Need help! 260 rem with H4350 and 140 AMAX bullets

[bender338]

I just took delivery of my custom AR chambered in 260rem. The reloading manual states that the max load for 140 amax is 42 grains of H4350 (2677fps). Most of the guys are running anywhere between 43 and 44 grains.

Why are most of the shooters are loading past Max recommended load? Should I start an 39 grains (2530fps according to manual) and work up till ___?

Also, does it make a difference in the brass that I use? (Lapua,Remington)

Any info is appreciated.

 

[427Cobra]

Brass wise, Win 7-08 is the way to go, simply put a piece through your 260 FL die and it's 260rem, Lapua 260 is expensive, and mine didn't shoot any better than Rem260 brass or Win7-08 Brass and the primer pockets were done after 4-5 firings, Rem brass is soft, by the time it needs to be annealed the primer pockets are toast, but it shoots good, I had some Win7-08 that had over 30 firings, I'm sure in Rem brass 41.5 - 43 grains of H4350 will be the ticket, I only used CCi primers, 2750fps is all that is needed, if you push it 2800+ all your doing is destroying your brass, especially in a semi auto.

 

[longrangefool]

Tag, im in the same boat.

 

[bender338]

Thank you for feedback. I already have Lapua brass as well as Rem brass. Will try to load 41.5-43gr of H4350 and make sure to check for pressure signs. I am usin K&M Neck turning tool to turn the necks on the brass. Btw, K&M is an outstanding tool and CS is amazing. These guys really care about the customers and spend over 40 min on the phone explaining how to turn necks. Should I increase the amount of powder charge for Rem brass vs Lapua brass?

Does COAL really matter in AR platform? I'm thinking to just load it to 2.785 which is the Hornady recommended length.

 

[bender338]

Tag, im in the same boat.

Are you also loading for AR?

 

[longrangefool]

Yea, 260 gap-10. For the 139s and 140s im getting pressure signs right around 41gn of 4350. Im interested in seeing what others are running in similar rigs.

 

[bender338]

Have you tried different powders? I know that some people are also using H4831sc with great results. What length are you seating the bullet at?

 

[427Cobra]

If you had a bolt gun .015 off the lands shoots good, in a SA I would find powder sweet spot first, then adjust seating depth starting a max mag length and work in .003(Ojive measurement) at a time until it bug holes. You may notice when the bolt locks back that round is a flyer, make a dummy round and load it first in the mag so the carrier is riding it.

 

[longrangefool]

I just picked up a can of 4831 this weekend. Waiting for the rediculous wind here to die down before trying it out. Ive been seating to 2.75ish as the magpul mags are pretty much 2.8 exactly.

 

[bender338]

Thanks for advice. I will load some rounds and report with results.

 

[17874]

Yea, 260 gap-10. For the 139s and 140s im getting pressure signs right around 41gn of 4350. Im interested in seeing what others are running in similar rigs.

If you are seeing pressure signs at 41 grains of H-4350 you have a pressure spike somewhere. I would be willing to bet its because you don't have enough neck clearance. Are you neck turning? I had the same issue when I started loading .260.

Take a fired caseing and try and slip a bullet into it. If it's tight or won't go, you need to neck turn. My fired castings measured .295 at the case mouth. The neck thickness was .015.

(.015 X 2)+.264= .294. With any high spot larger than .015 and I would get a pressure spike. I turned my necks down to .013 for clearance and haven't had a problem since. I don't see pressure signs until 44.5 grains of H4350 pushing a 142 SMK.

 

[FCS]

I just took delivery of my custom AR chambered in 260rem. The reloading manual states that the max load for 140 amax is 42 grains of H4350 (2677fps). Most of the guys are running anywhere between 43 and 44 grains.

Why are most of the shooters are loading past Max recommended load? Should I start an 39 grains (2530fps according to manual) and work up till ___?

Also, does it make a difference in the brass that I use? (Lapua,Remington)

Any info is appreciated.

Several questions come to mind:

How much freebore in your chamber?
How long is gas system?
Port size?
How long is barrel?
Rifle or CAR buffer?
How heavy is buffer?
Fixed or adjustable gas system?

What did 42 gr of H4350 chrono at from your rifle?

Yes, it does matter what brass you are running. Lapua is typically 0.7 gr or so less powder to get same velocity as RP.

H4831sc in a gas gun comes with other issues. You get lower peak pressure but you raise port pressure (increase pressure present when case is extracted) and gas volume available to cycle BCG. You also need 6-7.5% more powder to get same velocity which you may not have room for with 2.800" ish OAL mag constraint of DPMS/Pmag/KAC pattern.

If you have an adjustable gas block, turn gas down until you have a single shot. I've seen plenty of ARs unlocking too soon because of port size/location which gives pressure signs but for reasons other then peak pressure as seen with bolt rifle. Once turned down to "single shot", do your pressure signs go away? If yes, then an amount of gas to cycle BCG issue. If no, then you have a peak pressure issue / load issue.

Need more data, too many unknowns to really be able to give you any solid guidance.