Powerfactor Influences

[spook]

OK, I chronoed my loads two days ago. I shoot a 625-2 Smith & Wesson 5" "Model of 1988.

I use 230 grain copperplated bullets (actually 227 grains), federal LP150 primers and VV N320. According to the manual I should make major with about 4,9 grains (180 PF). So I chronoed my loads (4,9 grains) , with mixed cases. MY LORD! PF ranged from 132 to 151!!! I was shocked. First of all because of the LOW velocities. Secondly, because of the extreme differences between the different cases. I know the VV manual uses a 6" barrel, but HOW IN THE WORLD, do they get velocities like that??

Tonight I'm off to the range again , with new loads. I made my new loads a lot shorter (from 1.268" to 1.248") and made loads that range from 4.9 to 5.4 grains. I wonder if I can even make major with this powder

Does anyone have any idea what can cause this? Could it be that the bullets have a diameter that is too small? I have the feeling my gun could use .452 bullets, but right now I use .451.

[Patrick Sweeney]

Thus the need to chrono. Your problem appears to be insufficient ignition and burn, (the large spread in PF) and may be due to one or more of:

Insufficient crimp, insufficient neck tension. Without enough resistance, the intitial burn (even the primer burn) can push the bullet forward too quickly, upsetting the initial burn of the powder. Crimp to .468" and your powder drop belling tube o.d. should be .446-.447"

You may have a large cylinder gap or a "slow barrel." Gap is supposed to be "as small as possible and not be a problem", .003-.005" In the old days, S&W varied in what was allowed, and I had one gun returned with warranty work disallowed because the .012" gap was "within spec." If you have a slow barrel, you could be dropping 50 fps or more. I once built two identical Open guns with Bar-sto barrels fromt he same production lot, and one was always 50 fps faster than the other.

Your powder measure or measuring technique is off, and your "4.9 grains" could actually be 4.7. Are you weighing ten consecutive/total powder drops and averaging?

Reliable, accurate, dependable ammo is something that doesn't just happen. Track down the variables and report back.

[spook]

Patrick, first of all: thanks for the fast response, i appreciate it.

The insufficiant burn is evidently a problem. The ammo is very dirty and I have a lot of unburnt powder. So crimping to the specs (I tapercrimp BTW) you give is not a problem with copperplated bullets (even if I cut the plating)?

I'm pretty sure my measuring is OK. I average 10 charges and use a laboratory scale thats accurate to app. 0,0001 gram (sometimes more frustrating than helpful )

The slow barrel thing sounds like something that could be a factor on my gun. I'll check it out. See if I can measure it.

I'll check it out and try a load with the crimp you suggested.

Thanks again.

[spook]

Oh and Patrick, what do you mean with "your powder drop belling tube o.d. should be .446-.447" Do you mean the the size of the case (inside) after belling?

[TBF]

The only advice I can add to what has already been given is:

Try your next load with sorted brass ( mixed headstamp and old /new mix can cause variations)

Never trust velocities from powder manufacturers, they use barrels that are not like any revo,

or much like most semis for that matter. ( very tight and non vented )

It sounds like you need to bump up your load a little anyway from the velocity, this may also help

with consistancy and cleanliness of load.

Travis F.

[spook]

I just got back from the range. I made major . The crimp helped. I still think I could use some more, because there were still some wide (about 7 PF) differences between individual cartridges with the same load. And I still have some unburned powder. But I'm not sure how much I can crimp with a copperplated bullet. Some say it's not good to cut the copper plating, but I wonder if that's right. It's not like a metal jacket. It's really thin and not as "loose"as a jacket.

I went from 4.9 grains to 5.2 grains to make major. Made average of 175 PF.

Thanks again (you too TBF) for helping me out.

[Flexmoney]

Spook,

From my understanding, you don't want to cut the copper plating. It will fly apart and the bullet will tumble.

Have you measured the bullets to ensure they are the advertised diameter?

A Lee Factory Crimp Die ($13) should help the brass grip the bullet without the need to go with an excessive crimp.

You might want to measure the wall thickness of the brass you are using as well. Make sure the bullet diameter plus the thickness of the walls of the case add up to what they should.

[wide45]

The Lee Factory Crimp Die sometimes does not work so good with plated bullets. If the lead cores are too soft, it will size the bullet down inside the case. The brass case will springback more than the soft lead/copper bullet. Result is the bullet loose in the case.

Consider that some powders that work excellent in auto's are not great in revolvers. You won't see the unburned powder in an auto, but it sure knots up your cylinder.

[George D]

I agree with Travis on powder manufacturer velocities. I have never found any resemblence between their figures and the actual velocities acheived through my revolvers.

As for the variation, have you checked your variation in OAL's?

[Run n Gun]

FWIW here’s my experience with different crimps and West Coast’s 200gr plated SWC. I bought a box of 500, came home and ran them through my Dillon that was setup for LSWC without changing anything. The taper crimp was set at .469. I went to the range, and from sandbags at 10yds was grouping 1 ½”-2” with 25yd groups going 6”-7”. My Kimber Gold Match usually shoots MUCH tighter than that. Then I remembered when I ordered them that Red said to “go easy on the crimp” so I loaded some more at .471. Now that’s ONLY .002” and that was the ONLY change I made. The 25yd groups shrank to 1 ½” and the 10yd groups were about 1 ½ BULLET WIDTHS!

I know that you are having other problems (good luck with those) but, at least from my experience, don’t OVER crimp the plated bullets.

Ed

[Skywalker]

I agree with Flex:

cutting the copper plating is not what you'd want to.

Actually, if the copper plating rips during firing (due to excessive crimp) the bullet will probably not engage the rifling in the proper way.

This happened to several Modified shooters here in Italy in the early days of copper plated bullets: too thin plating, too much crimp, too light bullets (145 grs) and voilà, the copper plating was separating from the core at crimp level, giving erratic velocities and keyholes on targets.

[Steve RA]

You might also try roll crimping instead of taper crimping.

[Sarge]

You might also try roll crimping instead of taper crimping.

You realize this thread is like seven years old right?

[RePete]

You might also try roll crimping instead of taper crimping.

That will definately cut into plated bullets, stay taper crimp.