Resilts of bore slugging: Help with interpreting?

[agit-prop]

OK, I have just slugged the bore of a BSA commercial M17 sporter as follows:

I took a once fired cartridge, and bored out the head to 5/16. I put the drill bit into the case, shank first, until it seated against the shoulder. I put the whole arrangement into a vice, and filled the neck of the case with lead that I melted from a couple RNHP bullets.

Once cooled, I removed the drill bit, chambered the case, and hammered the slug through using a taped rod with a rounded tip

The measurement for the grooves appears to be somewhere between .308 to .309, while the lands measure somewhere in the .3035 to .3045 range. Measuring this is difficult with a vernier caliper, hence the margin of error.

I'm thinking I don't have a barrel problem contributing to inaccuracy. Considering that this is a sporter profile barrel with zero float,and no action bedding, I think I may be able to make some improvements by bedding/floating.

Would you agree, or is it fool's errand to try to make this rifle work well with the current barrel installed?

 

[savagefan]

Do it, it's fun.

 

[cosmic]

I have a couple of the BSA conversions, albeit in 303. They were pretty well bedded at the factory - certainly much better than the average Bubba job. They also have very good barrels - at least they did when they left the factory. Mine were both bedded to yield a light pressure point at the forend - typical of English rifles of the period. Both of mine shoot moa with "tuned" handloads.
Considering that the Enfield stocks enjoy pillar bedding, and BSA did a pretty good conversion job, I'm not sure I'd jump into a rebedding effort. If the rifle is not shooting well, even with different bullet weights, I'd start by removing the pressure point. You could sand it out (permanent), or shim up the action (temporary) for a trial.
Oh - your barrel is probably OK. Unfortunately, by pushing the slug through the complete bore, you've miked the tightest part of the barrel. Throat or muzzle could be sustantially larger. Perhaps you could check these areas with the slug - threaded on a cleaning rod. Alternatively, pull the bolt, look through the bore at a low power light. Bore should be bright, both lands and grooves, and the rifling should be sharp on the leading edge, (Rounded rifling shows as a shadow on the leading edge - making the rifling look deeper.)

 

[agit-prop]

Nope, no pressure point at the front, just a pinch fit on either side of the barrel from front to back. There isn't any bedding to speak of except an obvious pressure spot at the back, just to the left of the safety.

There is a large flat just behind the recoil lug, and a couple surfaces on either side of the rear action screw. I was planning on bedding these areas as well as the recoil lug recess. My thoughts were to place shims under the full length of the barrel to stock contact area, maybe the thickness of heavy card stock. The idea is to bed in such a way that the barrel floats, and remove the card material once the bedding has set.

Sound like a reasonable plan?

 

[sunray]

That's a lot of fuss when all you need do is hammer a cast bullet through the barrel and measure it. However, your numbers sound ok.
"...a pinch fit on either side of the barrel..." That's likely your problem. As the barrel heats it expands and has no place to go.

 

[Chavez]

I've only slugged a bore once, and my mic read either .314 or .316 for a 7.62x54, I forget which. My point is that I could feel various tight and loose spots in the bore, and i'm told that affects accuracy by those more experienced than I, although not enough to worry about for hunting, and probably not enough to worry about unless you're already grouping .5 MOA or less. I could be wrong.