Gunsmithing does the style of crown produce better accuracy ?

The_AKD

The_AKD

Private
Minuteman
Jul 29, 2010
47
0
40
#1
Does a barrel that is cut flat and crowned suffer in accuracy compared to a barrel that is recessed a tad and than crowned ?

seams to me the bottom photos only advantage is durability to protect the crown ?


( I personally would put more effort in to get rid of tool marks ect,, just an example of the style for you to get the idea)
new-crown-closeup.jpg


vs


1022_crown.jpg
 
#2
Re: does the style of crown produce better accuracy ?

I like a Sharp edge. I can't shoot well enough to tell the diff between an 11* and 90* but someone will say that NASA did a test in the flux capacitor and the 11 was .004% better.
 
#3
Re: does the style of crown produce better accuracy ?

The main reason im wondering is because I bought a savage TRR-SR in .17 HMR and the crown looks kinda lacking. I live in Canada and will never have a need for the suppressor threads so I was thinking about cutting that 1/2" of the barrel off and crowning it my self. I just dont have a lathe to do the "nasa" cuts.


picture of crown
 
#4
Re: does the style of crown produce better accuracy ?

IMHO the only portion of the crown that matters is the intersection of the bore with the face of the muzzle. Vintage rifles had a dead flat crown which was polished white after the barrel was blued. Rifles of this era were shot with grease groove lead bullets and the polished muzzle face let them keep track on the "performance" of their bullet lube as it would leave a star on the muzzle. I have crowned barrels flat , recessed, and with the 11/79 degree. I can find little difference in accuracy potential between the three but the recessed or 11 degree do offer protection to the important part of a crown...that previously mentioned intersection between the bore and the outside world. Brownell's sells a crowning tool that uses a pilot like a chamber reamer and can be ordered for a flat face or the 11/79 degree recessed. I have never used this tool but I thnk that if were used correctly it would provide a nice, square crown without the need for a lathe. You will still need to check the exit of the bore and lightly polish that exit corner. I use a lathe for crowning. After the machining is done and I have polished all the tool marks out. I hold a small fine cratex cylinder at 45 degrees against the exit corner for a few seconds....I also reverse the lathe and do the same op....results are a nice , accurate crown without the huge bevel you see on so many rifles
 
#5
Re: does the style of crown produce better accuracy ?

I've heard of folks using a ball bearing with various grit lapping compounds to retouch crowns. Obviously, the spherical bearing will self-center in the bore, and only make contact at the intersection of bore-to-crown. This method is only able to remove a slight bit of material, but if all you need is a slight retouch, might be the ticket.

It sounds reasonable to me, in the absence of a lathe to do it "right".
 
#6
Re: does the style of crown produce better accuracy ?

the crowns relation to the depth of the thread protector has little effect on most crtridges and none on your 22lr. IMO, you are removing value to the gun, creating possible heart burn if the crowning does not go well and not getting anything out of the deal. the gun appears absolutly normal to me in your pic. I would leave it alone unless it shoots truly horrible.
 
#7
Re: does the style of crown produce better accuracy ?

I've used the marble/BB method to quickly clean up <span style="font-style: italic">slightly</span> dinged factory crown - works fine. Obviously, cutting a nice sharp corner on a lathe is preferable, but sometimes you gotta deploy a crude method.
 
#8
Re: does the style of crown produce better accuracy ?

I have heard a couple schools of thought on this topic in that an angled crown will allow a bullet to be thrown off IF one of the lands or grooves is deeper than the others. Think about what's happening as the bullet is exiting the crown. A shallower groove will open up on one side vs a deeper groove in a different position if the crown is angled. Where as a 90* crown will have the bullet exit at all points at the same time given that the bullet is of equal length around it's circumference, even if one groove is deeper. With a good match barrel it's rare to find lands and grooves of varying depths so it's somewhat of a non-issue, but the theory is still there. Not to mention the non-uniform deformation of the bullet would probably be a bigger factor anyway.

I use both, but prefer 11* crowns if it's going to sit under a brake or in a can.
 
#9
Re: does the style of crown produce better accuracy ?

To add fuel to the fire because I have heard this most of my career and no one has yet to convince of a standard with regards to 11 degree crowns.

Is is 11 degree off the tool post?
Or an included angle with the tool post at 5.5?

laugh.gif
 
#10
Re: does the style of crown produce better accuracy ?

I set the compound to 79 with the tool parallel to the compund...I always understood the 11 degrees was off the face of the muzzle... the 79 on the compund plus 11 equals 90
 
#11
Re: does the style of crown produce better accuracy ?

As long as the crown is symmetrical/even and the bore is perpendicular to the crown it will fire true. When the bullet exits the muzzle the gasses push off the crown in the same way a helicopter pushes off the ground. If the helicopter is on uneven ground or on the edge of a cliff it will want to drift to one side because its not a flat surface. This is the same in rifle crowns.

I think the difference in target crown and 11 degree crowns differs only in preference and style. I do not like 11degree crowns because they are harder to protect from dings and nicks, but that is personal preference.

So to my understanding <span style="text-decoration: underline">the type of crown does not matter, what matters is that the crown is symmetrical (even and without burs or blemishes)and perpendicular to the bore.</span>Accuracy will not be affected if these rules are followed.
 
#13
Re: does the style of crown produce better accuracy ?

Hogwash! 11 degree or die!

LOL. Sorry- to be honest on hunting rifles I still have a couple of 60 degree radius hunter crown bits I had to grind for school years ago and I do use them from time to time, especially to tighten up barrels with that existing crown.
 
#14
Re: does the style of crown produce better accuracy ?

The best crown is a burr-free, indicated off of bore. Recessed crowns is just to protect rifling. Most benchrest shooters use just flat. Tactical use just about anything.
 
#15
Re: does the style of crown produce better accuracy ?


Right on boys. I thank you all for the wealth of info. I knew an american site would have the best firearm info and I can tell that was right.

I can see nicking the end off is usless so all ill do is a quick lap to clean to crown of a slight bur and it should be good to go.

thx again gents.
 
#16
Re: does the style of crown produce better accuracy ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The_AKD</div><div class="ubbcode-body">
Right on boys. I thank you all for the wealth of info. I knew an american site would have the best firearm info and I can tell that was right.

I can see nicking the end off is usless so all ill do is a quick lap to clean to crown of a slight bur and it should be good to go.

thx again gents. </div></div>

America....fuck YEAH!
 
#17
Re: does the style of crown produce better accuracy ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LongArm</div><div class="ubbcode-body">


So to my understanding <span style="text-decoration: underline">the type of crown does not matter, what matters is that the crown is symmetrical (even and without burs or blemishes)and perpendicular to the bore.</span>Accuracy will not be affected if these rules are followed. </div></div>

I would agree. Precision Shooting did an article a month or so back where Quarter Minute Magnums did some testing and found that barrel crown had basically nothing to do with accuracy as long as it was concentric, but barrel length had more effect in accuracy.

Mark
 
#18
Re: does the style of crown produce better accuracy ?

Mark...

I guess I'm running the thread in another direction, but since the OP's question has been answered, and you raised another issue...

I have always read that barrel <span style="font-style: italic">length</span> has no effect on accuracy, only velocity. Can you post a link, or explain?
 
#20
Re: does the style of crown produce better accuracy ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Paduan Learner</div><div class="ubbcode-body">I'm guessing that shorter is more accurate. BR is all about short, fat barrels. Short and fat means greater rigidity. Greater rigidity = greater accuracy.

Am I right? do I win a cookie??

N

</div></div>


Maybe half of a cookie.

BR barrels are short/fat because the weight restriction on the gun prohibits them from getting much bigger. The popular cartridges like PPC's, BR's, etc are tailored to shoot the lighter (60 grain-ish) bullets most efficiently from barrels of this length/caliber. Bench rest is a poor comparison on a variety of levels for a number of things. It's a very specialized game designed to work in a vary narrow set of parameters. Apples/oranges.

The PPC/BR cartridges were tailor made for this game. The guns are literally built around the cartridge. They work well in other applications, but the guns often don't.

In truth:

Barrel contour/length has virtually nothing to do with the accuracy potential of a rifle. A #1 sporter is just as capable of shooting well as a max heavy varmint.

The difference is the sustained rate of fire.

Hope this helps.

C.
 
#21
Re: does the style of crown produce better accuracy ?

I think that Mark's comments were aimed a very specific point which was hypothesized at the end of this article, but it is not a new concept for those familiar with the applications of OBT methodology.

If you work for a department that only shoots 175 FGMM from duty rifles and you are in charge of ordering new rifles then you want to get something that happens to shoot 175 FGMM the absolute best it possibly can.

Same if you have a department that is going to shoot 140Amax 6.5CM ammo (and to my surprise there are some departments moving to it now). IE, you need a rifle that the sweet spot is 140Amax @ 2.810 OAL and 41.5gr H4350

If you're not allowed to touch the ammo that goes into the rifle, then make the rifle in such a manner that it LOVES the ammo you must use. This is the concept behind the TacOps rifles which are setup specifically to shoot 168 FGMM into unbelievably small little groups.
 
#23
Re: does the style of crown produce better accuracy ?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: M.Gordon</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LongArm</div><div class="ubbcode-body">


So to my understanding <span style="text-decoration: underline">the type of crown does not matter, what matters is that the crown is symmetrical (even and without burs or blemishes)and perpendicular to the bore.</span>Accuracy will not be affected if these rules are followed. </div></div>

I would agree. Precision Shooting did an article a month or so back where Quarter Minute Magnums did some testing and found that barrel crown had basically nothing to do with accuracy as long as it was concentric, but barrel length had more effect in accuracy.

Mark </div></div>

Mark,
I remember that article (if we are talking about the same one) and the last crown given to that barrel (which was chambered for a .308 win if I remember correctly) was a deep recess 90 degree or flat inside of the recess and it shot much better than the others. I think the author commented on Richard Franklin using a similar crown, I think it was called a quiet crown or something like that. I give all my P.S. to my dad after I read them so I dont have it to verify. Im not tring to disagree with you just making an observation because I have NO ground to stand on in this conversation. Im just tring to get as much out of it as I can. Thanks for all the great info guys. Lets keep it rolling with scientific data, I find it very interesting.
 
#24
Re: does the style of crown produce better accuracy ?

I will try to dig up the article. I have all my copies of Precision Shooting laying around.

If I recall correctly, the author mentioned that the same load under similar conditions with the only variables being the change in crown design and the barrel length changing roughly .250", produced groups that were on both ends of the accuracy spectrum.

My experience and I believe what the author was trying to get at, was the crown design was most likely not the cause of the change in accuracy, but the barrel length was.

From my records and testing, I have found that certain barrel lengths work better with a given ammo than others. Also, some barrel lengths have shorter sweet spots when tuning a load, while barrel lengths like 26 and 22 have larger sweet spots. I think this is directly related to length, and not crown design.

Mark
 
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