Tight bore reloading question

[ckpj99]

I have to confess that I've never paid much attention to bore diameter. I'm not into casting, and I've never really wanted to spent tons of money of custom cast bullets, but I've run into what my might be a problem.

I've been reloading using 510 grain "Hunters" hard cast bullets, advertised as .459 diameter with a 15 brinell hardness. They are round nose, but very cylindrical with straight walls. I'm attaching a picture.

I just measured them and before the driving bands, they are .459 then there is a small step up at the driving band where the bullets measure .460-.461.

I've been using them with some success in my H&R Buffalo Classic. I seat them far into the bore. When a round is chambered, the first driving band just makes contact with the rifling, but the front of the bullet doesn't at all.

I recently purchased a Pedersoli Rolling Block. I went to chamber one of the rounds I made for my H&R, and it sticks way out. The block won't close. No amount of thumb pressure will get the round to fully seat in the chamber.

I pull the bullet out and notice a ring around the nose of the bullet where it's hitting the rifling/throat/barrel. (On my H&R, I'm used to seeing actual rifling grooves get engraved on the bullet, this was a solid very fine ring)

At this point, I realize that my H&R likely had an extremely loose bore or throat, but now I'm scared that these .459 bullets with .460 driving bands are going to make the Pedersoli blow up because they're so tight.

I measured the ring engraved on the bullet and it appears to be .458.

The locations of all the measurements can be seen in the photo.

So is this bullet way oversized for my gun? Is it dangerous to shoot? Or am I so used to using a gun with an oversized bore that this is actually normal?

I'm going to slug the bore of the Pedersoli, but I've read their barrels can be choked so if I drive the slug in from back to front I'm guess what comes out the muzzle may be undersized.

I suppose I could also slug it front to back to see if the slug loosens up on it's way to the chamber.

I've done research online and I've read articles that say Pedersoli bores are oversized, others say they are tight, others say they have long throats (which I assume means the bore is oversized at the chambers and takes a long distance to close down to the proper bore size, but I guess I could be wrong).

I also have read hundreds of times that lead bullets should be .002 over the bore diameter. That makes me think I might have the perfect bullet for the rifle.

Any help would be great appreciated.

[ckpj99]

Both the H&R and the Pedersoli are 45-70. I forgot the mention that.

[ckpj99]

So I had a few minutes to do some more measurements.

The COAL of the rounds I normally load in my H&R is 2.885.

I did a test to see how deep I would need to seat the bullet to get the round to chamber in the Pedersoli, and the overall length was 2.550 (which is similar to the recommended OAL for a 405 grain flat nose bullet).

You can see the attached picture for a comparison.

Secondly, I measured the groove and land diameter AT THE BORE of the Pedersoli. It's .459 in the grooves and .443 on the lands, but this was a rough measurement.

Again, any help would be appreciated.

[Unclenick]

It sounds like the bullet hit the start of a chamber freebore. A freebore is a short length of smoothbore usually at 0.001-0.002 inches bigger than the groove diameter of the rifle, leading to throat of the rifling. However, the standard SAAMI chamber for .45-70 doesn't have any freebore. Instead it has what is called a ball throat, which is a fairly steep taper (for a chamber; 12.5°) from the case diameter straight to the throat. So I don't know what your chamber is like without a chamber cast or slug of the chamber.

You don't say how you made your measurements. That can affect results, too. I flat don't trust any inside diameter measurement made with caliper ID measuring jaws. It's difficult to get them closer than about 0.002" in small holes. Even making an OD measurement on a slug, I prefer to see a micrometer used, as calipers can deflect a bit easily. But for comparative purposes the caliper does OD measurements OK.

You can get a Lee 0.457" bullet sizer die and size these slugs down if it becomes necessary. If you want something larger you can either hone one out for yourself with wet-dry paper on a split dowel with a drill, or pay Lee to do it if you find a wider diameter would work better. The Lee tool is inexpensive and just mounts on a loading press, so there's no special press to buy. Figure you'll likely get half a thousandth spring-out of a bullet that diameter from the die. Depending on the bullet alloy, you might even get 0.458".

[ckpj99]

Thanks unclenick - So once I get an accurate measurement of the barrel, should I size my bullets to the groove diameter? .002 less than the groove diameter? .002 more than the land diameter regardless of the groove diameter? Smack in the middle of the land and groove diameter?

Like I said, since I've always used (what I would call) factory components, I've never really worried much about this.

Also, what if the barrel is choked. Should I measure the barrel at the chamber end and go off those measurements?