What are the effects of brass that is shorter than reccomended?

[headhunter1111]

Hello fellas,
been a while since I was on last. I recently formed a few rounds for a 22 Cheetah from .243 brass and thought I'd try trimming all of my brass down to length before forming the cases, thus reducing the amount of neck that had to be resized (this was all done after having crunched a couple cases in my FL die). This did not solve the problem and only after switching to my NK die w/o the expander and then back through the FL die was I able to size them without making an accordion out of the shoulder. The moral of this story is, the brass that I trimmed ended up being 18 thousandths below the prescribed trim length so rather than being 1.976 they measure 1.958 or so... Whoops. So, my question is, what will this do to accuracy, pressure, velocity, etc, etc? These rounds will need to be fireformed and I know that will push them out by about 5 thousandths so i will only be .023 below maximum length and this is where I walk away cursing myself under my breath and hope my gut feelings are wrong... thanks beforehand for any info you have.

 

[TonyR]

Excellent question. I know that brass that is too long can cause significant problems if the bullet can't release properly but this seems to be a different sort of problem. I have about 0.035 clearance at the end on some of my cases and I haven't seem any problems yet. Tony Boyer talks about a ring of carbon that can build up in the space between the end of the case and the end of the chamber neck that must be cleaned carefully in order to avoid accuracy problems. He recommends using a brush sized to the chamber neck instead of the bore to clean this area. He says that he uses his borescope to check this area carefully after cleaning. I'd be interested to hear other opinions.

 

[fdshuster]

Yes, a ring of carbon will build up in front of the case mouth. The longer the gap, the more severe will be the buildup. I've watched it happen with my borescope, and the reason why when I spec my chambering reamers, the chamber O.A.L. is kept at .010" longer than max case length. No different than firing a large number of 22 shorts in a long rifle chamber. I have no way of proving that it effects accuracy, but if severe enough seems like it must effect pressures.

 

[artbosco]

the brass that I trimmed ended up being 18 thousandths below the prescribed trim length...what will this do to accuracy, etc?

Nothing. In fact, it just might improve it.

Jack Neary, the latest Benchrest Hall of Fame member trims his 6PPC brass 35/1000ths shy of the end of the neck chamber that his reamer cuts, and it put him in the HOF. His reamer cuts to 1.525" and he trims to 1.490".

Listen to him describe his story in parts One and Two of these videos, which, by the way, transition automatically into the next one: http://www.youtube.com/view_play_list?p=7D85822FD9E41FF2

Listen to both parts. The statement I made about 35/1000ths starts with an explanation of his trimming method and "trim to length" in Part One, but doesn't mention his reamer's neck length, until about 4 minutes and 30 seconds into Part Two.

Although he talks about the 6PPC, many techniques can be carried over into other cartridges.

 

[tenring]

If you buy a new reamer, always ask for the reamer print. Or ask your smith for it. This will show you the length of your chamber. I initially trim about .015" short of max length; after first firing, I trim a few thou again to uniform them. With a SAMMI chamber, I trim about .020" just to be safe. The key is keep them all the same length. No matter how short the brass is, carbon ring build up is a given. If it feels tight or borescope shows it, try twisting your brush instead of pushing straight thru. I put OMC carbon cleaner on a brush and let it sit for half hour before wiping it out.

 

[MGYSGT]

While trimming some brand new 6BR Lupua brass, The set screw on my trimmer loosened and I cut a few shorter than the others by about .020 of an inch. I refuse to throw away new brass, so I marked them and loaded them the same as the others. Thought I would use them as fowlers, but they shot to the same POI as the longer cartridges. Only a small test, but I will worry less about small differences on cartridge lenghts now.

 

[headhunter1111]

Interesting stuff fellas. I will shoot them as soon as possible and let you know what happens.