Reloading for the new .277 Fury from Sig

[Mike D Texas]

What is the relative capacity of the the 260AI to the brass-cased 277 Fury? The Fury has a 30° neck, but the shoulder is pushed forward. How much taper is removed from the 260 in AI guise?
Thanks.
I have been surprised when I looked at the low taper of some recent SAAMI cartridges. For example, the SAAMI 22 Creedmoor had less taper than the 22-250AI chamber print that I had seen.

Got some capacity measurements for you.

 

[Batsin]

Got some capacity measurements for you.

Thanks! I suspect that the fired 277 Fury case would gain some volume, so they are very close.

 

[Mike D Texas]

Thanks! I suspect that the fired 277 Fury case would gain some volume, so they are very close.

Yep.

 

[Eric_F]

For lug setback?

I know with my new barrel, the bolt closes on a Go gauge, but not on a Go gauge with 0.003" of tape on it. If it ever starts closing on that, I assume I've had lug setback. Indirect but seems like it should work.

 

[thanat101]

What did you do to be able to run 80kpsi on an AR10?
Generally the AR's can't even handle a normal bolt gun 65kpsi load.

Or are you just going to run brass cases?

I continue to load in small grain increments and will have more data soon. I have both the straight brass and the hybrid brass/steel cartridges.

With the loads right now, I'm around 50,000 psi. I don't plan on going over around 65,000 psi with my loads. Just looking for a nice cycling, good functioning round for the semi-auto.

The factory rounds I'm shooting from SIG 135 full metal jackets are way over the published muzzle velocity. Close to 2900 and when suppressed it just destroys the fired cartridges neck and heads.

I have the hitman industries 277 fury barrel that supposedly will handle 80,000 psi, a high-pressure bolt carrier group, SA adj gas block. I'm using the a Toolkraft BCG with reduced pin hole diameter size for the extra gas.

 

[thanat101]

as far as being able to read pressure when loading the hybrid brass, there's not really a way to tell where you are at. I'm curious what the volume of the brass vs the hybrid cases are? I would think, if they are the same, a guy could use normal reloading pressure indicators while working up using the all brass. once you start getting pressure, you know you'd be roughly 65k-70k psi and be able to move up another grain or so from there in the hybrid??? also, to be even more careful, just stay right in there. typically, you end up finding accuracy a bit below max but maybe you'd still have the accuracy using the hybrid case with the same liad and not have to back down to find accuracy. that'd only give you maybe 75ish fps increase over the all brass case but an idea??? from what I've heard (I think from straight jacket) even the numbers with the all brass case are pretty comfortable.

Not exactly scientific, however, with both type of cartridges, the exact same trim length, each cartridge will hold 51.1 gr of powder up to the top of the neck.

Yes. I agree you're not able to read the actual pressure, but you sure can feel it when firing in a semi auto rifle. I bet in the future SIG factory rounds won't generate as high pressure, because it's uncomfortable for the shooter.

 

[thanat101]

Got some new data on muzzle velocity for 277 Fury on my gun. PLEASE NOTE YOUR GUN WILL HAVE DIFFERENT RESULTS. START AT MINIMUM LOAD and work up to safe level. I started with 33.4 gr. of powder. See prior post from April 14, 2024.

I continued reloading in small increments. I shot 3-4 round groups using magneto speed pro 3 on a suppressed 277 Fury AR-10 Build, 16 inch barrel.

135 grain FMJ with 16" barrel on .277 AR-10 Build.
Used Pulled Sig 135 grain FMJ projectiles.
Used Accurate 2015 smokeless powder
Used Unis Ginex, 5 5/N primer for large rife
Used once fired Sig 277 Fury Brass
Trimmed case length was 2.0185 inches
Overall cartridge length was 2.805 inches

35.5 gr - 2520 muzzle velocity
36.0 gr - 2550
36.5 gr - 2570
37.0 gr - 2600
37.5 gr - 2644
38.0 gr - 2652

grouping was all tight, I saw no noticeable difference for standard hunting/plinking.

I think between 38.5-40 gr. of "Accurate 2015" smokeless powder is going to be the sweet spot for an AR-10 style Fury. Will let you all know. I want to keep the pressure well below 65,000 psi chamber pressure for wear n' tear.