Question about 1884 Trapdoor bore slugging?

[namsag]

I am finally getting serious about loading some BP cartridges for my fine old M1884 Trapdoor, it has an excellent bore and I have high hopes for it (although there is some side-to-side-play in the Buffington sight - another thread to come about that). I have Spence Wolf's authoritative work and I have combed through @Larry Gibson's awesome thread. What a treasure of information and experience from those two sources.

I am starting by following Wolf's recipe using the Lee 405 hb but I am wanting to go rather quickly to target loads more fitted to the rifle so I want to order a custom mould for a 500-gr M1881 arsenal-type bullet.

With this in mind I undertook to slug the barrel and I am a little surprised by the results. I drove my slug through with no problems, it went smoothly, there were no snags or hang-ups from muzzle to breech end. I do not have the special fitting to measure the three grooves diameter so I used the strip of beer can technique. My beer can strip (Yuengling Traditional Ale!) measure a thickness of 0.004". So I wrapped the strip around the bullet and cinched it up snug, held the ends with pliers, and mic'ed it at 0.464". Now if I subtract the two layers of beer can shim that gives (according to my 12 years of advanced education and training) 0.464" - 0.008" = 0.456".

Right? This is a surprise to me because I thought these were all supposed to be between 0.460-0.464?

It occurred to me that perhaps there was 130 years' accumulation of crud in the bore that would make it measure smaller but this rifle is really nice, I bought it from a guy I trust, and the bore looks really good with sharp rifling. I did spend some time cleaning the bore when I got it, and it did not take a whole lot of patching and brushing to get clean patches out of it. And, the bore is easy to clean after shooting BP rounds through it.

Can anyone comment? This just seems smaller than I expected, and a custom mould will be expensive, I want to get it right.

Any comments/advice appreciated,

thanks, namsag.

[Larry Gibson]

You can "cinch it up" too tight, especially with pliers. The thin soft beer can strip will flatten out in the land grooves in the slug and give a false reading smaller than it should. Try holding the shim strip just tight with your fingers and measure it.

Also, if measured with a caliper, you might check to see if the caliper is measuring correctly. I have tested some calipers, especially the more inexpensive ones sold for reloading purposes, that measured "short" against pin gauges in the .40-.50" range.

[rancher1913]

I just mic'ed just the lead and it showed 459 on mine, so thats what I have been sizing to and its been working just fine.

[Chill Wills]

I would not argue with anyone that measures their bore and groove diameters to better size their bullets. That is just smart. With odd groove barrels, often we are making a "best guess" with these work-a-rounds used to measure them.
On the other hand, BPC rifles with the barrels using odd numbers of lands/grooves like the Springfield, accuracy can be had not knowing exactly.
You are right to suspect the 0.456" measurement you got was not correct.

Basically, all the NRA national records for Midrange ( 200y, 300y, 500y, & 600y) and longrange 800y, 900y, &1000) are held by three people. Dennis Bruns, Richard Wood and V-bull Frank who's last name I can't spell for the life of me. Dennis and Richard (Woody) have both been my shooting partners years ago and I have been spotting for them when they set some of those records. V-bull and I were on the NRA 2006 NRA long-range team and we traveled to South Africa together. (sorry - that may be a little more than you needed to hear) Anyway, I know about their loading's for the Springfield and what was working for them.

I am sure if they read this they would make some corrections to what I advise, but in short, here it is on bullet selection. Well cast bullets in 20-1 or in Woody's case, 25-1 shot as they came from the mold at 0.459" or 0.460" become the bore and groove diameter and shoot very accurately when that big red light comes on behind them. In all cases, their bullets weigh in excess of 500 - 525 grains by design.
There are lots of other details but, they are just that. Ask ten match winning BPCR riflemen about their loads and methods and you will get ten slightly different answers about what to do. At the same time, you will get agreement on what works in the big picture.

[marlinman93]

I too would be suspect of a bore less than .459" in a old Trapdoor. They usually run at least .460" and larger. I also would never trust dial calipers for accurate bullet measurements. I've checked my micrometers against my dial calipers, and there's enough difference to make me not use the dial calipers for some things. It might be best to invest in a micrometer that can read 3 groove measurements with the V shape needed to do these. Or find a local gunsmith who has a V micrometer and give him a freshly slugged bullet to measure.

[Good Cheer]

Mine was stamped 1889, still had all its blue and machine shop shavings behind the lock plate.
Was of 0.463" groove diameter and required soft lead to expand into the rifling whether greased or patched, more exacting measurements being pointless except in satisfying curiosity. Lost it in 1988. Still miss it.

[ndnchf]

FWIW - I had a m1884 that measured .4575" groove diameter.

[Chill Wills]

FWIW - I had a m1884 that measured .4575" groove diameter.

Did you have that CBA member measure it. (years ago) I think he is gone now.

[ndnchf]

Yes, he was in his 90s and lived outside DC, maybe Fairfax. He did several for me.

[Deadeye Bly]

Hey, Chill, I broke some of those national records and tied another but it was not a registered match so they never got recorded. I've beaten Woody on several occasions, the last time in Friendship on his home range but by only 1 point. At 74 yrs old those sights are getting hard to see and my last match I had to judge how much fuzz to allow on the target for a proper sight picture.

I shoot a .462" diameter Baco bullet cast 25/1 that weighs 535 grains with 60 grains of 1 1/2 Swiss.. If you have pin gages determine the bore diameter. It should be .450 and will be consistent through the length of the bore. Upset your bullet in the bore, remove it and measure from a land to a groove. Subtract the bore diameter and double the difference you get. Add this number to the bore diameter and that should be your groove diameter. Shoot a bullet that size or add .001 for your bullet diameter. Undersize bullets can shoot well if they bump up to fit the bore. I used to shoot a Gov't 500 grain bullet at .457" diameter in an Italian Sharps with a .462" bore and it shot well. I think the nose fit had something to do with that. Best of luck with your trapdoor.

[rockrat]

My 1884 came out to .461"

[Chill Wills]

Hey, Chill, I broke some of those national records and tied another but it was not a registered match so they never got recorded. I've beaten Woody on several occasions, the last time in Friendship on his home range but by only 1 point. At 74 yrs old those sights are getting hard to see and my last match I had to judge how much fuzz to allow on the target for a proper sight picture.

Yes, Woody mentions your name a lot John. I follow the Friendship match results and Georgia results. I know you are good.
Some of the better advice on here comes from people that have had experience and success like yourself.
That does not mean others don't have great wisdom too. I don't mean that!

October used to be the military and Trapdoor BPCR silhouette match month when I held them in Rifle, Colorado. Back in those days Woody most likely would whoop-up on us. .....But I was his spotter. "5 up and 5 right" could fix that.

[tmanbuckhunter]

My 84 has a groove of .460. Shoots a .462 govt bullet (500gr cast from 25:1) over a dollop of 2F scary well. Can't quite work up to shooting this rifle in a silhouette match yet. I can't see beating the snot out of it when I have my CPA for that, but maybe one day

[namsag]

Thank you guys for all the great information. I am going to have another go at it, soon as I get off a bad stretch at work this week.

[Char-Gar]

I looked back in my records. My 1873 (fiscal year 1882) Infantry rifle had a groove diameter of .459. My same year Carbine runs .460 in the grooves.

[namsag]

Revival - well I had the chance to get back on this. I swabbed the barrel out good a few more times and re-slugged. I held the beer can shim snugly but not tight as Larry suggested. This time I come out with .458. Still smaller than I expected, but at least this is (barely) within the tolerances published by Spence Wolf. If this is correct, I figure the bullets sized at .459 should work pretty well. Gonna load and shoot some this week if it ever stops raining; Mississippi is about to wash away.

[John Taylor]

A 120 degree V block could help in measuring a slug from a three groove barrel.
https://testequipmentusa.com/fowler-...yABEgIH2PD_BwE

[namsag]

Yeah thats a lot for a one-time measurement.