throat angle

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bruce moulds
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Joined: Sun Jun 19, 2005 4:07 pm

throat angle

#1 Postby bruce moulds » Sat Jan 12, 2019 8:11 am

a bit of preamble.
i have a 9.3x64 brenneke consisting of a mauser action with a lothar walther prechambered barrel fitted.
the barrel is like a shilen no3 profile, about 0.6" at the muzzle.
as originally set up it shot about 3/4 moa with a number of bullets (hunting, not match) which requires a bit of mental effort with the ammount of recoil.
in order to load certain bullets to mag length, the throat was extended.
ammo that was safe in the shorter throat suddenly blew primers!
the opposite should have been the case, as one would assume lower pressures with a longer throat.
the new throat was 1.5 degrees, and a study of c.i.p specs revealed that the original was 0.5 degrees.
here was the problem.
the purchase and use of a corret to spec throater restored lower pressures.
there was a small but barely noticeable loss of velocity from the shorter throat, but accuracy returned.
in fact 1 bullet has 0.2" jump and shoots 0.8 to 0.75 moa.
it night do better, but with over 40 ft lb recoil i can do no better with an 8 power scope.

we all take 1.5 degrees as standard now but i cannot see why other angles are less accurate and could have more to offer for velocity at reasonable pressure.
older weatherby cartridges were noted for freebore, and a look at saami reveals that some of this is achieved by lower throat angles than 1.5 degrees.
and i have used 3 degrees and 7 degrees with cast bullets, but that is a different story.

has anyone tried less than 1.5 degrees, and if so what was the result.?
after the 9,3x64 experience, i am wondering if there is a benefit to be had in the 284 win in velocity gain while accuracy is still acceptable.
whenever i ask this question, the answers always include "i just use 1.5 degrees".
this answer is irrelevent, because these people have only used that angle by default.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

Matt P
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Re: throat angle

#2 Postby Matt P » Sat Jan 12, 2019 9:54 am

Bruce
I've gone the other way and some of my reamers have 2.5 per side, I dont see any real difference in load or pressure. I do see more consistency in accuracy and slightly better throat life.
Matt P

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#3 Postby Frank Green » Sat Jan 12, 2019 10:20 am

Bruce, I wouldn’t necessarily agree the 1.5 degree angle is used as a default. I would agree that it seems to be a given over the years that for best accuracy in a target type gun it’s what is needed.

That being said I’ve shot plenty of guns chambered with a 2 degree 30 minute angle throat, 3 degree throat and had no complaints on accuracy.

Things with a very heavy angle or a drastic change in throat size over the length of the throat with jacketed type bullets I have seen effect accuracy or maybe I should say make the barrel/accuracy more temperamental.

I personally feel the bore rider throat reamers/bore rider bullets are also more tempermental. The throat if the chamber/barrel is the first thing that is going to start wearing and this will change the tune of the barrel/gun as well. The faster this changes to me the faster the accuracy changes/gets effected.

I started typing this before Matt P posted and had to come back to doing the post. I feel Matt is seeing/feels the same thing.

Later, Frank

bruce moulds
Posts: 2535
Joined: Sun Jun 19, 2005 4:07 pm

Re: throat angle

#4 Postby bruce moulds » Sat Jan 12, 2019 10:22 am

interesting matt.
i wonder if accuracy is affected by how the throat holds the bullet back as ignition happens.
possibly a steeper throat would hold the bullet back a microsecond longer than a shallower one offering a more consistent start to the bullets.
but then sometimes more accuracy comes with more jump, which in that situation would suit the lower angle with less resistance.
goddam?
a benchrester told me that if your gun shoots better with long jump it suggests that the chamber might be crooked.
i sometimes think that a good straight chamber might be the most forgiving in ammount of jam/jump.
then powder burning rate might be affected by how a throat angle variation might affect how the bullet starts.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

bruce moulds
Posts: 2535
Joined: Sun Jun 19, 2005 4:07 pm

Re: throat angle

#5 Postby bruce moulds » Sat Jan 12, 2019 10:24 am

frank,
glad you joined this thread.
you might have seen more of this than most of us.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#6 Postby Frank Green » Sat Jan 12, 2019 10:26 am

Hard for me to prove it but I do feel that changing from one type of bullet to another type of bullet in the same gun that after x amount of rounds being fired to some what of an extent the throat will change and modify it’s self to some extent to a given bullet. Again hard for me to prove.

I also do know that as the throat wears from shooting and possibly in conjunction from cleaning that the throat at the 6 o’clock position of the chamber/bore of the barrel will have more wear to it than at the sides and the top. Why? Loose debris, powder particles, carbon particles etc...tend to lay more at the bottom.

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#7 Postby Frank Green » Sat Jan 12, 2019 10:47 am

We all know that a crooked chamber per say vs. a straight chamber effects how the bullet makes the jump into the barrel. The more the bullet starts out of true centerline to the bore...that any runout the bullet/ammo has it basically has a premature wobble to it. The more the bullet starts crooked in the bore of the barrel the more the accuracy will suffer.

I also feel the more and more radical design bullets that keep coming out the harder it will be to keep the gun in tune and or if you want to say it differently the shorter the barrel life will be. Kinda. You following me?

Take for example the older and still being made 190gr SMK. In .30cal. I’ve seen test data where the bullet was shot out to 1k yards and compared to other more radical designs like VLD type bullets. Let’s call it the secant vs tangent type bullets. The VLD design type bullets yes more pointy etc...and get higher b.c. Numbers I also feel don’t always fly as consistent and can be more erratic.

I was just talking to a ammo/bullet maker about this a month ago. It started out as a barrel life question posed by someone to me and the ammo in question being used. I won’t name him or what he does. Sorry! While the ammo/bullet maker and I where talking and emailing back and forth they feel that especially in regards to shooting loaded factory type ammo the accuracy will suffer earlier with a VLD type bullet or I should say a bullet with a more radical profile/design then with a more conventional match type bullet. I tend to agree.

Us shooters who are handloading vs. a guy who is stuck using factory loaded match ammo have a way around this. We can chase the throat and try to keep the gun in tune longer. Others cannot.

Why do I bring this up? I feel it does work in conjunction with throat angles as well as bullet design.

Something to think about!

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#8 Postby Frank Green » Sat Jan 12, 2019 10:56 am

To kinda add to post #7 of mine....back when we started Bartlein Barrels and being on our own and gone from Krieger.

I made a sample barrel for a really good customer of mine. His customer keeps excellent data and shoots hi power rifle across the course. If I recall correctly in his .223 gas gun in a given month between practice and matches he was shooting some where around 3k rounds a month.

That first sample barrel we made my customer/gunsmith for his customer at some stupid round count of like 15k rounds or more....he had one bullet (more of a hunting type bullet than a match bullet) would still shoot sub minute of angle and even though a high round count he would still use it for practice. I have the data/emails at work but will have to dig for it. That was like 14 years ago now.

His other match bullets he normally used wouldn’t hold sub moa anymore but that silly hunting bullet would.

bruce moulds
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Joined: Sun Jun 19, 2005 4:07 pm

Re: throat angle

#9 Postby bruce moulds » Sat Jan 12, 2019 11:13 am

strangely berger vld bullets are generally shot jammed by target shooters who chase the rifling religiously.
however when used in hunting rifles they seem to work well enough with massive jump.
but not in between.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM

pjifl
Posts: 655
Joined: Fri Jun 17, 2005 12:15 pm
Location: Innisfail, Far North QLD.

Re: throat angle

#10 Postby pjifl » Sat Jan 12, 2019 12:11 pm

One of the historic reasons for a jam is to partly counteract sloppy gunsmithing. I think barrel fitters working on target rifles are better these days but there have been many misaligned chambers cut. Of course, there are other reasons people use jump as a useful variable.

It is well known that Field Artillery with fixed cases usually shot less accurately, (especially with worn tubes) than separately loaded shells which are jammed into place before the charge is loaded. Artillery often wears asymmetrically after many shots as well as simply wearing.

My own experience with jump seems to indicate that in my very carefully chambered barrels jump does not matter much as far as accuracy goes.
In fact, I well remember an 'accident' I had when loading. Some gremlin must have changed the die seating depth and I had about 7 loaded - all 160 thou jump - before I realized. I was pushed for time so I decided to load another few to make a match set. The case, however, was a very snug fit so was held central.

And the score was excellent.

None of this is proof but it reinforces my belief that people get too fixated on some things and underrate others which may be more important - like excellent gunsmithing and also case preparation.

Peter Smith.

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#11 Postby Frank Green » Sat Jan 12, 2019 3:24 pm

bruce moulds wrote:strangely berger vld bullets are generally shot jammed by target shooters who chase the rifling religiously.
however when used in hunting rifles they seem to work well enough with massive jump.
but not in between.
bruce.


I don’t agree with this. I for the most part would only shoot the VLD’s when I do shoot the Bergers. I never jammed them. When I tried jamming them they never shot better for me. 6mm or 6.5mm or in my 7’s. Never shot .30 Berger’s. O.K. I did try some.

Finally convinced a customer and shooting buddy that we’ve shot team matches together to try it. He took his Palma rifle to the range and benched the gun at a 1k yards. He took pre loaded ammo and a hand press with a micrometer seating die. He would shoot 10 shot groups and after each group seat another 10 rounds deeper off the lands. He started with his usual .020” jam. He went all the way to .040” off the lands.

Watching for the vertical at .020” jammed the gun was shooting about .7moa for vertical. At .020” off the lands the group sizes where cut in half.

Frank Green
Posts: 241
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#12 Postby Frank Green » Sat Jan 12, 2019 3:33 pm

Peter makes some more good points.

When testing my new F class gun mid summer of 2018 in .300PRC. I started loading another batch of ammo with the 225 Hornady’s. By mistake on my part when I adjusted the seating stem down further I actually seated the bullets .050” off the lands. I didn’t pull the bullets but shot them as is. I only had 10 of them loaded when I caught my mistake but shooting them side by side compared to the ones at .010” off the lands there was no appreciable difference in accuracy. They held .4xx moa.

Another good example is my .338 Lapua when I was doing testing back around 2010 for the PSR solicitation and for Remington. I was supplied box Swiss RUAG match ammo with both 250gr. And 300gr bullets. The reamer I used in my barrel had a shorter throat then CIP/SAAMI spec. But would still chamber box ammo with no issues. What I mean by no issues is the 250gr bullets where jumping .160” and the 300’s where jumping .100” and for the most part none of the groups measured bigger than a .750” at a 100 yards. They held that accuracy out to 1200 yards.

Yes my handloads shot consistently better but for box ammo I couldn’t complain about it in my rifle.

My 6.5CM I’m running the 150SMK at .015” off the lands and they just pound the target with nice small groups.

I tell guys that for the most part up to .060” off the lands the gun could shoot better than jamming the bullets. Yes usually closer is better but it’s not a guarantee.

pjifl
Posts: 655
Joined: Fri Jun 17, 2005 12:15 pm
Location: Innisfail, Far North QLD.

Re: throat angle

#13 Postby pjifl » Sat Jan 12, 2019 4:26 pm

FWIW, a few years ago I shot a 7 SAUM in the NQRA Queens using Berger VLDs and about 20 thou jump. My X count was well above anyone elses. One was on the wrong target, however, which put me out of 1st place !!!!!

At the time, the consensus was that VLDs would not do this in a SAUM and everyone was chasing Hybrids although some thought VLDs were OK in a 284. Many were preparing for the Canadian Team shoots and I have to respect these peoples testing and opinions but my experience diverged.

Next year, I used Hybrids and did something similar but kept them on the right target and won the shoot. Same 20 thou jump.

All standard - no neck turned cases. Very very carefully fitted barrels and very careful loading - especially matching cases. 12 shot Vsd was down under 4 f/s.

I never did the painful jump tuning that everyone else was doing, often wearing out their barrels prematurely in the process. Since my initial guess of 20 thou produced very good results I never tried anything else.

Again, this proves nothing. Just that blindly following the prevailing wisdom may not be as useful as many think.

The lead angle was standard at 1.5 deg but the reamer was honed down to a minimum size. The first shoot used fireformed cases with a collet neck die. For the second I resized with a die I made from a honed down reamer so it was a minimum resize. Again, no neck turning.

Draw your own conclusions.

Peter Smith.

wsftr
Posts: 86
Joined: Tue Jan 30, 2018 12:58 pm

Re: throat angle

#14 Postby wsftr » Sat Jan 12, 2019 6:28 pm

I'm not sure about jump not mattering IME it definitely does. Some ogives are more sensitive than others. The single biggest issue is no one can explain why it matters more with some ogives.
Personally I would struggle to believe that a specific ogive shape wouldn't shoot in a specific chambering, I can't see how that adds up.
Thats not to say that the precision seating depths aren't cyclical in that there is more than one depth that works. Maybe the rest of the world has sloppy chambering and barrel fitting but I believe there is plenty of evidence out there that show seating depth matters.
IME a long bearing surface with a tangent ogive is a very forgiving combination capable of very good precision but not great in the BC department
However everyone has their method of obtaining a precise load and they all work to some degree or other.
Rules of thumb are a good guide/starting point but not the only way.

bruce moulds
Posts: 2535
Joined: Sun Jun 19, 2005 4:07 pm

Re: throat angle

#15 Postby bruce moulds » Sat Jan 12, 2019 7:24 pm

theories were made to come tumbling down.
i had a 6.5x284 that would not shoot berger vld jammed, but shot them at 0.030 jump very well.
if you start testing jammed, you at least will not increase pressures as you shorten the coal.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880

http://youtu.be/YRaRCCZjdTM


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