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Muzzle crowns....industry observation

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Hold_Over

Hold_Over

Member
Dec 18, 2021
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Massachusetts, United States
I am not going to highlight any 1 particular brand with this since it seems to be something industry wide. The quality of muzzle crowns is not everything it should be on many AGs, on some there has been zero effort made to create one. Most do not own the necessary equipment to recrown barrels themselves. Yet there are many posts of every make and model with people achieving good accuracy, and fans of every brand out there. Out of curiousity do any of you own a rifle with a mediocre crown that exceeds accuracy expectations?
 
Sqwirl57 said:
No crown is going to be better than a bad crown. I've only had issues with two guns that had bad crowns that made for beyond questionable accuracy. I'm lucky enough to have the equipment to fix them and when I did the accuracy improvement was astonishing.
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Was the largest improvement seen in group size, poi shift making it easier to zero etc? How much difference are we talking about?
 
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Ugly crowns often shoot better than expected. However, some defects always lead to grouping trouble, such a a heavy burr that build up an uneven speed bump of lead at the muzzle. So, ugly and dysfunctional are not synonyms.

That said, driving with soft tires does not always cause immediate harm, but keeping appropriate tire pressure eliminates the possibility of low pressure induced trouble. In a similar way, having a good crown, or fixing a bad looking one removes one factor, in the event you need to diagnose poorer than expected grouping ability. Or it starts OK and then goes bad after so many shots.

Burrs at the crown, the chamber or transfer port are throwing away systems capability and value. It is a bit like shipping a vehicle with some spark plugs having too small or too large an electrode gap. Easily fixed, and sloppy if not set to the best functional state.
 
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subscriber said:
Ugly crowns often shoot better than expected.
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This is kind of what I am getting at. Clearly the industry has decided they can save money not offering higher end crowning on a lot of rifles. Probably more now that many of them are hidden behind permanent moderators. Yet I also see occasional comments on here that the muzzle crown is the absolute number 1 most important thing related to accuracy. It would seem more likely that consistent fps with a small overall deviation, and pellet properly matched to the rifle are potentially playing a bigger role.
 
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the only 2 things that matter on a crown is that it is uniform all the way around, square to the bore of course and burr free. Both a lathe tool or a grinding system if improperly applied will leave a small ridge at the beginning of the chamfer in the bore. the particular angle is not that important either. Really hard part is that you cannot rely on the bore being perfectly centered to the exterior of the barrel. So you must indicate concentrics from the internal portion of the bore a couple thousandths deeper than your planned start point. It is easier to use a gauge pin inserted into the bore than to try and read off the lands. Course if you dial indicator is not set very rigidly all bets are off. The actual work takes very little time. The set up is the key as always.
 
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Some crowns shoot well for a small number of shots, before they deteriorate. Other than a burr at the "exit", crowning tools pilots can scar the tops of the lands, perhaps an inch into the barrel. Such circular scratches may scrape the projectile and accumulate lead, so that accuracy degrades until the barrel is cleaned - or better yet deburred or recrowned.

This guide may help diagnose trouble with crowns and leades, with proposed fixes:

Barrel troubleshooting and accurizing guide

The following article is intended for the do-it-yourselfer that is interested in either finding and fixing a problem with a barrel, or improving the accuracy of an already good performer. You don't have to be a master machinist to get excellent results. The techniques described here can be...
www.airgunnation.com www.airgunnation.com
 
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ChrisT,

If you make the muzzle face completely flat, then you do not need to indicated off the bore. Besides, how do you insert a close fitting gauge pin into the bore, in order to indicate the barrel ID, until you have a burr-free crown to begin with?

Perhaps cutting anything but a flat crown requires first creating a flat burr-less crown, that will accept a gauge pin. Then indicating that in to center the bore, using a "spider" in a lathe. Then cutting an 11 degree or rounded crown can be cut concentric to the bore.

This dual step for concentricity is why many gun makers just use a piloted crowning tool - it is much faster and cheaper to use. When they use it badly, or with metal chips between pilot and the lands, that is when poor crowns result, with scarred lands. Yanking the pilot out as it spins has some operators pulling the barrel sideway to free it from the crowning tool, before withdrawing the spinning tool. The damage that causes is real obvious. I think the barrel fixing guide I linked to above has images of such damage.
 
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I have seen some truly poor crowns shoot well. I've also seen some pretty decent looking crowns shoot poorly but be salvaged by re-crowning. Perhaps at times the defects balance out, or they're dominant in the grooves of the barrel where they'd presumably have less effect. In any case, you can't make a crappy crown that shoots except by accident, so you make as perfect a crown as possible.

Most people have what they need to make a decent crown - the crown lap, or round-head brass screw, a drill and a little patience will often do the trick. (Not my preferred method, but it works well for those that don't own a lathe.)

ChrisT,
subscriber said:
If you make the muzzle face completely flat, then you do not need to indicated off the bore. Besides, how do you insert a close fitting gauge pin into the bore, in order to indicate the barrel ID, until you have a burr-free crown to begin with?

Perhaps cutting anything but a flat crown requires first creating a flat burr-less crown, that will accept a gauge pin. Then indicating that in to center the bore, using a "spider" in a lathe. Then cutting an 11 degree or rounded crown can be cut concentric to the bore.

This dual step for concentricity is why many gun makers just use a piloted crowning tool - it is much faster and cheaper to use. When they use it badly, or with metal chips between pilot and the lands, that is when poor crowns result, with scarred lands. Yanking the pilot out as it spins has some operators pulling the barrel sideway to free it from the crowning tool, before withdrawing the spinning tool. The damage that causes is real obvious. I think the barrel fixing guide I linked to above has images of such damage.
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You can indicate off the bore with an indicator that does not touch the 'crown'. Even if you don't a burr that's a few ten-thousandths won't move a gauge pin appreciably, and most smiths aren't going to dial anything in to 0.0001" or even 0.0005" regardless. Anything under a thou is probably going to give you as good as it gets.

GsT
 
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I have used cone shaped die grinder stones for cutting and rough polish on crowns or the little Dremel ones for small caliber. Slow and steady let the bore tell you what it wants and most time it's turning it in fingers keeping it square.There are threads online about coning muzzles on muzzleloaders so there is no need to use a short starter to load the patched ball and the effect on accuracy for those that wish to look into such things. Some say there is no effect or little and some that it ruins accuracy! There are a lot more variables involved with those than airguns though.
 
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Oddhawk said:
I have used cone shaped die grinder stones for cutting and rough polish on crowns or the little Dremel ones for small caliber. Slow and steady let the bore tell you what it wants and most time it's turning it in fingers keeping it square.There are threads online about coning muzzles on muzzleloaders so there is no need to use a short starter to load the patched ball and the effect on accuracy for those that wish to look into such things. Some say there is no effect or little and some that it ruins accuracy! There are a lot more variables involved with those than airguns though.
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Yikes.
 
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thumper said:
Yikes.
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That's pretty much what it said! But I didn't buy it dinner first! Lol

20240606_151755.jpg
 
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