Part 2 Max velocity exceeded w/ starting charge

HARV6 · Feb 27, 2012

For those interested in the first post on the subject the first time, I figured I'd update you on the progress. I backed down off of 6.0 grains of unique to 5.5 gr, changed nothing else and got the following results. The first shot, like the last time was the fastest. This time it was almost 100fps higher than the average which was 1022fps . The other shots in this group were around 30fps of eachother. The primers on all showed the slightest bit of cratering, but nothing like before. This time however I had 4 or 5 failures to feed. Just leaving the slide open. Maybe an 8th of an inch. One actually closed enough that I didn't notice it hadn't fed properly, pulled the trigger and nothing happened...light firing pin strike left on the primer. So any ideas what would cause the failures to feed? I also ran the Blazer Brass 180's over the chrony for a baseline and they averaged 953fps. So as some of you mentioned, even though Frontier recommended to use FMJ load data I'm still a bit over pressure and will back off another .5 grains to get in line with plated/lead load data.

rcmodel · Feb 27, 2012

There is just no way you should be getting 1,000+ with 5.5 Unique/180 bullet.

Take the barrel out of the gun and chamber check the loads.

Sounds to me like they are seated too long, and jamming into the rifling.

That will keep the slide from closing all the way sometimes.

And also raise pressure and possibly give you higher then expected velocity.

rc

HARV6 · Feb 27, 2012

Thanks for a little more insight on what to look for RC. Can you describe how to chamber check a round? I imagine just drop a round in and see how it fits compared to a factory round? Maybe look for rifling marks on the bullets?

jerkface11 · Feb 27, 2012

I imagine just drop a round in and see how it fits compared to a factory round? Maybe look for rifling marks on the bullets?

Yup.

MEHavey · Feb 27, 2012

Sorry, guys, but 5.2gr of Unique will give you 1,000fps with
a 180 lead bullet--and out of a 4" barrel. (Check Lyman's if
you don't believe it.)

You are effectively dealing with a lead bullet.
Calibrate, and proceed from there.

~~~~~~~~~~~~~~~~~~~~
As to correct OAL and failure-to-close, it's either one of two things:

- The case mouth is not sufficiently taper-crimped in the final step
...(should be 0.420"-ish, and 1st thing to check)

- The bullet is not seated "quite" deep enough. After checking #1 above,
...drop the cartridge into the barrel/chamber and listen for a clean "plunk"
...sound at it easily seats home. If any resistance at all, gradually seat deeper
...until it passes the "plunk" test.

~~~~~~~~~~~~~~~~~~~~~

At 180Lead/Unique/5.5gr/1,000fps, you are unlikely to be having cratering problems
due to pressure. Quickload and Lyman agree there. I'd quit worrying about it and
just confirm crimp dimensions/OAL and shoot what is a nice moderate load.

.

longdayjake · Feb 28, 2012

MEHavey,

Do you shoot plated bullets?

I am thinking that RCmodel is probably right on this one. If the gun is feeding them into the chamber but unable to feed them all the way it is one of two things or a combination of the two. It could be they are seated too long or you didn't get rid of the bell in the crimp stage. (Post a picture of your loaded rounds that wouldn't chamber). Or, I have also seen where a sizing die does not properly size all the way to the base and you get a very tight fit at the base. This could also affect your pressures and velocities a little.

MEHavey · Feb 28, 2012

While the chronograph tells the tale, I've committed (in another Forum string) to grabbing some Frontier plated and running velocity checks against both the manual predictions and QuickLoad.

I note Berry's caution that their own plated bullets "fall somewhere between lead & jacketed" to use low/never exceed mid jacketed loads.
Note also that Rainier/Accurate Powder using their plated bullets for the 180/40S&W list powder levels waaaay lower than even starting loads for jacketed.
http://web.archive.org/web/20050502161132/www.rainierballistics.com/loaddataAA.htm

The OP's chronograph is desperately trying to talk to us.

Film at Eleven....

243winxb · Feb 28, 2012

After looking at both of your posts & photos, my thinking is your Ruger SR40 bolt face might have something to do with the appearence of the primers??

longdayjake · Feb 28, 2012

I note Berry's caution that their own plated bullets "fall somewhere between lead & jacketed" to use low/never exceed mid jacketed loads.
Note also that Rainier/Accurate Powder using their plated bullets for the 180/40S&W list powder levels waaaay lower than even starting loads for jacketed.

Both Berry's and Rainier are thinly plated bullets. If Frontier bullets turns out to be plated as thick as Berrys and Rainiers then I agree they should be downloaded a little. Also, did you measure the diameter of the bullets? They may be sized a little big.

MEHavey · Feb 28, 2012

Here is a visual comparison of plating/jacketing across some heavy African game bullets.

From left: 390CSGR, 370Frontier, 325gr Swift A frame, 300gr Hornady mag, 300gr Sierra and 300gr Speer

Some sources state Frontier plating is 0.006" thick

Other (http://forums.1911forum.com) sources note that recovered Frontier bullets show
the rifling having cut through to lead in every case. If that's the case (and the OP could collect
a few fired booolits and check), their structural properties are effectively that of the internal
lead core.

I'd compliment the OP for using a chronograph and recommend applying the Duck Test:
http://en.wikipedia.org/wiki/Duck_test

longdayjake · Feb 28, 2012

Sounds like frontier bullets are some of the thinnest out there. Both Berry's and Rainier claim to be at least .008" and those are considered thinly plated. If Frontiers are .006" then that would definately explain what is going on. MEHarvey is probably right about them reacting like lead bullets.

Plated bullets like Powerbond or X-treme are supposedly guaranteed to be at least .011 thick. With those bullets I have always used full power jacketed loads with good results.

Part 2 Max velocity exceeded w/ starting charge

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