Is the seating depth, or distance to lands, important for accuracy when loading straight walled cases? I'm starting to load for a 445 supermag rifle (22inch) that was given a very long throat. I was told that a long jump does not affect accuracy in this type of cartridge, but it is different than everything I know about rifles for bottleneck cases. When I do this again I'd like to be smarter about specifying length of throat or leade. As is in this case, I have a jump of .25" at a minimum, and longer with most bullets. As a rule of thumb, does reaming a tighter throat give better accuracy? Thanks
Throating opinions
- Thread starter cptmclark
- Start date
I have never spent much time with straight-walled cartridges, but I suspect that the same applies to straight-walled cartridges as bottleneck cartridges since it is bullet alignment to the lands and the bore that makes a rifle accurate. If the bullet is not centered and aligned with the lands as it starts to grave, it will be slightly off-center and out of axial alignment as it travels down the bore, and after it leaves the bore it will not fly true. I suppose you could argue that a longish bullet might be able to bridge the gap and still stay true since it is being held by the case. I see black powder cartridge rifle shooters doing the same tricks match shooters did 150 years ago, i.e. placing a paper-patched bullet into the lands and loading the cartridge behind the bullet for top accuracy, so I suspect someone is trying to convince you that the Earth is flat because they have already done the work and don't care to re-do it.
FWIW, I agree with Scorch. A bottle-necked case IS a straight wall case for the part that matters; what is behind that is irrelevant.
With a long leade, you will get bullet misalignment and a high degree of throat erosion, not to mention skidding that can result in inaccuracy. When the bullet exits the case mouth, the sooner it enters the lands and seals the gases off from the throat and barrel the better. If a long throat lets a lot of gas get past the bullet, throat erosion will occur very quickly.
Jim
With a long leade, you will get bullet misalignment and a high degree of throat erosion, not to mention skidding that can result in inaccuracy. When the bullet exits the case mouth, the sooner it enters the lands and seals the gases off from the throat and barrel the better. If a long throat lets a lot of gas get past the bullet, throat erosion will occur very quickly.
Jim
Long leads are a trick used to reduce insane chamber pressures that would otherwise cause blown primers and swelled case heads. I've never seen a long lead that I thought shot particularly well. Once a crooked bullet starts into the lands, it stays crooked. The max distance to the lands should be closer to 0.02" for an accurate rifle.
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Throats
Did you ever look at a older Weatherby rifle? Uncle Roy always had a specific throat length which you wouldn't see in the same caliber in a different company. The trick is used to reduce pressure in very hot calibers. Today we don't see the throats or the pressure. I have some old reloading books that have loads for the 300 Weatherby that you use a 1ft drop tube to get the powder in the case. We are Conservative today which is good I thank, but we still see re loaders trying to make magnum out of something! Doc
Did you ever look at a older Weatherby rifle? Uncle Roy always had a specific throat length which you wouldn't see in the same caliber in a different company. The trick is used to reduce pressure in very hot calibers. Today we don't see the throats or the pressure. I have some old reloading books that have loads for the 300 Weatherby that you use a 1ft drop tube to get the powder in the case. We are Conservative today which is good I thank, but we still see re loaders trying to make magnum out of something! Doc
Well, not encouraging so far. Of course the proof will be in the shooting. The gunsmith speicalizes in custom revolvers and lots of TC contenders and the like, along with custom chambering lever guns. I asked his advice BEFORE the job and thats when he said his technique give the best accuracy and sited moa and near moa groups shot regularly with revolvers. I'm not expert and he's been making a good business of this for many years, so I said "whatever is best"
Next question is how much bullet needs to be in the case for proper alignment as well as combustion.
Next question is how much bullet needs to be in the case for proper alignment as well as combustion.
Harry Bonar
New member
throating
Sir:
A-Square solved the throating problem by a "paralel throat." It is a reamed section of indeterminate length about .001 over bullet diameter and then ends in a pretty well standard throat. What it does is give the bullet some inertia when it contacts the throat and, most importantly, keeps the bullet in the chamber aligned with the bore in a way other than with the case neck tolerance of the chamber. It gives the bullet a good "start in life" properly aligned with the bore not laying sloppily in the bottom of the chamber.
A-Square has won me over with their manual, Any Shot You Want - the A-Square shooters manual. They have done research no other company has, built rifles no one else has, and hunted the dangerous game all over the world.
They have saved many of our old fine cartridges (such as the 338-06) and standardized them in SAAMI for us. Because of this I believe they have suffered undue criticism from individuals in the shooting scene.
Art Alphin, last time I spoke with him had taken back control of the company and assured me "we are in the black."
They also manufacture many calibers previously not made with proper headstamps which a trip to Africa necessitates!
ok up their manual and let me know if you feel as I do.
Harry B.
Sir:
A-Square solved the throating problem by a "paralel throat." It is a reamed section of indeterminate length about .001 over bullet diameter and then ends in a pretty well standard throat. What it does is give the bullet some inertia when it contacts the throat and, most importantly, keeps the bullet in the chamber aligned with the bore in a way other than with the case neck tolerance of the chamber. It gives the bullet a good "start in life" properly aligned with the bore not laying sloppily in the bottom of the chamber.
A-Square has won me over with their manual, Any Shot You Want - the A-Square shooters manual. They have done research no other company has, built rifles no one else has, and hunted the dangerous game all over the world.
They have saved many of our old fine cartridges (such as the 338-06) and standardized them in SAAMI for us. Because of this I believe they have suffered undue criticism from individuals in the shooting scene.
Art Alphin, last time I spoke with him had taken back control of the company and assured me "we are in the black."
They also manufacture many calibers previously not made with proper headstamps which a trip to Africa necessitates!
ok up their manual and let me know if you feel as I do.Harry B.
Range report
Well, here's a range report that I think is interesting.
First thing was to get it on target, and I used the 44 mag load that had been accurate before the re-reaming, at least in the one group I shot. Once on target with four left, I shot at 50 yards a one hole three shot group and then a flyer to 6:00, about 1.5 inches. All groups at 50 due to windy conditions. Chrono not used for the same reasons. It would have blown down. All loads with Hornady max charges of W296 and CCI 250 primers. Temp was about 30 degrees, and the barrel never got hot to my touch.
---300 xtp long loaded and not crimped, three in 1.2", then a flyer 4" at 6:00, then three more in 1/2 inch close to the first. Cleaned barrel.
---300 xtp loaded normally for the 445 in the long cannulure started vertical stringing to 4 inches. Two flyers both at 6"00. Cleaned barrel.
---265 Hornady fp produced a three shot 8 inch vertical string. I quit burning ammo at this point.
All bullets struck within about a bullet diameter of being in a perfect vertical line.
Today I floated the forearm which was bearing at the tip, and on the aft portiion of the lug screw hole. I suspected that this rifle needs aft pressure into the reciever, which it got from a pinch fit between the lug and the reciever. Now I doubt that, and I relieved the hole. Now, there is only downward pressure on the barrel at the lug point, depending on how I torque the lug screw. If this works, I'll glass the screw chamfer and the forearm where it is torqued into the barrel lug.
I'm making all this stuff up since I have zero experience with this type of rifle. It acted like it wanted to group. I'd be grateful for your expertise and wisdom on making this thing a shooter. Examining the reaming job carefully, it looks flawless, with very even starts to the lands and no tool marks. I guess I don't know what a "throat" on a straight walled chamber is, but it must be just a continuation of the case diameter, since it headspaces on the rim.
Harry, I haven't looked at the A-square info yet, but I will. I saw no step down from case to bullet diameter, and I think that's what you were describing. However it does look like a very short forcing cone going from case diameter to bore diameter, then maybe ten or so thousanths to the lands, which are also tapered giving a gentle entry to the rifling. All this takes place in a very short distance, and appears evenly done.
Any advice before I go back to the range will be greatly appreciated.
Thanks much.
Well, here's a range report that I think is interesting.
First thing was to get it on target, and I used the 44 mag load that had been accurate before the re-reaming, at least in the one group I shot. Once on target with four left, I shot at 50 yards a one hole three shot group and then a flyer to 6:00, about 1.5 inches. All groups at 50 due to windy conditions. Chrono not used for the same reasons. It would have blown down. All loads with Hornady max charges of W296 and CCI 250 primers. Temp was about 30 degrees, and the barrel never got hot to my touch.
---300 xtp long loaded and not crimped, three in 1.2", then a flyer 4" at 6:00, then three more in 1/2 inch close to the first. Cleaned barrel.
---300 xtp loaded normally for the 445 in the long cannulure started vertical stringing to 4 inches. Two flyers both at 6"00. Cleaned barrel.
---265 Hornady fp produced a three shot 8 inch vertical string. I quit burning ammo at this point.
All bullets struck within about a bullet diameter of being in a perfect vertical line.
Today I floated the forearm which was bearing at the tip, and on the aft portiion of the lug screw hole. I suspected that this rifle needs aft pressure into the reciever, which it got from a pinch fit between the lug and the reciever. Now I doubt that, and I relieved the hole. Now, there is only downward pressure on the barrel at the lug point, depending on how I torque the lug screw. If this works, I'll glass the screw chamfer and the forearm where it is torqued into the barrel lug.
I'm making all this stuff up since I have zero experience with this type of rifle. It acted like it wanted to group. I'd be grateful for your expertise and wisdom on making this thing a shooter. Examining the reaming job carefully, it looks flawless, with very even starts to the lands and no tool marks. I guess I don't know what a "throat" on a straight walled chamber is, but it must be just a continuation of the case diameter, since it headspaces on the rim.
Harry, I haven't looked at the A-square info yet, but I will. I saw no step down from case to bullet diameter, and I think that's what you were describing. However it does look like a very short forcing cone going from case diameter to bore diameter, then maybe ten or so thousanths to the lands, which are also tapered giving a gentle entry to the rifling. All this takes place in a very short distance, and appears evenly done.
Any advice before I go back to the range will be greatly appreciated.
Thanks much.
Harry Bonar
New member
Throating
Sir:
Jim is right on Weatherbys and all else (as usual).
What A-Square is talking about is right in front to the case neck the paralel throat of perhaps .001 over bullet dia, tends to hold the bullet straight with the bore - a barrel must be chambered like this when the chambering is done - then a pretty much standard throat (entry into the rifling) is done at the end of the paralel throat.
This is the principle we strive for with revolvers in the cylinder exit holes - to have them groove dia. or .001 bigger to ease the entry into the bore (we have recently gone to an 11 degree forcing cone in the bbls) and it is a good idea in rifles and also in shotguns (a long forcing cone to not disturb the shot pattern.
As Jim is pointing out now - "freeboring" is an effort to ease the initial pressure - the funny thing though is a freebored gun will need more powder to compensate for the lack of initial pressure curve. Initial pressure is reached very close to the chamber (viz., the reason why bbls are heavier at the breech or reinforce. I don't like freeboring - we might think that the paralel throat is in a sense freeboring but it is for a different reason 1. You can seat out as far as your mag well will allow you to and 2. it aligns the bullet by only having .0005 space on each side of the bullet while a non-paralel throat will not - the bullet just lies there till you pull the trigger and then only God and Dupont are in control.
In bedding I only bed the recoil area and on some guns the rear of the action. On Mausers the screw holes should be relieved and the bottom of recoil lug ought to be relieved - the barrel should not TOUCH ANYWHERE THERE IS AN INCLINE OR ANGLE so it is free to vibrake evenly and you adjust your accuracy by the load and good handloading.
I don't mean this in a dogmatic way - different smiths do it differently.
Now, those who have standard throats but no BOSS system ) I don't like them) they to a large degree with powder charge and SEATING DEPTH do the same thing and DO NOT seat bullets so they are touching the lands in a seandard throat!
The arms companies would chamber their rifles with a [aralel throat but I suppose it would cost more and no one would be interested in it anyway.
Harry B.
P.S. Spark photos have shown that the base of the bullet moves before the tip so here is another way the paralel throat is good - a .308 would be .309 entering the regular Throat on your barrel.
, or less.
Sir:
Jim is right on Weatherbys and all else (as usual).
What A-Square is talking about is right in front to the case neck the paralel throat of perhaps .001 over bullet dia, tends to hold the bullet straight with the bore - a barrel must be chambered like this when the chambering is done - then a pretty much standard throat (entry into the rifling) is done at the end of the paralel throat.
This is the principle we strive for with revolvers in the cylinder exit holes - to have them groove dia. or .001 bigger to ease the entry into the bore (we have recently gone to an 11 degree forcing cone in the bbls) and it is a good idea in rifles and also in shotguns (a long forcing cone to not disturb the shot pattern.
As Jim is pointing out now - "freeboring" is an effort to ease the initial pressure - the funny thing though is a freebored gun will need more powder to compensate for the lack of initial pressure curve. Initial pressure is reached very close to the chamber (viz., the reason why bbls are heavier at the breech or reinforce. I don't like freeboring - we might think that the paralel throat is in a sense freeboring but it is for a different reason 1. You can seat out as far as your mag well will allow you to and 2. it aligns the bullet by only having .0005 space on each side of the bullet while a non-paralel throat will not - the bullet just lies there till you pull the trigger and then only God and Dupont are in control.
In bedding I only bed the recoil area and on some guns the rear of the action. On Mausers the screw holes should be relieved and the bottom of recoil lug ought to be relieved - the barrel should not TOUCH ANYWHERE THERE IS AN INCLINE OR ANGLE so it is free to vibrake evenly and you adjust your accuracy by the load and good handloading.
I don't mean this in a dogmatic way - different smiths do it differently.
Now, those who have standard throats but no BOSS system ) I don't like them) they to a large degree with powder charge and SEATING DEPTH do the same thing and DO NOT seat bullets so they are touching the lands in a seandard throat!
The arms companies would chamber their rifles with a [aralel throat but I suppose it would cost more and no one would be interested in it anyway.
Harry B.
P.S. Spark photos have shown that the base of the bullet moves before the tip so here is another way the paralel throat is good - a .308 would be .309 entering the regular Throat on your barrel.
, or less.
Range report addendum
Thanks for the primer on parallel throating Harry. Now I have another problem to overcome with this single shot project rifle (It wasn't intended to be a project rifle). Bulging cases.
I was planning to partial size the 445 SuperMag cases after firing, then compare accuracy to new and to fully resized. Never worked much with straight walled cases.
All fired cases (Starline, 445) are bulged next to the web, with some appearing to be beginning to crack. The 44 mag cases I fired same day do not show this. Also some soot on the breech. Bad news. My son drove off with my dial calipers yesterday, so can't measure the brass and chamber till later. Thoughts anyone? No, no, boat anchor is not an option yet.
Thanks for the primer on parallel throating Harry. Now I have another problem to overcome with this single shot project rifle (It wasn't intended to be a project rifle). Bulging cases.
I was planning to partial size the 445 SuperMag cases after firing, then compare accuracy to new and to fully resized. Never worked much with straight walled cases.
All fired cases (Starline, 445) are bulged next to the web, with some appearing to be beginning to crack. The 44 mag cases I fired same day do not show this. Also some soot on the breech. Bad news. My son drove off with my dial calipers yesterday, so can't measure the brass and chamber till later. Thoughts anyone? No, no, boat anchor is not an option yet.
Harry Bonar
New member
throating
Sirs:
Paralel throat dimensions are, by A-Square, .0005 to .001 over bullst dia.
Harry B.
Sirs:
Paralel throat dimensions are, by A-Square, .0005 to .001 over bullst dia.
Harry B.