BORE ????

[older than dirt]

Hi, a question on 45-70 TD bore sizes. I read were it says that most TD`s the bore is .459-.460. Is that the groove size or the lans size? Thanks in advance.

[Dick Hosmer]

That would be the groove dimension.

Nominal was .458", but measurements (which MUST be taken carefully with mike "centered" right on the "edge" of one of the lands on your slug, to assure that you get the maximum reading) have been reported up to .463", at least. Tom Trevor once provided a table of actual land and groove dimensions from, IIRC, about a hundred rifles, which was most interesting.

Many people pay attention to this variable, and there are plenty of reported cases of poor accuracy, even keyholing, being cured or at least substantially improved by using a better-fitting bullet.

It can be dangerous to voice this opinion here lest one ire a particular poster who claims it is bunk, and that (nearly) all TDs will do well with "standard-sized" bullets. I respect what works for him - that is his business - but I resent his rude manners, ill-concealed anger, and insulting know-it-all attitude. For some reason, he harbors a particular animosity for the late Spence Wolf, whose book I (and MANY others) consider to be a valuable tool, especially for beginners.

Bottom line, be safe, but experiment to see what works best in your rifle, and, most of all, have fun.

[ebeeby]

Spence Wolf, calculating using his (admittedly small) database of TD's concluded that the .459 bullet was optimum. IIRC, he collaborated with Lee to produce a .459 hollow base bullet mold for the 405gn bullet.

That said, it seems that many issues can be avoided by using the later 500 gn flat-based bullet design.

Of course, for your particular rifle, nothing beats slugging the barrel to see what you have.

[sdkrag]

Original bullets were all of hollow or concave base design. The Wolf 405 gr. is designed to duplicate the 405 carbine bullet. I have found original 500 gr. bullets on the Ft. Randall rifle range and they have a slightly concave hollow base. I think that instead of paper patched bullets the Govt. used a hollow base that would act like the old BP Minnie bullets. Using the Wolf designed 405 Lee mold and a Rapine 500 gr. solved the persistent tumbling problem We encountered in the early 90's as we became serious about firing the trapdoors in competition. I tried smokeless factory loads in 1979. I go with strictly BP loads ever since.

[Dale in Louisiana]

I recommend the Wolf book if you're serious about your Trapdoor.

Most people go wrong on the Trapdoor because they try to make it shoot modern jacketed ammo. Jacketed bullets are generally .458, and you're shooting them in a .460 barrel, and they don't upset like soft lead will. Handloads with either black powder or fairly fast smokeless (for upsetting bullets) and soft (1/20 or 1/30) lead bullets make the old things TALK, to the point of astounding a lot of people on adjacent targets with the latest magnums.

dale in Louisiana

[raymeketa]

If you'll look at the base of the different Cal .45 bullets used over the years, you'll find that the base cavity varied quite a bit. In the original cartridges, the cavity was used to bring the bullet to its proper weight without affecting the outside form. Any advantage by causing the base to upset and seal the bore was a bonus, but not the primary reason for the cavity. In the Carbine loads with the base wads, it's doubtful if the cavity made any difference at all.

Beginning with the M1881 bullets, the cavity changed to a shallow depression. Many of the contract bullets had a flat base with no cavity or depression what-so-ever.

Don't give up on shooting jacketed bullets with charges of slower burning powders. I've had a couple of barrels that were especially accurate with Hornady 350 grain jacketed RN bullets over 40 grains of IMR 3031. It duplicated the original ballistics. With good sights it would shoot right along with any Sharps or Rolling Block rifle all the way out to 600 yards and more.

The only way to know what a particular barrel likes is to try it.

Ray

[older than dirt]

Hi, a question on 45-70 TD bore sizes. I read were it says that most TD`s the bore is .459-.460. Is that the groove size or the lans size? Thanks in advance.

Well after putting at least 500 rds. down the barrel of my TD, I finally slugged the bore. I slugged it two times using .490 round lead balls. They shaved off quite abit of lead going in & required tapping the dowels all the way to the chamber. I miked them & my machinist friend did also. We both came up with .457. This bore is shinny & flawless & I don`t think it was ever fired until I got it back in 1960. I paid $10..00 for it. It was in the white & only had sitting around in a closet rust on it. The barrel under the bands & stock were shinny white. I believe this TD to be a Bannermans put together rifle. The stock is long wristed, has a 1863 lock. S/N says it was Mfg. in 1888, & it had a heavy paper liner between the barrel & stock. If I read it right, Bannerman used a lot of surplus (unfired) barrels, so that would count for the tight bore. I reload for it & the only bullets that I`ve shot in it are 405g jacketed in front of smokeless powder. When I shoot it, I rest it on sand bags at the 1st barrel ban from the breech & the butt stock in my shoulder. As long as I do my part, I can put them in a 6 inch bull at 100 yds. & in a 14 inch bull at 200 yds. I`m very happy with that.

[mhb]

relationship with the trapdoor rifle. I had my first one when I was 14, and have had many since.
I've never been happy with the wide (indeed, wild) variation in groove diameters in the barrels.
I'm a barrel maker, and have the means to measure bore and groove diameters directly, rather than rely on slugging and measuring the resulting slug, which is difficult to do accurately in a barrel with an odd number of grooves.
In measuring some hundreds of trapdoor barrels, I've found only ONE which had near the nominal groove diameter. Bore diameters are more closely standardized, probably because the bore dimension is established by reaming, and reamer diameters can be held to close tolerances, while proper reaming leaves the finished bore little, if any, larger than the reamer itself - the average trapdoor bore measures .451" - .452".
The typical groove diameters, on the other hand, are all over the dimensional map - on the large side, running from .460" up to .468" in barrels I've measured, with an average close to .462" - and I limit those I measure to specimens in visually near-perfect condition internally.
This irks me (as a barrel maker) because the only explanation I can come-up with is poor quality control in the rifling operation. Since I use a rifling machine (Pratt & Whitney sine bar) which works essentially the same way as those in use at Springfield in the trapdoor era, I can't excuse this as unavoidable. I can and do hold groove diameters to a tolerance much less than plus or minus .001", by measuring directly as rifling progresses. Admittedly, Springfield produced larger numbers of barrels than I have, but the simplest solution would have been simple plug gauges, used to determine when rifling depth approached and finally reached required depth - or exceeded the permissible tolerance (if there was one). It appears that the rifling machine operators at Springfield simply let the machine run whatever they felt was the 'right' length of time before stopping the process - and I can't believe there was any serious attempt at maintaining tolerances, since they could have achieved a plus or minus .001" range without real difficulty.
The popular apology for this condition is that it doesn't matter because the soft lead alloy bullet 'slugs-up' with black powder ammunition, which may be true to some extent - but I've never found any evidence that it is possible with smokeless (indeed, one of my first indications that there might be something amiss in an apparently perfect trapdoor barrel came when my first rifle pitched its .458" 500 grain bullets sideways at 25 yards - and, at the same time, made me familiar with the peculiar buzzing howl that such a bullet makes as it flies). In any event, I do not believe there is any advantage in depending on the bullet to slug-up in order to fill the grooves, rather than using bullet and groove diameters which are the same, or with a slightly larger bullet.
In fact, in the trapdoor chamber, it is impossible to seat a full groove diameter bullet in the case and still chamber the round, if the bullet is much bigger than .460".
In the end, I had to give up on the trapdoor as a likely candidate for an accurate shooting rifle, without exceptional trouble in matching ammunition to the barrel, if at all possible.
But I do still measure them, when an otherwise nice specimen is offered (the one nominal one got away from me at an auction where someone wanted it worse than I did). I guess love dies hard, hope springs eternal, etc. The darn things ought to shoot well, if they were within the dimensions the Government said they were.
Rant mode off.

mhb - Mike

[Dick Hosmer]

Thank you, Mike!

I would only say that the odd-numbered groove (certainly true of a 5!) statement seems a bit generalized here, and should not be quite so difficult in the TD with its' (unique?) feature of having three lands and grooves of nearly equal width.

Given that configuration, if you are careful, I'd think you should be able to get a pretty good groove measurement, by miking right on the 'lines'.

[mannparks]

Mike,thanks for your insight.Refreshing
Charles