30-40 issues

[Battis]

I slugged the bore of my Krag again (that makes about eight times) and I keep coming up with .3095. I tried .309 jacketed bullets and they were coming out sideways. I just bought a batch of .312 cast bullets (160 grs) and sized them down to .311. I only loaded 10 rounds and they all chambered and fired, but I made the mistake of trying to test out the load (27 grs H4895) AND set up a new 1903 front sight. I should have just fired to see if they grouped but I kept adjusting the sight. Of course the holes in the paper were all over the place but at least they were nice and round.
I loaded up a dummy round using the .312 (not sized to .311) and it chambered fine. If it chambers, it should fire - correct?

[7br]

You might check the muzzle. I have my dad's old argentine that was cleaned by some recruit with three left hands. It slugs about .312 through most of the bore and .315 at the muzzle. shoots jacketed fine. Cast boolits tumble past 25 yards. Just my experience.

[Char-Gar]

I am certain I have posted this in response to one of your Krag questions before. But for the final time:

Krag throats are large. Use cast bullets as large as will chamber freely in your rifle. I use .313 to .314 bullets in my four Krag rifles. .312 bullet will most assuredly be fine in your rifle.

That said, a .309 bullet fired down a .3095 barrel will not keyhole (hit the target sideways) unless there is something wrong with the barrel, such as deeply pitted with sections of the rifling missing. An undersized jacketed bullet by .0005 - .0020 will not deliver optimum accuracy but they should not turn in flight. There is something else wrong going on with your rifle. You need to run that down.

[Battis]

I get it - use as large a bullet as will chamber. Which means what - keep buying bullets and molds in increments? A bore should have a bullet-size limit, correct? And from what I've read, that should be around .312 for a bore of .3095.
Then, you might say, you have answered your own question...again.

[Char-Gar]

Let's do a short primer on bullet fit, because I don't think you have it yet.

1. The bore size is almost irrelevant with cast bullets. You can push oversized bullet down the barrel with no negative consequences.

2. The critical dimension is the barrel throat. A bullet needs to fit the throat as close as possible without shaving lead when it enters the throat. A clearance of .0005 to .0001 is all you need. The reason this is important is because a cast bullet that is a good fit to the throat will enter the barrel straight and not cockeyed.

3. If you use a bullet so large the case neck it to large to chamber the round freely then you have another problem. The loaded round need about .0005 to .0001 to allow the brass to spring away from the bullet, freeing it to go on it way into the throat and barrel. If this clearance is not there, high pressure can be induced as the brass can't spring away from the bullet.

To recap...

1. use a bullet that fills the throat but does not shave lead.
2. As long as the loaded round doesn't chamber hard due to an enlarge neck, you have no problems.
3. In a few cases, to get a bullet large enough to fill the throat and not enlarge the neck too much, you need to neck turn the brass a little to reduce it's thickness and have the proper clearance.

You don't need a huge number of molds. A standard 30 caliber mold should throw bullets .311 or smaller to be sized to fit the throat of most commercial 30 caliber rifles. .311 to .310 will be right most of the time. An occasional rifle with a worn throat will do best with a .312 bullet.

The Krag with it large throat needs a "fat 30" caliber mold that throws bullet .314/.313 to size to fit larger throats like the Krag, the Mosin, 303 Brit and 7.64 Belgian/Argentinian.

The old mantra is "slug the bore" needs to be discarded as the critical dimension is the barrel throat/freebore. The throat will provide the size limit and not the bore.

If a fellow is looking for cast bullet accuracy in his rifle, he needs to understand bullet fit. There are more points and issues, but the above is a good place to start.

BTW....Krag barrel groove diameter will run .308 to .314 with .3095 being the most common, so your measurements sound good to me, not that it matter, which it doesn't. My Krags run .308, .3095 and .312 and I shoot .313 bullets in the all. In fact I use the same ammo in them all.

[Bullshop]

I get it - use as large a bullet as will chamber. Which means what - keep buying bullets and molds in increments? A bore should have a bullet-size limit, correct? And from what I've read, that should be around .312 for a bore of .3095.
Then, you might say, you have answered your own question...again.

In rifles I like to run my boolits the same size as the inside neck diameter of fired cases fired in that rifle.

[Battis]

I am placing too much emphasis on the "slugged" size. Measuring the muzzle and comparing it to the bore size makes sense. I should have done that before (maybe I did - not sure). Measuring the inside neck diameter of a fired case also makes sense. Checking the throat dimensions, maybe with another Cerosafe casting, is also great advice.

[madsenshooter]

I just got the idea of bigger into my noggin also. My .001 over groove diameter loads weren't doing bad, but I noticed the ID of fired cases were .315". I have a couple oversize molds, .316 versions of molds made by NOE that I can size .314. I did a head to head of the same bullet sized different diameters the other day, .314 vs .311 and the .314 shot better. Your keyholeing with jacketed is puzzling though, perhaps a worn muzzle or bad crown.

[Mk42gunner]

Any way we can get Char-Gar's post #5 in this thread as a sticky? Hopefully by itself and locked.

It is the most concise explanation of how to fit a cast rifle bullet to the gun that I have read in many years.

Robert

[leadman]

I seldom slug the entire bore unless I suspect a problem. Usually slug the throat and the muzzle, or do a Cerrosafe pour in the throat.

[madsenshooter]

One of my 92/96 rifles has a reversed taper to the groove diameter. Let me think, I can't remember how much it is right off hand. Seems like it's .308 at the chamber end, .3095 or .310 at the muzzle. Not a big difference in 30" of rifling. The bore diameter is a consistent .301 though. I slugged it several times to verify. I forgot to mention, there was less lube blown back onto the caseneck of the .314 sized rounds, less gas getting past the check and driving bands, momentarily floating the bullet and perhaps allowing a little shifting to take place.

[mikeym1a]

Have you done a chamber cast, to include an inch or two of rifled barrel? that would tell you the size of your throat. Somewhere there is an instruction of making a 'pound cast' of the chamber. Tried it, wasn't successful. Need to find it myself and re-read it. good luck. mikey

[fatelvis]

In rifles I like to run my boolits the same size as the inside neck diameter of fired cases fired in that rifle.

I like that. Excellent tip.

[Pb2au]

Let's do a short primer on bullet fit, because I don't think you have it yet.

1. The bore size is almost irrelevant with cast bullets. You can push oversized bullet down the barrel with no negative consequences.

2. The critical dimension is the barrel throat. A bullet needs to fit the throat as close as possible without shaving lead when it enters the throat. A clearance of .0005 to .0001 is all you need. The reason this is important is because a cast bullet that is a good fit to the throat will enter the barrel straight and not cockeyed.

3. If you use a bullet so large the case neck it to large to chamber the round freely then you have another problem. The loaded round need about .0005 to .0001 to allow the brass to spring away from the bullet, freeing it to go on it way into the throat and barrel. If this clearance is not there, high pressure can be induced as the brass can't spring away from the bullet.

To recap...

1. use a bullet that fills the throat but does not shave lead.
2. As long as the loaded round doesn't chamber hard due to an enlarge neck, you have no problems.
3. In a few cases, to get a bullet large enough to fill the throat and not enlarge the neck too much, you need to neck turn the brass a little to reduce it's thickness and have the proper clearance.

You don't need a huge number of molds. A standard 30 caliber mold should throw bullets .311 or smaller to be sized to fit the throat of most commercial 30 caliber rifles. .311 to .310 will be right most of the time. An occasional rifle with a worn throat will do best with a .312 bullet.

The Krag with it large throat needs a "fat 30" caliber mold that throws bullet .314/.313 to size to fit larger throats like the Krag, the Mosin, 303 Brit and 7.64 Belgian/Argentinian.

The old mantra is "slug the bore" needs to be discarded as the critical dimension is the barrel throat/freebore. The throat will provide the size limit and not the bore.

If a fellow is looking for cast bullet accuracy in his rifle, he needs to understand bullet fit. There are more points and issues, but the above is a good place to start.

BTW....Krag barrel groove diameter will run .308 to .314 with .3095 being the most common, so your measurements sound good to me, not that it matter, which it doesn't. My Krags run .308, .3095 and .312 and I shoot .313 bullets in the all. In fact I use the same ammo in them all.

Chargar,
That was an excellent post sir. Thank you for summing that up so well.

[Janoosh]

Chargar, great post and to the point. Thank You...
I think most of the problems with milsurp rifles is the aggressive cleaning of the muzzle, thus enlarging the muzzle past bore dimensions.

[Char-Gar]

Springfield Arsenal had a learning curve on the Krag barrels which were the first to use smokless powder and be of less than 45 caliber and have jacketed bullets. The black powder 45-70 rifles had loosey goosey barrel specs because the sudden ignition of the black powder expanded the base of the lead bullet to fit whatever barrel it was fired in.

Well, the jacketed smaller caliber bullets set loose by slower progressive burning powder was a whole nother animal that Springfield didn't know it had in it's zoo. Accuracy was lousy and the Army was not doing well in rifle competition. Springfield brought in master barrel maker Harry Pope to try and diagnose the problem. It didn't take Harry long to find out the lack of uniform barrels specs were the problem. In fact, I understand he gave them a piece of his mind. Thereafter, the Krag rifles started to act better as Springfield learned the craft of 30 caliber barrel making for jacketed bullets powered by smokless powder. They had it down by the time the Krag was discontinued in favor of the new Model 1903 rifle.

Looking back, we don't see how Springfield rifle makers and engineers could have over looked such a basic thing as the need for a barrel of proper and uniform specs. But it help to remember it was all new stuff for them and they were after all goverment employees.

The Krag rifle is a favorite of mine, but it is far from the best rifle every made at a government arsenal. It was a transition rifle from large caliber black power to small caliber smokeless powder and from single shot to bolt action repeater. One can expect to find all sorts of anomalies and issues with transition rifles. The Krag rifle meets these expectations.

[Char-Gar]

Measuring the inside diameter of the neck of a case fired in your rifle can give you some good information, but it has limited use for the following reasons;

1. The outside diameter of the neck of the fired case minus the spring back of the brass when it is removed from the chamber will indeed give you a reasonable number as to the size of the chamber neck.

2. the inside diameter of the fired case neck will vary depending on the thickness of the brass in the neck. Measure enough cases of different makes will show you these vary and vary enough to throw a monkey wrench into that being a reliable number on which to base the bullet size.

3. The inside diameter of the fired case neck will give you a decent idea of how large a bullet can be fired in that case in that rifle without the loaded round binding in the case neck area when being chambered. I would consider the ID of the fired neck minus .001 to be the max size of the bullet that can be fired in that case in that rifle.

4. However as stated above, the barrel throat diameter is the controlling number. If the chamber will allow a larger bullet to be used that the throat will not accept without shaving lead, then you have gained nothing by use of the larger bullet, in fact you have lost ground.

Measuring the ID of a fired case will give some valuable information, but this information by itself will not determine what is the best bullet diameter for a good fit to the barrel throat.

[Char-Gar]

My non-scientific, non-chamber case, non-slug pounded way of determining which bullet size best fits the throat.

I am not a science type, nor much of a mechanical type of any kind. I tend to find my own way to do things with out regard to such things as casting, slugging and the like.

Over the years, I have accumulated 30 caliber sizing dies that run from .309 to .314 in .001 increments with a few in between the whole numbers. I take a large cast bullet and size it larger than I think I will need. I then load it in a dummy round and chamber it in my rifle. I take a look at the bullet with a strong light and a magnifying glass. If, it shows lead shaving of any amount. I size another bullet .001 small, load another dummy round and repeat. When I chamber a round that shows no lead shaving, but only a slight burnishing of the bullet surface, that is what I use. You could probably go .001 smaller and still do just fine.

This ain't science or engineering, but it works for me. An actual bullet in an actual case, chambered in an actual rifle IMHO is better than all the number in the world on a piece of paper.

I am sorry for the multiple posts on this subject. I don't want to sound like an arrogant jerk, but some of you guys showed an interest in learning about this stuff. I didn't learn any of this stuff on my own. I learned it from those who had traveled the road before me. I tested it out and found it to be true and it enabled me to get just about any rifle to perform well with cast bullets with a minimum of frustration, hair pulling and failure.

Bullet fit is the place cast bullet accuracy starts, but not where it ends. You must still consider;

1. Bullet style as it pertains to the internal profile of the barrel and it's rifling.
2. Bullet temper vis-a-vi, the pressure of the expanding gas.
3. The twist of the rifling vis-a-vi the length of the bullet and it's velocity.
4. Bullet lube that either works or doesn't work.

The above are not in order of importance, but if bullet fit is not correct, then all attention to other factors and details are a waste of time. Get the fit right and start from there.

[Battis]

Keep posting. You have knowledge and a "certain" way of presenting it that works for me, and apparently others.
I've just learned to duck after I ask a basic question...
The ID diameter of my fired rounds keeps showing .311, which is what I sized the 160 gr bullets to.
I've been using H4895 powder but a caster that I bought from told me that the IMR 4064 might work better. I'll give it a try.

[Bullshop]

""""2. the inside diameter of the fired case neck will vary depending on the thickness of the brass in the neck. Measure enough cases of different makes will show you these vary and vary enough to throw a monkey wrench into that being a reliable number on""""

That's why we turn case necks for uniformity. Annealing case necks on a regular basis also helps with a consistent bullet pull in the case neck as well as a consistent spring back of the neck.
The inside case neck diameter is where I start and most often end my search. Turning and annealing necks just helps keep things on an even keel.
Just as important is uniform ignition (thanks Felix) and one big aid in this is to de bur flash holes. It is amazing how a bur on one side of a flash hole inside the case can cause such havoc on uniform ignition. This is one reason case orientation helps because the internal bur is always in the same position always pushing the primer fire in the same direction. Spin that bur randomly and you get random ignition. Remove the bur and cut a venturey cone for a circular flame and you have the best possibility of uniform ignition.
First fit the boolit yes but then the search goes to uniform ignition.