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badgeredd
10-17-2012, 03:00 PM
After talking to a friend, I realized he was having trouble visualizing the relationship of the chamber, throat and the loaded cartridge so I decided to try to give some folks a visual.

Below is a cut-away of a 30-06 chamber, an empty case and a 311291 boolit. Notice the highlighted red area is the "throat."

http://i533.photobucket.com/albums/ee338/badgeredd/posted/PICT0563.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/PICT0563.jpg.html)

Below is the empty case sitting in the cut-away chamber.

http://i533.photobucket.com/albums/ee338/badgeredd/posted/PICT0564.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/PICT0564.jpg.html)

Below is a checked, sized, and lubed 311291 boolit in the throat.

http://i533.photobucket.com/albums/ee338/badgeredd/posted/PICT0569.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/PICT0569.jpg.html)

Next, the assembled dummy starting into the throat.

http://i533.photobucket.com/albums/ee338/badgeredd/posted/Picture026.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/Picture026.jpg.html)

Next is the assembled dummy pushed into its fully seated position. Sorry... still a little fuzzy.

http://i533.photobucket.com/albums/ee338/badgeredd/posted/PICT0570-1.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/PICT0570-1.jpg.html)

Lastly, note the end of the throat is indicated by the light red line in the flat above the chamber and how the entire throat is nearly filled by the boolit.

http://i533.photobucket.com/albums/ee338/badgeredd/posted/Picture027.jpg (http://s533.photobucket.com/user/badgeredd/media/posted/Picture027.jpg.html)

I hope this helps some fellows to understand what we are talking about when we talk about "filling the throat."

BTW, notice the chamber cut-away has an area highlighted with red marker (in the first picture), commonly called the "throat."

Edd

P.S....I tried to get a couple pictures of better quality but still have one that is a little fuzzy. Hope you can still get the picture...pun intended!

2/6/15: I was able to find the pictures on an old hardrive and up loaded them into my Photobucket account. Apparently Photobucket has some issues and my original links went dead. Hopefully everyone can make use of the stickie in its restored state.

blikseme300
10-17-2012, 03:18 PM
Thanks for sharing. Sticky?


Bliksem
Sent from my iPad using Tapatalk

**oneshot**
10-17-2012, 03:58 PM
that is worth the thousand words!!!

Thank you for sharing.

Blammer
10-17-2012, 04:00 PM
very nice!

Dutch4122
10-17-2012, 04:47 PM
Thanks for sharing. Sticky?



I heartily second that motion!:goodpost:

badgeredd
10-17-2012, 05:12 PM
Well if I was a better photographer, it would be a bit better, but I seem to have gotten the point across. I sincerely hope it helps those among us that benefit from visual images. Thanks guys for the comments.

Edd

Lefty SRH
10-17-2012, 07:21 PM
Awesome, nice to see a visual. Now whats the difference between throat and "freebore", so I've heard it mentioned before.
I really hate to ask this but where does the rifling start in the top pic?

badgeredd
10-17-2012, 07:37 PM
Awesome, nice to see a visual. Now whats the difference between throat and "freebore", so I've heard it mentioned before.
I really hate to ask this but where does the rifling start in the top pic?

The area often called freebore is part of the throat as is the leade. Freebore to my understanding is the length a bullet has to jump before the bullet starts to engage the rifling. I'm sure someone else may explain it more correctly than I.

The rifling in the chamber above starts at the end of the red highlighted area away from the case in the top above picture (the first one). Clear as mud?

Edd

badgeredd
10-17-2012, 07:43 PM
Steve,

If you click on the link to the album, you can enlarge the picture a bit and actually see some of the rifling in the left end of the chamber cut-away. Like I said above, the throat ends basically where the rifling begins or at the end of the red area.

Edd

Lefty SRH
10-17-2012, 07:54 PM
Steve,

If you click on the link to the album, you can enlarge the picture a bit and actually see some of the rifling in the left end of the chamber cut-away. Like I said above, the throat ends basically where the rifling begins or at the end of the red area.

Edd

So if "freebore" is the lead to the rifling then am I correct by saying this chamber doesn't have any "freebore" since it goes from throat straight to rifling?

badgeredd
10-17-2012, 08:37 PM
OK...perhaps this will help.

http://www.bellmtcs.com/FAQ/ChamberThroats101.htm

Use the pictures to kinda reference the parts of the throat that are mentioned in the article at the link.

Edd

stubshaft
10-18-2012, 01:39 AM
So if "freebore" is the lead to the rifling then am I correct by saying this chamber doesn't have any "freebore" since it goes from throat straight to rifling?

The boolit is seated out eliminating freebore. IF, it was seated to the crimp groove then the portion exposed would be the free bore.

The chamber has freebore but the fit of the boolit eliminates its existence.

crabo
10-19-2012, 12:05 AM
Alright! I have milled out my chamber like you did. What do I do next to get good boolit fit??

badgeredd
10-19-2012, 09:58 AM
Alright! I have milled out my chamber like you did. What do I do next to get good boolit fit??

[smilie=1:[smilie=1::bigsmyl2:

Funny guy you are. I 'spect you'll see pressure problems very early in your research.:kidding:

Edd

blackthorn
10-23-2012, 01:30 PM
If you hold the "Ctrl" key down the image can be scrolled larger or smaller using the Mouse! (A trick I learned right here on this site!!!)

MT Gianni
10-23-2012, 10:06 PM
I decided to stick this before I got through Edd's pictures. Great write up.

_Hawkeye_
10-27-2012, 10:18 PM
Very interesting. Would this weapon only then shoot this shape boolit>?

badgeredd
10-28-2012, 10:31 AM
Very interesting. Would this weapon only then shoot this shape boolit>?

No, the chamber/cartridge combo is not limited to this particular boolit. I used this particular boolit because a) it was readily available and b) it pretty much demonstrated what I wanted to show.

The idea is to fill the throat as much as possible with a boolit regardless of its shape. If the boolit shape doesn't lend itself to mostly filling the throat, one cannot expect good results. A person MAY be pleasantly surprised, but the likelihood of a boolit working well and not at least mostly filling the throat is not in one's favor.

Edd

303Guy
11-07-2012, 03:37 AM
Great thread, badgeredd. :2_high5:
That's such an informative set of photo's - thanks! :drinks:

In fact, those photo's are so valuable in my opinion that I feel obliged to ask that you beg steel or borrow a high resolution camera for these photo's.

Good one, crabo. Someone had to say it! :mrgreen:

GMW
12-16-2012, 01:22 AM
Thank you for the Great pictures! I learn something everyday on this site.

Boneguru
12-16-2012, 11:53 AM
excellent visual, thanks.
Ray

vogironface
01-14-2013, 09:12 PM
I recently measured the relationship between the throat and bullet of my 9mm. I do not think it would be possible to load a boolit that would fit properly with any boolit appropriate for the caliber. the distance is best described as a chasm. Accuracy is a frustration with that gun. Is inaccuracy what one would expect with a boolit seated to far back? I know accuracy can be improved in rifles (and I assume handguns) by seating just off the lands and I infer from that that an extremely poorly fitting boolit might have the opposite effect.

jabilli
01-30-2013, 02:53 PM
Stinking Brilliant. Thanks! (Where'd you get that cutaway?)
Is it a common occurrence for reloaders to not fill the throat? :-p

badgeredd
01-30-2013, 07:52 PM
I recently measured the relationship between the throat and bullet of my 9mm. I do not think it would be possible to load a boolit that would fit properly with any boolit appropriate for the caliber. the distance is best described as a chasm. Accuracy is a frustration with that gun. Is inaccuracy what one would expect with a boolit seated to far back? I know accuracy can be improved in rifles (and I assume handguns) by seating just off the lands and I infer from that that an extremely poorly fitting boolit might have the opposite effect.

In a 9mm about the only thing a fellow can do is load a fat boolit to help align the boolit in the throat/chamber and load the cartridge as long as the magazine will allow. Chances are you'll never get your firearm to shoot cast boolits accurately, and chances are just as good that jacketed ammo will not improve accuracy significantly. Some guns just aren't built in a way that is inducive to accuracy.

Edd

badgeredd
01-30-2013, 07:58 PM
Stinking Brilliant. Thanks! (Where'd you get that cutaway?)
Is it a common occurrence for reloaders to not fill the throat? :-p

I cut away the chamber area on a old 03-a3 barrel that had been removed from a friends rifle. We put on a much better barrel and I thought the visual would be helpful to some. It appears I was correct.

As far as loading to fill the throat to help improve accuracy, we can do a lot to improve fit by knowing what our chamber and throat are shaped like and what boolit we use to help fill the void. THAT is precisely why you'll see the expression "Fit is king".

Edd

jabilli
01-30-2013, 08:35 PM
I cut away the chamber area on a old 03-a3 barrel that had been removed from a friends rifle. We put on a much better barrel and I thought the visual would be helpful to some. It appears I was correct.

As far as loading to fill the throat to help improve accuracy, we can do a lot to improve fit by knowing what our chamber and throat are shaped like and what boolit we use to help fill the void. THAT is precisely why you'll see the expression "Fit is king".

Edd

Makes me wonder- ammo when you go grab it off some shelf...Considering all things equal (which, is certainly not the case) some brands/designs will work better for some guns and not so well with others... Gunmakers...Knowing this...can they and do they somehow make their product more able to shoot whatever someone grabs off the shelf accurately?

badgeredd
01-31-2013, 11:29 PM
Makes me wonder- ammo when you go grab it off some shelf...Considering all things equal (which, is certainly not the case) some brands/designs will work better for some guns and not so well with others... Gunmakers...Knowing this...can they and do they somehow make their product more able to shoot whatever someone grabs off the shelf accurately?

Considering the chambers I have found in some commercially built rifles, my guess is they build rifles to be a good (adequate) fit for the maximum SAAMI ammo. I suspect ammo makers in general make their ammo to fit the minimum SAAMI chamber. Throats seem to vary quite a bit with some manufactures seeming to always have long throats. I'm sure that in our litigation society, everyone is trying to cover their posterior. At any rate, we as handloaders can improve ammo for our particular firearm by loading to fit OUR gun. I don't see any way a manufacturer can load ammo that will be accurate in all firearms chambered for any given cartridge.

Edd

mikeym1a
04-02-2013, 12:18 AM
No, the chamber/cartridge combo is not limited to this particular boolit. I used this particular boolit because a) it was readily available and b) it pretty much demonstrated what I wanted to show.

The idea is to fill the throat as much as possible with a boolit regardless of its shape. If the boolit shape doesn't lend itself to mostly filling the throat, one cannot expect good results. A person MAY be pleasantly surprised, but the likelihood of a boolit working well and not at least mostly filling the throat is not in one's favor.

Edd
New to shooting lead boolits in rifles. Have read of what you said. NOW that I have seen it, I understand it. In this case (for me) the thousand words are made clear by the pictures. Thank you.

waksupi
04-02-2013, 01:02 AM
Excellent addition to the board, thank you!

popper
04-03-2013, 04:05 PM
So, Edd, I think you are saying to size cases as large as will fit/cycle reliably, same for the body of the boolit/throat, with the nose sized to barely engrave the rifling. For best accuracy. The average caster probably sizes the CB body to fit the throat, possibly with slight engraving, then sizes the case to prevent reducing the body and provide proper neck tension. Thus sometimes grossly oversized CBs for the BORE slug.

Doby45
04-04-2013, 11:40 AM
Bottle neck rifles, as shown, are slightly different than normal handgun ammo. You always want your bottle neck rifle brass to be fire formed to the chamber and then work with your neck sizing based upon your bore slug. Bottle neck rifle brass in semi-autos is also different, such as an AR-15. You would always FL size that bottle neck brass.

DougGuy
04-07-2013, 06:45 PM
Brilliant photography AND essay. Pictures are worth many thousand words..

I worked over a M77 in .308 and the last thing I did to it was something that cut groups totally in half and put it under an inch @200yds shooting from laying prone with no sandbags. I had loaded with fire formed brass, but crimped in the cannelure of a 180gr plain base. Groups were manageable for a hunting rifle but nothing to write home about. The last thing I did was assemble a dummy round with no crimp, just the neck tension, and closed the bolt on it, letting the rifling seat the bullet. I pushed it out from the muzzle with a cleaning rod, stuck it in a seating die and adjusted the plug down until it touched. Took the dummy out and turned the die 1/2 turn farther down and locked it. I used that measurement to load all the subsequent rounds with, and collet crimped them. Amazing what that 1/2 turn of freebore did for the groups.

Stephen Cohen
04-27-2013, 09:11 PM
Very good sir, that should be a sticky for sure. Nothing explains as well as pictures.

popper
04-28-2013, 02:06 PM
So I chambered an unsized 165 TC 40SW in XDm. Interesting, not engraved, a step between throat and chamber - case mouth is 0.422. CB is 0.404, throat is 0.401, I slugged the groove 0.400. I can see where the throat is on the CB, see a .001" ring .03 from the mouth, throat is >.05 long. I've been sizing to 0.401, should I size to 402 and let the throat size to 401, groove to .400? Looks like I can also seat longer to get closer to the rifling. I need to run the same test on the rifles.

303Guy
05-01-2013, 01:42 PM
Something about the term 'free-bore' - technically it's a portion of the throat that is groove diameter but has no rifling. Some super magnum rifle manufacturers gave their guns long free-bore to reduce chamber pressure, something in the order of a full bullet length comes to mind but I don't actually remember. So a standard chamber could be free-bored by cutting the rifling out and moving the rifling leade further forward. This differs slightly from a chamber with a long throat which is cut to accommodate a long seated bullet - compare the 303 Brit with the 308 Win or better yet the 6.5 Swede or 7x57 with the 308. The 6.5 has a long throat but the leade is still fairly close to the bullet ogive.

ylexot
05-18-2013, 09:51 AM
Could you add a pick of an unfired cartridge with the same boolit in the chamber? I'd like a better sense of the 'before ignition' scene. Namely how far the boolit moves before it engages the throat. Thanks!

badgeredd
05-28-2013, 09:15 AM
Could you add a pick of an unfired cartridge with the same boolit in the chamber? I'd like a better sense of the 'before ignition' scene. Namely how far the boolit moves before it engages the throat. Thanks!

The idea is to load your boolit so it DOESN'T jump to the throat. If the boolit fit is correct there is no run to engage the throat. The last picture is of a loaded round in the firing position, pretty much filling the throat and leade.

Edd

graphic914
09-15-2013, 06:06 PM
how do you know how what the COL of the reload will be?

badgeredd
09-17-2013, 09:51 AM
how do you know how what the COL of the reload will be?

Perhaps others will chime in with their methods to determine COL.

I set the COL this way. First I insert a cast bullet I intend to try into the chamber using light pressure to insure it is actually touching the throat, I then use a cleaning rod from the muzzle to touch the inserted bullet and mark the rod with a piece of tape. I them remove the bullet and then touch the breach face with the same cleaning rod and mark the rod. Then I measure the over all length on the rod. I load ONE dummy to a length .025 to .050" longer ( sometimes I go even a bit longer initially) and check the feed and seating of the dummy in the rifle. IF it appears to function in the magazine and chamber, I load 5 to 10 rounds and try them. If it seems the dummy is too short, I adjust the bullet out or if it is too long I try a shorter COL. One needs to do his/her own work to get it done. There isn't a substitute for taking the time to fit and try a cartridge. Obviously, different bullets need to be adjusted for the optimum COL.

Edd

Slow Elk 45/70
09-24-2013, 12:47 AM
Just my openion, this would make a great stickey, more info for "New Shooters , IMHO:bigsmyl2:

cdngunner
09-09-2014, 10:01 PM
This thread could be great if the pictures were still available.

357tc
09-20-2014, 09:16 PM
I would like to see the pictures as well ;/

Rizzo
09-21-2014, 11:37 AM
Ditto

William Yanda
09-21-2014, 01:26 PM
Well, I'll say it. Without the pics, in my opinion, this does not qualify for sticky status.

cainttype
09-22-2014, 05:50 PM
So what happened to Badgeredd's photos?
Did he remove them or is it a site-related issue?
It's a shame to see such a well illustrated contribution to the site get lessened. Badgeredd's time and generosity with his photo layout has been appreciated by many here. Hopefully the pics will be reinserted and saved for future referrences.

badgeredd
09-24-2014, 02:33 PM
Perhaps the all knowing pseudo Gods can put some photos up to replace the ones lost. I no longer give a hoot if the sticky is here or not so the powers that be are welcome to delete it as far as I am concerned.

Thanks for the appreciation by a few...posts like #45 are the reason I spend little time or effort here. Have a good day fellas. May the Farce be with you.

Edd

cdngunner
09-24-2014, 02:44 PM
Thanks...

cdngunner
10-20-2014, 06:31 AM
Starting to see what you are talking about...

badgeredd
02-06-2015, 10:56 AM
I was able to find the original photos and get them uploaded to Photobucket. I believe I have the original post restored. Thank you to those that have shown interest in the post for your patience.

btroj
02-06-2015, 10:59 AM
The photos tell the story. Excellent post Edd

Outpost75
02-06-2015, 12:53 PM
Here is an example of correct bullet "fit" in my Winchester Model 54 .30-'06 with standard factory barrel and chamber, showing a round which has been chambered and extracted without firing.

The bullet is HM2-.312-160-5

129706

62chevy
02-06-2015, 03:18 PM
I was able to find the original photos and get them uploaded to Photobucket. I believe I have the original post restored. Thank you to those that have shown interest in the post for your patience.

Thanks those pitchers sure help me understand.

cainttype
02-07-2015, 11:05 AM
Thanks for your time and effort, Edd.
This is probably one of, if not THE most helpful sticky on the site for the newer casters to start with (more than a few older casters having recurring issues, too). The fact that it sits at the top of the listings in this sub-forum seems highly appropriate to me.

lastborn
02-11-2015, 09:59 AM
Excellent post! Badgeredd, I'm sure this took considerable time to put this post together and I know that I do very much appreciate your time and effort.

ballistim
02-15-2015, 05:53 PM
I just found this so I had the benefit of the photos being added, great post badgeredd! I'll be doing my first poundcast and this helps me visualize what I'm looking for.

gamedog53
02-15-2015, 10:18 PM
Awesome post, Thanks for all your time and work on this. A great visual aid.

Animal
03-09-2015, 12:24 PM
Interesting write-up. I only own one rifle and it is a WASR-10 ak variant. I decided to do a little checking. I used a very soft lead .358 slug to check the measurement. My throat is .342 and my groove dia. is .313. I haven't cast anything for it yet, but I'd like to at some point. I knew my .313 groove diameter was going to be challenging to match a bullet too, but I didn't realize my throat was so far out of whack. I've had nice results with jacketed handloads. I never did close the book on my handloads as bullets, cases and supplies became scarce. I left off with 1.5-2.0 groups at 50 yards with iron sights and bullets .002 below groove dia. I felt I left the load prematurely with much to be desired.

Lee makes 2 bullet molds for 7.62X39r, it sounds like they are the correct design according to other casters of this caliber. But, even if I can get these bullets to size at a nice .313, how are folks having acceptable accuracy results (not pristene accuraccy, but respectable for this rifle) and not dealing with a mess of lead from an extremely oversized throat? I've read the sticky on "The practical dope on the 7.62x39" and the particular problems the writer has with accuracy and the Kalashnikov rifle are never really addressed, just kind of dismissed as being too irritating to deal with or speak of.

Maybe I am chasing Unicorns, but with my handloading experience I have no reason to believe that a 3in group at 100 yards isn't obtainable with this rifle. If I can achieve this with cast, or Jacketed this rifle will be able to easily fulfill multiple functions (I like to think of it as a survival rifle).

1. How can the common bullet molds (.312) for this caliber function with acceptable results with throat diameters up to .342?
2. Am I reading too much into this? I know it isn't a revolver, but when I think about matching bullets to throats, I think revolver principals.

largom
03-09-2015, 01:15 PM
Hornady now makes two tools [formerly Stoney Point] that allows one to measure the over-all-length of a cartridge with the boolit touching the lands, these tools work for cast as well as jacketed. After determining the length you adjust your seating to the length you desire. These tools are called: O.A.L. Gauges and Bullet Comparator Set.
These tools will plainly show that different guns as well as different boolits/bullets all take different seating depths.

Larry

badgeredd
03-09-2015, 02:50 PM
My throat is .342 ...not dealing with a mess of lead from an extremely oversized throat?

Maybe I am chasing Unicorns, but with my handloading experience I have no reason to believe that a 3in group at 100 yards isn't obtainable with this rifle. If I can achieve this with cast, or Jacketed this rifle will be able to easily fulfill multiple functions (I like to think of it as a survival rifle).

1. How can the common bullet molds (.312) for this caliber function with acceptable results with throat diameters up to .342?
2. Am I reading too much into this? I know it isn't a revolver, but when I think about matching bullets to throats, I think revolver principals.

I am guessing you've misunderstood part of this. Your throat will be the area immediately in front of where the case ends. The .342" dimension has to be in error. With a .313" grove diameter, the minimum I'd size my bullets to would be .314". As for a design...Lee makes a 125ish pointed bullet that casts .314" in my mold. I wouldn't hesitate to lap one out to get the minimum of .314" diameter. Lee also make a 150ish grain bullet mold that works quite well in AK/SKS design rifles. You SHOULD be able to get groups with cast bullets equal to jacketed groups, but I seriously doubt you can get better groups with cast. LUBE for gas operated semi auto needs to be like baby bear porridge...just right. Too soft or hard of a lube will foul up the works. Too much capacity will add unnecessary lube to the barrel (and therefore the gas tube).

Overall length of a loaded cartridge will be determined nicely with the tool mentioned above, BUT it will do nothing for filling the throat and for a load that is as accurate in your gun as possible.

I hope this is helpful.

Edd

Char-Gar
03-09-2015, 05:11 PM
Thanks for the pics. They should be helpful to many folks. However there will be some folks that even pictures won't help.

Animal
03-10-2015, 09:46 AM
I am guessing you've misunderstood part of this. Your throat will be the area immediately in front of where the case ends. The .342" dimension has to be in error. With a .313" grove diameter, the minimum I'd size my bullets to would be .314". As for a design...Lee makes a 125ish pointed bullet that casts .314" in my mold. I wouldn't hesitate to lap one out to get the minimum of .314" diameter. Lee also make a 150ish grain bullet mold that works quite well in AK/SKS design rifles. You SHOULD be able to get groups with cast bullets equal to jacketed groups, but I seriously doubt you can get better groups with cast. LUBE for gas operated semi auto needs to be like baby bear porridge...just right. Too soft or hard of a lube will foul up the works. Too much capacity will add unnecessary lube to the barrel (and therefore the gas tube).

Overall length of a loaded cartridge will be determined nicely with the tool mentioned above, BUT it will do nothing for filling the throat and for a load that is as accurate in your gun as possible.

I hope this is helpful.

Edd

This is what I have, maybe it will make some sense. The inner diameter of a fired case neck is .315-.317. The outer diameter of the same neck is .340-.343. The latter number is maintained forward of the case where the bullet resides. I can confirm this by measuring the lead slug, which gives .342 +/- .001. It then tapers down in size until it forms the lands and grooves of the rifling, which results in .313 groove and .300 land. I might need to take a pic of the slug. It will be easier to explain. Finding the right bullet to fit the groove diameter and provide sufficient weight has been a chore. What I am seeing (though possibly in error)with large throat numbers only makes the bullet hunt more interesting. Thanks.

cainttype
03-10-2015, 10:04 AM
This is what I have, maybe it will make some sense. The inner diameter of a fired case neck is .315-.317. The outer diameter of the same neck is .340-.343. The latter number is maintained forward of the case where the bullet resides. I can confirm this by measuring the lead slug, which gives .342 +/- .001. It then tapers down in size until it forms the lands and grooves of the rifling, which results in .313 groove and .300 land. I might need to take a pic of the slug. It will be easier to explain. Finding the right bullet to fit the groove diameter and provide sufficient weight has been a chore. What I am seeing (though possibly in error)with large throat numbers only makes the bullet hunt more interesting. Thanks.


You desrcibe your "throat" as basically being a funnel instead of a proper parallel-sided cut (not really unusual). Use your minimum inside fired case neck diameter and subtract .001 for clearance.
In this case your fired neck ID is .315, your groove diameter is .313. A cast measuring .314 would be a good place to start.

dg31872
03-10-2015, 10:22 AM
It is helpful to actually see the bullet, case and barrel as they fit together. And I thank Badgeredd for taking the time to educate us/me on this. I have a better understanding of the rifle now, but I was wondering if anyone has done this with a revolver. I am still not sure where the throat on revolver is. Is it in the cylinder, or past the forcing cone?

Animal
03-10-2015, 10:34 AM
You desrcibe your "throat" as basically being a funnel instead of a proper parallel-sided cut (not really unusual).
Yes, this is exactly how I see it. I would imagine these loose fitting tolerances would be very helpful to a rifle that is designed to run reliably in the most harsh of environments. I'm glad to know .313 bullets are still worth pursuing... That is already a chore enough.

Char-Gar
03-11-2015, 10:09 AM
This is what I have, maybe it will make some sense. The inner diameter of a fired case neck is .315-.317. The outer diameter of the same neck is .340-.343. The latter number is maintained forward of the case where the bullet resides. I can confirm this by measuring the lead slug, which gives .342 +/- .001. It then tapers down in size until it forms the lands and grooves of the rifling, which results in .313 groove and .300 land. I might need to take a pic of the slug. It will be easier to explain. Finding the right bullet to fit the groove diameter and provide sufficient weight has been a chore. What I am seeing (though possibly in error)with large throat numbers only makes the bullet hunt more interesting. Thanks.

When folks measure the ID of the fired case they are are not gaining useful information about the throat of their rifle barrel. The neck of the fired case is not in the throat but the chamber. Chambering reamers are cut to a variety of specifications with military chambers being the largest and match chambers being the smallest. Also there is a wide variety of brass thickness and the necks tend to increase in thickness if fired with high pressured loads.

Somewhere down the road of cast bullet shooting in recent years, somebody came up with the notion of measuring the ID of a fired case to determine cast bullet size. Such a measurement may or may not provide a guide for bullet diameter, but it is not a reliable method.

A true measurement of the throat is the only numbers that matter. A bullets that is .0005 or so under that number will introduce the bullet into the throat straight and that is what it is all about.

I don't know what kind of rifle you have, but some rifles, such as some Marlin and have almost no throat, just a chamfer at the end of the barrel in front of the chamber. These can be an issue for the cast bullet shooter. There are ways around it and ways to fix it, but it can be an issue unless dealt with.

If the outer diameter of fired case is the same as place where the bullet is, you are not measuring the throat, but a long chamber neck or a throat that has been severely eroded by the firing of many thousands of rounds.

Animal
03-11-2015, 11:08 AM
"long chamber neck" seems to be a better description than a throat. Char, the rifle is a Romanian made WASR-10 AK47 variant. Tolerances are pretty tall with this beast. Seems to me "the looser the better" was probably Kalashkinov's motto when designing the rifle. This approach has probably paid dividends in reliability.
Aside from that, I think the accuracy problems with this rifle are going do be obvious by design, but with my previous handloads I have found that the ammunition available for his rifle probably make up 50% of it's accuracy short comings. A good handload can make up for half of its problems. At least, this is what I have learned so far with my rifle.
This is why I found interest in this thread. Measuring the chamber and throat space will be very helpful when selecting bullets... Jacketed or Cast.
Where I live, a 100yrd shot is rare. But a good handload will make the difference between 3in group and 6in group. Factory steel cased ammo is plenty good for 75 and less, which is probably about 90% of the shooting that is likely to happen.

Char-Gar
03-11-2015, 11:21 AM
"long chamber neck" seems to be a better description than a throat. Char, the rifle is a Romanian made WASR-10 AK47 variant. Tolerances are pretty tall with this beast. Seems to me "the looser the better" was probably Kalashkinov's motto when designing the rifle. This approach has probably paid dividends in reliability.
Aside from that, I think the accuracy problems with this rifle are going do be obvious by design, but with my previous handloads I have found that the ammunition available for his rifle probably make up 50% of it's accuracy short comings. A good handload can make up for half of its problems. At least, this is what I have learned so far with my rifle.
This is why I found interest in this thread. Measuring the chamber and throat space will be very helpful when selecting bullets... Jacketed or Cast.
Where I live, a 100yrd shot is rare. But a good handload will make the difference between 3in group and 6in group. Factory steel cased ammo is plenty good for 75 and less, which is probably about 90% of the shooting that is likely to happen.

OK, that explains allot. The AK47 is a battle rifle deluxe and was designed to run full auto with it guts full of sand, mud and blood. Keep plugging away, victory will surly be thine!

DougGuy
03-11-2015, 11:39 AM
If you google "freebore" and click on "images for freebore" you will see a lot of photos and drawings which illustrate that person's view or concept of what freebore is, and also what part of the chamber/bore/whatever is called the "throat." Many of these drawings are from our own member blammer, who designs a few boolits and molds here and there. His drawings explain perfectly the difference between "freebore" and "throat" and they describe freebore as a section of parallel smooth bore, equal to or .0005" larger than the boolit diameter or the "bore rider" section of the boolit, and throat as the tapered part that contains the leade in to the rifling.

So, going by blammer's description, (which is as good an explanation as *I* have seen thus far) freebore, is not really free bore, as in the unsupported space you would have when firing a .38 Special load in a .357 Magnum cylinder, rather it is a smooth, parallel, section of bore devoid of rifling or taper, which by it's diameter supports the boolit in flight, aligns and guides it straight to the throat and into the rifling.

This explanation would be sufficient to describe freebore and throat as it is used in a rifle chamber.

For a revolver, the word "throat" is generally used to describe the smooth parallel section of cylinder in front of the chamfer at the end of the chamber, and since this part is located in the cylinder and not the barrel, we generally accept the term "cylinder throats" and associate this terminology with the cylinder. By dimension, since this is a smooth parallel section that the boolit travels, shouldn't it be called freebore? If you apply the terminology used to describe a rifle chamber then it would be correctly called freebore. However since this is a revolver (which has separate firing chambers detached from the leade in to the rifling and detached from the bore), freebore would apply more to unsupported space that the boolits must travel through to reach the throats, or the distance from the case mouth to the cylinder throat in a caliber where you could shoot companion cartridges. .38 Special in a .357 Magnum cylinder, .44 Special in a .44 Magnum cylinder, .45 Schofield in a .45 Colt cylinder, etc..

For an autoloader, which does not have a separate firing chamber like a revolver, it should also be described using the same guidelines one would use with a rifle chamber. IF there is smooth parallel bore in front of the chamber, then this should be known as freebore. IF there is taper in the area in front of the chamber, it should be known as throat. Yes you can have BOTH freebore and throat in an autoloader barrel, also in a TC barrel, or any firearm that does not have a separate firing chamber such as a revolver.

I think I learned something by this thread, the difference in freebore and throat and how to tell one from the other...

I also learned that freebore in a rifle means smooth parallel section of bore, and freebore in a revolver means totally unsupported space between the case mouth and the rear of the cylinder throat. Two totally different things both described correctly I might add, by the same word, freebore.

Edit: And yes, a revolver's barrel DOES have a throat. The throat would be the length of bore that contains the leade in to the rifling, which would begin where the machined angled surface of the forcing cone meets the barrel's groove diameter, and ends where the rifling gains it's full height.

Edit #2: While we are discussing this, let's not overlook the word "freejump." Freejump, would be a description of how far the boolit can move when it pulls crimp and begins to travel, until it encounters either the taper in the throat OR the leade in to the rifling, OR the chamfer leading into the cylinder throat, if it is a revolver cylinder.

For example, my Ruger M77 in .308 caliber has approximately .240" of freebore in front of the case mouth when a round is chambered. When I seat my boolit out long, where it touches the rifling when chambered, I have 0.00" of freejump. If I screw my seating stem in about half a turn, this gives my boolit approximately .025" of freejump, this is the distance that the boolit can travel before it begins to encounter the leade in to the rifling. If I seat the boolit in the cannelure, it has .165" of freejump, which for the sake of discussion, opens up groups to the size of a tennis ball @ 100yds. With .025" of freejump, groups shrink to the point that I can cover a 3 shot group fired @ 200yds with a guitar pick. THIS is why I felt it important not to leave out an explanation of the word "freejump" when discussing freebore and throats, because these three things all work together.

Animal
03-11-2015, 01:35 PM
DougGuy, nice description. Thanks

cainttype
03-12-2015, 06:20 PM
The large funnel shaped section you're dealing with, as you've surmized, is often associated with reliable functioning under possibly adverse conditions. The AK47 "battle rifle" certainly is a good candidate for that line of reasoning, but even SAAMI chamber specs for the 458 Winchester Magnum have a similar design for the same purpose.
My 458 WM has a taper from .470 to .458 that stretches over 1 inch before reaching the lands. For that reason, I generally ignore the normal fit-to-throat wisdom and try to find a projectile by starting .001 above groove and work up in diameter to see if I have improvements. The casts that are long enough to start the nose into the lands while the base is still in the neck seem to work really well, but in the 458 that makes them very heavy.
You stated earlier that your minimum neck clearance from fired casings was .315 and your groove diameter was 313. I would start at .314 because of those measurements, ignore the big taper, and try to find a design that was long (and wide-nosed) enough to provide some fit at it's nose. Hopefully, your case neck can help give some alignment help at the rear as your cast's nose reaches the barrel's groove diameter origin.
If culling casings for fired neck IDs with a minimum of .316 is no problem, I'd consider trying casts up to .315 to see if I could see any improvement.

That funnel shaped end-of-chamber/start-of-throat is also obvious in a Sako 375 H&H I have, but it isn't very long so I just ignore it and use throat measurements taken about 1/4" from the end of the chamber's neck.
There are just starting points that work for me in rifles with similar issues. YMMV

Animal
03-12-2015, 09:48 PM
Cainttype, that is the logic I'm following. It seems like the bullet should have a long enough profile that it can engage the lands and grooves while the base is still supported by the mouth of the case-neck. Also, the forward portion of the bullet should be broad enough that the bullet can index more efficiently as it starts its trip into the rifling. A .315dia should engrave in the rifling very nicely. The challenge at this point is to find a bullet that doesn't push the weight limit of standard cast 7.62x39 rounds. Most bullet molds I see for sale that meet this requirement are 180gr and up. I've considered the prospect of trying one of these molds, but load data for such a combination in this caliber is elusive at best. A mold like this looks promising if I can size it down efficiently to .314, but it's flat-point concerns me that reliable chambering might be an issue. Mind you, these loads would be treated like a fine wine--Seldom fired, and never rapid fired. It wouldn't be much heavier than the Lee 160gr bullet that is made for this caliber.
http://www.midwayusa.com/product/383491/rcbs-2-cavity-bullet-mold-32-170-fn-32-caliber-321-diameter-170-grain-flat-nose-gas-check?cm_vc=ProductFinding

49FMarlin
04-15-2015, 10:25 AM
thank you for this post
the pictures helped me understand it more

brass410
08-29-2017, 12:15 PM
I just happened upon this thread it answers my questions beutifuly visual aids are great when trying to explain something like this, kudos to the originator.

M-Tecs
08-29-2017, 01:08 PM
Yep a picture is worth a 1,000 words.

Yooper003
08-17-2018, 09:49 AM
It seems like a lot of people are missing part of the point, as nobody seems to be talking about the ogive of each different bullet, or "boolit" in each case. In different cast boolits I load, indeed to have some 340 gr. .040 shorter than 405 gr. Boolits, or they are jamed into the end of the throat.there are several ways to check this & I check proper oal, for each different bullet I shoot.i have found some factory ammo that .110 off the rifling in my rifle.

Yooper003
08-19-2018, 08:52 AM
After reading this thread for another hour, & maybe understanding a little more, I guess I want to explain. Having gone as far as I can on sizing my boolits, I am tying to seal the bore by seating each different boolit in the cartridge as long as i can without actually jamming it into rifling.

rockydoc
08-20-2018, 12:28 PM
I am unable to see the photos. It says”Photos not found”. “Click for photos”. I clicked but nothing happened.

xgboy
06-07-2023, 02:53 AM
Any way to resurrect the deleted photos?p

No_1
06-07-2023, 07:29 PM
Any way to resurrect the deleted photos?p

No, they have been removed by the poster.