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Advanced Reloading Forum

New Tool

Advanced Reloading Techniques for long range shooters and more

New Tool

Postby Shepard » Sun Jun 16, 2013 11:51 am

In my last post I wrote about case length being different according to the information proved by the powder or bullet manufacturer. The numbers in load book USA vary up to .024 of an inch depending on who's writing the data. Why do you trim your cases? I trim so the brass does not start to move or flow in to the bore and cause accuracy or over pressure problems.

Some of the re-loaders here have said that they have problems getting a good over all length because -- basically they don't have a case long enough. If you knew how long the chamber is --- you can trim your brass to fit your gun.

I made a tool to measure the neck length of your chamber so you can grow your brass so it fits your chamber better and to achieve a longer OAL if you need it. It's close to the OAL tool we use to set how far off the lands we set our bullet in the case. I have measured a barrel that has been removed and an action I'm going to use in my next build. The barrel measures different then the whole action meaning not every chamber is the same length. Here are some pictures of what I have done.

Let me know what you think and if you think this would help in your reloading efforts.

Remember that you have to add .064 to the number to add the case base length.
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Re: New Tool

Postby ShootnMathews » Sun Jun 16, 2013 2:23 pm

Just remember the case is going to stretch when you shoot it. Lots of factors determine how much it will stretch so its hard to predict. Some Factors but not limited to only this lists: if the brass is annealed or not, if the brass was neck sized or FL sized, how hot the load is, bullet size. Just make sure that the brass is short enough that it does not stretch to the lands and pinch the bullet causing pressure spikes.

I can see where your gauge would help some in those guns with super long throats. It would give you a little more brass on the bullet

Jared

Looks very finely made I'll add, great job. :thumbup:
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Re: New Tool

Postby Shepard » Sun Jun 16, 2013 3:36 pm

In measuring the test barrel I was amazed at how much room there is in front of the brass. Brass grows each time its fired -- new Lapua brass out of the box measures 2.087 + or - a few thou. The first time I fired it the brass grew about .010 as it filled the chamber for the first time. After that it grows a few thou each time its fired. The test barrel is a 1954 Romanian M44 barrel with lots and lots of mileage left in it. The total length of the chamber is 2.171 long --- Lees trimmed brass is 2.114 long. That leaves you with .057 space in front of the brass -- it will never stretch that far in one shot so you can grow your brass .040 and still have .015 in front of the brass. You'll have to trim your brass every other firing.
Firing new brass out of a new chamber leaves me with cases that only size the neck of the case. The die doesn't touch the body of the case. I have PPU brass that was fired out of a 91/30 with an original barrel and chamber. These cases sized hard as they full length compressed to size. The chamber is definitely out of spec in size compared to a fresh reamed one. The one thing that I have thought tho is that the gun has to fit ammunition from other countries and the last thing you need in combat is a weapon that doesn't chamber its round.
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Re: New Tool

Postby 0933 » Sun Jun 23, 2013 12:13 pm

Jerry, you are definitely right!! :thumbup: The chambers from stock soviet Mosins are GENEROUS... I've been measuring different case dimensions from fired brass out of different Mosins, and ALL the Russian Mosins have quite generous chambers.

It seems like the UK-59 barrels (once trimmed for chamber length) are a little tighter, and the Finn barreled Mosins are the tightest. Measuring the dimensions of my reamer, I find that it is quite a bit tighter than the russian chambers, and about on par with a Finn M39 (I've only had a chance to measure cases fired out of two rifles though).

As far as your tool, it looks great!! :thumbup:

I typically trim my brass for consistency when crimping, or to make sure that the neck is not long enough to influence the bullet/throat relationship... Benchrest guys however will go into great depth on the whole neck chamber thing. Custom cutting chambers, neck turning to match, trimming untill the neck is a perfect length, etc. I'm not convinced that even .020" of distance between the case mouth and chamber (lengthwise) would affect accuracy that much... however most people that are going for accuracy either pay someone to do it right the first time, or do it themselves right the first time. ;)
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