.38-40, do I need hollow based bullets?

[SNELLN2]

I have an old Colt, New Service that is very inaccurate. Using a slug and my trusty calipers I measure the cylinder to be .400~.401 and the barrel bore to be .403~.405. I have been using .40 S & W .400 store bought lead bullets to no avail. Would a .400 bullet with a hollow base expand enough to grip my bore? I have been searching for moulds and can't find a hollow base mould. Does anyone sell a hollow based boolit that would work better for me in my gun? If so, please let me know. Thanks, Alton. :sad:

[405]

Don't know if the hollow base would work or not in a revolver. I know some hollow base wadcutters can be very accurate in revolvers but those revolvers may have a better match between the throats and the bore. I always think of hollow base bullets as an iffy kinda deal. A light pistol charge will no doubt expand the base.... but the pressure has to do it twice- once in the chamber and once in the forcing cone. 'tis iffy in my mind. Also, IMO, any hollow base in any type of gun is limited it what it can do. Most will seal the bore. But they can't be pushed too hard. Also, with a light pistol charge only the rear part of the bullet will expand.... that leaves the front part unsupported, especially bad if it is undersize. Meaning that the back part is expanded to fill bore but the undersized front part will likely slump to the side.... bad for accuracy.

I read your numbers and don't understand what you mean by bore diameter. There are two different bore diameters. The bore and the groove. The groove diameter is the more important of the two. No matter, the numbers you gave indicate a recipe for poor performance in that revolver no matter the bullet. If the gun is not a high dollar collectible the best solution is to open the cylinder throats to whatever the groove diameter is of your bore then shoot that size bullet.

[SNELLN2]

405
Thank you for the quick reply. I pushed a slug through my barrel and then measured the OD of the slug to get my bore diameter. The bore is tighter for the first 2 inches from the muzzle and then pushes fairly easy and hangs just a tad upon exit. How do I find a .403~.405 dia. boolit?

[405]

OK, When you say OD I assume the largest measurement.... that would be the groove diameter. Assuming that your cylinder throats are .401 and the groove diameter of your bore is .405 then what is happening is your bullet is getting swaged down to .401 as it passes thru the throat (no matter what is was when it leaves the case) then has NO chance for taking the rifling enough for good accuracy when it hits the forcing cone then on thru the bore. The best possible scenario for a revolver/bullet is for the full shank of the bullet (the part that supports it and takes the rifling) to leave the cylinder throat, hit the forcing cone dead center, then pass into the bore with a diameter of full groove diameter.

The specs of your revolver won't allow that to happen. You can try a hollow base bullet that is sized to .401 and see what happens but the outcome IMO will be iffy. If it works super! But, I don't know of a common or even an available .401 200 gr hollow base pistol bullet off the top of my head. Nor do I know of a .405 200 gr plain base pistol bullet either. You might poke around on the various custom bullet caster's sites and see about the possibilities.

So, it may come down to two steps for that revolver if you want it to shoot to its full potential. 1) have a competent smith (or DIY) open the throats up to match the groove diameter of the bore and 2) have a custom mold cut for your gun, say a SWC, plain base, grease groove design of about 200 gr with an as cast diameter of .406- allowing the option of trying it at .406 or sizing to .405. The custom molds I use when faced with odd bore diameter guns are cut by Mountain Molds. You have to design the bullet on the MM site and the cost per mold is about $90-110. COMPLETE attention to detail is required to design a bullet- what you design is what you get :) There's more to it than meets the eye. Good luck and what you describe is fairly common in the revolver world.

[bhn22]

If you're using store-bought bullets, they're probably too hard anyway. Do some scouting around for some properly designed 38-40 bullets with a bhn (brinnell hardness number) of 10 or less. You didn't tell us what load you're using, but I'm guessing it probably not very hot out of respect for the age of the revolver. A soft bullet might obturate (expand) a bit at the base & seal the bore. Another option is to have the throats of your revolver reamed out to match your bore groove diameter. I suspect you might find correct 38-40 bullets in a suitable hardness from someone like Mt Baldy Bullets.

[woody1]

Would a hollow base boolit work? I don't know. I do know that finding a .405-.406 boolit won't solve your problem unless and until you get the cylinder throats more in line with the bore diameter. If you do that you would possibly get booits that will work by sizing down to your needed diameter. I have a .38 WCF rifle that requires a .406" and I make 'em by sizing down from .452". Regards, Woody

[9.3X62AL]

Good info above. I agree that your throats need to be opened up a bit to at least match the groove diameter of your revolver's barrel, maybe .001 larger (.406"). A boolit at .407" would not be out of the question, as long as there is .002" of diametric clearance at the case mouth to allow safe boolit release.

A boolit mould of this diameter would be a semi-custom project, a la Mountain Molds or another specialist maker. Dan at MM does GREAT work, and there are vendor sponsors here that may be able to help.

A hollow-based mould may work if relatively soft alloys are used, but the consistency of expansion and centeredness of the expanded boolit is subject to variance under the best of circumstances. I would opt for re-throating the New Service, myself. I imagine those undersized boolits rattling downbore also leave some leading in their wake.

If you elect to go the custom mould route, I would suggest a shoulderless round flatnose with very short front drive band (.050"-.075") ahead of a healthy crimp groove, then 2 body bands bracketing a lube groove roughly the same width as your bracketing body drive bands. Weight should be +/- 180 grains, so that the fixed sights co-register downrange with that bullet weight at 1880-level velocities (about 900-925 FPS). If all this sounds a great deal like a 40 S&W load, well........there is not much new under the sun, as the late Frank Barnes once said in "Cartridges of the World".

[405]

SNELLN2,
I don't envy your dilema. I shoot three 38-40s. A Colt SAA and two Win lever guns. I'm lucky that the groove dia in all my guns is very close to spec at .401. It's one of my favorite pistol/carbine cartridges- overlooked my many because of the glamour of the 44-40.

Out of curiosity, how does your revolver shoot the .400 Jbullets? If it does well, one long shot possibility is to try to imitate that hardness with a .401 cast. Maybe a 180gr RFN or SWC..... as hard an alloy as you can find. Maybe even a gas-checked very hard cast at .401. One warning about gas checks and light handgun loads- the bullet can leave the gas check in the bore :(

[SNELLN2]

SNELLN2,
I don't envy your dilema. I shoot three 38-40s. A Colt SAA and two Win lever guns. I'm lucky that the groove dia in all my guns is very close to spec at .401. It's one of my favorite pistol/carbine cartridges- overlooked my many because of the glamour of the 44-40.

405: Three 38-40s, wow. I love this very large gun with its 7 1/2" barrel because of it uniqueness. The fragile, bottle necked cases take a lot of TLC so as not to destroy them...this is not an easy cartridge to load. I have only bent one case mouth so far. I am presently trying to make cases from .303 British cases. Looks promising.

Out of curiosity, how does your revolver shoot the .400 Jbullets? If it does well, one long shot possibility is to try to imitate that hardness with a .401 cast. Maybe a 180gr RFN or SWC..... as hard an alloy as you can find. Maybe even a gas-checked very hard cast at .401. One warning about gas checks and light handgun loads- the bullet can leave the gas check in the bore :(

405: I'm not sure what you mean by Jbullets. Jacketed? My very first loads back in 1995 were with .40 S & W jacketed bullets and accuracy was terrible. I switched to lead bullets, 3D swaged, 180gr. SWC with 7 grs. of Unique (approx. 800fps). Accuracy still suffered.

[QUOTE=405;1112367]OK, When you say OD I assume the largest measurement.... that would be the groove diameter. Assuming that your cylinder throats are .401 and the groove diameter of your bore is .405 then what is happening is your bullet is getting swaged down to .401 as it passes thru the throat (no matter what is was when it leaves the case) then has NO chance for taking the rifling enough for good accuracy when it hits the forcing cone then on thru the bore. The best possible scenario for a revolver/bullet is for the full shank of the bullet (the part that supports it and takes the rifling) to leave the cylinder throat, hit the forcing cone dead center, then pass into the bore with a diameter of full groove diameter.

The specs of your revolver won't allow that to happen. You can try a hollow base bullet that is sized to .401 and see what happens but the outcome IMO will be iffy. If it works super! But, I don't know of a common or even an available .401 200 gr hollow base pistol bullet off the top of my head. Nor do I know of a .405 200 gr plain base pistol bullet either. You might poke around on the various custom bullet caster's sites and see about the possibilities.

Thanks 405. Yes, OD is my groove diameter. Seeing as how this six shooter was built in 1912, I really don't want to change anything on it. I may try polishing out the throats of the cylinders a tad, use a softer lead and see if that helps accuracy a bit.

[SNELLN2]

If you're using store-bought bullets, they're probably too hard anyway. Do some scouting around for some properly designed 38-40 bullets with a bhn (brinnell hardness number) of 10 or less. You didn't tell us what load you're using, but I'm guessing it probably not very hot out of respect for the age of the revolver. A soft bullet might obturate (expand) a bit at the base & seal the bore. Another option is to have the throats of your revolver reamed out to match your bore groove diameter. I suspect you might find correct 38-40 bullets in a suitable hardness from someone like Mt Baldy Bullets.


bhn22: Thank you for your thoughtful reply. I'm just now getting back to fooling with this gun since 1995. All the records I once had were destroyed in a storm we had down here along the Gulf Coast of the US. What I can recall is that I last used 180gr., 3D swaged SWC bullets with 7 grs. of Unique for ~800fps. Yes, in this old, 1912, gun I did not want to load anything hot. A softer bullet makes sense to me and I will look for a proper 38-40 bullet, starting with your suggested vendor. Thanks, Alton.

[SNELLN2]

Would a hollow base boolit work? I don't know. I do know that finding a .405-.406 boolit won't solve your problem unless and until you get the cylinder throats more in line with the bore diameter. If you do that you would possibly get booits that will work by sizing down to your needed diameter. I have a .38 WCF rifle that requires a .406" and I make 'em by sizing down from .452". Regards, Woody


Woody1: Thank you. I will look into this sizing down procedure. Sounds interesting. Thanks, Alton.

[SNELLN2]

Good info above. I agree that your throats need to be opened up a bit to at least match the groove diameter of your revolver's barrel, maybe .001 larger (.406"). A boolit at .407" would not be out of the question, as long as there is .002" of diametric clearance at the case mouth to allow safe boolit release.

A boolit mould of this diameter would be a semi-custom project, a la Mountain Molds or another specialist maker. Dan at MM does GREAT work, and there are vendor sponsors here that may be able to help.

A hollow-based mould may work if relatively soft alloys are used, but the consistency of expansion and centeredness of the expanded boolit is subject to variance under the best of circumstances. I would opt for re-throating the New Service, myself. I imagine those undersized boolits rattling downbore also leave some leading in their wake.

If you elect to go the custom mould route, I would suggest a shoulderless round flatnose with very short front drive band (.050"-.075") ahead of a healthy crimp groove, then 2 body bands bracketing a lube groove roughly the same width as your bracketing body drive bands. Weight should be +/- 180 grains, so that the fixed sights co-register downrange with that bullet weight at 1880-level velocities (about 900-925 FPS). If all this sounds a great deal like a 40 S&W load, well........there is not much new under the sun, as the late Frank Barnes once said in "Cartridges of the World".

9.3x62al: Thank you for such an in depth response. Alton.