Gunsmithing Recessed Crowns: Too much of a good thing?

[lonely_wolf]

What are the thoughts on recessed crowns? I assume the USMC spec is somewhat of a standard, but then I've also seen some really deep crowns too. TacOps rifles, for example.

Deeper may offer more protection, but is there a point it becomes detrimental to accuracy? Is there an ideal depth?

 

[turbo54]

Re: Recessed Crowns: Too much of a good thing?

The crown could be recessed 10 feet and it wouldn't hurt accuracy. The key to a crowns accuracy is its symmetry.

At some point, the crown is deep enough to be well protected. At some point, the barrel is too long to be maneuverable. No one wants a 26" barrel to get 20" velocity/performance.

I love the crown print an 11° target crown makes, but its too easy to bang them up...so I cut the 11° crown, then thread, and make a thread protector that also recesses the crown ~3/16", which I think is plenty.

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

Too deep and I mean way to deep and muzzle gases will pass the the bullet and hurt accuracy. Same thing applies to muzzle brakes.

 

[LRI]

Re: Recessed Crowns: Too much of a good thing?

"Bloop tubes" (sight extension tubes) have been used for decades on both smallbore and highpower position rifles with great success.

Great success means:

Olympic medals.
National championships.

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

Chad,

I agree bloop tubes have not been a problem. I have never used one but my understanding they have a large diameter bore which reduces pressure quickly. A deep recessed crown would be a much smaller diameter and maintain pressure for a longer period allowing the gas to pass the bullet. I have seen high speed video comparing muzzle exit gases of two different types of powder. Very enlightening and explains several things I've learned the hard way concerning muzzle brakes with expansion chambers. Muzzle gas velocities are in 7,000-9,000 FPS range for modern rounds. That speed drops very quickly but even with the best of powders the bullet is passed by the gas in the first 2". Now what exactly happens in that cloud I don't know. I know in a brake with an expansion chamber longer than 1.5" accuracy suffers.

 

[Greg Langelius *]

Re: Recessed Crowns: Too much of a good thing?

Hmm, you have given me an idea.

Suppose we had a bloop tube that also contained a concentric narrow tube that served as a sort of narrow blast shield against muzzle gas impingement on the free flying bullet. The bullet would jump about 1/2" inch free beyond the crown, then enter and traverse the narrow blast shield tube. Might this enhance bullet stability/accuracy? Such a shield might also allow the bypass gas to be redirected to counteract muzzle flip, etc., without having any effect on the shielded bullet's flight.

I think care would need to be taken to avoid any significant sound suppression, or the concept might run afoul of class III legal intent.

BTW, does sound energy redirection qualify as sound suppression?

Just blue-skying here...

Greg

 

[lonely_wolf]

Re: Recessed Crowns: Too much of a good thing?

@Chad & Dave- Turbo54 listed 3/16" (.1875") and the USMC is spec'd as .090" deep. What are your preferences on recessing a crown?

If I am infringing on any trade secrets I apologize.

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

Greg,

The quicker we can redirect the gasses the more accurate the rifle will be. I remember Skip Talbot, always experimenting with something, had a two piece muzzle brake. Not to reduce recoil but to wipe off the gasses as quickly as possible. The first piece was the standard thread on baffled brake. The second part screwed in from the front a point close to the muzzle, maybe .500" and was cone shaped. The ID of the coned part was very close to bullet diameter. It made sense to me. I've never built one but have passed that information on to a suppressor manufacture and they have to some degree incorporated that into their design.
You could use the screw on section of the brake to mount the bloop tube on. How and where you direct the gasses would be dictated by the rules. I do know it would only take a small delay in gasses moving forward to allow the bullet to stay clear of the turbulence.

 

[jrm850]

Re: Recessed Crowns: Too much of a good thing?

I would love to see that high speed video. Does the rifling create any vortex at all or is it just a violent blast?

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrm850</div><div class="ubbcode-body">I would love to see that high speed video. Does the rifling create any vortex at all or is it just a violent blast?
</div></div>

Just a blast.

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lonely_Wolf</div><div class="ubbcode-body">@Chad & Dave- Turbo54 listed 3/16" (.1875") and the USMC is spec'd as .090" deep. What are your preferences on recessing a crown?

If I am infringing on any trade secrets I apologize. </div></div>

I go about .030" deep. Depends somewhat on the type of rifle. Many short range BR guys just face it off and slight polish and go shoot.
I've learned with expansion type brakes, meaning counter bored to the muzzle of the brake, radially drilled, say tap drill diameter that once you get to 1.5" you're going to have trouble. I think that style brake is more efficient than one with a small through hole, but it does have it's limits.

 

[DAVETOOLEY]

Re: Recessed Crowns: Too much of a good thing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Tooley</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jrm850</div><div class="ubbcode-body">I would love to see that high speed video. Does the rifling create any vortex at all or is it just a violent blast?
</div></div>

Just a blast. </div></div>

This is similar to the videos I've seen with the exception of one video I've seen gas completley encompassing the bullet. This is from AMU.

http://www.youtube.com/watch?v=50RV2ZJ8F7I

 

[Greg Langelius *]

Re: Recessed Crowns: Too much of a good thing?

Dave;

Thank you especially for both your quick response and anecdotal info. My best guess is that the idea has merit, and that the conical shield would/could be even more effective than my own tube idea.

Greg

 

[jrm850]

Re: Recessed Crowns: Too much of a good thing?

Very interesting video. I did not expect the gas to cool and decelerate that quickly.

Thank you for finding that. The only one I could find was the mini-14 which really only shows the muzzle whip.