Maximum amount of sizing down a bullet

[wv109323]

I bought a Mi-Hec 360- 158 SWC mold about 2 years ago. The accuracy results from that mold are terrible. Groups from a ransom rest are 12" at fifty. Bullets are key holeing and some are completely off the 20X24 target backer. I can't sort this mold out.
The boolits are .3600 to .3603 as cast. I am sizing through a Star .358 sizer. These bullets are coming out at .3577 to .3573. Is this too much sizing?
Yesterday my RCBS 158 RN boolits shot 2 1/16" with 3.6 gn. Of WST and 2 3/4" with 5.0 of unique. Same gun same everything. Also results from a NEI mold are satisfactory. I just can't figure this one out.

[Dusty Bannister]

Is it necessary that you size the bullet at all? How do the other bullets you mention fit the cylinder throats (if it is a revolver) since you are not even mentioning caliber or firearm used. Some times a soft alloy (could be related to sizing immediately after casting) tends to stay a little undersized. You could provide a bit more solid information if you are looking for good suggestions.

[JSnover]

.003 is not asking too much. Start with a bore slug. If it's a revolver, measure the throats. As Dusty said, you may not need to size them.

[fredj338]

I size to 0.358" for my 357mags/38sp, so I wouldn't bother sizing unless it's part of the lube process. I've resized 0.459" bullets down to 0.452" bullets for hvy 45cvolt loads with no issues. It does depend on the groove depth though.

[Outpost75]

If groups are THAT large I would expect out of square base, or severe mismatch of bullet diameter to cylinder throat.

Sizing to barrel groove diameter is a waste of time. Cylinder ball seat is what matters. Bullet should fit THAT!

[Frank V]

I'd try the bullets in the chambers & see if they fit. If you can push them through with moderate pressure I think they'll work. I don't think you are sizing them too much.

[wv109323]

I reckon I left a lot of things out. The Firearm is a S&W Model 14-6 with the full underlug barrel. The five groove barrel makes it tough the slug the barrel to .001.
A sized bullet of .3573 will not fit any of the 6 cylinder throats. A .356 bullet will fit into three cylinders and too large for the other three.
The mold casts an excellent boolit. The base and all grooves are the finest boolits I can cast. Edges a razor sharp. Boolits weigh within + or - .3 grains. Bullets are lubed in a Star with White's Carnuaba Red.
The alloy is the same, The rounds are all loaded on the same Star reloader. The rounds are rolled crimped in the crimping groove.
I can get satisfactory results from the RCBS 158 RN and the NEI 158 SWC. These two molds drop right at .358. The group size mentioned in the OP was shot through the large and small cylinder throats. I segregated the large and small cylinders. I shot 6 rounds through the large throats and six rounds through the small throats. Group size was not affected.
The RCBS and NEI are 2 cavity and the Mi-Hec is a 4 cavity. I bought it to decrease my casting time but results are not there. I am shooting in the NRA Distinguished Revolver Competition.
I may try to tumble lube and shoot some as cast boolits.

[JWFilips]

Well I have sized down a .326" 130 gr Mauser boolit to .311 for a 30 -30 Did ok but I had to use 3 coats of BLL ( since the lube grooves near disappeared!)

[Artful]

If you size first at as dropped diameter in your star to fill the lube grooves and take them down in 0.002 increments, I have done 0.008 without harm to accuracy. - but the issue sounds to me like your cylinder's throats are too small. Ideally the throats and barrel should be the same size in my experience.

[44man]

Gun needs cylinder work for sure. Throats are the poorest size die made, I bet they are smaller then the groove so your boolits just skate through.

[dubber123]

I would really recommend you send the cylinder off to DougGuy here on the board to have the cylinder throats equalized, (it's cheap), then check for a thread constriction at the frame. If you find one, firelap it out. Your 50 yard groups will certainly improve.

My first model 14 averaged right about 1.5" at 50 yds. from a hand held rest. Best was a .9" cluster at 55 yds. with 4 witnesses. I'm thinking you have a very fixable problem. The 12" groups are pretty baffling though, I have never seen that.

[44man]

I would really recommend you send the cylinder off to DougGuy here on the board to have the cylinder throats equalized, (it's cheap), then check for a thread constriction at the frame. If you find one, firelap it out. Your 50 yard groups will certainly improve.

My first model 14 averaged right about 1.5" at 50 yds. from a hand held rest. Best was a .9" cluster at 55 yds. with 4 witnesses. I'm thinking you have a very fixable problem. The 12" groups are pretty baffling though, I have never seen that.
Number 1. Fix the gun because the definition of insanity is to do the same thing over and over expecting better results.

[wv109323]

Why would the small throats affect just the bullets From the the one mold? The RCBS and NEI molds do reasonably well. Alloy was the same.

[9.3X62AL]

You don't have firm numbers on the groove diameter or whether or not that crush-fit barrel has a constriction, so 1) find a gunsmith or machinist with a V-block or tri-poise micrometer and see what the groove diameter REALLY is before removing any metal. 2) Put a snug patch on a cleaning rod's patch jag and run that critter down-bore from the muzzle. If there is a tight spot where the barrel root screws in, you will feel it. If so, some sort of lapping may be in order. 3) S&W Model 14 revolvers have a STELLAR reputation for accuracy right out of the box, so I would be VERY hesitant to do any machining of throats or lapping of barrels until I KNEW TO A CERTAINTY that dimensions were whack. Let's remember that 2 bullets you have tried DID shoot acceptably well.

I know how you feel, I have a Ruger Bisley Blackhawk in 45 Colt that was "built backwards"--i.e., .448"-.449" throats and .452" grooves. No tight spots, though. It too scattered most cast bullets tried, and was none too special with the jacketed critters either. One cast bullet DID shoot well, though--Lyman #454490, a 255 grain SWC/GC design that is Thompson-like (but I don't think Mr. Thompson designed it.......where is Floodgate when ya need him?). Sized at either .452" or .454", it shot darn well in that cock-eyed roller. Don't ask me, I just worked there. So before doing the throat surgery on the BisHawk I thought long and hard about turning wrenches on something that sort of worked. I am happy with the outcome, I opened the throats to .453" to use .454" bullets.......use properly-dimensioned expander spuds to get case mouths correct......and a steel sizing die that reduces case diameter to .476"-.477" (case make-dependant) instead of the $%#@ tungsten-carbide RCBS die that reduces diameter to .469". In short, SAAMI is your friend--and that org. should be consulted when tooling and processes don't seem to be producing proper outcomes. The old carpenter's caveat rings true here--"Measure twice, cut once.......measure once, cut twice." An old detective mantra applies, too--"Test everthing. Trust nothing. TEST EVERYTHING. Confirm things 6 ways from Sunday".

ETA--The Lyman Manual I used to get started in this hobby field said that in rifles every .001" of size-down tends to result in a 1" group expansion at 100 yards, and that a rifle barrel is no better than a sizing die for this purpose. I'm not sure about that, myself. If I do any significant size-down, it gets done per the method listed above--fill the grooves with lube at or near as-cast size, then work downward in .002" steps with non-compressible lube filling those grooves--not very compressible air. There is value in knowing ahead of time what diameter the rifle or handgun throat(s) have, so that a mould cavity can be cut or chosen to correspond to your firearm's needs. In the case of the Ruger I spoke of above, I polished out the resulting .4525" throats post-reaming to .453", knowing that my H&I die produced a "true" .454" bullet in unalloyed lead. Use of wheelweight metal, 92/6/2, or Linotype alloy will cause a "tenth" or two of fatter diameter, following the rule that the harder the alloy the more the springback from sizing.

These are subtle things, though--I do use unalloyed lead to test-check all of my H&I dies, and have been known to polish out a few of them for being undersized. That's OK, I'm sure Lyman predicates their boring and honing to #2 alloy specs. Lymans have been dead-on for me with #2 alloy or 92/6/2. Call me fussy, I suppose. I kinda went far afield here, sorry about that.

[dubber123]

Why would the small throats affect just the bullets From the the one mold? The RCBS and NEI molds do reasonably well. Alloy was the same.


That is why I said I found it baffling. It is a standard weight boolit from an excellent mold maker. I could see it not shooting WELL, but 12" is just awful. The out of square base suggestion by Outpost75 is a possibility, but it seems unlikely given Mi-Hecs reputation.

I would still suggest starting over, with even cylinder throats. Have you repeated the tests back to back with the other boolits? Is it possible the gun was not firmly in the Ransom Rests inserts?

[GooseGestapo]

What brass are you using? You may be further aggravating your situation by using brass thats over thick, further sizing your bullets. Or mixed brass, some excessively thick.
Some of the Winchester milspec brass used in the PGU-88 high intensity .38 spl loaded for the U.S. Airforce in '60's would ruin lead bullets loaded in them, or, wouldn't chamber in a tight chambered gun. IRRC these loads used a .38Super 130gr bullet (.356"), and brass was a tad thick to accommodate this. Made terrible brass to load with. Would squeze lead bullets under size or shave lead when crimped. Non existent accuracy. I was given a large quantity of them. Ended up selling them to local PD as reloads when I had a Mfg. FFL.

OTH, I have a tight chambered Mod-14 like yours, ( custom replacement cylinder by S&W Performance Center; won the '98 PPC Distinguished match at the Nationals with a 597x41x, irrc). I exclusively use R-P no-cannulure cases. They are the thinnest brass I've found and allow the use of a soft swaged bullet at .358". I prefer Precision-Delta 158gr SWC ( Star, but they are out of business), stripped and re lubed with LLA, cut with mineral spirits, resized to uniform dings, ect.
check for correct measure/charge? mistakes happen... Btdt.
THAT GUN SHOOTS! Ransom rest at 1.25" at 50yds. (Fed small pp 3.6gr #231 or 3.1 Bullseye. TAPER CRIMPED! Roll crimped = 3+").
your bullet may not like your loading technique, either.