How much oversize is ok?

[KYShooter73]

I'm loading 300blk with Lee 312-155 aluminum checked in the 1800-2000 FPS range. 14.5 in pistol gas port using win 296 and lil gun. I need to re slug the bore because I don't trust my last measurements. Using COWW + 2% tin, water dropped, and experimenting with a harder alloy with some copper. Shooting 5 round groups half were .309, half were .311. Group sizes were similar. Very little leading, just a streak or two. My .309's showed some horizontal stringing, but vertical was dead on. I'll retest accuracy later on, cause it was cold as whiz and those are not my peak shooting conditions. My question is, if it will chamber, how many thousands over bore can you safely go? Everyone who has done much reading knows the problems shooting undersized, but I can't search up any info on the pros and cons of going oversize. Thanks.

[runfiverun]

in this case if it chambers it isn't oversized it is closer to correct sized.
you do have a limit on the stresses the boolit can withstand entering the barrel though.

[KYShooter73]

Thanks Run.

[Wolfer]

IMO if it chambers it's good to go. Woody

[dubber123]

As stated, chambering freely works for me. You have to have enough clearance for a clean release from the case is all. I have fired .005"-/006" over bore with no issues, and very good accuracy. It was a special instance, and I don't normally do it, but I had no problems.

[mikeym1a]

You should check you mould. My Lee mould, same one as yours, threw 2 different size boolits, by about .002. Don't know how much difference that would make for you, but, there it is.

mikey

[GabbyM]

You should check you mould. My Lee mould, same one as yours, threw 2 different size boolits, by about .002. Don't know how much difference that would make for you, but, there it is.

mikey

Many times if you want to win some match competition it pays to use bullets from the same mold cavity. But that's splitting hairs type accuracy that only matters in a match. given you have a decent mold. If you want t shoot one hole groups at 100 yards it's a thought. But if your Lee is dropping .002" deviation I'd just turn that into a single cavity mold and use the one that fits. You could also weight sort them after casting both cavities and easily separate out .002" from the weight.

[GabbyM]

IMO if it chambers it's good to go. Woody

Ditto:

shoot a round with no chamfer on the neck. So you don't have it there after firing. Then if the bullet after sizing slips into the fire formed case neck. It's not to large. Brass will spring back a thousandths or so. Depends upon the hardness. Annealed brass will not spring back as much. But if the bullet will go in fired brass necks it surely would of had enough room to get out.

One theory is the bullet will obdurate to fill the throat anyway so why size it down just to bump it back up. Variables play into this line of thought.

[popper]

The more the bbl sizes it, the more force applied to the CB. Sized lead has to go someplace & work softens the lead. Larger may allow slow powder to burn better. Not really an answer but some ideas. If 309 leas & 311 doesn't, I'd try 310.

[mikeym1a]

KYShooter. hmmmmm. I have to ask, does it make a good lube? :-D

[runfiverun]

horizontal stringing can be attributed to several issues.
if it's a nice day and you're on your game I'd suspect ignition issues.
it could also be as simple as rolling the rifle between shots.

[KYShooter73]

I definately was not on my game, cold as a witches titty. The horizontal spread wasn't bad, about 2 inches @ 100, the vertical was excellent. It was probably me or the cheapie scope I'm using to test loads. Rifle is normally fitted with a red dot for KY hill country shooting. Btw, my mold is fine. I deliberately sized some .309 and some .311 for testing. I have six five round sets loaded .311 seated to decreasing oal, all with same powder charge and primers to see if that helps the horizontal at all. There are mixed opinions on this here inter web whether seating depth helps with horizontal stringing, thought I would try it. I guess next I will try a load with only .309 and see if it leads the barrel. It's too damn cold to powder coat, so these are just double coated alox. I annihilated the throat out of a barrel recently, and don't want to repeat my mistake. Thanks everyone!

[GabbyM]

.0020" is the magic number for minimum bullet release. .002" being the spread between bullet diameter and I.D. of a fully expanded case under pressure as it's fired. That's the guide for neck turning for tight throat chambers. You wouldn't have to have .002" to release a bullet IMHO. But you need to build in some tolerance. Then there are match shooters that set the neck so tight they don't even have to re size the brass. wouldn't want to take that setup out in the prairie dust to play.

popper: Sounds like a valid point. Work softening lead. Suppose you refer to heat treated bullets?