So I slugged the bore on my rifle. Now what?

[Southern Raider]

I just slugged the bore on my Ruger #1 in 375 H&H. The answer is 0.376", but it was obvious from the feel that the last 2" of barrel near the muzzle is perceptibly tighter than the rest of the barrel.

What can/should be done about this? I suppose I could fire lap with 0.376/0.377 bullets that would do more work on the muzzle end. I guess I could also just use larger bullets and accept the constriction at the end of the bore.

I'm favoring fire lapping as I'd like to push lead bullets above 2000fps, but what is the general concensus for something like this?

 

[fineredmist]

I wouldn't be concerned about the restriction. If you insist upon firing lead bullets at 2000 fps you should be aware that leading can become a big problem as the velocity goes above 1700 fps. This will happen with very hard cast as well as the softer varieties. If you are thinking that 2000fps will promote expansion you are off the mark as solid lead bullets do not expand the same way as HP or SP bullets do at that velocity. Solid bullets, wether lead or bronze will break bones, cause all kinds of damage and usually go through and through.
Look at the load data for reduced loads for lead bullets and you will see that they do not recommend velocities above 1700 fps.

 

[Southern Raider]

Just for reference, I don't hunt, so this isn't about terminal performance. I just don't see the need to have this rifle and load it to 44 magnum levels.

There are some newer theories on cast load development that revolve around loading for pressure. Most of the classic cast loads use small amounts of fast burning powder which hit the pressure limit quickly. In any event, it's something I'd like to go for and see how close I get.

My main problem at the moment is that accuracy sucks! Using 0.376" bullets, my groups are terrible. now that I have an understanding of the bore characteristics, I'm just looking for my next move.

 

[Jim Watson]

Strange, a little choke is normally considered advantageous in a cast bullet gun. Of course ol' Harry Pope wasn't shooting no 2000 fps, either.

If I had a .376" barrel, I'd want .377" or .378" bullets for it. (I use .379" in my little .378" .38-55 with good results, but I don't shoot 2000 fps, either.)

I trust your bullet hardness and lube are of the best.

 

[243winxb]

Lyman cast bullet info lists rifles .002" to .003" larger than groove diameter. Handguns .0005" to .001' larger than groove dia.

 

[jeepmor]

My main problem at the moment is that accuracy sucks!

Are you slinging the lead too fast for accuracy out of that gun? My reloading experience, be it only a few years now, is that nearly all of my guns, regardless of bullet type, has been that the accurate loads are generously low on the min to max chart. Usually just a tad below 1/2 way between min and max. It has provided my rifles the best accuracy. Not sure why, but I'm noticing a trend. I need to start taking beter notes.

You might want to toss the lead at it's optimal accuracy speed considering you are just slinging em at paper. Since it's paper you're shooting, why would you worry about speed? I'd go for accuracy.

And a benefit to you is reduced recoil over your existing 2000fps target. If you like the umpfh of the higher speed round, buy a larger bullet and toss it below you lead scrubbing regimen you are creating.

Hope this helps,
jeepmor

 

[Southern Raider]

I guess I should have been more thorough, but the posts are going in a direction I did not anticipate. Here's where I am:

I am sending 265gr, gas checked, hard cast bullets downrange at 1550fps per my chrono. At 25 yards off an improvised rest, my first two rounds are touching in the bullseye. My next two rounds are touching, but are 2-3 inches outside the bullseye. My fifth round is off by itself somewhere in the general vicinity...

The only time I've seen something like this is with a 25ACP pistol with a worn out barrel. It leads me to believe that the bullets I'm using are undersized with respect to the bore, which seems now confirmed after slugging, and are not properly engaging the rifling down the length of the barrel.

So, I think I need larger diameter bullets, but is there anything else worth doing in terms of bore treatment to make the bore diameter more consistent? I think I have one vote to keep the constriction at the end.

 

[35 Whelen]

I'd be willing to bet that's not a constriction at the end of your barrel. Ironically, i just came infrom slugging the barrel on my Springfield 03A3. It has a new old stock barrel on it and the bore is mirror smooth. It's been my experience that when you drive a lead bullet/ball through a barrel, there is some resistance for the first few inches, then it slides effortlessly the remainder of the way. I've found this to be true with all my milsurps so long as they have nice smooth bores. In fact, my procedure is to oil the ball lightly, tap it into the muzzle with a hammer until it's flush with the crown, tap it as far as I can with a 4"-5" long 5/16" wooden dowel, then push it the remainder of the way through the barrel with a longer piece of dowel. I never have to drive the slugs through the barrels unless they're rough.
You could find out for sure by driving the slug from the chamber end. At any rate, you should size your bullets minimum of .001" over groove diameter. If this doesn't help, try using a filler such as PSB or Cream of Wheat. PSB has done wonders in some of my Enfields with oversized bores.
In the Springfield 03A3, I've been shooting a gas-checked bullet cast from straight air-cooled wheelweights. Initial groups were under 1 1/2" @ 100 yds. Finally got a chance to chrono them today and they're running right at 2000 fps without a hint of leading even after close to 20 consecutive shots.
If it were me, I'd exepriment with my cast bullets before I went as far as lapping the bore.
35W

 

[243winxb]

The Lyman "M" die might be of use to you. This does 2 things, keeps from shaving lead off the bullet on seating and the extra diameter given the neck of the brass helps to center the bullet in the bore.

 

[fguffey]

Southern Raider, I do not want someone to get dizzy or pass out so I will not go into 'slugging' a barrel but if you are going to lap I would not suggest 'fire lapping' I know there are a lot of fans of this technique, I just do not agree with the rational because sending a lap-per down the barrel, laps the whole barrel, I would suggest the old fashion way, find the restriction and lap that part until the pull of the bullet is even from one end of the barrel to the other. Stock removal is slow, in the old days a cleaning rod (with a free floating handle) was placed in the barrel, the barrel was plugged, melted lead was poured into the barrel around the threads of the cleaning rod, once the lead hardened, the cleaning rod was tapped with a hammer to free the bullet, then lapping compound was added, and only the restriction was lapped, if the lead lap-per is removed by accident, start over, there is another way but when explaining that method some get dizzy and or pass out.

F. Guffey

 

[Southern Raider]

I'd be willing to bet that's not a constriction at the end of your barrel...You could find out for sure by driving the slug from the chamber end.

After the initial slug was made and measured, I did indeed run it back from the chamber end just to feel out the barrel. It is indeed constricted at the end, and at a point or two in the middle.

If this doesn't help, try using a filler such as PSB or Cream of Wheat.

What is PSB? What is this actually doing? I've heard of fillers being used to take up case capacity in underloaded cartridges.

The Lyman "M" die might be of use to you.

It is! I'm using one.

 

[35 Whelen]

After the initial slug was made and measured, I did indeed run it back from the chamber end just to feel out the barrel. It is indeed constricted at the end, and at a point or two in the middle.

Hmmm...I've never had to deal with this, but if I did, I'd size my bullets to the largest portion of the bore.

What is PSB? What is this actually doing? I've heard of fillers being used to take up case capacity in underloaded cartridges.

PSB is a shotshell buffer. (Available from Precision Reloading). It's granulated plastic and it flows like ball powder. Excellent stuff. It does two things: One, it holds the lighter charges of powder, normally associated with cast bullet charges, against the primer hence providing more consistent burning of the powder. Two, in my experience it eliminates leading when you have to use a slightly (.001") undersized bullet. Here: Using Fillers with Cast Bullets you'll find an excellent article on fillers.

Hope this helps!
35W

 

[Jim Watson]

It is indeed constricted at the end, and at a point or two in the middle.

That is an exceedingly bad sign. When it passes the first tight spot in the middle, it will not likely bump back up to fill the standard dimensions and get any benefit out of the muzzle choke. If I were a real cast bullet expert I would be talking about hand lapping (not fire lapping) that barrel to get the lumps out... but I am not.

 

[cracked butt]

I am sending 265gr, gas checked, hard cast bullets downrange at 1550fps per my chrono

How hard is your lead?

At those velocities I wouldn't run anything much harder than straight wheelweights.

Have you slugged the throat? This dimension is by far the most important for shooting cast. The muzzle dimension is inconsequential so long as its the same or less than the rest of the barrel.

 

[cracked butt]

I am sending 265gr, gas checked, hard cast bullets downrange at 1550fps per my chrono

How hard is your lead?

At those velocities I wouldn't run anything much harder than straight wheelweights.

Have you slugged the throat? This dimension is by far the most important for shooting cast. The muzzle dimension is inconsequential so long as its the same or less than the rest of the barrel.

 

[Jubjub]

The sling swivel band on those Rugers is swaged on, and often with enough force to crush the barrel a bit and produce a tight spot. It might be possible to lap the thing out, but they generally have a pretty poor reputation as cast bullet guns.

 

[Southern Raider]

How hard is your lead? At those velocities I wouldn't run anything much harder than straight wheelweights.

I have no way of determining that, and bought the bullets I have second hand. I could go back to the manufacturer and check. I'm guessing you'd want me to push harder bullets faster? Let's pretend these are at the top of the cast hardness scale. (28-30 Brinell??)

The sling swivel band on those Rugers is swaged on, and often with enough force to crush the barrel a bit and produce a tight spot.

Well that would explain a thing or two...I need to seem if I can correlate the midbarrel constriction with the swivel. I bet it does.

This cast bullet stuff is quite a bit more work than it seems at first. Maybe I need to just stay with jacketed bullets.