quote:

Originally posted by sigfreund:
experiencing a large degree of yaw due to a too-slow barrel rifling twist rate,

Thank you for mentioning twist rate.

My brother had mentioned doing a barrel swap — the one we looked at (haven’t purchased yet) lists a 1:7 twist. I believe the barrel on this rifle is marked 1:8.

I expect to be able to get this rifle to the range again mid-next week.

Another thing to be aware of about bullet stability that I alluded to, but didn’t emphasize is that velocity matters as well as rifling twist rate. That’s why subsonic bullets are less stable for any particular twist rate than higher velocity projectiles. Not only are subs typically heavier and therefore longer, they’re also obviously traveling slower than supersonic bullets.

I had long suspected that was true, but only recently did it occur to me to actually research the question on the ’net, and the explanations confirmed my belief.

Alignment rod arrives tomorrow; I’m hoping it brings warmer weather with it!

So the first response, mine, was actually correct? lol. Crush washer? That was a lot of talky talky to get around to the first suggestion to check.

quote:

Originally posted by pedropcola:
So the first response, mine, was actually correct?

I use Thunder Beast muzzle devices that the can threads directly to. They very firmly state to not use crush washers.

quote:

Originally posted by pedropcola:
So the first response, mine, was actually correct? lol. Crush washer? That was a lot of talky talky to get around to the first suggestion to check.

Possibly so! I know there was a washer in the setup, and I know it wasn’t in the place shown in SIG’s manual. In fact, I don’t even think this particular washer would fit where the SIG washer goes.

I’ve swapped a few emails with Tyler at SIG customer service over the past few days, and he made me a gracious offer on a new crush washer. FedEx is scheduled to be bringing it tomorrow, so if all goes well I can go do some more testing over the weekend.

I do appreciate all the responses. As I’ve said a number of times before: I’ve got a lot of learning to do, and a lot of it gets done around here.

Something else I don’t think I understand is why the muzzle brake goes on before the can goes on. I always thought those were “one or the other” items.


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Edited to add pics from pages 13 and 14 of the manal:

The funny thing is that I’ve always read, across all sources, that if you are using a can you should NEVER use a crush washer. Regardless of being in the “right” place. Shims, torque, thread fastener. No crush washer.

I can’t say that from personal experience but I haven’t found a single source that says different.

I would NOT install that crush washer.

What’s the purpose of the crush washer to begin with?

allow some degree of rotation of the muzzle device while still being tight. It looks like that is how Sig is using it with the brake so you can get the ports in the right orientation. and of course you don't need it with the flash hider and they advise that.
I have always been told never to use them but that has always been in the context of between the barrel and the muzzle device, but here in this case the mfg. is providing one and telling you to use it. And its an odd one because normally they don't have a taper. I would use it if you need it per the Sig instructions, if its an issue its 100% on them.

As mentioned, crush washers make it much easier to properly time something like a brake or flash hider because they can be … well, crushed to the point when the device is aligned properly. The problem with them is that they may “crush” unevenly, allowing for some misalignment of the device with the bore. The alternative, peel washers or shims, often require much more fiddling with to get the alignment correct. And although a friend was very unhappy with his shims experience for some reason, they are what I prefer over peel washers.

Regarding the crush washer with the SIG device, does the suppressor attach directly to the brake or flash hider? If not, then some small misalignment of the hider with the bore would not matter, as is normally true when other brakes or hiders are installed with crush washers.

From the picture it looks like the threads for the suppressor attachment are on the QD mounted on the muzzle and not related to the FH or the brake that is mounted to that QD. Which is why I don't think its relevant to the rule we all have in our head about crush washers.

quote:

Originally posted by hrcjon:
From the picture it looks like the threads for the suppressor attachment are on the QD mounted on the muzzle and not related to the FH or the brake that is mounted to that QD.

That was my impression as well, and the reason for my question (thanks for the pictures).

quote:

Originally posted by vthoky:
What’s the purpose of the crush washer to begin with?

Properly timing the brake.

I use steel suppressor spacers that range from .002 up to .020.

That just seems like an odd device in general. It’s like a QD with a QD. It QD’s to the suppressor and it QD’s to what appears to be whatever flash hider or brake that you prefer. Talk about layering Swiss cheese holes together. Ugh.

I assume that it gives you the ability to quickly change the actual muzzle device without changing the suppressor mount. In fact it looks to my dumb eye that you could attach a can without any brake/hider at all. The threads for the can are back in the “permanent” portion. Perhaps the “taper” portion is on the second part, the threaded beaker tough to tell.

I need context as to why anyone (Sig) would make that their stock profile. It seems overly complex with little to gain for certainly civilian use.

It does QD to the suppressor, but the brake (which I have) or flash hider (which I don’t have) screws into the QD mount. So I guess the advantage there is that one could leave the brake on all the time, and quickly attach/remove the suppressor as necessary.

I seem to have this knack for latching onto things that get discontinued… dangit. I can’t just toss it out and start over, though, particularly when my very talented machinist friend can duplicate that QD mount for me (since they’re no longer available on the market). He’s a “lathe guy,” so making one of those is almost a cakewalk for him.

Hrcjon is correct regarding threads for the suppressor being unrelated to brake/FH attachment. Essentially, the QD mount has some fairly coarse external threads for the suppressor, and has internal threads for brake/FH.

We’ve got it all put together again now, with a plan to go exercise it again this afternoon.

Oh, and we did pick up an alignment rod this past week — the assembly looks a lot closer to correct this time around.

Well, friends and neighbors, the mystery may be solved.

1) The washer that was in place between the muzzle and the QD should certainly have not been there.
2) The crush washer SIG suggests putting between the QD and the brake was not there; it’s there now. I still don’t know how that helps if the can is installed over the brake, but that’s just more learning I’ve gotta do.
3) An alignment rod doesn’t help install a can straight, but it sure helps identify when one is installed not straight.

We took this rifle over to the range this afternoon and got results:
1) There truly is less noise, though it’s not “pellet-gun quiet” like my brother’s setup. Idunno what all he has done differently; not too worried about it.
2) Bullets are leaving nice, round holes like they’re supposed to, not those crazy oblong holes we saw last trip out.
3) As usual, RTFM is a good place to start.
4) As an observation, the Hornady Black ammo we shot was noticeably quieter than the Winchester Super Suppressed.

I’ll call it a success, and move on to the next topic: how to get this darned thermal sight dialed in. I’ll start a new thread for that after while.

Thanks, all, for your help.