Gunsmithing Muzzle crown pic--Question

[Firefour]

Seems to me in the past on the crown there was residue on the crown where the grooves ended at the muzzle, not all around as in the pic.
New bartlien .308 barrel. Reason I ask is I can't get it to shoot a solid tight group (pic) 100 yds. Handload, 168 sie, 42.0 varget, gm210m,
lapua case, 100rds down bbl. Off rests, in a manners t5a stock.
Ideas from those in the know?
Thanks

 

[NorthernBorn]

Re: Muzzle crown pic--Question

What's the bore look like? From what I'm seeing there is rust on that crown. If the bore looks the same you need to take a serious look at how you treat your weapons.

 

[insight3b]

Re: Muzzle crown pic--Question

Roll a q-tip between your thumb and forefinger to loosen the nap. Make sure you loosen it pretty well. Then insert the q-tip into the bore and drag it across the inside edge of the muzzle all the way out and all the way around. If any cotton gets pulled from the q-tip and remains 'stuck' the crown needs to be polished. About 60% of rifles will fail this test

 

[Firefour]

Re: Muzzle crown pic--Question

Trust me, there is no rust on the muzzle. Lint, fuzz, etc. from the rifle case is all thats there. I treat my weapons very well, thank you.

Tried the qtip test, no snags, pulls, etc.

 

[Rooster931]

Re: Muzzle crown pic--Question

I cant say as I see any claring muzzle dings or damage but for a finished rifle crown looks pretty rough to me may be the picture. Is this a proven load in the gun....then there was problems or is this the first time you shot that load? Next with a group like that I would check the scope and mount for correct torque. If your scope is tight and it passed the Qtip test, I would measure the chamber and work a load up from there and see what you get. Just my 2 cents.

 

[Firefour]

Re: Muzzle crown pic--Question

Muzzle is actually clean and smooth. Had a hard time catching the light right for the pics, didn't want to wipe the fuzz off to keep the residue on the end.

It's a proven load, at least in my other 308's. Rings are steel, torqued on scope and to base.
Thanks

 

[338RUM runner]

Re: Muzzle crown pic--Question

You need to make that a sharp edge and not a chamfer on the bore, it will shoot much better with out a chamfer from the bore to the crown.

 

[jbell]

Re: Muzzle crown pic--Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: xp100man</div><div class="ubbcode-body">You need to make that a sharp edge and not a chamfer on the bore, it will shoot much better with out a chamfer from the bore to the crown. As C.Dixon would say if it's not a sharp edge it's not good. </div></div>

Not to disagree with Mr. Dixon as I am by no means a expert on the subject but if done properly a chamfered crown will shoot very well. I have had far too many barrels with one that could hold their own to beleve other wise. Just saying.

To the OP, if you are not able to get your rifle to shoot and feel it could be the crown there is only 1 way to find out for sure. Send it to a reputable gunsmith and have it recrowned. It is cheep enough that you could pay for it with the ammo you will save troubleshooting.

 

[338RUM runner]

Re: Muzzle crown pic--Question

If the chamfer is done right is the ??? Why put an 11 or whatever degree on the crown and then chamfer at 45, might as well cut a 45 crown. Just my .02

 

[hdbiker1]

Re: Muzzle crown pic--Question

Have you ever considered that the new barrel or chamber doesn't like that load as well?

 

[eddief]

Re: Muzzle crown pic--Question

To insist a "sharp" crown is the only accurate crown is utter bullshit, period.

Concentric to the bore, absolutely.

My guess is your problem may be somewhere else other than the crown.

 

[z28kid]

Re: Muzzle crown pic--Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hdbiker1</div><div class="ubbcode-body">Have you ever considered that the new barrel or chamber doesn't like that load as well? </div></div>

I was thinking that as well.

 

[jonaddis84]

Re: Muzzle crown pic--Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eddief</div><div class="ubbcode-body">To insist a "sharp" crown is the only accurate crown is utter bullshit, period.

Concentric to the bore, absolutely.

My guess is your problem may be somewhere else other than the crown. </div></div>

Nobody else posts pictures of another way though, so that has to be the only correct way to do it!

Concentric is the key, as far as I know no one has proven any particular style to be any better than another.

To the guy asking why you would put a chamfer, the downfall to a sharp crown is how easily they can be damaged by the slightest mishap while cleaning.

As far as the OP question, Id be in the boat of trying another load, if it was developed for a stock barrel then you could be way low on powder charge might need to heat it up a bit. Normally a tight chambered quality blank will handle a lot more load. But dont just go out there and add 5gn of powder to it, work it up as you normally would.

 

[insight3b]

Re: Muzzle crown pic--Question

Maybe try the same load with the same components in anothe rifle? I've had different lots of varget give 200fps difference with the same charge...the sole reason I stopped using it.

 

[Firefour]

Re: Muzzle crown pic--Question

You are correct, I was focused on a proven load that did work, in another barrel. I'll load up some more in small increments
with varget, and another powder and give them a shot, with the chrony.

Sometimes one (me) can get fixated on something that worked, then doesn't work. duh

Still curious about the dispersion of the residue on the crown not being out the grooves only.
Thanks all.

 

[300sniper]

Re: Muzzle crown pic--Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: eddief</div><div class="ubbcode-body">To insist a "sharp" crown is the only accurate crown is utter bullshit, period.

Concentric to the bore, absolutely.

My guess is your problem may be somewhere else other than the crown. </div></div>

Yep.

 

[338RUM runner]

Re: Muzzle crown pic--Question

First poster wanted the star on the crown and you get that from a sharp crown.

 

[Jhnmdahl]

Re: Muzzle crown pic--Question

Might try a slightly different load and see if results change. 43.5 grains of Varget seems to be a much more common sweet spot for 168gr in 308.

 

[300sniper]

Re: Muzzle crown pic--Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: xp100man</div><div class="ubbcode-body">First poster wanted the star on the crown and you get that from a sharp crown. </div></div>

I thought his concern was the lack of accuracy.

 

[Firefour]

Re: Muzzle crown pic--Question

Lack of accuracy is the major concern, and I was equating that somewhat with the funky looking residue on the crown.
But due to the posts here, it got my head off a one rail track to the other varibles I was not thinking of, ie, different powder wts, different powder, and not the crowns fault.

More testing this week will elimanate a lot of those variables.
Thanks for all the heads up. I've just been doing this for 45 yrs or so, guess the memory banks need a reboot. lol

 

[338RUM runner]

Re: Muzzle crown pic--Question

Check every thing twice. From a 65+ shooter

 

[Gene Poole]

Re: Muzzle crown pic--Question

This is what a C. Dixon crown print looks like. This rifle out shoots me, but my buddy (whom I reluctantly admit is a better shot than me) put 5 through the same hole at 100.



This was my 10-shot group (one marked called flyer) after barrel break-in (using my NOT worked up break-in loads*):





* 43.0 Varget, Austrian surplus brass, CCI BR2s and 175 M118LR pulls seated to 2.800.

 

[LRI]

Re: Muzzle crown pic--Question

Just to clarify:

I've never stated that a rifle won't shoot unless it has a crown done the way I do it. (sharp)

I appreciate the intent, but it's simply not true. There's a great many rifles in service shooting exceptionally well with crowns that don't look like the ones I do.

I don't want this to erode into a pissing match.

My thoughts:

If anyone here fiddles with car engines its not too hard to visualize the similarity between barrel crowns and valve seats on cylinder heads. When I worked for Richard Conley and Bill Craddock in the 90's (at the time, two well known engine builder/cylinder head development guys from the Pro Stock/Top Fuel community) I was told that sharp transitions at each valve angle are desirable. The heads flow better this way. No big secret in the hot rod world.

Take that and stick it in your hard drive for later.

We've all had the benefits of eleven degree target crowns beaten into our skulls since the day we took an interest in precision rifles. It's a topic that surfaces here fairly often. I realize that a great many guns are crowned at 90* too. I'm not arguing that it too works just fine.

The eleven degree crown enjoys the soap box as the reigning champ though. Assuming this is true:

Is eleven degrees across the face of the crown with a forty five degree edge break at the bore/crown intersection? OR is eleven degrees just that? -Eleven degrees from the edge of the outer periphery all the way to the bore's edge?

Decide for yourself. For me its across the entire face including the bore/crown intersection.

That is why I cut them the way I do. The razor sharp edge is to promote a radial/resistance free escape of propellant gases as the boat tail (taper) transitions into free flight. I have no idea if this is actually happening. It would be very difficult to evaluate and that means expensive-(money I just don't have to spend) The uniform/radial gas residue on the face of the crown after a few rounds get through it does suggest were on the right track though.

The absence of burrs/inclusions is just good machine work. We'd want the same for any machining operation. It just happens to be more critical in this application because it elevates the risk of disturbing the bullet as it transitions from supported movement to free flight.

Judging by the end user feedback, the idea behind it isn't hurting anything as the rifles are shooting well. That's ultimately what I'm concerned with.

The crowns are more delicate yes. If your a gorilla with a cleaning rod there's a good chance you'll muck it up. If you treat it for what it is (a precision rifle) then it'll last to and well past the service life of the barrel.

Hope this helped.

C.

 

[Firefour]

Re: Muzzle crown pic--Question

Okay, trip to the range this morning with the results.
Everything rechecked, re torqued
Upped loads to 43.5-44.0 varget, 43.5 RL15, sie 168's, Lapua
and FC prepped brass, GM210m primers, 2.80 oal.
Pic of crown residue.
Still not happy with grouping, can't seem to get a consistent
solid group, although the groups are a tad bit better than the 1st round. Maybe I'm jumping the gun to soon, or just missing something. Gap's and other rifles I've had built in the past produced good solid groups, time after time. Don't like them flyers. Diamonds are 1".

 

[LRI]

Re: Muzzle crown pic--Question

I see vertical.

Initial thoughts:

Parallax in the scope
Looking at the tgt instead of the reticle
Lot of mirage barrel/tgt
Loads goofy
Bedding sucks
Loose guard screws
shooter isn't holding elevation as well as he/she should be


Another test:

Clean the bore. After its clean shoot 10 rounds at the berm. Don't even try to put them in paper. This is to foul the bore so that you get accurate feedback.

Now shoot 5x groups. 10 of these is ideal. (50 rounds total on 5 different tgts) Use the same load for all 50.

Evaluate and then decide.

If you done this already, great, if not, I'd do it before changing anything.

 

[10at6]

Re: Muzzle crown pic--Question

Try a NM load of 4064, 20 off and if that won't shoot,still show vertical, start looking per Chad's advice
Forget the crown and the crap that accumulates

 

[eddief]

Re: Muzzle crown pic--Question

I would have somebody else that's a known good shot, shoot the rifle??