UltraSlim Crush Washer R&D

[BluntForceTrauma]

Guys, I'm testing an UltraSlim Crush Washer to mate with our Alpha, Bravo, and Delta line of UltraSlim muzzle devices so that they can be timed.

Got three stainless steel metal 3D-printed prototypes — suckers cost $50 each! — of my UltraSlim crush washer design and am testing its installation. Results, so far, are mixed. Have gotten 90° rotation, but the outside diameter (OD) enlarged such that I can't slip a standard .750 gas block on and off — which was one of the goals. Also, I thought the torque force required for this smaller washer would be less, but it stills seems like I'm cranking it a lot toward the end.

Trying to decide whether pursuing this UltraSlim crush washer is the best method or whether I should pursue UltraSlim sets of super thin shim washers.

Some say crush washers can induce cant to your muzzle device, causing inaccuracy and potential strikes (if using with longer devices like suppressors), and that they're not reusable like shims when one wants to remove for cleaning. Others say shims are too fiddly.

Attached photos show the three stainless UltraSlim crush washer prototypes and a standard 5/8 crush washer (Yankee Hill).

Anyway, what you guys think? Crush washer or shim set? Pros and cons?

   
   
   
   

[grayfox]

Neither, a third suggestion instead -- first some points to consider.
1. Sounds from your description that the prototypes are basically "MIM" ie, metal injected, a term I'm using to differentiate from a sheet metal, cut out and stamped or whatever shim. If it's not from a continuous sheet then the metal-grain boundaries won't be as strong or aligned as from a sheet. So I'm not sure you can bank on torque consistency or consistent behavior under torque/presssure... which means each shim can behave differently from the others.
2. Crush washers do apply uneven torques to the barrel and the muzzle device because they don't crush evenly all the way around, some parts stick out more than others, or contort a bit more than others, etc.
3. The REAL way, IMO, is to develop a rather thin, knurled jam nut. And either forget about sliding the gas block on after (ie, the knurl should be slightly larger diameter than the barrel, so the grip device will not scratch the barrel when you grab the jam nut), or else allow for some gap for the pliers... I don't know if you can make a strong enough 5/8-24 hex sided jam nut that is a max of .750 (assumed diameter of your barrel), this would be from vertex to vertex not flat to flat dimension... so that it's less than barrel diameter/gas block sliding.
I think the muzzle device should always go on after the barrel is set with gas block (and gas tube). Using a jam nut will allow you to change it at will, and also to take off easily for gas block work if desired. ps, there are some "thin blade" crescent wrenches that can help for those tight dimensions between device and jam nut also. I have one for the hex style jams.
Torquing of jam nut/muzzle device imo is not as critical as with a shim. slightly more than hand tight works b/c after a few shots, the carbon buildup will further inhibit it from turning.

Most fancier "non-tuning" muzzle devices are including a slip-type jam nut style "extension" (re, Fat Bas**rd latest version) on the rear of their device... which would be kind of $$$ to develop. You can get jam nuts from amazon for a few dollars each.
I use jam nuts almost exclusively, and am not going "to war" so torquing, per se, is not a spec I need.
Further note: I also use a bit of anti seize on threads/devices before installing, again to allow for removal without fear of galling.

Since this has a lot more detail than most opinions, I'll say "my $0.10" vice "$0.02" -- LOL!!!

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OK, here's another idea that will help folks in tuning... can you make a small "match mark" line at Top dead center on both the barrel tip and your muzzle pieces... (muzzle piece might be harder if they are symmetrical, as in you can "time" it in any of 3 or six different alignments... ). At least tdc on the barrel, at the end of barrel and right before the threading so it's available to observe while tightening down. Even if it's a white or black "paint" mark instead of an etched groove...

[BluntForceTrauma]

GF, thanks for your thoughts. What are the pros and cons of shim sets, in your opinion?

[grayfox]

I use brakes on all of my rifles, except maybe one. Makes them sooooo much easier to shoot, find accuracy etc.
A shim set like the accuwasher, works fine, you just need to find the one that works for your barrel... and for the second barrel, well you might have already used the one you need... been there!! For the set I have I've tied the similar ones together, it's a pain to sort thru the bunch just out of the bag (do I want the I-iii or the II-ii, or what...?)

So if there was an accuwasher setup with a few thin ones (0.001 and/or 0.002) thrown in, so you can be sure you'll be able to do more than one barrel with the set, well that would be really good. The accuwashers cost a fair bit, kinda spendy as shims go. I had a couple other sets with just some relatively unmarked 0.001's, 0.003's, 0.007's, 0.028 and they did ok, but again you'll need a combo, not just a single one like accuwasher. Accuwashers seem to be re-useable even after torquing, one advantage there.
Problem with most shims (skinny and crush) IMO is technically they are only good for one use. If you torque them they will be distorted when you loosen and take off the muzzle device...
Other big disadvantage to shims is you need to play with them to find the right setup, then torque it down.

I've switched over to all jam nuts... well maybe one accuwasher is still in use. This way if I want to use a suppressor I can take my brake off at the range (pair of pliers and small crescent for the knurled ones) and thread on the suppr. Using that 419 adapter thingabob which is a great idea for spinning up the suppressor. Then switch back. I don't like the suppr's "brake" by itself -- they don't work as well as the VG6's. I also put a small dab of vinyl paint at TDC on both the VG6 and the barrel tip ("match marks" right before the threads end) so I can "time" the VG with the pliers/crescent, eazy-peazy, even a cave man can do it.

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I should add that I only use brakes that have some flats on them too, typically at least parallel ones in the vertical. No pliers on hex or flats... only for the knurled jams.

[grayfox]

As far as "eyeball" estimates of how far off your brake is from timed (ie, tdc), I would say estimating by degrees of the circle, 15, 30, 45, 60* are relatively easy for the eye to see. Based on 30-60-90, 15 is 1/4 of a hex flat... and so on.
To move the brake on a 5/8-24 threading, every 15* is a thickness of 0.00174", 45* is 0.0052".
So if you tighten up your brake and it is (for example), 15* past tdc, you need a shim of 0.005" to set it back to straight... but that's not torqued. You need a shim some X thou's MORE beyond 0.005 so that when torqued to your desired inch (or ft)-lbs you are timed. How much is that extra? Idk, but probably on the order of ~0.005 more (just a guess). I think I read somewhere that going 15* was an acceptable amount of torque... but don't remember exactly.

Another thought. If your barrel mfr could always start the thread pitch at the same spot on the barrel circumference, and the same spot on your brake, you would know pretty much that they both would time to tdc when mated up. If that "mate-up" was finger tight at, say, 15* before tdc, then torquing to tdc would put you there... that sort of logic. May be too hard to get mfrs to do this however. And would not apply to using any other barrel... just brain storming here.

[alwie]

Guys, I'm testing an UltraSlim Crush Washer to mate with our Alpha, Bravo, and Delta line of UltraSlim muzzle devices so that they can be timed.

Got three stainless steel metal 3D-printed prototypes — suckers cost $50 each! — of my UltraSlim crush washer design and am testing its installation. Results, so far, are mixed. Have gotten 90° rotation, but the outside diameter (OD) enlarged such that I can't slip a standard .750 gas block on and off — which was one of the goals. Also, I thought the torque force required for this smaller washer would be less, but it stills seems like I'm cranking it a lot toward the end.

Trying to decide whether pursuing this UltraSlim crush washer is the best method or whether I should pursue UltraSlim sets of super thin shim washers.

Some say crush washers can induce cant to your muzzle device, causing inaccuracy and potential strikes (if using with longer devices like suppressors), and that they're not reusable like shims when one wants to remove for cleaning. Others say shims are too fiddly.

Attached photos show the three stainless UltraSlim crush washer prototypes and a standard 5/8 crush washer (Yankee Hill).

Anyway, what you guys think? Crush washer or shim set? Pros and cons? I would also think that the material properties of the 3D printed metal would be different than the mass produced product being sold.

Im excited that you are working on these.  Since they don't need to be timed, what is the benefit of washers or shims? I’m thinking that the metal properties of the 3D printed parts would be different than the final product. So, testing the strength of the 3D printed device may not be consistent with the mass produced product.

[BluntForceTrauma]

GF, I've heard that a final torque adds about .002.

I'm leaning toward shims for these reasons:

1) Though crush washers give ease of timing — within their limits — I don't like the amount of torque required for a crush washer relative to the degrees of rotation you get. I was cranking like hell on my prototype UltraSlim washers just to get 90°. It seems crush washers are a down and dirty way for military armorers to mass install timed A2 muzzle devices when the accuracy standard is 2-4 MOA. Many claim crush washers do not crush evenly and thus can introduce cant to the installed muzzle device. This could lead to accuracy degradation if the walls of the device are not acting evenly on the expanding gas, and, worse, to baffle strikes if the angle of cant and the length of the device create the perfect storm. Anyway, it's a different set of parameters for the civilian home builder who has more time and more stringent accuracy expectations.

2) I feel the thickness of crush washers and jam nuts subtracts too much from the available muzzle threading, leading to less and less thread engagement. Typical 5/8-24 muzzle threads are .625 or so long, and subtracting a standard crush washer thickness of .150 leaves .475 thread engagement. We put premium 3A male threads on our barrels and 3B female threads on our muzzle devices, so good engagement is important to me. I feel that the microscopic "rattling" of a "loose" muzzle device is detrimental to accuracy.

3) I've calculated it and with not more than a max of three shims mixed and matched from a kit with four shim sizess — .002, .003, .007, .015 — one can get 180° rotation with a linear travel of .021 in .001 increments. Any fudging can be done by slightly more or less torque effort. It's amazing to me how much rotation one gets for how little thickness per shim. This allows almost exact alignment and timing while retaining maximum thread engagement. I think shims are mostly reusable; one can always add or replace a .002 shim if one feels a shim has been crushed too much. But they're flat washers, so there's not any flex to really crush.

Personally, I don't bother timing my three-prong Alpha and closed three-prong Bravo devices, but I might if I have a shim set — and I certainly plan on aligning my Delta muzzle brake with its four ports at 3 and 9 o'clock.

[grayfox]

Copy. Understand better now where you're trying to go.