Why I don't size bullets larger than the throat entrance diameter

Ian

Notorious member
I know that 7.62 x51mm NATO chamber specs are still supposedly 'classified', or whatever, but FN Belgium has them, as does IMI...and their products are not inaccessible for measuring.

Revolvers are a series of funnels. My whole point here is that if you have a smooth funnel, size the bullet to what shoots best. BUT, if you get leading, you might just be shaving lead on the sharp edge of a too-small hole somewhere. The exact same thing applies to the modern plastic pistols that have extremely sharp throat entrances that react poorly to oversized cast bullets.
 

smokeywolf

Well-Known Member
BUT, if you get leading, you might just be shaving lead on the sharp edge of a too-small hole somewhere.

This is what I was alluding to in my previous post.

Wish we were closer in proximity to one another. Your freebore to leade to rifling issue is a very good crossover from the engineering/R&D and machining that I've done in the motion picture industry for well over 30 years. Solving this type of problem is what gets me going. It's one of the most fun things one can do while still in a vertical orientation.
 

45 2.1

Active Member
Read the thread title Joe. Nobody is suggesting to size under throat size, it says why Ian doesn't size over throat size.
There is over, there is under, and there is right to throat diameter. Pretty simple really.

If it's that simple Brad, then nobody here should be having any problems. The CBA pretty well determined A solution for bolt guns, but not the only one or possibly the best and they sure don't know squat about HV semi-auto loading. Other folks determined what works in other things... it's all in print, except not on the internet in the places most look at.
 

45 2.1

Active Member
I know that 7.62 x51mm NATO chamber specs are still supposedly 'classified', or whatever, but FN Belgium has them, as does IMI...and their products are not inaccessible for measuring.

Revolvers are a series of funnels. My whole point here is that if you have a smooth funnel, size the bullet to what shoots best. BUT, if you get leading, you might just be shaving lead on the sharp edge of a too-small hole somewhere. The exact same thing applies to the modern plastic pistols that have extremely sharp throat entrances that react poorly to oversized cast bullets.

Having the actual specs and measuring something made from from them are NOT THE SAME. That process is called reverse engineering and is quite troublesome.

If you remember, I told you two to find out what alloy constituents do to for you....... good and bad. This is one of those things......... work with the pressure level you want to shoot at.... tailor the alloy (each alloy and percentage constituent has a pressure range it likes... hard or soft) to that and particularly harden via heat treatment to the working pressure. A lot of constituents are usually a bad thing. That will solve your problem..................
 

Ian

Notorious member
I'm not reverse-engineering anything, just making observations and building ammunition to fit the rifle I have. I've measured all of mine and the M1A I have is cut pretty much identically to the SAAMI .308 Winchester minimum, which is about as far away from the NATO chambers I've measured as one can get and the ammo still function, and fortunately I don't own any rifles cut to NATO specs. Somehow, everyone here is in disbelief that my throat entrance and parallel freebore is .310" exactly, but it is.

Ok, as for the alloys, let me get this straight: Are you saying that finding the correct alloy and temper for the pressure curve used will allow a person to shoot larger-than-throat bullets without shaving the bullet as in my photo in the OP?
 

Ian

Notorious member
This is what I was alluding to in my previous post.

Wish we were closer in proximity to one another. Your freebore to leade to rifling issue is a very good crossover from the engineering/R&D and machining that I've done in the motion picture industry for well over 30 years. Solving this type of problem is what gets me going. It's one of the most fun things one can do while still in a vertical orientation.

Some people, John Ardito comes to mind, have been known to solve this issue in standard production and military rifles by reaming the throats out to as large a .314" and shooting bullets as large through them. This reduces the chamber neck clearance of the cartridge with standard brass to a thousandth or less, which is one way of improving accuracy with cast bullets significantly. Creating bullets that mimic the new throat shape is done in conjunction, making for a really close static and dynamic fit all around. Not the only way, but A way of getting better accuracy. Bob is right though, these guys don't shoot at very high velocity nor do they shoot semi-automatics in competition.
 

45 2.1

Active Member
Ok, as for the alloys, let me get this straight: Are you saying that finding the correct alloy and temper for the pressure curve used will allow a person to shoot larger-than-throat bullets without shaving the bullet as in my photo in the OP?

Works for me since I've been doing it for about 30 years with several thousand recovered bullets as proof that it works.
 

JWFilips

Well-Known Member
Ian,
Can you tell me where that displace ring of sheared off lead ( as in your examples) will go If it is fired in a rifle?
 

Ian

Notorious member
Sometimes it gets smeared all down the bore, other times I suspect it gets trapped in the lube groove behind it and jettisoned. Still other times it ends up at the end of the chamber. Many times I've picked intact lead rings out of the front of the chamber, after every shot, with a bronze cleaning brush. Even sizing smaller than throat entrance won't prevent those rings if your bullet is too soft and your powder too fast, as that combination tends to bump the bullet base metal into every available recess. I've cracked the code on launching throat-sized bullets without any of these problems, but not how to get an oversized bullet into a sharp-edged throat without shaving off a ring. Worn, radiused throat entrances aren't much of a problem.
 

fiver

Well-Known Member
those sharp edged rifling ends will just peel away lead when it comes into square contact.
a square shouldered boolit doesn't make it any better, and going to a harder alloy doesn't help.
but man oh man does it ever grip the rifling.

this is a common problem with many of the newer semi-auto pistols and bout the only way I have found around it is to make the boolit smaller, or in other words exactly the same diameter as the barrel, and work the taper crimp to that last .0005.
 

Brad

Benevolent Overlord and site owner
Staff member
This makes me want to revisit my Marlin 1894C in 357 with semi wadcutterrs. I always sized for this rifle to .359 because that is the sizer I had for the Star. I wonder if sizing a bit smaller might make a difference.
This rifle shoots SWC bullets very poorly. Like 5 inches at 50 yards or worse.
I know it has a very short, abrupt throat and wonder if a smaller bullet might make the transition in better shape.
 

Brad

Benevolent Overlord and site owner
Staff member
Those didn't do much better. The Lee 158 RNFP and 125 RNFP weren't a lot better than the swc. I just about got rid of the rifle when I bought a MP 359640. That bullet does at 100 what the others can't do at 50. Since then the rifl has been fed a single bullet.
 

Cherokee

Medina, Ohio
Brad - a single bullet design that works is all you need. Finding what works is part of the fun...Interesting discussion.
 

Brad

Benevolent Overlord and site owner
Staff member
True enough. Good thing I found it too, the rifle had been the bane of my existence for over 6 months. It was beyond irritating. I read all the stories by Glen on the Marlin 357 and wondered what he knew that I didn't. I think mine has a short, steep throat and that makes all the difference.
 

Mitty38

Well-Known Member
Revolvers are a series of funnels. My whole point here is that if you have a smooth funnel, size the bullet to what shoots best. BUT, if you get leading, you might just be shaving lead on the sharp edge of a too-small hole somewhere. The exact same thing applies to the modern plastic pistols that have extremely sharp throat entrances that react poorly to oversize cast bullets.
As for the pistol issue
Just ran into something like this on my Taurus 66 .357
Its internals are .360 at the forcing cone in the cylinder.
.359 in the throat of the barrel with a slight 10 thousandths deep 11 degree crown.
.3.58 at the beginning of the lands.
.357 at the muzzle.
I shoot .358 thru it and I can, and have been working up a fairly accurate loads with no leading.
I shoot .359 the accuracy goes stellar. Every thing is functioning flawlessly.

Now I would think, with the cylinder cones measuring .360 and the throat at .359.
Having that 10 thousandths deep 11 degree crown it should funnel down at the cylinder to barrel throat transition OK, after the jump.
At .360 three of the cylinders shoot the .360's with the same accuracy as .359 bullets. BUT with 4 cylinders the gun sheers or is flame cutting? a small amount of lead at the barrel throat. Then throws it back in my face, and all over the cylinder, Running .360 also causes a small amount of leading in the throat.
Now I am pretty sure, but could be wrong on this. That 4 of the cylinders are machined a bit off and a little bit deeper crown to the barrel throught, or just some polishing, would probably allow for better alignment. Thus the .360 shooting well.
But with the revolver shooting well (meaning way better than my ability) at .359 on all cylinders, why should I go there?
 
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