throat angle

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pjifl
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Re: throat angle

#46 Postby pjifl » Wed Jan 16, 2019 6:42 pm

BTW, all of my 7mm SAUM (and 284W) are 9 twist except for a Kreiger I had at 8.5. In my opinion it was never as good as either my Bartlein or Madco barrels in 7mm although I know others have seen good results from them. I will eventually get onto the 7mm ELDs.

I do not think I have seen any significantly superior results from the 6.5 x 147s as opposed to 140 grainers and I agree that chasing that supposed slight BC advantage is often more of a selling point that a winning advantage.

Peter Smith.
Last edited by pjifl on Thu Jan 17, 2019 2:44 am, edited 1 time in total.

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#47 Postby Frank Green » Thu Jan 17, 2019 1:01 am

Peter, twist rate calc on the 147's and 150's.

147's @ 2600fps. I get a min. of 1-7.656 twist.
@ 2800fps. I get a min. of 1-7.92 to 1-8.052 twist depending on the numbers I use.

So I say 8 twist is ragged edge for the 147's.

150SMK @ 2600fps. I get a min. of 1-7.392 twist.
@ 2800fps. I get a min. of 1-7.524 twist.

So I say at a bare min. 1-7.5 and a 1-7.25 or a 1-7 twist would be better for the 150's.

John T
Posts: 241
Joined: Sat Jan 07, 2006 5:42 pm
Location: Brisbane

Re: throat angle

#48 Postby John T » Fri Jan 18, 2019 6:37 pm

Hello Frank and Peter.

I'm with you, I'm a jumper.

It's one of the polarising issues; jump or jam. Not much point in a debate, neither side will convince the other. Floaters take care of themselves.

But I would like your views on this proposition. If you jump, it is likely that you will not need to change your seating as the throat wears. Reason; whilst the throat wear will increase the jump, it is unlikely to increase the jump from, say, 0.020 to more than 0.060, meaning there will be no appreciable change in accuracy. There is no need to chase the wearing throat - same seating, same internal load configuration, with a slowly increasing jump of no consequence.

Peter, you do NOT NECK TURN. This opens a number of ancillary issues which are generally regarded as critical to accuracy. Can I boldly ask you to open a new topic, or shall we continue here?

Regards,
John Tracey.
18.01.19.

pjifl
Posts: 883
Joined: Fri Jun 17, 2005 12:15 pm
Location: Innisfail, Far North QLD.

Re: throat angle

#49 Postby pjifl » Fri Jan 18, 2019 7:19 pm

John,

I neck turned when I started on a 284 because I borrowed a 310 thou reamer to get started. Previously I had lightly touched up some other calibre necks with a minimum clean up. Since then I have always considered it an unnecessary curse.

My understanding is that it became regarded as necessary because many were using second rate cases and my experiences with Lapua has been that the batches are better than what a lot of earlier shooters has with other brass. I suspect US made brass has improved but going back, in general, it was usually not up to Lapua. Get the best brass possible. It is perhaps more important than the projectiles and very often forgotten about.

Short range BR shooters seem to run tighter neck clearance than LR shooters. My ideal neck clearance is about 4 thou - ie about 2 thou per side. Never under 3 thou. Too fine and V becomes more erratic. Shooting at 100y does not place much emphasis on consistent V. If I want a slightly tighter than factory reamer neck, I just lightly hone down the reamer neck to get the fit I want. BUT you need good consistent brass to do this. Perhaps any gains in LR shooting are hidden by other more important factors.

It is just my experience that neck turning is unnecessary for very high X counts at long distance. It does have some downsides - like if you lose your ammo it is a huge drama to recover with new stuff and not always easy to later turn other sets of brass necks to match earlier turned batches done a few years earlier.

I have seen some poorly turned necks that are worse off than good unturned ones. This is newer shooters who have other worse problems but have been hypnotized by promises of accuracy and have not correctly prioritized their efforts.

Just my experience. I am not trying to convince everyone to do the same - but to seriously question just what contribution it makes to the whole basket of variables possible in LR accuracy loading.

I am sure that neck turning done well can be beneficial to poorer cases. But is it worth while ? For someone who really understands the pros and cons - and has all other loading parameters under control, by all means if you want to neck turn. I would not be trying to convince new shooters along this path.

I mentioned a 90-12 recently at 600y. This was by a fairly new shooter using a stock standard 6.5 Swede - standard cases and reamer. And the Lapua cases are about 1/2 price of all the new yu-beaut 6.5 fads. And usually available in Australia. Sorting to order the cases was a waste of time - they were so uniform.

The biggest challenge facing new shooters is keeping them away from all the web sites that promise everything without an understanding of all of the elements that need to be brought together. Like how often have you seen a new shooter agonize over one parameter but then find that they have serious runout or sizing variation even to the point of misfires. They get blinkered.

Peter Smith.

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#50 Postby Frank Green » Fri Jan 18, 2019 11:14 pm

John T wrote:Hello Frank and Peter.

I'm with you, I'm a jumper.

It's one of the polarising issues; jump or jam. Not much point in a debate, neither side will convince the other. Floaters take care of themselves.

But I would like your views on this proposition. If you jump, it is likely that you will not need to change your seating as the throat wears. Reason; whilst the throat wear will increase the jump, it is unlikely to increase the jump from, say, 0.020 to more than 0.060, meaning there will be no appreciable change in accuracy. There is no need to chase the wearing throat - same seating, same internal load configuration, with a slowly increasing jump of no consequence.

Peter, you do NOT NECK TURN. This opens a number of ancillary issues which are generally regarded as critical to accuracy. Can I boldly ask you to open a new topic, or shall we continue here?

Regards,
John Tracey.
18.01.19.


To quickly mimic what Peter said about neck turning....with good brass I don't worry about doing it at all. Load good ammo and shoot the gun.

I do check the sizing die and pay attention to the set up. A bad die or decapping rod assembly and can induce run out into the brass. Which in turn puts run out into your loaded ammo/bullet.

I'm with Peter....on some of my guns I prefer a no turn neck chamber. I consider this +.003/.004" clearance over your loaded rounds. I don't want under a .003" clearance. That's getting to tight and when that happens I feel you have to really watch your neck sizes and or turn necks.

As the throat wears with a given load over X amount of rounds you will lose some velocity and the bullet will be jumping further. I will chase my throat/seating and bump my powder charge to get my velocity back where I had it and keep the gun in tune. Again only if I'm seeing any velocity loss etc....when I check the gun from time to time if it's giving me what it should be doing I don't get all worked up about a little throat wear.

When using a bullet on a new barrel/chamber when checking seating depth etc...keep that bullet for the duration of the barrels life as a reference. Going to a different bullet or a different lot can give you false readings from when you started.

williada
Posts: 969
Joined: Wed Jul 22, 2009 12:37 am

Re: throat angle

#51 Postby williada » Sat Jan 19, 2019 9:33 am

There are carbon issues with tight necks and long strings. I like about .003" clearance i.e. 0.0015" either side of the loaded round. It was Boyer who demonstrated how the correct neck clearance can be determined by the carbon wave on the neck. It is meaningful in determining that your rifle has been competently smithed as it also demonstrates the engagement of the locking lugs which determine the wave shape and symetry - all of which effect harmonics. May I suggest to new shooters, the emphasis should be on the gunsmith chambering a parallel and relatively tight freebore rather than tight necks to minimise in-bore yaw as the projectile bumps up from behind to engage the rifling. As for seating depth, it should be tested to see where the best performance lies rather than use an arbitrary figure. It also comes in cycles as you move back with greater distance away from the lands. Some maybe surprised how well a modified barrel with just the last 8 inches rifled and the rest with no rifling (free bore) will shoot to go to the extreme while not match standard an interesting experiment many years ago. Yes, I am a believer in chasing the throat, otherwise the pressures drop off, even if you are jumping and the position in the harmonic cycle changes (for want of better words be inclusive of shock waves) because the gong is hit with a different force. You may also nip the crown back to accommodate the subtle change in pressure. The analogy being that pressures rise with shorter barrels. It is also a reason why some loads flatten primers in short barrels and not in long barrels and the use of other people's data is not always going to optimize your barrel . Really scaled down because it is there, a minor adjustment with powder in the order of .1 or .2 of a grain as the throat is chased is useful. The British consortium on pressure trials found that tight barrels increased pressure and this lead to the 150 rule for chambering .308 i.e. the Bisley reamer with larger neck diameters. My testing revealed the tighter barrels with higher peak pressure did not speed the projectile up but slowed it down. The energy was lost in the throat when the bullet was being swaged to size creating the pressure spike. That is different from a closely fitting freebore and that is where the bullet selected must be a better match too. Looking a little further into the mud, the boat tail design, as separate from its diameter, can be an influence the way the bullet bumps up and influence the pressure profile. It is this aspect combined with lower peak pressure of a jump and more energy applied to velocity, that may assist optimizing performance. A lot can be learned from the black powder guys too as the projectiles are more delicate.
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wsftr
Posts: 202
Joined: Tue Jan 30, 2018 12:58 pm

Re: throat angle

#52 Postby wsftr » Sat Jan 19, 2019 10:22 am

John T wrote:Hello Frank and Peter.

I'm with you, I'm a jumper.

It's one of the polarising issues; jump or jam. Not much point in a debate, neither side will convince the other. Floaters take care of themselves.

But I would like your views on this proposition. If you jump, it is likely that you will not need to change your seating as the throat wears. Reason; whilst the throat wear will increase the jump, it is unlikely to increase the jump from, say, 0.020 to more than 0.060, meaning there will be no appreciable change in accuracy. There is no need to chase the wearing throat - same seating, same internal load configuration, with a slowly increasing jump of no consequence.

Peter, you do NOT NECK TURN. This opens a number of ancillary issues which are generally regarded as critical to accuracy. Can I boldly ask you to open a new topic, or shall we continue here?

Regards,
John Tracey.
18.01.19.


Hi John,

I'm not a Frank or Peter but IME the seating depth sensitivity is very much bullet design dependant. My testing and experience has been with .308 and a 6Br. Both very reliable and easy to work with cartridges so changes of significance show up and can be clearly identified and rectified...cause and effect.
A bullet I am using in .308 that is marked as seating depth insensitive needed a .003 tweak in jump to pull it into line. From memory a season of shooting yielded .001" of throat wear.
I believe there is a window of tolerance within any one setting or measurement of anything and that collectively those measurements/settings provides its own window of tolerance and you can end up on the edge of that tolerance.

I don't neck turn either. One of the issues here is its not defined whether its a large or small contributor to precision. The same could be said for ES. There are plenty out there including LR BR that place ES/SD as a secondary decision to what the result is on paper. Even though the theory is sound and can't be argued with until you get to results on paper.
For me unturned necks provide a level of precision and consistency that sits inside what I can reasonably hold and shoot so I don't bother.
My loads would get me a solid last place in SR BR :cry: however within the Fclass world my non neck turned loads have given highest x counts at nats etc and will shoot under .5moa at 900/1000.

I've attached a picture of what being .003 out in SD at 1000 looked like for me.
WP_20160326_001 - Copy.jpg
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bruce moulds
Posts: 2900
Joined: Sun Jun 19, 2005 4:07 pm

Re: throat angle

#53 Postby bruce moulds » Sat Jan 19, 2019 12:08 pm

pete,
i can think of at least 1 website that has become the bible of many. offering the promise of easy solutions to great results to the uninitiated.
some prefer to rest easy based on the dogma of such sites and not the path of reaping the rewards of work.
problem is the dogma usually involves some subtle form of marketing.
fortunately there are some like yourself who have been down the road and see the path you really have to take.
bruce.
"SUCH IS LIFE" Edward Kelly 11 nov 1880
http://youtu.be/YRaRCCZjdTM

Frank Green
Posts: 343
Joined: Wed May 28, 2014 11:48 pm

Re: throat angle

#54 Postby Frank Green » Sun Jan 20, 2019 2:29 am

williada wrote:There are carbon issues with tight necks and long strings. I like about .003" clearance i.e. 0.0015" either side of the loaded round. It was Boyer who demonstrated how the correct neck clearance can be determined by the carbon wave on the neck. It is meaningful in determining that your rifle has been competently smithed as it also demonstrates the engagement of the locking lugs which determine the wave shape and symetry - all of which effect harmonics. May I suggest to new shooters, the emphasis should be on the gunsmith chambering a parallel and relatively tight freebore rather than tight necks to minimise in-bore yaw as the projectile bumps up from behind to engage the rifling. As for seating depth, it should be tested to see where the best performance lies rather than use an arbitrary figure. It also comes in cycles as you move back with greater distance away from the lands. Some maybe surprised how well a modified barrel with just the last 8 inches rifled and the rest with no rifling (free bore) will shoot to go to the extreme while not match standard an interesting experiment many years ago. Yes, I am a believer in chasing the throat, otherwise the pressures drop off, even if you are jumping and the position in the harmonic cycle changes (for want of better words be inclusive of shock waves) because the gong is hit with a different force. You may also nip the crown back to accommodate the subtle change in pressure. The analogy being that pressures rise with shorter barrels. It is also a reason why some loads flatten primers in short barrels and not in long barrels and the use of other people's data is not always going to optimize your barrel . Really scaled down because it is there, a minor adjustment with powder in the order of .1 or .2 of a grain as the throat is chased is useful. The British consortium on pressure trials found that tight barrels increased pressure and this lead to the 150 rule for chambering .308 i.e. the Bisley reamer with larger neck diameters. My testing revealed the tighter barrels with higher peak pressure did not speed the projectile up but slowed it down. The energy was lost in the throat when the bullet was being swaged to size creating the pressure spike. That is different from a closely fitting freebore and that is where the bullet selected must be a better match too. Looking a little further into the mud, the boat tail design, as separate from its diameter, can be an influence the way the bullet bumps up and influence the pressure profile. It is this aspect combined with lower peak pressure of a jump and more energy applied to velocity, that may assist optimizing performance. A lot can be learned from the black powder guys too as the projectiles are more delicate.


Speaking of pressures and tight bores.....

Changing the bore size (tops of the lands) doesn't have as much of an impact on pressures (it does effect it though) but changing the groove size has the biggest impact. Anytime you change the overall surface area of the bore you will effect pressures. Overall smaller usually it goes up and bigger usually it goes down. I agree just because pressure goes up doesn't always mean you get more velocity. Some times you do lose the velocity.

Yes chamber and throat design have impacts as well.

Around spring time/early summer of 2018 we made some ammunition pressure test barrels in .300AAC Blackout. Made them for 3 different ammo makers at one time. We always supply a bore and groove and headspace inspection report with every test barrel we make and ship. The bore and groove dimensions are giving to the customer to the 4th decimal place. Being as ammo makers, bullet makers etc....for the most part cannot measure/inspect the barrels for dimensional conformity. By us doing this they have information in front of them so if they have problems they can start ruling the barrel out etc...

Anyways first customer got there barrels and started using them right awayand I get a phone call. Pressure is up 4k-6k psi and velocity was up a little as well with the SAAMI spec. reference ammunition. Ref. ammo is not available to the public. It is ammunition that is loaded to a given pressure and velocity and they will use the reference ammunition to confirm/qualify a barrel when new and also to check the barrel over the course of it's life while shooting it etc...Also what was interesting was some ammo would chamber all the way and some wouldn't. We chambered all the barrels we made at one time for each of the three customers. So same reamer was used. A Saami min. spec. chamber reamer.

They asked for help and I told them to send the ammunition test barrels back (think it was 3 of them) so we could double check them. They also sent 5 different types of loaded ammunition along with 5 rounds of the reference ammo. First thing I did was measure/check the bores. All in spec. so nothing weird there. Sure enough I start checking ammo and putting it into the chambers and some would go and some wouldn't. All of the reference ammo that was supplied wouldn't chamber. At least the rim thickness would stick out of the breech face instead of sitting flush like they are suppose to. That told me it was something with the ammo or the chamber or a combination of both. The AAC chamber has a freebore that is straight and cylindrical for like .187" (going off of memory right now) with a diameter of .3090". So I grabbed a bore gauge and measured the throat diameter. I was getting .3089". O.K. .0001" under min. tolerance. So I took our reamer to a local machine shop that we've known the owners for years and they have a clean room and they have two CMM machines. The CMM machines run like $125k each. So we had them put our chamber reamer in the CMM machines and measured the reamer. Guess what the freebore section of the reamer was measuring .3089". So chambers and reamer dimensions are matching up and making sense.

I then measured the reference ammo/bullet diameter. Guess what. The bullets on the major diameter where measuring .3090"! Not good! Then I looked at the ammunition spec. per SAAMI drawings. They spec. a .3090" bullet diameter -.0030" on the diameter. I'd like to meet the rocket scientist that spec'd a throat diameter of .3090" with a max. allowable bullet diameter of .3090". Your just asking for problems. Basically it's size on size.

So I ordered another brand new chamber reamer right away and in the mean time I called both of the other manufactures that we made test barrels for and asked them if they had used them. The answer was no. I told them why I was calling. Both places ran some ref. ammo thru the barrels later that day. Both places told me the same thing. Pressure and velocity was up 4k-6k psi. The one place asked if it was o.k. for them to take a reamer they had by them and hand cut the chamber. I said go ahead. They did it and reran the test and pressure and velocity dropped to normal.

So in this case a .0001" tighter on the throat diameter with a bullet at the max. allowable dimension drove up the pressure and velocity.

We got our new reamer in and recut the chambers and yep it just took a little out of the throat. Sent them back to the customer and they worked like a million bucks.

The other thing we run into is when a company or individual is loading ammo and in the seating process cocks the bullet a little bit they can enlarge the case neck a little and this can cause chambering issues as well with the loaded ammo when the tolerances are tight.

With all of this happening the one ammunition makers is recommending to the SAAMI board to change the specs on the reamer or reference ammo and or both.

williada
Posts: 969
Joined: Wed Jul 22, 2009 12:37 am

Re: throat angle

#55 Postby williada » Sun Jan 20, 2019 1:25 pm

Hi Frank, some of what you have been describing has confirmed what I was comparing with the Bisley reamer and the 95 Palma in a dozen test barrels of varying land and groove depth way back.

The neck clearance for the Palma was about .002” and the Bisley was about .004”. Warner went for performance and the English went for safety. We explored that a bit further and were trying to make the barrel fit the bullet that was issued in relation to groove size and the suitable transition from the throat to the leade as it impacted on barrel lift for the contour we were using which was lighter whippier barrels. FOpen barrels are stiffer and require different tuning methods but the concentric alignment still applies to ammunition as it rests in the six o’clock position in the chamber. We also varied land height to keep the ratio of bore/land intact. Radway Green ammo was notorious for variance in component size and powder quality which changed pressures. I know top performers still take more than one barrel with different internal dimensions to Bisley to match the powder performance to compete on a level playing field. They know what they are doing even though the necks meet the Bisley 150 rule and spend big to get the results. Australians have experienced powder changes from the expected in England before, let alone the brass for which a longer headspace was required. Gone are the days of social adventure to England.

These days our bullet choice is wide and so are barrel contours. Having this choice also poses a risk because of varying dimensions of projectiles from different manufacturers let alone the same one IMO.

The SAMI or CIP reamer dimensions were designed for safety in mind so that one size could fit all. The likes of Warner and Gamboa refined these dimensions within safe limits in response to different projectiles to maximise performance with tighter necks and shorter throats depending on bullet length for high performing teams and not the average Joe. The problem becomes the average Joe applies the dimensions to everything and in the wrong hands becomes a potential hazard. We are now using longer and heavier bullets which change the friction profile which at the cutting edge suggests these chambers are obsolete. It’s a journey like all of us have gone through but it’s the safety of self and competitors that should be foremost. The laws of negligence were built on firearms incidents. There is nothing like building up to a load in view of safety because we share the range and the anti-gun lobby use incidents to promote their cause.

It is rightly the groove depth that boosts the pressures in tight barrels with the most significance. The pressure effects translated to throat diameter of the free-bore are potentially hazardous with an interference fit - great investigation. The advantage of the Ozfclass is a site where knowledgeable people can explore performance and know the safe limits to set the tone and culture. Thank you for your continued contribution Frank.

When Mr Pearce and I were working alongside Winchester in Geelong Australia to refine the quality assurance for a Palma Match we found that bullets supplied in bulk from Sierra came from 4 different machines and their dimensions differed somewhat because the wear must have been different on each die in the four different presses. Any mixing of bullet batches as had previously been the case was a problem in the fine accuracy stakes despite the final product of cartridge having the same batch number.

In terms of the fine accuracy stakes, the throat diameter can be relatively tighter than SAAMI within reason so there is no interference fit and safe if bullets were pressure tested. My “Sierra” experience means I sample check bullet sizes for specification. A shooter may use a ring gauge to ensure there is no interference fit or a micrometer and that assumes the reamer specs are accurate. A Redding case neck button of the appropriate size can be ordered custom in 0.0005” differences and can be used as a ring gauge. As Frank has indicated a .0001" interference fit is a real problem in chambering but I imagine the bump up of the base on ignition if it was force fitted would exacerbate the problem.

It is the throat that gets hammered for wear and probably from cleaning. The chamber reamer also cuts over their stated size a tad. So there tends to be a safe buffer if reamers are of specified size. Shooters should measure their reamer because the specs do not always match the measurement and beware gunsmiths stone up old reamers which reduces diameter. My issue is with sloppy throats and poor gunsmithing to match the bullet being used for best performance. If it does not start straight, it will not perform to its design.

!Peter!
Posts: 150
Joined: Sun Oct 30, 2016 6:35 am

Re: throat angle

#56 Postby !Peter! » Sat Jan 26, 2019 2:42 am

Thanks to all for this great discussion and sharing of knowledge!


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