I have a S&W 629 who has .432 throats. All my Keith bullets don't shoot very good with these bullets. I really like the Keith type bullets. Can anyone suggest what I should do?
Thanks,
Marsh
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I have a S&W 629 who has .432 throats. All my Keith bullets don't shoot very good with these bullets. I really like the Keith type bullets. Can anyone suggest what I should do?
Thanks,
Marsh
Cast bullets have to be a tight slip-fit in a revolver's cylinder's throats. If you are shooting 0.429-.430 lead bullets, they are going to suffer gas-cutting in the throats.
Large bullets or new, tighter cylinder.
Well, I am aware of that. What I want to know is what I can do to make the gun shoot better.Quote:
Originally Posted by noylj
I has also noticed other in the 70's-80's series of S&W .44 mags similar throats. Is this typical? My 29-5 Classic has .430 throats and is very accurate.
Marsh
First, one question. Does the revolver in question shoot jacketed bullets accurately? If it does and the problems only appear with cast then keep reading below. If it won't shoot jacketed, then IMO there is no sense bothering with it as the work it needs will not be cost effective. In that case I would sell it and get another.
Slug your forcing cone. Assuming that the bullets are not undersized (the most common cause), the biggest accuracy problems with cast bullets come from undersized throats, followed by a forcing cone that is too tight, and then from a barrel constriction. (I know what a PITA it is to accurately measure a 5groove S&W barrel slug, so check out the FC first.) Remove the cylinder, drive the slug into the FC from the rear with an oversized dowel so it will not enter the barrel, then drive it back out with a smaller rod from the muzzle. Measure it with a mic, not a caliper. The caliper is simply not accurate enough, even if it has a fancy digital readout to four decimal places it is really only accurate to two places (.01+/- .005"). A mic is accurate to three (.001 +/- .0005") and you need that degree of precision to get meaningful results when measuring slugs. You can usually tell if you have a constriction with a very tight cleaning patch on a slotted jag - you will feel greater resistance as you try to move the patch through it. Likewise with the FC, but it's much easier to measure a FC slug.
It is very common to see a cylinder with the throat measurements different for each chamber and often undersized from trying to get just one more sharpening out of a reamer before discarding it, and not at all unusual to find a FC that is too tight or to find a constriction in the barrel where it screws into the frame. Either will cause accuracy problems with cast bullets, but not with jacketed. A decent pistolsmith can ream your FC if necessary - it is neither difficult nor expensive. A constriction is cured by hand lapping and can be done by you at home with several grades of carbide grit, some oil, a very tight patch and an hour or two of your time.
Most commonly the throats are the problem, but you are lucky enough to have a cylinder where that is not an issue, so you must focus on the next two most common difficulties. Oversized throats are not an issue - accuracy problems develop when a bullet is forced through a smaller throat, cone, or constriction then must obturate to the larger grooves of the barrel.
Gas cutting happens in the barrel, not the throats, when the increased friction from contact with the lands slows the bullet and allows gas to come around the now undersized bullet base before the bullet has properly obturated. The key indicator is lead fouling on the breech end of the barrel, though it is almost impossible to see clearly if the barrel is 4" or less, and with a GC on the bullet sometimes it's hard to see at all even when it's happening.
Assuming that you are already sizing at .430-.431, larger diameter bullets will not cure the problem, but you might try a softer alloy (I use 1:4 WW's : pure lead for practice but would go up to 1:2 or 1:1 for full charge hunting loads) so that you will get better obturation.
Thats a great post.
The first thing to is try some jacketed bullet to see if it shoots.
Marsh