Berry's 180 gr Flat Top in G20 explainin why slighty longer OAL fails battery

[Clint007]

New to 10mm. For that matter new to Glocks also. I have a new G20 with new KKM barrel. I loaded some Berry's 180 gr flat top bullets. I understand that 1.250" is the rec max OAL. I always start with measuring the max OAL for my barrel by measuring the max length with 5 'push test' rounds using a fired case and bullet. I learned that with this bullet in the KKM, the max oal before the bullet would hang up is 1.360".

1.25" with this bullet puts the case mouth almost onto the ogive of the bullet (it's a truncated cone design). So I lengthend a round to 1.275" and assumed - because they plunked well at 1.360 - that this slight variation would not be a problem for loading.

But these 1.275" rounds will not go into battery. Even tho the bullet appears to drop into the removed barrel easily and fully, like factory ammo. I"m used to too long bullets 'hanging' on the lands but these didn't do so yet would not go into battery.   And they fit into the mag well, and even without the mag (dropping into the chamber through the breech) they don't go into battery.

When I shorten to 1.260" they all go into battery fine.

Can anyone recognize this issue and can explain it to me?  Or do I need to go back and test this again to make sure I didn't mess something up...Because if a round passes the plunk test, I have to assume it should go into battery normally, because the rim is at the same height from the breech face as the factory ammo that chambers fine..

[The_Shadow]

Clint, first the cartridges have to fit the magazine for the 1911 45 ACP ball ammo the 1.275" length was fine.
I think you are saying the Berry's 180 seated to 1.2500" is crimping on the smaller diameter of the ogive.
Seated longer they will likely change the tipping angle as they feed into the chamber even though they fit the magazine.
What is the shortest COL you can do and not have the crimp on the ogive.  1.2600"?  1.2620"?
You might need to play with that length till you find a happy place of load them or trade them for use in 40 S&W where the bullets can be sticking out further.

However when you have bullet with flat noses or Truncated Cone the length maybe shorter because of the wide area of the flat point.

[Clint007]

Thank you. Great info....

Yes the crimp is now just a frogs hair from the ogive, but still on the bearing surface of the bullet.

The curious thing is that I also dropped it down directly into chamber and the G20 still won't go into battery.

They work now at 1.260...but not at 1.2750.  But for reasons I didn't expect. I figured it WOULD be a problem fitting in the magazine, from what I've read.  this bullet plunk tested far longer (1.30"+)and sits flush into the chamber like a factory round with barrel remove. I wasn't expecting the battery problem.  This is new Starline brass BTW.

Thx

I only bought a few as I work up some loads so i'll See how they work.

[The_Shadow]

If you are dropping rounds into the chamber and letting the slide run up into battery, please don't!  Here is why...
The extractor has to try an jump up and over the casing's extraction rim.  This can possibly damage the extractor either bending it out of adjustment as on 1911 and other types or can break or chip the extractor itself.  Some pistols can handle this better than others, but it should be avoided.  Just so you know!

The firearm is designed to feed from the magazine and the casing's rim slide up the breech face and under the extractor.

You mention you are working with new Starline brass, it is great brass.  Do you have a good caliper to measure your cases?  They can be had at harbor freight for as little as $9.99 on sale with coupons in their sale papers.

Have you measured the case around the diameter at the mouth?, where the base of the bullet sits inside?  This measurement over 0.4230" may indicate that the crimp is bulging the brass somewhat.  The forward area of the chamber can be tighter than the entrance.

While using the barrel as your gauge is OK, nothing compares to a true cartridge case gauge, as their dimensions are much tighter tolerances than any barrel chamber!

You can try backing off your crimp, (the brass headspaces on the case mouth edge) and try seating your bullet and test the fit as well.

While the bullet may look like its ogive is at or slightly below the edge casing's opening, as long as the casings tension on the bullet is the important factor.  Because the crimp is there to push the casing back against the bullet, for feeding purposes and not so much to secure it in place, although it does...

The edge of the casing mouth as pressed against the bullet should measure 0.4215" on the tight end and 0.4225" as almost straight with the very slightest taper crimp.

I hope you find this info useful...

[Clint007]

Shadow, thank you this is useful info. I have a 1"-0001 micrometer.

I typically set my crimp (de-belling) only enough to gauge well, then measure the mouth to double check I'm within a thou or so of spec.  In this "case" (har har) I'm at .4225 which I accepted.

Thank you I didn't realize that chambering from the breech wasn't a good idea.....

Where again on the case does one measure for pressure expansion....down on the web?  I cannot find that thread here now....which I saw earlier.

Lastly, one of my test rounds didn't chamber, and I discovered that some of the plating actually shaved and bunched up on the ogive. Never saw this with 9mm plated before...lead and coated, yes. And I thought I had belled the case enough, too. Is this a nuance issue with 10mm?  I have used oversized expanders on occasion with coated bullets in 9mm for select bullets. It was sometimes relevant to users if the U die also. Just curious if there is something I should be doing differently. I chose the Berry plated mainly because they were cheap, for practice...

C

[The_Shadow]

Yes cast bullets and plated bullets can shave on the case mouths, the balance of case expansion, bullet diameter and pushing them down into the casing without the seater / crimp die causing the casing to start closing against the moving bullet all play a part.  Glad you found that issue on the non chambering cartridge...

Usually pressure will cause the cases to expand and fill the chamber to seal it, it is when they expand beyond the chamber size that they will show brass flow where the casing was sitting over the feed ramp at the 6 o'clock.  This measurement is different for different makes of barrels.

The Glock factory barrel chamber that max is usually 0.4340", my S&W 1006 is 0.4280", any thing larger is pushing the limits of the brass.
Primers are not real reliable but attention to them is still viable to examine...Primer pockets can also expand and loose seating primers are of concerns.
Brass can also be very different, Starline new brass is very malleable / soft, this is because it is a reloaders brass.  As you continue to resize after each use it will be come stiffer by work hardening.  This is why annealing is needed during the production and why rifle handloaders do it to soften the brass.

As you reload, the stiffer brass may not show the same results with respect to pressures acting on it.  Older NORMA & Winchester brass use to exhibit better strength with heavier loads.  The Norma may have been thicker in the web and Winchester was stiffer in my using it.

[Clint007]

I have seen images of smileys. so it's this area, down at the bottom of the case where a smiley would occur due to incomplete chamber support, that should be measured in the process of working up loads. I did recall that 0.434 as one number of merit for overpressure indications.

I have a KKM barrel in the gun currently.

C

[sparkyv]

Great stuff, The_Shadow. I appreciate your expertise.