The weird Sig Cross - general concept conversation

[Dfin]

I picked up a Sig Cross for my daughter and am rebarreling to 6 Creedmoor. I noticed a few things that stand out as odd to me and wanted to start a discussion about the benefits, or lack thereof, of these features. I'm looking for some general understanding of what they were trying to accomplish.

First, this rifle has a triple lug bolt, in the form of a bolt body and floating bolt head. What's odd is when the bolt is closed the floating bolt pin is not horizontal and perpendicular to gravity like a Savage floating bolt system, but is rotated to approx 50° as compared to horizontal. It also doesn't seem to have much "float" movement. I've always thought the floating system was to offset the impact gravity has on the sagging end of the bolt opposite the chamber. At the angle that exists with the Sig I don't see how it is of any benefit.

Second, the bolt lug bearing surfaces are machined conical and not square to the centerline of the bolt. The lug seats in the barrel extension are also machined to mate with the conical bearing surfaces. This could be accurate iIf all parts were machined perfectly concentric with the centerline of the bore and then the bolt face is machined square with the bore, but I would think it would be much easier to get everything flat than getting the bolt face flat and everything else concentric.

It seems like they could have made a few design changes and had something significantly better. What am I missing with this one?

 

[Long Range 338]

I'm only jumping in here to comment that I've had 2-3 of these that I have shot and all of them have been very accurate. I'm not a machinist or expert of any kind by any means so my comments are worth what they cost you.

My understanding of the floating bolt head (by any manufacturer) is to allow the bolt face to be true to the chamber. I can't imagine that "sag" is considered in any manner, as machined tolerances and pressures have to be controlled.

As far as conical shape of the back on the bolt lugs, ARC does this same thing and is very successful with it - another design that is supposed to aid in being true with the bore. The link below is better information than I could ever articulate.

Support | American Rifle Company

www.americanrifle.com

 

[Supersubes]

The two piece bolt is probably far cheaper to machine than a single piece. Also opens up a bunch options for material selection and treatments. I have a Cross here but havent looked it over very closely, including the bolt. Likely not designed to float at all, like an AI for example.

Conical lugs mating to conical abutments in the extension would center/align the two parts, and do so without needing tight clearances.

 

[Makinchips208]

The bolt lug on the one made by ARC has a toroidal surface, very technical and for a very specific purpose. A bit different shape than what appears on the bolt of the Sig Cross.
I am guessing sig did this for ease of manufacturing? Make all the same bolt and just change bolt head if needed for caliber.

 

[Dfin]

I'm only jumping in here to comment that I've had 2-3 of these that I have shot and all of them have been very accurate. I'm not a machinist or expert of any kind by any means so my comments are worth what they cost you.

My understanding of the floating bolt head (by any manufacturer) is to allow the bolt face to be true to the chamber. I can't imagine that "sag" is considered in any manner, as machined tolerances and pressures have to be controlled.

As far as conical shape of the back on the bolt lugs, ARC does this same thing and is very successful with it - another design that is supposed to aid in being true with the bore. The link below is better information than I could ever articulate.

Support | American Rifle Company

www.americanrifle.com

I am a machinist and engineer. I’ve measured several bolts with an indicator and all droop on the back end and take the bolt face slightly out of square while doing so. I shouldn’t say all, because we drilled and tapped one action and sent a brass post up through to support the backend of the closed bolt.

 

[E. Bryant]

I am a machinist and engineer. I’ve measured several bolts with an indicator and all droop on the back end and take the bolt face slightly out of square while doing so. I shouldn’t say all, because we drilled and tapped one action and sent a brass post up through to support the backend of the closed bolt.

What happens to this "droop" when you install a trigger and firing pin assembly?