Reloading for the new .277 Fury from Sig

[Batsin]

About three weeks ago, the Ultimate Reloader YouTube channel had a video in which he pushed Alpha Munitions 308 brass to an estimated 103,000 psi in several increments, so you might be able to glean something from that.

The issue with an AR10 is the bolt strength. With the XM7, the bolt is made from a fancy alloy to deal with the added force.

There was an interview clip from Ron Spomer where a SIG employee mentioned that there have been some accuracy issues at full pressure and future civilian hybrid-cased ammo will be closer to 70,000 psi. I wonder if this is the dreaded "bullet nose slump" issue seen around 2010 from some Berger .338 bullets with spicy magnum rounds. IIRC, the acceleration was so great that the ogive of the bullet sometimes deformed in the barrel. Berger began running thicker jackets to deal with it. I wonder if bullets designed for the 270 might exhibit the same thing from the 277 Fury?

 

[akmtnhnt]

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.

The all brass case has less capacity than the steel. Don't have my notes in front of me but I think it's 2-3gr.

 

[akmtnhnt]

About three weeks ago, the Ultimate Reloader YouTube channel had a video in which he pushed Alpha Munitions 308 brass to an estimated 103,000 psi in several increments, so you might be able to glean something from that.

The issue with an AR10 is the bolt strength. With the XM7, the bolt is made from a fancy alloy to deal with the added force.

There was an interview clip from Ron Spomer where a SIG employee mentioned that there have been some accuracy issues at full pressure and future civilian hybrid-cased ammo will be closer to 70,000 psi. I wonder if this is the dreaded "bullet nose slump" issue seen around 2010 from some Berger .338 bullets with spicy magnum rounds. IIRC, the acceleration was so great that the ogive of the bullet sometimes deformed in the barrel. Berger began running thicker jackets to deal with it. I wonder if bullets designed for the 270 might exhibit the same thing from the 277 Fury?

Mono's don't have that problem for sure.

 

[Eric_F]

Just in case anyone in this thread isn't aware, American Reloading has pulled hybrid cases and a ton of 270 projectiles available

e.g.: https://americanreloading.com/product/270-135gr-solid-copper-bt-blems-250ct/

I've bought a bunch of their hybrid brass and projectiles, just not for 270/Fury. Sizing down to 6.5 CM works well though.

 

[Batsin]

Mono's don't have that problem for sure.

The interview didn't mention exactly what was causing the accuracy issues at higher pressure, so it might be something else. The fact that the initial of hybrid ammo I have seen on the SIG site used 150 grain Accubond bullets instead of a monometal is what made me wonder about nose slump.

 

[Mike D Texas]

Just in case anyone in this thread isn't aware, American Reloading has pulled hybrid cases and a ton of 270 projectiles available

e.g.: https://americanreloading.com/product/270-135gr-solid-copper-bt-blems-250ct/

I've bought a bunch of their hybrid brass and projectiles, just not for 270/Fury. Sizing down to 6.5 CM works well though.

Works pretty good for 260AI as well.

 

[Bravo 4]

Mike, those are similar to velocities I've seen with these cases necked up to .308 & 150 SBD II's.

Not re-reading this whole thread to see if this is mentioned: lug setback is a thing (seen it), and can cause some real (bad) problems in short order!

 

[Mike D Texas]

Mike, those are similar to velocities I've seen with these cases necked up to .308 & 150 SBD II's.

Not re-reading this whole thread to see if this is mentioned: lug setback is a thing (seen it), and can cause some real (bad) problems in short order!

Yeah I did it just as an experiment to see how it would perform. The primer failed but extraction was still very easy.

If I were to be serious about pushing hard long term I would pick up a BAT action.

 

[Batsin]

Works pretty good for 260AI as well.

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.

 

[Batsin]

Yeah I did it just as an experiment to see how it would perform. The primer failed but extraction was still very easy.

If I were to be serious about pushing hard long term I would pick up a BAT action.

Bolt thrust is related to the max chamber pressure pushing the "piston" of the interior diameter of the case. Running some rough numbers, the bolt thrust of the 277 Fury at 80Kpsi is about 13% LOWER than the fatter WSMs at 65Kpsi. It is also slightly less, about 4%, than a 6.5 PRC, so there are a lot of actions that should be able to handle it.

 

[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.

I haven't measured non fired vs fired yet. But you make some very good observations. Here's a few reference pics.

 

[Mike D Texas]

I'm sure there are. I've just grown quite fond of BAT actions since purchasing my Vesper.

 

[K.E.C.]

Let me see if I got this right. Your necking down the 277fury, for a 260ai. Or are you making a 260fury. I have been looking at this since I made my 270/308. To me is a great cartridge. I'm really close to a 270win with performance.
EDIT: Can I take a 277 fury reamer to my 277 chamber 308. Or will I need a different barrel.

 

[Eric_F]

Let me see if I got this right. Your necking down the 277fury, for a 260ai. Or are you making a 260fury. I have been looking at this since I made my 270/308. To me is a great cartridge. I'm really close to a 270win with performance.
EDIT: Can I take a 277 fury reamer to my 277 chamber 308. Or will I need a different barrel.

I'll let Mike speak for himself, but I'm not sure what you mean by 260 Fury. Do you mean a straight necked down version? Clearly the shoulder angle is different, but compare a 260 AI print to the Fury and it's quite close in brass OAL, shoulder diameter, and neck-shoulder junction height.

As far as a Fury reamer for your chamber, compare the SAAMI print to yours: https://saami.org/wp-content/uploads/2020/11/277-Sig-Public-Introduction-Orig-2020-11-11.pdf