1 and 2...

This impact is not as great in a bolt gun, even with a round like a 300 RUM or 338 Edge using large amounts of N570.

Because all of the gas is going forward, and not heating up the chamber like an AR does. When the round is extracted while the powder/gas is pushing the bullet out of the barrel, and some of the hot gas is coming back into the chamber.

Thanks

 

[SnowMan]

Maybe nothing? I would think your routine is different when you single feed. Comparable to a bolt gun, cycling the bolt vs single feed? Maybe there is more time between shots?

 

[Thumper580]

Thumper580, what powder(s) are you using in your loads?

The reason I ask, is that in the past, I've used temp sensitive powders before min an AR load...

And by the time I got to the 3rd and 4th shots, the chamber had gotten so hot from the previous rounds, the temp powder in the brass/round was increasing, and the velocities climbed dramatically....greatly effecting the grouping of any shots after 1 and 2...

This impact is not as great in a bolt gun, even with a round like a 300 RUM or 338 Edge using large amounts of N570.

Because all of the gas is going forward, and not heating up the chamber like an AR does. When the round is extracted while the powder/gas is pushing the bullet out of the barrel, and some of the hot gas is coming back into the chamber.

Thanks

Typical 308 powders... IMR4064, IMR4895 and this group in the photo was Varget....

 

[Thumper580]

Maybe nothing? I would think your routine is different when you single feed. Comparable to a bolt gun, cycling the bolt vs single feed? Maybe there is more time between shots?

I'm not speed shooting it... Taking time between shots. For the reply about it being a semi auto, we obviously think differently. If this was a muzzle loader I'd be doing the exact same thing... How accurate can I get the weapon to shoot.... Not just make noise.

 

[bfoosh006]

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

This.

 

[mtrmn]

I have an AR15 (Colt) that would shoot to one POI when feeding rds from the left side of the mag and another POI when feeding from the right side. Someone on another forum suggested that I remove the ejector and round off the sharp edges of the ejector face. This did indeed help a lot with my problem and I now do this to all of my ejectors if they are not already rounded. The theory is that when feeding from the right side of the mag, the ejector's sharp edges were providing more resistance when the case head slides up the bolt face during feeding. This would result in the BCG settling in a slightly different position relative to the round and chamber. Allegedly. True or not, the problem pretty much went away when I rounded the ejector.
I round mine by chucking the ejector into a drill and holding the ejector at an angle against an old "carborundum" sharpening stone while spinning it with the drill. All it takes is to round off the sharp edge.
Since that time (early 2000's) I've seen pictures of high end bolts with with the ejector face being completely hemispherical.