How to slug a rifle throat

[AlaskanGuy]

Slugging a throat??? Why???? There are many reasons to slug a throat, but i started doing it to basically measure wear and tear on some of my older guns. To see if there is erosion of the barrel throat, and to make sure that my beautiful cast boolits that i work so hard on are being supported all the way home to the rifling..... But there are many reasons that effect accuracy... I will leave that subject to somebody that is worthy of discussing, like one of our resident rocket scientists... You know who you are....lol... So here is a step by step on how I do it.... I did much reading about it from places like LASC.US and also discovered this reference to throat/bore 101... So i did not invent this stuff, but I do try to practice this stuff... Someday i hope to immortalize one of my efforts that would be worthy of a permanent sticky in this awesome forum, but this is not one of those times.... For this demo, i am going to slug a 375 H&H Mag, as it will be easier to see with my crappy ipad camera. Here are the 5 steps.

Step 1... Prepare to prepare...
First thing to do is to prepare some cases and some pure lead for the rifles that you would like to slug.... I like to use a reject case for the 375 as them cases are expensive.... Get some pure soft lead started cooking in your bottom pour pot, and an empty case for your caliber that you are going to slug. Also grab the longest nosed mold that you have for that cal... Place the mold on a hotplate just like you would to cast some boolits... Also place the case you selected AFTER YOU VERIFY THAT IT HAS A SPENT PRIMER seated. What I do for the spent primer part is actually deprime the case first, visually verify that the primer is spent, and then replace the primer into the case. It just acts as a plug for our slugging.... Once you are sure, just add the cases to the hotplate.

Getting ready...
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Heating up the molds and cases.
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Step 2. Filling the cases and pouring the slugs.

Once the molds and cases are nice and toasty go ahead and grab one of the cases with needle nose pliers and fill it with lead all the way up to the shoulder with lead.... If you mess up, and over fill it, feel free to pour out a bit back into the pot and try again till you get it full to the shoulder... This is why we pre heat the cases... Not many can stop the pour in the right spot on the first try.. Here is how it looks.

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Once you have the cases filled and are cooling grab your mold and cast a few slugs.... They don't have to be uber perfect, but no wrinkly messed up ones... I always cast a few extras as it seems like i always need them for something....

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And drop them on a towel or a tray and let them cool....

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Step 3.... Assemble your throat slugger..

Once everything is cool, get your lead filled case, one of your bullet slugs that you just poured and grab your bullet seating die and install it into your press... Mount the case into your shell holder in the press. If the boolit needs help to get started feel free to flare the case a bit and then seat the boolit JUST ENOUGH SO THAT IT WILL JUST CHAMBER in your rifle... Might take a couple try's of seating a smidgen, and then checking to see if it will chamber. I actually just seat mine a bit, stuff it into the rifle, and tap the bolt with a rubber mallet until i can close it, but either way will work. You have finished this step when the slug and case are in your rifle with the bolt closed...

Step 4.. Get your rod ready....

For this part, I use a steel rod that I purchased from the hardware store... Only requirements for it is that it is tuffer then lead, longer then your barrel, and can take a good beating.... Get yourself a file and file any ruff edges off the end that you are going to insert into your barrel as a ram rod. Then grab some medical tape, as it is soft and a bit thicker and will protect your barrel and wrap the end of your rod with at least one complete wrap of tape.

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Once the tip is done, continue to wrap the rod with at least one wrap of the soft tape every 8 inches or so to protect your barrel. It should looks something like this....

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Once you have done this, you are ready for the last step...

[AlaskanGuy]

Step 5.... Measure your throat....

At this last step, you should have the case and slug in your gun with the bolt closed, and the taped rod in your hand... Carefully slide the rod down the barrel of your rifle till it touches the boolit slug. Then, with a steel hammer or what have you pound the rod down until you feel the slug hit the bottom of the case filled with lead.... Give it one more good wack cuz you can.

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Carefully remove the rod and VERY carefully open the bolt and remove your throat slug... It might be tuff to open and feel free to give it a tap with a rubber mallet... It should look something like this......

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You have your throat measurements.... I keep these in a special case for easy reference for each of my rifles.... Now if I can just get a certain ROCKET SCIENTIST to chime in with some cool facts and such, this tutorial will be complete....

Blessings,

AlaskanGuy

[runfiverun]

I like a gas check on top of the boolit and below the rod this squares everything up.
I also use a fire-formed case and leave the neck blown out.
super soft lead for the boolit and a bit harder internal lead works best for me too.

that's pretty dang good neck to chamber length on the case there. B.T.W.

[AlaskanGuy]

Thanks Fiver... You must be one of them Rocket Scientists i was talking about... :)

[Green Lizzard]

check out goodsteels sticky

[AlaskanGuy]

Awwwww C.r.a.p....now ya tell me lizzard.... Wish i would have seen that before... Sorry goodsteel.... I searched for something about it, saw nothing, so figured i would write something up... We need a way to index this stuff....lol

[runfiverun]

:lol:
I knew about the sticky, but this can still be used as a discussion about the throat measurement relationship....... and why we want to measure this area.

[btroj]

Maybe we need a sticky on stickies.....

AG, this kind of post is always a good thing. Sometimes there is more than one way to skin a cat. Besides, it got Run to comment and that is never a bad thing. Well, until you try to follow what he is saying.

There certainly isn't a lot of extra space at the end of that chamber. Helps keep a bullet from riveting into that spaces under pressure.

I need to redo mine, the bullet wasn't soft enough and it fell out of the case too. Makes it hard to understand.

[AlaskanGuy]

Well, because i offered up this work of art thread....lol... Can somebody explain what defines good, bad, or ok neck to chamber length??? There is so little info out there that i could find.... I did this work to hopefully spark some discussion on throats, good, bad and ugly, and how it effects accuracy and such... Here is something that I scalped that shows a nice blowup of a throat... Feel free to scalp and make notes all over it...

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[bhn22]

Since it's sort of related, and my post count is lagging :grin:, here's one of my early throat slugs from a 1911 barrel. It was done simply by tapping an oversized egg sinker from the chamber end until it was where I needed it to be. In one operation I got the throat dimensions, the first 3/8s or so of the rifling, and the chamber diameter at the case mouth. I must have done this ten years ago or better. This 1911 will safely chamber .454 bullets if I feel the need. I ended up lapping my Star die out another half thousandth to cure a leading issue that made no sense. It turns out that my bore is slightly tapered back to front, and that I was sizing to the smallest bore diameter, which was at the muzzle. Meanwhile, the gun leaded from the chamber, which was telling me I had some sort of sizing problem.
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[btroj]

The ideal, to me, is to have the neck end maybe .005 short of the end of the chamber. Just enough room for a bit of crud but not enough to let the bullet rivet into that space.

Think about what happens to your malleable alloy bullet when the pressure kicks it in the butt. The bullet moves and changes shape somewhat, it fills in space around it. The gap between the end of the case and the end of the chamber is ripe for getting filled. Fast burning powders at higher charges will make this situation worse.

It is a bit of a balancing act. The chamber, case, bullet all need to work together the get the bullet into the throat as straight and undamaged as possible. A slower powder helps as it pushes rather than shoves the bullet at ignition.

There is, I'm sure, more to it than this but I like the abridged versions at times.

[MBTcustom]

Dont you dare apologize! You did it different than I did, and you pictures were better. Well done indeed.
What if I merged the two threads into one? Get all the info in one place? What do you say to that?

[runfiverun]

it might be worth doing the merge I really wanted to let this discussion rid,e beyond the doing it to the why department.

i'll drop a little hint as to the why.
it has to do with the centerline of the barrel and NOT using the boolit diameter to make the corrections.
think about what happens to the trailing edges of the boolit once it gets squeezed that extra amount oversizing creates.

[AlaskanGuy]

I am fine with either, merging or staying... Just want the discussion herd... And the learning.... And someday, a permanent record inn the sticky archive.. :)

Shows i was here... Lol... But maybe it the new years thing ... And i should put the glass down...lol

[milkman]

If your brass's neck is shorter than btroj's .005, What can you do about it other than not trim it till it expands forward?

[btroj]

Not much unless you have the option of making the case from a different case that allows it to be longer. Like making 308 cases from an 06 case, you control the neck length.

[brotherdarrell]

Very good write-up. The only thing I like to do a little different is to trim the brass short so that I get a good impression of the end of the chamber for both length and diameter. Diameter is important if you are forming from longer brass and will aide in knowing if you will need to turn the necks.

Darrell

[62chevy]

i'll drop a little hint as to the why.
it has to do with the centerline of the barrel and NOT using the boolit diameter to make the corrections.
think about what happens to the trailing edges of the boolit once it gets squeezed that extra amount oversizing creates.

I'm thinking when you squeeze an over sized boolit the lead has to go some place and that would be the base of the boolit. One would also think the boolit would stay centered being over sized but that could depend on how it was placed in the case.

Did I pass the test or is this green horn way off? Inquiring minds want to know.

[Doc Highwall]

I like both write ups and the pictures say a 1000 words themselves.
I would like to see some of the stickies saved as a Pdf format so they could be downloaded.

[runfiverun]

the lead will go towards the base of the boolit it has nowhere else to go.
not only does the body of the boolit go that direction but so does any un-supported lead hanging in front.
since we all know that the base of the boolit is the most important part when exiting the barrel, imagine what 4-5 little stringers of lead hanging back there are doing.....

[bhn22]

Any displaced metal forward of any grooving, like the grease groove, will enter the groove itself. Anything past that groove would flow back to the next groove, or the bullet base, where it would encounter resistance from the chamber pressure, but I would expect the lead to win that tie, causing imperfections in the steering end of the bullet, the base. Accuracy could suffer.

[62chevy]

Thanks for the replies guys. I've been wondering about that but haven't had the chance to recover any lead boolits to examine them.

[gnoahhh]

Interesting stuff indeed. Is there an advantage to making a male model of the throat in this way over simply doing a Cerrosafe casting? When I do a chamber cast with Cerrosafe I include the throat and ½" or so of the rifling.

[btroj]

An impact cast like this never changes dimensions, cerrosafe does.

[runfiverun]

the impact slug allows you to see what you are dealing with.
angles, sloping features, angle changes, and actual diameters.
using a 315 diameter boolit to make things 'work' in a 308 barrel is not the answer.
adding thickness to your brass and using a 309 boolit with a forward drive band that mimicks [or actually touches] the throats angles and shape changes held in alignment with the barrels centerline would provide much better results.
not only in accuracy but it also unlocks your velocity potential....

[KYCaster]

it might be worth doing the merge I really wanted to let this discussion rid,e beyond the doing it to the why department.

i'll drop a little hint as to the why.
it has to do with the centerline of the barrel and NOT using the boolit diameter to make the corrections.
think about what happens to the trailing edges of the boolit once it gets squeezed that extra amount oversizing creates.


Any displaced metal forward of any grooving, like the grease groove, will enter the groove itself. Anything past that groove would flow back to the next groove, or the bullet base, where it would encounter resistance from the chamber pressure, but I would expect the lead to win that tie, causing imperfections in the steering end of the bullet, the base. Accuracy could suffer.


Awww, MAN.........you guys are killin' me. I was just thinking about where to go next with my .222 and .308 trials, now you throw a monkey wrench in the works.

So, R5R......ASSuMEing my brass fits the chamber, what is there, other than boolit FIT to the throat, that I need to be concerned about? I'm talking about gas checked boolits, so what happens to the trailing edge?

Like bhn22 says, friction tends to drag the displaced metal into the available space, but one of the functions of lube is to fill the available space with INCOMPRESSIBLE material so the integrity of the boolit is maintained. Since the pressure in the confined space of the chamber is applied equally to all parts of the chamber then, if the boolit is started straight in the chamber, it will continue straight into the barrel.

That's the reason for the chamber slug. Are you implying that there's something more to it? If so, what is it?

About displacing the excess metal from an oversized boolit.....I think of it as the same as extruding. When pressure is applied to the slug in the chamber, there is no where for it to go but in the direction of lower pressure....out the barrel. If there is excess diameter, the excess will result in an increase in the length of the boolit....toward the nose. It can't elongate toward the base because that's where the pressure is applied.

If I did my home work and the boolit FITS like it should, then my results should be good. If, on the other hand, my boolit FITS poorly, it may not be in perfect alignment or it may expand to fill the available space before being extruded into the barrel. Either of these conditions will probably result in poor performance.

Any thoughts on this?

Jerry

[WALLNUTT]

About the case length to chamber length thing, would this also be important with a revolver?

[gnoahhh]

An impact cast like this never changes dimensions, cerrosafe does.

I make a detailed drawing and note the dimensions when the casting hits the "sweet spot", then eventually toss it back in the pot. Been using the same ingot of cerrosafe for about 30 years now, and have a small notebook filled with chamber/throat dimensions. No need to maintain a collection of impact slugs, but to each his own! It's all good.

[brotherdarrell]

I offer up an impact cast of my M77 tang safety 25-06 for possible discussion. This was my first firearm purchase, brand new in 1986 at the age of 19. I would say it easily has less than 300 rounds through it, the majority of which were j-words and 4831 or factory.

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The specifics:

diameter @ start of throat - .267"+

diameter at start of rifling - .258" to .260"

length to start of rifling - .130" - .166" (yup, chambered a little crooked)

o.d. of chamber neck on slug - .289" - .290"

o.d. of neck on fired brass - .290"+ (both factory 25-06 and re-formed from 30-06)

i.d. fired case neck at mouth - .259" ish.

This has never been a very accurate rifle with jacketed. Other than one load involving a 75 gr. sierra hp and a bunch of Varget (around moa @ 100 yds.) most loads hover around 2" @ 100.

I offer up two questions for discussion:

I have shot this rifle with two cast boolits, 257420 and NOE 100 gr. Both sized @ .260" and lubed with TAC#1 and using appropriate amounts of reddot and 2400. Results were very consistent with both boolits. Anyone care to look into their crystal ball and predict what my results were?

If this was your rifle how would you approach working up a cast load based on this impact slug?

Thanks for your time

Darrell

[MBTcustom]

I just slugged the neck, throat, and rifling of one of my personal rifles. This one is a Japanese Arisaka that I rebarreled in 308 Winchester. I used a 308 Palma Match reamer, and set it to minimum headspace.
Here's the slug attop the case it was slugged in, next to an unfired case. Looks like I won't have to trim very much.
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Here's a side view of the same thing much closer:
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This allows me to take very precise measurements concerning what is going on as the boolit leaves the neck of the case.
Please note that the case neck was trimmed back a good portion so that I could easily take good measurements of the neck area of the chamber.
The neck area measures .3433
The throat measures .3093 and extends about .100 past where the neck stops to where the rifling begins.
The groove measures .3070 right smack dab on the dingy.
No problemo!

[DRNurse1]

:bigsmyl2:See, this is one of the reasons why straight cased pistols attract me....way to much rocket science here!:bigsmyl2:

I think I can make these guides for a pistol barrel and for bolt and semi-auto rifle barrels with the great instruction and visuals provided. Is there a way to do this for my revolvers without disassembly?

Now for my contribution to this thread(a reference, not my original idea): There is a google search method that allows searching the cast boolits site from google (a better search engine that the embedded one). One of our other members referred to this in another thread, and I tried it. I have to fine tune the technique but it seems to work if you are logged into the site prior to the search.

Now, where did I put that bigger hammer....:drinks:

[vintagesportsman]

Could the same be accomplished by making a chamber cast with cerrolite or am I missing something?

[btroj]

Cerrosafe changes dimensions with time, an impact slug doesn't.

[MBTcustom]

Could the same be accomplished by making a chamber cast with cerrolite or am I missing something?

You're missing several things. First of all, it's called Cerrosafe not cerrolight.
It get's you within .001, but it changes all the time after the casting has been made. Not only that, but you have to preheat the chamber just like a mold which put's you over by a few ten-thousandths of an inch right off the bat do to the thermal coefficient of expansion (Ie, hot stuff is a little bigger than cold stuff).
The pound slug is done cold, and it produces a true rendering that can be accurately measured to .0002 inches (ie 1/15th of a human hair).
This does matter if you are wanting to get good results from cast lead. Not only that, but a chamber slug can be measured in a year and will be closer to the true size of your actual chamber than a brand new Cerrosafe casting right off the bat.

One reason why this matters:
Say you want a boolit mold to be made by Tom at Accurate Molds, or designed by 45 2.1 or some such. Say you want to send them a rendering of your chamber. If you cast one out of Cerrosafe, you could be .002 inches off the mark by the time it get's to those gentlemen. You're not going to be happy with the result!!!
However if you send them one of these slugs, then sweet fruition will be yours to have and to hold till death do you part.

Now, lest you figure I am bashing cerrosafe, nothing could be further from the truth! I use it in my shop all the time to determine unknown chambers or to find out what internal thread I'm dealing with etc etc etc.
Good rule of thumb for any measurement operation to hold water, then you must be able to achieve 5 times better accuracy than you really need.
SO, how accurate do your cast boolits need to be in order to get good results?!?!?! Most here would say .001 is good nuff for 99% of all operations.
What is 1/5th of .001?
Why that would be .0002 inches wouldn't it? Cerrosafe falls on it's buttocks at ten times that (.002) therefore, I only trust it to give me measurements of .010 inches or more.