Loading .303 with Black Powder. Will it Work?

[loadedbutbroke]

Hi, I have a Martini Enfield single shot .303 Nitro Proofed with a good bore. Putting the sights to one side, it is remarkably accurate with 38grn Vit 140 behind a 174grn (old military spec MK 7 Ball) I am about to enter a competition which requires black powder only; what load should I use? will it work?

I have Swiss #3 and #4 plus some fine powder I used for .44 percussion revolver.

I have the 170grn .303 FMJ BT Bullets PPU Open at the rear ( is this what is called a spritzer?).

I have never had much luck with cast bullets in any of my .303s but if I have to what load? My lee mould throws a 185grn boolit.


Range for comp 200 yrds

[Outpost75]

While the early .303 ammunition was loaded with black, you will need a bullet which carries enough soft lubricant to keep the fouling soft, otherwise, even with the best Swiss powder, accuracy will degrade rapidly with fouling unless the bore is wiped between shots. In my .303s I have had best results with the CBE bullets in .316" diameter. Unless you Beegle your Lee mold it will probably not cast a bullet large enough. NOE also makes a copy of the Ideal 299 bullet in .316" diameter which should work well. The best thing would be to cast your chamber and measure the diameter of the unrifled section ahead of the case mouth, before the rifling starts, and you want a bullet which fits the ball seat at the origin of rifling exactly.

To determine the correct bullet diameter for a rifle, the groove diameter of the barrel is NOT the determinant. If you forget EVERYTHING you ever read about slugging barrels and trying to measure barrel groove diameters simply cast chambers from now on, and make bullets fit the ball seat, you will be far happier in the long run.

The factor which limits bullet diameter is neck clearance. Measure the neck diameter of the chamber on the cast, and ensure that the diameter of a loaded cartridge is 0.0015" SMALLER than the chamber cast at that point, to ensure safe expansion for bullet release. Most .303 chambers are generously toleranced, so this is seldom an issue.

129399

[45 2.1]

+1 .... excellent advice

[herbert buckland]

+ 2 0n the advice the longer 215-220 gr bullets of .214 have worked well for me,a good BP lube is essential with this ,Swiss FFF should work well,look at loading data for the BP 32-40 to get a starting point

[loadedbutbroke]

Wow some very comprehensive replies, thank you all.

First thing I had not considered properly is the fouling issue! Of course the Martini action does not lend itself to easy wiping out. In fact it will need to be done from the muzzle. Not practical me thinks for a competition
So assuming I get plenty of lube on the boolits should I be OK for 22 in a row? I think unlikely, I only have 25 minuets to complete it.

I then have 10 kneeling and 10 standing but no time limit so I should be OK for wipe out or two.

I have to use lead so my next question is how hard? I use 25:1 for my Sharps. My previous attempts with .303 were much harder. Maybe another reason they were not very good.

You might be wondering why I don't use the sharps for the comp! Unfortunately it is an unsupported shoot, both prone, kneling and standing ,but slings are allowed which the Martini has, the Sharps does not.

Adrian

[1Shirt]

It is my opinion that any centerfire can be loaded with black powder. That said, the issue then becomes how much time you are willing to invest in cleaning modern weapons fired with black powder? After trying it in 30-30, 45-70, and a couple of others years back, it shot ok, but cleaning was no fun, and a whale of a lot of extra work. To each his own I guess.
1Shirt!

[Dan Cash]

A grease wad or grease cookie under the bullet will help with fouling control but may require you to go to a 180 grain bulletto have room. A blow tube (plastic pipe that will fit into the chamber throat) inserted into the breech and 3 or 4 long breaths blown through it will keep fouling soft. The soft 25:1 alloy you use for the Sharps should work for the .303.

How much powder? All you can pack. I think the original BP charge for the .303 was 70 grains but you are not going to get that in there. I would use the #4 powder, trickle about 30 grains into the case and then compress it with about 50 lbs pressure. Fill the rest of the case (trickle the powder in) to the point you can compress the charge enough to seat the bullet and a cardboard wad. Do not use the bullet to compress the powder. If you choose to use a grease wad, you will have to reduce the powder charge a little to have enough room. Don't over do the compression or you will bulge the case and it won't chamber. With luck you will get 15 to 1700 FPS and have much fun

[45 2.1]

Something that has not been mentioned:

1. By you is whether or not the load is a straight BP load or is duplexing allowed. If duplexing is allowed, you can use a normal bore riding boolit since the duplex charge burns the solid residue from the BP out and leaves a fairly clean bore.
2. If it is a straight BP load, the BP fouling WILL NOT allow a bore riding nose design to chamber after about the second shot. BP rifles have an undersize nose boolit to allow the cartridge to chamber over the top of the fouling in the throat. The 31125 was such a design for the 303 British with BP loads and the nose is way undersize on it.

[skeet1]

I guess my question is why would anyone want to load black powder when there are so many good smokeless powders to work with? If black powder was such a good idea they would still be using it in that caliber.

Ken

[kens]

I guess my question is why would anyone want to load black powder when there are so many good smokeless powders to work with? If black powder was such a good idea they would still be using it in that caliber.

Ken
Because it is a black powder match, not, a match of old ideas vs new ideas.

[ascast]

Because it is a black powder match, not, a match of old ideas vs new ideas.

what he said, gotta start reading at the top lol

[bruce drake]

http://castboolits.gunloads.com/showthread.php?152924-303-British-Black-Powder

Here is a bit more information from our forum on shooting blackpowder in 303 British rifles.

[loadedbutbroke]

Morning, at least it is here, just after 9am .

More excellent stuff I need to consider and I have had a look at the other thread mentioned by bruce drake.

Just a couple of quick points. The club is strictly black powder only, no duplex I am afraid. This comp is unusual in as much as it is for military rifles over .30 caliber. I am being a bit cheeky looking at my Martini in .303 because it does not have an exposed hammer. You have probably guessed that 99% of the time we shoot Sharps, High wall, Rolling Block and the ilk with the Shiloh being the most prized. However I can only dream about that and make do with my 32" Pedersoli (which actually I like very much).

Getting back to the .303 I am going to have to do some careful thinking about this fouling issue, I think can make something up to clean the chamber out between shots, its the barrel that worries me. I will also think about the blow tube idea, again I will have to make one I think.

Just as an aside my rifle was originally made in 1877 presumably as a Martini Henry for 577/450 boxer? (before being converted to .303 in 1899). Question how on earth did they cope with the fouling back then? Hard I would think when being charged by a thousand Zulus!

[Boz330]

The 577-450 barrel was tapered in the first 8in from .468 down to .464 and the ammo was undersized to just fall into the chamber. Quantity of fire was favored over quality of fire.

Bob

[45 2.1]

Getting back to the .303 I am going to have to do some careful thinking about this fouling issue, I think can make something up to clean the chamber out between shots, its the barrel that worries me. I will also think about the blow tube idea, again I will have to make one I think.

The BP lube and quantity of lube will decide what the barrel does. Look at diagrams of the original loading to see what they did also. There is more than one idea and way to go about it.

[groovy mike]

of course it will work. Just remember to thoroughly clean rifle and brass afterwards!

[Outpost75]

When I used to shoot Trapdoor Springfields with blackpowder, I cleaned after each five shots, heating water in a canteen cup with an Esbit cooker, then inserting a 2-foot piece of rubber tubing into the chamber, which had a small funnel in the other end, then pouring about 300ml of hot water down the bore while the rifle was standing muzzle-down in the range gun rack. The tube would then be removed and I would drop a pull-through cord out the muzzle, pull one dry patch through the bore to pull out the loosened muck, then follow immediately with another lightly oiled patch using ordinary gun oil or nondetergent SAE30 weight motor oil.

This worked well and with blackpowder loads, bullets cast 1:40 tin/lead and lubed with equal parts of lard and beeswax, I could expect 30 out of 40 hits on the full sized steel ram, or Army E silhouette, depending upon the match program, firing standing at 200 metres. Benched iron sight groups were in the order of 12-15 cm for five shots and under 20 cm for ten, with a wiping break mid-through.

These results were fairly typical for the blackpowder military rifles.

[loadedbutbroke]

OK you guys have convinced me; I am just going to go for it with bullets I shall make using my Lee 90371 mould. Unfortunately I am running out of time on this one as the meet is at the end of the month so no chance to do a Chamber cast I will make up some dummies however to check that things aren't binding.

I shall make the rounds up the same way I do 45-70 using a propitiatory soft lube and put as much powder in as the case will comfortably take lightly compressed. Card disc and gently seated bullet set out so it is just short of the rifling.




129608129609129610

In case they are of interest here are some pictures of the rifle.

Somehow I don't think I am going to win anything this time but I shall enjoy trying!

Adrian

[Surculus]

Just as an aside my rifle was originally made in 1877 presumably as a Martini Henry for 577/450 boxer? (before being converted to .303 in 1899). Question how on earth did they cope with the fouling back then? Hard I would think when being charged by a thousand Zulus!

They coped with it by using Henry rifling, hence "Martini [action]-Henry " When the .303 first came along in its original BP loading, it was chambered in the brand new "Lee [action] - Metford [rifling] magazine rifle." When the .303 was updated to use the new smokeless Cordite ["NG spaghetti" ;)], the Metford rifling that had resisted BP fouling so effectively would burn out in short order [under 1k rounds iirc?] and they had to come up with a new rifling scheme. They shortened the rifle some time later, giving us the SMLE ["smelly"] - Short Magazine Lee-Enfield [Same magazine-fed Lee action, but now with new & improved Enfield rifling! And that wasn't just marketing hyperbole: Enfield rifling is truly some pretty good sheisse when using hot burning smokeless!]

BTW, the method used to get the BP into both the 577-450 MH and the .303 LM bottleneck cartridges was to put it in the straight-walled case [B]and only then[ neck it down for the bullet. The .303 in fact used a pre-compressed fuel grain [kind of like a BP rocket motor] which was dropped in, + a couple of card wads & a grease cookie, necked & then bulleted.

Best of luck! Be very careful w/ loading the black into those bottlenecked cases, & don't forget there is no room for loose powder in the mix: all BP loads [I]must have some compression to avoid a KB!

[Ballistics in Scotland]

Morning, at least it is here, just after 9am .

More excellent stuff I need to consider and I have had a look at the other thread mentioned by bruce drake.

Just a couple of quick points. The club is strictly black powder only, no duplex I am afraid. This comp is unusual in as much as it is for military rifles over .30 caliber. I am being a bit cheeky looking at my Martini in .303 because it does not have an exposed hammer. You have probably guessed that 99% of the time we shoot Sharps, High wall, Rolling Block and the ilk with the Shiloh being the most prized. However I can only dream about that and make do with my 32" Pedersoli (which actually I like very much).

Getting back to the .303 I am going to have to do some careful thinking about this fouling issue, I think can make something up to clean the chamber out between shots, its the barrel that worries me. I will also think about the blow tube idea, again I will have to make one I think.

Just as an aside my rifle was originally made in 1877 presumably as a Martini Henry for 577/450 boxer? (before being converted to .303 in 1899). Question how on earth did they cope with the fouling back then? Hard I would think when being charged by a thousand Zulus!

The Martini didn't cope very well with fouling. Some of the rifles used at Rorke's Drift glowed visibly in the dark and cooked off rounds left in them. But it did have the advantages of slower rifling twist and more bore area for the fouling to be spread over. In both respects the .303 is worse off, since the rifling, which has to be deep to resist smokeless erosion, comes closer to being a series of transverse corrugations. The short neck is also a disadvantage with cast bullets. I would rather use some neck length on the lube cookie if gas-checks are forbidden, or the longest possible bullet bearing surface if they are allowed.

Mr. Metford developed the "Enfield" style rifling and used it very successfully (in shallow, gain-twist form) in target muzzle-loaders. Then he invented an exploding Minié bullet, which the government rejected. Later they found that that hollow pointed bullet, empty, gave superior accuracy in the very slow-twist Snider. But they wouldn't pay him royalties on something non-explosive. Being annoyed, he refused to submit a rifle for the trials which led to the Martini-Henry. That is why it had Henry's rather angular rifling, which picks up fouling much worse. The powder pellet was tried in the Snider and proved unsatisfactorily consistent. It may have been tried in the Martini, but the normal load was granulated powder.

A later form of Metford rifling, with shallow rounded grooves, was decided upon for the .577 Martini's very superior .402 replacement. But this was superseded before issue by the Lee-Metford. The cordite which proved so erosive had a much higher nitroglycerin content than the First World War Mk2 cordite, which in turn had more than most modern double base powders.

The .303 round was designed in the knowledge that smokeless powders can be used. Although smokeless powder was a great secret in France, with French soldiers threatened with ten years in jail if they opened a cartridge, their use of a "chemical powder" is mentioned in the British 1886 Treatise of Small Arms. I don't believe any black powder loading could produce the velocity the solid pellet, pierced in the centre like a rocket propellant, did. Even so, the Lee-Metford sights were graduated for a higher velocity, which they felt confident of firing in it when the necessary smokeless powder became available.

Initially the intention was to use the pellet system the Swiss had combined (experimentally) with a straight case and brass collar instead of a neck. The pellet could thus be inserted and the collar crimped in. But this proved to sometimes detach itself in the chamber. So the .303 case was necked down after insertion of the pellet.

[longbow]

My understanding is that the original .303 loads used a cupro nickel jacket and that would probably scrape fouling out with each shot. It is unlikely any military would issue weapons that fouled so badly they would be inaccurate or worse difficult/impossible to chamber rounds in after just a few shots so they must had had a system that worked.

Having said that, if you use a gas checked boolit of appropriate size with a grease cookie or wad under it you may get a few rounds through the gun before fouling becomes too bad.

A pull through with a wet patch on it might work for wiping the bore every few shots... just drop through the chamber then pull the wet patch through from the muzzle.

Regardless of how well it works (or not), you will probably have fun and learn some things. I know I'd try it.

Longbow

[pdgh59]

The bp .303 cartridge can not be duplicated by the handloader. Before the case was formed a compressed pellet of bp was inserted into what resembled a brass .410 cartridge that was then formed into the final shape. A duplex load could go someway to obtaining the correct velocity but this is not allowed under your match rules.

[loadedbutbroke]

Written in haste

I am having a problem with seating the bullet in full length re-sized cases. The neck is crushing the driving bands and shaving off lead.

Diameter of boolit .314 neck .306 (Copper spritzer .3105 which I normally use). Should I

1. Re-size the boolit in a Lee re-sizer without Liquid Alox?

or

2. Invest in a neck expanded die from Lyman

(From reloading 45-70 In understand it is better not to size the boolit)


Second problem is compressing the powder. I can only seem to get about 45grn os Swiss #4 in the case. Track of the wolf don't seem to do a compression die for .303. Perhaps I could try a piece of rod in my 45/70 compression die???

Help
Adrian

[loadedbutbroke]

While the early .303 ammunition was loaded with black, you will need a bullet which carries enough soft lubricant to keep the fouling soft, otherwise, even with the best Swiss powder, accuracy will degrade rapidly with fouling unless the bore is wiped between shots. In my .303s I have had best results with the CBE bullets in .316" diameter. Unless you Beegle your Lee mold it will probably not cast a bullet large enough. NOE also makes a copy of the Ideal 299 bullet in .316" diameter which should work well. The best thing would be to cast your chamber and measure the diameter of the unrifled section ahead of the case mouth, before the rifling starts, and you want a bullet which fits the ball seat at the origin of rifling exactly.

To determine the correct bullet diameter for a rifle, the groove diameter of the barrel is NOT the determinant. If you forget EVERYTHING you ever read about slugging barrels and trying to measure barrel groove diameters simply cast chambers from now on, and make bullets fit the ball seat, you will be far happier in the long run.

The factor which limits bullet diameter is neck clearance. Measure the neck diameter of the chamber on the cast, and ensure that the diameter of a loaded cartridge is 0.0015" SMALLER than the chamber cast at that point, to ensure safe expansion for bullet release. Most .303 chambers are generously toleranced, so this is seldom an issue.

129399
I have run into more problems and decided to give up on this attempt for now. The above post probably puts its finger on the main issue.

Basically I got hold of a Lyman neck expanding die which solved the problem of the over tight neck. I made up a type of compression die and loaded up a test round with 55grn of Swiss 4, lightly compressed, a small card patch and then seated the lubed bullet. I thought I had cracked it, but the round was too tight to chamber easily.

I have a feeling that the chamber on this rifle is actually tighter or a slightly different profile to my other .303 rifles and even though the brass has been very carefully fully re -sized and was checked in the chamber first, once the bullet is seated it is just too tight to fit. I tried with a 170grn sritzer and there was no problem.

I can only suppose that the black powder/bullet combination are causing the case to expand slightly and hence the problem? Tried without the powder, the round will load OK

130839
The spritzer chambers perfectly th 185 grn lee does not once the powder is added.

So back to the drawing board.

Adrian

[Dan Cash]

I agree that you are likely swelling the case during powder compression. Try compressing in stages, i.e. drop 1/2 the charge and compress then drop other half and compress. Might get you bhrough.

[Keith Andersen]

I was not going to get into this thread. But I just cant believe some of the replies from guys that very obviously don't have a clue how to load or most likely ever shot a black powder cartridge rifle.
A black powder cartridge rifle modern or vintage is no harder to clean then a rifle shot with smokeless, most likely a lot easier.
Just what in the heck is a black powder pellet???
The only thing that might give you a little problem is cleaning your bottle necked brass if your not set up for it like the small ceramic media in a tumbler. Water and a small brush will do the job but not as good as a tumbler and ceramic media.
The next thing especially if you want to shoot "dirty" with out using a blow tube to soften the fouling. That RN bullet your using in your photo might give you a little problem. That bullet has a very long bore riding section. If it is tight to your bore you will almost have to use the blow tube because of the fouling control. If that bore riding portion is undersized by about two thousands or a slight bit more you will be able to load and shoot with out a problem and you will still hold fair accuracy because that nose will expand to fill the bore.
Shoot that fine rifle and enjoy the match.
Heck I shoot my 1911 and several lever rifles using black and in the 40 some odd years the black powder never ruined a single shooter I have or had.

[Keith Andersen]

I forgot.

The reason your having a problem chambering the loaded round.

If your seating that bullet and compressing the powder with it doing this your most likely increasing the bore riding nose. Look at the bullet you cant get seated to see if you have land cuts on the bore riding section.
Lee moulds are not the best for holding tolerances. They are all over the place.

[longbow]

A bit of advice on neck sizing.

I was having some problems with my NOE 0.314" x 129 gr. boolits ~ poor accuracy at first. I had lapped the mould to drop 0.316" since my guns all run about 0.314" groove. I had notice some lead shaving even though I was chamfering and belling the case mouths, so I pulled some boolits and found the problem right away. The narrow driving bands were being significantly resized by the brass.

This had not been a problem with my NOE 316299 but they have more meat at the driving bands. So, I checked and found that my RCBS die was sizing the necks to about 0.310" which might be just fine for nominal jacketed bullet diameter of 0.311"/0.312" but a wee bit much for boolits of 0.315"/0.316". Also all that neck sizing and expanding is hard on brass.

So, I made a larger expander button to leave the necks at 0.313" inside and that solved the boolit resizing issue and accuracy problems but not the brass being overworked. So next I bought a Lee Collet sizer and set it up to size to 0.313". Worked like a charm! No more boolit resizing by the brass and no more excessive working of the necks.

I now get good accuracy and am being gentle on my brass as well.

So, as a minimum, you should get a larger expander button or better invest in a Lee Collet die (or one of the other adjustable neck sizing dies). That should solve the lead shaving issue... as long as you are belling case mouths as well.

Annealing the necks will help too. I regularly anneal mine.

Longbow

[loadedbutbroke]

Hi, I guess I owe you guys, who have taken the trouble to reply to this thread, an apology for giving up. I have simply run out of time and following the most recent posts from Dan Cash, Kieth Andresen and Longbow have come to the conclusion that I need to look a lot deeper into this problem; I don't think there is a quick fix.

To start with I am going to have to have a good look at this chamber


Outpost75
The factor which limits bullet diameter is neck clearance. Measure the neck diameter of the chamber on the cast, and ensure that the diameter of a loaded cartridge is 0.0015" SMALLER than the chamber cast at that point, to ensure safe expansion for bullet release. Most .303 chambers are generously toleranced, so this is seldom an issue.

I have in the past had a few stuck cases in this rifle unlike my other .303 bolt action rifles even though the cases were full length re sized and checked before loading. Maybe this chamber is unusually tight?

Then the bullet which I suspect is c--p


Keith Andersen
That bullet has a very long bore riding section. If it is tight to your bore you will almost have to use the blow tube because of the fouling control. If that bore riding portion is undersized by about two thousands or a slight bit more you will be able to load and shoot with out a problem and you will still hold fair accuracy because that nose will expand to fill the bore.

and

If your seating that bullet and compressing the powder with it doing this your most likely increasing the bore riding nose. Look at the bullet you cant get seated to see if you have land cuts on the bore riding section.
Lee moulds are not the best for holding tolerances. They are all over the place.


Then the seating of the bullet


Longbow

I had notice some lead shaving even though I was chamfering and belling the case mouths, so I pulled some boolits and found the problem right away. The narrow driving bands were being significantly resized by the brass.

This had not been a problem with my NOE 316299 but they have more meat at the driving bands. So, I checked and found that my RCBS die was sizing the necks to about 0.310" which might be just fine for nominal jacketed bullet diameter of 0.311"/0.312" but a wee bit much for boolits of 0.315"/0.316". Also all that neck sizing and expanding is hard on brass.


Then the reloading process. Because of the necked case compressing the powder is difficult. So as I found is getting a card disk or wad in which fills over the top of the powder.
Using a grease cookie appears to me anyway to be even more problematic.


Longbow
Having said that, if you use a gas checked boolit of appropriate size with a grease cookie or wad under it you may get a few rounds through the gun before fouling becomes too bad.

And of course the case expanding before fitting the bullet.


Dan Cash
I agree that you are likely swelling the case during powder compression. Try compressing in stages, i.e. drop 1/2 the charge and compress then drop other half and compress. Might get you bhrough.

I am sure there is so much more people have commented on which will effect the practicality of reloading the .303 with black powder and lead which also needs to be considered.

Finally a coulpe of additional thoughts from me.

The Martini action I have was originally designed for an enormous but short round which is reflected in the huge loading chute, lets call it, which leads to the chamber. This being a converted rifle uses the same chute but for a much smaller round which makes entry into the chamber more difficult in fact you have to squeeze the round in as the rim pushes the rising bolt (chute) down. A tapered FMJ round goes in relatively smoothly. But is the fatter lead topped round fouling too early to be practical?

I recon 55grns Swiss #4 might be the most which will go in the case slightly compressed. I only use 60grn in my 45-70 with a 535 grn boolit for 600yrds so is this not too much behind only 185grns of lead in my .303? (For this rifle I usualy use 38grn Vit 140 with 175grn FMJ)


Adrian

[Keith Andersen]

Adrian.

Here is a bullet you might look at if your groove is good enough for a .311 diameter bullet. http://www.buffaloarms.com/Lyman_Bullet_Moulds_it-160702.aspx?CAT=4119 The shape of the ogive will allow you to load in a fouled throat a lot longer then a bore rider will. A lead bullet will slug up to a degree. It might do you some good if you get a cast or slug your throat to see what the ideal diameter would be.

[yulzari]

Some extra (probably useless) background. The .303 MLM black powder rounds had the pellet prepared in a bronze mould and filled with a moistened (by alcohol?) black powder paste and compressed. My opinion is that the rod forming the hole down the middle was retained until the case was formed and then pulled out but I have not found out how they actually did it. The Austro-Hungarians used a black powder pellet in the Mannlicher M1888 8x50R but this one was made as a rod then some powder was trickled in around it so it burned from the outside in. In reverse to the .303 MLM. Had the technology continued I expect that there would have been much research into different hole cross sections. Much as there is on solid fuel rockets. Incidentally, whilst Enfield claimed that Cordite eroded Metford barrels faster, the change to Enfield rifling coincided with the introduction of a cooler burning Cordite and target shooters continued to order Metford barrels and the Japanese had no problems with nitro powders in their Arisaka rifles with Metford rifling made over many years in the millions (and used by Britain in WW1). The pellet technology was the product of Colonel Rubin's research in Switzerland (but they went straight for smokeless powder) and Enfield bought some of Rubin's rifles and experimental ammunition as part of their search for a magazine rifle post Martini.

[seppos]

While the early .303 ammunition was loaded with black, you will need a bullet which carries enough soft lubricant to keep the fouling soft, otherwise, even with the best Swiss powder, accuracy will degrade rapidly with fouling unless the bore is wiped between shots. In my .303s I have had best results with the CBE bullets in .316" diameter. Unless you Beegle your Lee mold it will probably not cast a bullet large enough. NOE also makes a copy of the Ideal 299 bullet in .316" diameter which should work well. The best thing would be to cast your chamber and measure the diameter of the unrifled section ahead of the case mouth, before the rifling starts, and you want a bullet which fits the ball seat at the origin of rifling exactly.

To determine the correct bullet diameter for a rifle, the groove diameter of the barrel is NOT the determinant. If you forget EVERYTHING you ever read about slugging barrels and trying to measure barrel groove diameters simply cast chambers from now on, and make bullets fit the ball seat, you will be far happier in the long run.

The factor which limits bullet diameter is neck clearance. Measure the neck diameter of the chamber on the cast, and ensure that the diameter of a loaded cartridge is 0.0015" SMALLER than the chamber cast at that point, to ensure safe expansion for bullet release. Most .303 chambers are generously toleranced, so this is seldom an issue.

129399
I agree.. beegle it up with aluminium tape.
184385

S

[Multigunner]

"Incidentally, whilst Enfield claimed that Cordite eroded Metford barrels faster, the change to Enfield rifling coincided with the introduction of a cooler burning Cordite and target shooters continued to order Metford barrels and the Japanese had no problems with nitro powders in their Arisaka rifles with Metford rifling made over many years in the millions (and used by Britain in WW1). "

Mk1 Cordite most definitely did erode Metford rifling very quickly, this was proven in both the field and in rigorous testing.
Mk1 Cordite continued in use for some time after the development of the Enfield rifling and Cordite MD eroded more conventional rifling faster than it eroded Enfield rifling.

Single base powders are far less erosive than double base powders when neither are modified with coolants. Even then the higher molecular weight of the products of combustion make gases of double base powders more erosive at the same temperatures.
Also the burning of Cordite produces nitrious acid fumes.

The Japanese used Cordite propellants for Naval main guns, but I'm not sure what they used for rifle cartridges.