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GM 40 With Conical

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nkbj

nkbj

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This is a follow-up to another thread concerning stabilizing conicals.
Green Mountain .40 barrels have a 48" twist.
Just tried out some soft lead slugs in a 28" long GM barrel, cast from the relatively short (squatty body) Lee .41 195 grain SWC and sized .406".
The conicals were loaded into the barrel like a Lee REAL using hand pressure. Used egg carton over powder wads and lanolin lube.
Fired shots at 40-45 yds into cardboard to check for tipping. 35 grains of FFg definitely showed the beginnings of tipping at this range. Holes from 50 grains of FFg showed greater stability.
The 35 grains may not have had sufficient pressure to expand the bullet base into the GM grooves. So, maybe the 35 grain load is kinda wallowing it's way down the barrel.
Perhaps leaving the front driving band a larger diameter would be a good idea? Perhaps another day will tell.
A 40 barrel with a little bit faster twist, somewhere between 16" and 48", would be really neat.
 
I agree that a faster twist would help stabilize the 195 gr .410 bullet - OR even a little more velocity.

Did you chronograph either of the loads? How long is the 195 gr bullet?

I was trying to get the same result with a .410 in a .40 cal 1/66 twist barrel but calculations said I wasn't going to get enough muzzle velocity and therefore revolutions per second.

Good luck!
TC
 
GoodCheer said:
This is a follow-up to another thread concerning stabilizing conicals.
Green Mountain .40 barrels have a 48" twist.
Just tried out some soft lead slugs in a 28" long GM barrel, cast from the relatively short (squatty body) Lee .41 195 grain SWC and sized .406".
The conicals were loaded into the barrel like a Lee REAL using hand pressure. Used egg carton over powder wads and lanolin lube.
Fired shots at 40-45 yds into cardboard to check for tipping. 35 grains of FFg definitely showed the beginnings of tipping at this range. Holes from 50 grains of FFg showed greater stability.
The 35 grains may not have had sufficient pressure to expand the bullet base into the GM grooves. So, maybe the 35 grain load is kinda wallowing it's way down the barrel.
Perhaps leaving the front driving band a larger diameter would be a good idea? Perhaps another day will tell.
A 40 barrel with a little bit faster twist, somewhere between 16" and 48", would be really neat.
Click to expand...
If we can take a page from T/C's playbook, their .45cal/255grn conicals work great in their 1:48" x .005"-006" shallow groove barrels.

But I'd think a conical could never expand enough to fill up GM's deep .012"-.014" grooves in their round ball barrel...I'd suspect gas cutting, gas leaking up the grooves, leading, SD all over the place.

I too wondered about a .40cal conical after I got my GM .40cal Flint barrel...and its a tack driver with PRBs but has very deep grooves to make it so.
But if you were to come with a workable .40cal conical you might have a whole cottage industry opportunity
 
If the .40 barrel you are using has deep rifling grooves, you have to find a way to seal those grooves so that gas cannot blow by in the grooves and cut the sides of your conical. That means using a groove diameter, or larger OP wad behind the conical. I suspect that using a charge closer to 65 or 70 grains of powder will also give you enough velocity to stabilize that long conical in that barrel with that slow ROT. 35 grains is too light a powder charge to use with a slug that weighs 100 grains over the weight of your RB, IMHO.
 
Beefing up the powder charge achieved marginal stability in a 38" long GM 40 with a longer paper patched bullet. The 28" long barrel is... difficult.
Will try beefing up the charge some before calling it quits.
 
40 Flint said:
I agree that a faster twist would help stabilize the 195 gr .410 bullet - OR even a little more velocity.

Did you chronograph either of the loads? How long is the 195 gr bullet?

I was trying to get the same result with a .410 in a .40 cal 1/66 twist barrel but calculations said I wasn't going to get enough muzzle velocity and therefore revolutions per second.

Good luck!
TC
Click to expand...

No chrono...it croaked many moons ago.
The barrel contact length of this Lee 195 SWC bullet is .445". Too bad Lee doesn't make a 40 REAL!
 
GoodCheer said:
"...paper patched bullet..."
Click to expand...

:hmm: ...wonder how something like a .385" - 390" patched bullet might do?

Literally use a strong lubed pillow ticking patch...nothing says the projectile inside a patch has to be round does it :hmm:
 
I've only shot conicals from my GM a few times. I had a small handful of 172 gr. .41's. Offhand at 50 yards shooting at a 3" bull I got a half dollar size 3 shot group. I was using 60 grs. of fffg. The bullets were bare, lightly lubed with MaxiLube. Another fellow gave me these bullets. He had made a swage from a piece of barrel and pre-engraved the rifling into them. A few weeks later I killed a deer with one.

Last winter I was given a piece of barrel and I made a swage out of it, but I can't find any cast .41 conicals anywhere and don't have that mold. I'd like to experiment some more, maybe trying a base wad. The GM rifling is not that deep, but I'm sure there is some gas blowing by. I think it would be worth messing around with if nothing else just to get some more bullet weight for deer hunting.
 
.445 is adequate bearing surface but the over all bullet length is required to calculate the required number of revolutions per second and therefore the muzzle velocity needed to get that RPS.

I agree that a good over powder wad would seal the bore but is there still skirt expansion? Is it needed?
 
Since an expanding skirt's function is to seal the bore, it is performing the same function that an OP wad does. I don't see where you need both. If you use an OP wad, you just want a close fit to that hollow based bullet to your bore diameter. Stay within .001-.002" on that bullet diameter and you should be okay.

However, if you don't like the idea of leading the barrel with bare conicals, size any conical- flat based, or hollow based-- down, and paper patch the slug before loading it. That will give you the best accuracy.
 
40 Flint said:
.445 is adequate bearing surface but the over all bullet length is required to calculate the required number of revolutions per second and therefore the muzzle velocity needed to get that RPS.

I agree that a good over powder wad would seal the bore but is there still skirt expansion? Is it needed?
Click to expand...

I'm so used to using an over powder wad with solid based conicals...guess I don't even think about not using one. In this case it was definitely wanted because it was being greased and used as a barrier to facilitate swabbing, cleaning and then prelubing the barrel after trickling in the powder charge.
 
As one reference, I hunted a couple years back in the 90's with TC's .45cal/255grn "flat based" Maxi-Hunters with a .45cal Oxyoke wad over powder, and they were absolute tack drivers in TCs 1:48" shallow groove barrels...devastating on deer too.
 
Yea, but those southern deer are awful small, so you need a tack driver. Up here in Ohio we have REAL deer! :rotf:
 
Yeah, when I was growing up they were called brief case deer. All you needed to do was trim off the legs.
 
I know mine are small for sure, not hunting fenced in deer over bait piles they're just normal size...and worse, they're thick as fleas too !! Why, opening day of ML last just last November, I had to fill both buck tags in less than 90 minutes to keep from getting run over...just not much fun to it any more...never even got to finish the first cup of coffee.

The good news is I stop in at the local feed-N-seed store where there's usually a couple of suitcase handlers hanging around looking for a quick $50 each, and drink that cup of coffee while they run off and take care of business for me... :wink:

1-68PointRacksROTATEDTOHORIZONTAL.jpg
 
This is an update on the search for a 40 conical that will work in the 48" twist GM 28" long barrel. The Lee 195 grain SWC is starting to work out. Alignment is the issue. Sizing the rear half of the bullet to bore diameter and leaving the front big is the way to go. Loads just the same as a REAL or maxi. A 7/16" punch egg carton wad seated over the powder and a dab of lard on the bullet base seems to be working. Gimme a few years and I'll figure out the best load. I'd prefer a rock'em and sock'em "deer" load with FFg but a mid-range load with FFFg will probably be the most accurate.
And speaking of deer there are four new ones in the back yard. My better 2/3's brought home some apples for them. Wonder if they have names yet.
 
The deep round ball rifling has good points and bad points for conicals. It's tough to get the bullet to expand out into the rifling but it's also good to have something for the bullet to bite on when you load a bullet that engraves on the rifling.
Sized the back half of the Lee 195 SWC slugs 0.001" under bore diameter and let the front engrave on the rifling. Loading was done with thumb pressure followed by a short starter. With heavy duty max charges of FFg in the 28" barrel it's giving 2" at 50 yards. That's not the final word on how well it can shoot but an indication of what's available with very heavy charges.
I still suspect that the best accuracy will come from lesser charges of FFFg with the 38" barrel.
 
GC, just seeing this...and my apologies for missing the 12/10 update.
Sound likes you're making some headway...it would be interesting if a workable .40cal conical could be available in volume that's for sure...would definitely make folks .40cals more versatile.

As a related note regarding deep RB grooves...I like to use the next caliber size prelubed felt wad (Oxyoke, Dura-Felt, etc) with my PRBs on the assumption that they might seal a bit more.
For example, when I pick them up off the range, the edges look like they have tiny gear teeth suggesting that the pressure is expanding excess material out into the grooves at least a little bit. So in the end, if blowby becomes an irritant that might be worth remembering.
 
Hey there RoundBall.
It looks workable for the 40 but is perhaps more difficult as the bore size is smaller.
I've really come to appreciate the genius of the Lee REAL with it's huge lube grooves and each driving band being a brief tapered section that is self-aligning (and of course thin at the outside edge). Trying to cobble together such a thing at home with odds and ends on hand is a hobby in itself.
If I get the chance this afternoon some bullet recovery tests will be made. Should have made provisions to capture some to start with. Usually use a gallon jug or two of water backed up with bundles of paper work (taped together and submersed a couple of days).
 

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