Newbie needs help with 6.5L AR load 140 Berg Hybrid

[SG4247]

New to the forum, but have been reading here for years.

This is probably the best forum on the net, for solid reliable honest information. I really enjoy the wealth of knowledge here, so I registered today.

Trouble is with a new bolt action AR-10. This gun is side charge type, with the gas block turned off.

New 26" Krieger four groove SS, no brake. At 300 rounds now with this tube, and can't seem to make the 140 hybrids work using H4350.

Best load so far:

Lapua brass / 140 Berger hybrid
Necks turned once or twice to .0125" wall.
.261" inside Dia. checked with pin gauges.
Neck runout .003" or less with 21 Century gauge.
Best seating depths 2.725" or 2.800". Similar groups.
Bullet touches the lands at 2.815"
37.9 grains of H4350 measured to +\~ .02 grains
Seating depth +\~ .005" with redding seating die.
Loaded bullet runout at the ogive .003" or less.
Primer pockets cleaned up with PPC Sinclair cutter.
Flash holes cleared.
CCI 41 primer

Loads frequently have one or two slow rounds of a group of five that mark low and the chrony reflects this.

Load is inconsistent, one of five will be slow.

At my wits end with it.

Any ideas would be appreciated.

 

[stubbicatt]

Welcome to the forum.

I haven't tried H4350 yet in my 6.5x47L, as I cannot find any. However I follow any threads on this cartridge closely. If the experience of others with your combination is a touchstone at all, most seem to use somewhere near 40 grains of powder with that combination. CAVEAT EMPTOR, YMMV, and all that. Perhaps a search of the forum to review this data would help.

I am not familiar with your rifle, so I have nothing to add about that factor.

Hope you get it sorted. Mine loves RL17 and 139 Scenars. I still haven't found a good load for the 123's.

 

[Drop Port]

I just did a quick load test for a friends rifle last weekend, it has the same free bore as yours, should be approx. .160" judging from mine.

H-4350
140 Hybrid
CCI 450
2.815 Touches
Loaded at 2.810"

40.0 shot in the high .4
40.5 shot in the mid .2's
40.+ shot in the high .3's

No further tuning just wanted to see if the old Broughton Crucible barrel liked the Hybrids.
I see you turned the necks, one thing in mine was it liked neck tension, consistency and groups sucked in with a little extra.

 

[SG4247]

Thanks for the replies guys.

This is an AR-10. So, it has limitations in terms of bolt/firing pin and action strength, compared to super strong bolt actions that most use in this caliber.

Berger lists the maximum at like 38.9 gr of H4350 for 6.5x47L.

Would you feel comfortable running a production AR-10 rifle at 40-41 grains?

It flattens the #41 primer now at 37.9 grains. High pressure is sorta hard to read with Lapua brass.

What is odd is, I have another AR-10 with a 22" Krieger that shoots this load well.

Why would the 26" Krieger be different?

Been hesitant to exceed Berger's load recommendations, even though everyone says they are conservative.

 

[Drop Port]

I don't know about the gas guns, I only have experience with a LMT 308 and it runs factory pressure fine. With your gas block turned off you should be fine your FPS are slow for 26" most are in the mid 2700's low 2800's without exceeding factory pressure, based on that I would work up slowly.
There is a huge difference in a short free bore and generous free bore in this cartridge. In a tight chamber with .062 pin, mine wont show signs of primer pressure, you could be easily be getting a false read.

 

[SG4247]

So, the suggestions so far are:

1. Increase the charge towards 40 grains of H4350.
2. Increase the neck tension.
3. Use a different primer. 450, WSR, BR are options

Any other ideas would be appreciated.

 

[Eric Leonard]

I had my best groups with the 140s at 39 H4350 and 36 Varget,,both are in the mid to high 2700`s,,I am shooting the 123 Scenar and 42.7 H4350 at 2965 from 28 inch bolt rifle,,super accurate with 123 Scenar