Reloading M84 Trapdoor. Relationship between OAL & PSI/CUP

Hey all - after researching for an answer to my question, or a definitive direction, I decided to register and see what you all think. I'm sorry in advance for the wall of text.

I purchased a M84 SRC Trapdoor from TrapdoorCollector and I'm interested in loading smokeless for it. I bought some HSM "cowboy" loads for it, but they leaded the barrel something terrible. I purchased a box of HSM hard cast lead bullets from SportsmansWarehouse (.459, 405gr, single lube groove and loaded them over 24.3g & 25g of A5744) and they, too leaded the barrel. I've decided that perhaps the bullets @ .459 were too small, but they were absolutely too hard. The leading seems to start at the breech and walks forward towards the muzzle. It's leaded up and the groups walk out after less than 5 shots. By 10 shots the group is LARGE.

I slugged the bore and got .460+/-.

The factory HSM cowboy loads measured at OAL 2.535.
The max OAL to the lands with the HSM bullets for my reloads measured at 2.585.
I loaded the HSM bullets to a 2.580 OAL. Not a problem, that's more than the min OAL listed for the 5477 powder I was using, so I knew I was well under (ideally) pressure limits at the min load.

I've since bought a couple more types of bullets to try and sort the leading out. The two that arrived today have me wondering about OAL, pressure levels, and what's safe...

I bought two models from GTBullets (nice people - great communication and friendly) - a 390gr FlatPoint HollowBase and a 425gr FlatPoint flat/solid base, both cast @ .460. They use a 96-2-2 alloy, which seems plenty soft (can dent with a HB pencil - I couldn't even scratch the HSM bullets with same pencil), and each have two lube grooves.

My issue comes with the OAL when I seat the bullet(s) against the rifling (using cleaning rod method).

For the 425gr, I get a OAL @ impact of rifling of 2.4575.
For the 390gr, I get a OAL @ impact of rifling of 2.5225.

For the 390gr the closest load for A5744 in my Lee manual is the 405gr - which shows a min OAL of 2.550 at the "never exceed" load (@16.1kcup). I want to load .020 off the lands, so that puts my OAL of a finished round at 2.5025, which is .05 shorter than the min OAL listed (2.550). To compound my concern, the 390gr is 1.0295 long, whereas the 405gr HSM was 1.009. The longer bullet will be seated further in the case AND is .02 longer, meaning even MORE lead in the case and less open case volume (HOWEVER - there is a 385gr bullet listed with a 2.505 min oal @ max charge for a LOT of other powders, so I'm not as concerned with the 390gr as the 425gr).

For the 425gr there is a 420gr A5744 load in the Lee manual, but the min OAL is 2.600 (@16.1cup). Additionally, the 425gr measures 1.0345 long vs the HSM @ 1.009. (Again, the longer length (to me) means not only is the OAL shorter putting the bullet further back in the case, the bullet is deeper in the case than the HSM would've been at the same OAL because the bullet is longer.) If I go .020 off the lands, it puts the OAL for the 425gr @ 2.4375.

I want to start on the LOW end of the scale, and try and get a consistent, accurate load between 1150-1250fps with each of these bullets. I'll pick the most accurate load within that velocity range, if more experienced folks think that's a safe approach.

Because my OALs are SHORTER than published for max loads (most notably the 425gr @ .1625 shorter), I plan on starting the 390gr projectile @ 22gr (405gr min is 24.3) and the 425gr projectile @ 19gr (420gr published min is 25.6). If I generally follow the charge change based on OAL change, A5744 removes ~2gr per .05 reduction in OAL at max load levels.

Here's the questions...

1) Using A5744 (or H4198 which I also have on hand), is the shorter OAL a point of concern for an original TrapDoor at minimum load levels as long as I a) stay well away from "never exceed" loads and b) monitor velocity during testing and keep a reasonable goal of 1150-1250fps?
2) Can I assume, for my practical purposes, that given the "known" weight of the projectiles and moderate FPS goal, that I can develop safe loads even with the shorter OAL using FPS as my waypoints?
3) If FPS can work, should I adjust my "target", or is 1250 reasonable for a high end? (… understanding I may settle on a load slower than that depending on which load tests out most accurate.)

Who knows - after all this contemplating, they may not shoot well at all, and that I can handle. I just want to be safe while I work through this.

Thanks all.

Lane - Thanks for the response. I read it and then read it again - I appreciate you looking back to 93 for load up data. Every now and then I stumble across a post by someone loading BP in these, and usually what follows are good groups!

The Accurate 5744 is a very forgiving powder when it comes to location in the case, and it's become very popular for the 45-70 for that reason. H 4198 maybe less so, but still very popular with reloaders as being a forgiving powder in this application.

Did you record anything about your OALs? I understand OAL is most critical at max load levels - but I'm wondering if as OAL gets shorter, does the safe powder charge range move "relatively" down the scale. IE max is 25gr @ 16.1kpsi @ 2.500 oal & 1350fps. If I then load a 23gr charge to 2.46 oal and get 1250fps - will pressures then have been less than the 16.1kpsi load? I understand it may not be a linear, or directly correlated shift, but at 100fps less than the max load published for that weight bullet, is that a safe cushion margin of error?

I appreciate the solid, core, advice - start low, and stay low. Thank you.

mrawesome22-250 said:

If your groove diameter slugged at .460" you'll want bullets that are at least .461" diameter or expect leading and poor accuracy.

I have no experience with trapdoors but I shoot GTBullets 320gr CHPGC at 1850fps out of a Marlin 1895 with zero leading and excellent accuracy. I will be hunting deer with this load in a couple weeks. My barrel slugged at .4578" so I ordered .459" bullets.

I also got burned by the HSM single lube groove 405gr bullets. One of the worst purchases I've made in a long time. Horrendous leading even at mouse fart velocities. Their 250gr .452" bullets were equally awful.

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Thanks - GT listed the .460 as the largest, unless I went with "as cast" - so I went with that. I suppose I could've asked what the "as cast" usually drop at. I'm interested in seeing if the .460s work. Glad to hear you like them.

Yes the HSM were such an immense disappointment for a rifle I was so excited about shooting. Didn't matter if I slowed them down or sped them up.

LaneP said:

For bullet seating, I always just crimped at the bullet's crimp groove and didn't experiment with varying the seating depth. Someone will be along no doubt to address that with more experience. However, based on my experience with reloading all types of ammunition, case volume does influence pressure and velocity appreciably.

The nearest example of that is with .45 Colt handloads shooting the Lyman .452" 325 grain GC. This bullet has two crimp grooves to accommodate shorter or longer cylinders throats. I recorded a charge of 25.5 grains of H110 with this bullet and when seated to the lower crimp groove (bullet farther out, more case volume) produced 1321 fps from a 7.5 inch barrel.

I then reduced the charge to 25 grains H110 and seated it to the upper crimp groove (shorter, less case volume) and recorded 1338 fps. So 1/2 grain less powder produced greater velocity with a corresponding reduction in case capacity of about 1/10".

Only I don't know what pressure these loads are generating, and didn't take the charge to a point I was seeing excess pressure signs. These were fired from a .454 Super Redhawk.

I had a great time shooting the old Trapdoor and some day will get it out again.

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The numbers are GREAT, thank you. I spent some time re-reading the first part of the Lee Modern Reloading - and he talks at length about pressures, and the near linear pressure drop with charge reduction - but he doesn't really correlate it with case volume reduction. Too many variables, I suppose. He does state "The OAL must be at least as long as indicated in the load data for all maximum pressure loads. Bullets may be seated deeper for reduced loads." But that's the extent of discussion on reduced case volume...

ArchAngelCD said:

Welcome to the forum.

The OAL in your data or any load data is not the min OAL, it is only reporting the OAL they used for that load and that bullet. It is also not powder dependent. With bullets where the manufacturer supplies a crimp groove that is where you should crimp. It is the correct spot for that bullet.

As you though, you will get leading from a low pressure round when loading too hard a bullet. I load an 18 BHN 405gr bullet for my Trapdoor @1200/1350 fps with no leading. I could go even softer.

With the right powder you can generate 1750+ fps with no danger to your Trapdoor. Pressure, not velocity is your enemy.

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Arch,

Thanks for weighing in!

Unfortunately if I crimp either bullet at the groove, the bullet will be pressed into the lands. I'm not experienced enough to know about the pressure spikes that can cause, but I've read about that phenomena and was trying to avoid it.

Second, I'm sorry if I wasn't clear, I'm only concerned with a velocity ceiling figure as it (ideally) relates to pressure. Limiting pressure is what my concerns center around. I'm trying to find a safe start point, and to know where my ceiling should be.

ArchAngelCD said:

Most bullets with a crimp groove only have 1 actual crimp groove. Are you sure it's not a lube groove? Are these bullets actually meant to be crimped? A proper 45-70 bullet should not hit the rifling, you are correct not to load them so that they hit the rifling. That can cause high pressures as you mentioned.

Is there a possibility you can post a picture of that HSM bullet? I tried to find them on the net and can only find HSM ammo.

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Arch- yes the HSM bullet has a single lube groove, and then a crimp groove near the nose. Finding - any- info about the bullets is a pain online. Apparently HSM gets them from a lead caster near them in Montana. Either way, :-( I'm not going to use them again.

The GT Bullets that I received have two lube grooves and a crimp groove near the nose. If I load the 425gr GT bullet at the crimp groove, this is what I get...

mrawesome22-250 said:

Take a Hoppes tornado brush to your gun then re-try those rounds.

I'm guessing there is still a large amount of lead in your gun from those awful HSM bullets.

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I've gone through it with a brass brush wrapped with chore boy copper mesh - the lead was flaking out pretty good. I'll reinspect near the chamber, but that chore boy worked wonders!

Slamfire said:

Try dipping your bullets to create massive grease blobs to reduce lead fouling.

I did that in my M1884 Trapdoor with commercial cast bullets and AA5744 and the grease I used was old Lubriplate 130 that was separating.

A lot of grease went up the tube, and a lot was squeezed out the back! The air in front of the muzzle had for an instant an oily appearance, that was how much grease was blown out in front.The picture on the left is the first round, and the picture on the right is after many rounds. Notice how much grease is squeezed around the cases and into the action.

The important thing for me, was that the leading from these 0.458" hard cast bullets dropped next to nothing. Accuracy still stunk. I have not slugged the bore but based on what others have said, it is probably 0.460". One day I may experiment with bigger, and softer bullets. But I will continue to lube the heck out the bullets, but I am thinking of trying a mix of beeswax and crisco that dries hard. I can melt the stuff in a small pan and dip the bullet end of the loaded round just to the crimp groove.I don't like using these industrial greases because the stuff gets all over my hands, and then I suck my thumb, blow my nose, have a finger in the thermos coffee, and I end up eating the stuff. While CMP Talladega has bathrooms with hot and cold running water in the bathrooms (bliss!) my local gunclub is the typical no electricity, no running water, primitive facilities range.

I do have a reproduction Musket and I can say with that thing, there is no such thing as too much lube! These old smoke poles had heavily, externally, greased bullets. The grease went far down the cartridge case. I am certain it kept the fouling soft, and, it kept the bullet from leading

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I saw your original post when I was researching, and I was AMAZED at what the excess lube did. Ideally I can shoot without such a heavy coating, but the lesson I can take from it is the "right" lube - whether that be amount or type - makes a huge difference.

ArchAngelCD said:

I have had good success with Missouri Bullets, plain lead with lube and coated. Give them a try next.

https://missouribullet.com/details.php?prodId=81&category=6

https://missouribullet.com/details.php?prodId=205&category=6

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I wasn't entirely sure what a powdercoated bullet would do, either in final diameter, or safe to shoot in the trapdoor. I'll look into them.

Reeferman said:

I spent close to a month, lost count of how many brushes, about every chemical known to man and thousands of strokes to get the lead out of my grandfathers 1873 Trapdoor. Barrel looks almost new and it is .461”. I bought the Lee 405 hollow base mold using 30 to 1 lead/tin and bought the Pat Wolf book. I decided that I’m never going to go through any chance of leading that barrel so powder coated them and sized to .460. Bought the expanders from Track Of The Wolf which expands .67” down the case for Lee dies and followed Pats instructions.
With black powder or smokeless the COL is 2.52”. I tried using wads but discovered 60 grains of Goex with no wads is a very accurate load out of it. I pan lube with 50/50 beeswax and olive oil with black powder and use no lube when I use 27 grains of H-4198.
Now that I’ve gotten my cataracts done and multifocal lens these 62 year old eyes are able to shoot 3 inch groups with that Trapdoor at 50 yards and can hit a 8” round plate every shot at 100 yards.
I know many will say powder coating isn’t needed but it sure works for me. Clean up after black powder is a few wipes with water and Ballistol and no leading to ever worry about.
With H-4198 it doesn’t look like it was ever shot.

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crest117 said:

I have two Trapdoors, an 1873 and an 1884 which I shoot often. I load a Missouri Bullets 405 grain Hi Tek coated bullet over 28 grains of H4198. This gives about 1250 fps with low pressure and good accuracy. I have shot hundreds of rounds of this loading with no leading. This load approximates the original black powder closely.

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All the recommendations here for the 4198 may have me switching over. I'll run out the rest of this 5744 and see where I'm at.

Thank you all.

Reeferman said:

Rifleman if you’re serious about getting your Trapdoor shooting how it can I really recommend that you get Pat Wolfs book and the one by Poyer and Riesch especially if you are looking at another as it’s the bible of trapdoors.
https://www.amazon.com/Loading-cartridges-original-Springfield-carbine/dp/157579019X
Some say Pat Wolfs work is dated and there are some that have taken what he researched and improved on it but it worked for me. I used a 50 caliber Hornady lead ball to slug mine and spent $20.00 to have it measured at a gunsmith who has the high dollar micrometer to measure 3 groove barrels like the Trapdoor. Mine came out at .4615” which is right at what it should be.
Knowing this and the information from Wolfs book I have been able to get that Trapdoor shooting really well.

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I've got the text on order, figure it's a history lesson if nothing else. Thank you.

mrawesome22-250 said:

I think all these recommendations will be moot if you don't get a bullet that is the correct diameter for your groove diameter.

If your bore is .460" you are gonna want at least a .461" diameter bullet. Once that is accomplished, grease and powder coatings and the like won't be neccessary.

The main reason I started ordering from GT was they had the diameters my guns require.

My 1894 44mag slugged at .4310". I ordered .432" bullets from GT. Accuracy became terrific and zero leading.

My 1894CB 45Colt slugged at .4519" with a chamber the size of Texas. Ordered .454" bullets from GT and started partial sizing my cases. Accuracy with this gun is now incredible with zero leading.

1895 45-70 was the only Marlington purchase that had an acceptable groove diameter (after a trip back to the factory) at .4578". Standard .459" diameter bullets work well in this gun. Except for HSM hard as granite bullets. Avoid like the plague.

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I agree with you. I've already bought the .460 dia GT bullets, so I'm going to send some of them and see what's going on. Ideally the bullets I ordered from the bullshop come on the fat side, but I'll drop an email to verify. Maybe I'll email GT and see if they can cast their 395gr in a .461 vs the .460 they list on their site. Thanks again.