Modern Sporting Rifle Evolution
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Dogtired

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Soooo....I recently finished my Mongoose build and am wondering, do I need to and how precisely do I check headspace on this gun? It's an issue I haven't quite wrapped my head around yet (the checking headspace thing). I have a friend with a 556 "go/no go" gauge, will that work?

Also, I have a Forster case trimmer set up, and am wondering how I go about setting things up for trimming Mongoose brass? Should I get a Hornady modified case on the site and use that as the guide to set up the trimmer? Do I do that before or after fire forming the brass? Should I trim after running through the die, after fire forming, or both? Once I have the initial brass set, how often do I trim, and to what length?

Also, I've seen that some people run the brass through a 222 die at some point to avoid the donut. Is that useful? Useful enough to buy a 222 die? When do you use it?

A fine gentleman sent me about 80 pieces of fire formed brass to get me started, but I will need to get experience making brass myself at some point. I figure I may as well get started when I first take this to the range to start load development, but need to prep some more brass first.

Any brass work better than others? Any I should avoid? I have a bunch of once fired LC and once fired Perfecta. Probably a lot more too, just need to sort it.

Also leads to the question of load development... But I need to see what powders I have. R-15, Superperformance, Leverevolution are three I know I have in plenty... Also a ton of various military powders...A conversion for another thread, perhaps...

Like I said, stupid questions, but I gotta start some place [smile] Thanks in advance!
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BIGGDAWG

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Reply with quote  #2 
here are the specs

Max case length1.700
Trim to case length 1.69

that said on fresh brass i trim to 1.693 or so because when fired they shrink because the case is expanding. you want to form your cases then trim, check after firing and they will shrink at first after that they don't seem to grow much because of the 40 deg shoulder.

no you don't have to check head space. you load to your gun I do recommend for all reloaders to have the hornady headspace kit  https://www.midwayusa.com/product/479704/hornady-lock-n-load-headspace-gauge-5-bushing-set-with-comparator for the mongoose you use the 330 adapter.  i set my new formed brass to 1.421, then after firing you measure the cases again and subtract .003 and that is what you should resize to. 

as for the shoulder bulge on new formed brass it is nothing more than cosmetic don't hurt a thing

you can check out the data book for some load data and you can also use 6x45 load data to start too.  https://docs.google.com/spreadsheets/d/1dEmHCV3VyJP1s-RTpxW8G68UQ-cd1cfMfP25hDdiY9A/edit?usp=sharing

hope this helps if you need more info just ask.

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sleddoc

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Not sure if this is quite the topic for my question but what the heck. 
Bought a 6mm mongoose barrel about 6 months ago. just had no extra cash to move the project along.  When I received the barrel there was a sample cartridge in the box. ( so I thought)  Recently I bought some to me from me Christmas presents including a set of dies that were on sale ( so happy).   Went to the reloading shop tonight and one of the boys tagged along asked a ton of good questions while forming some 6mm brass. Then I remembered the sample brass. marked fc 223 rem , case length 1.737 , id on neck .280 .
Shoulder seems to be the same as 6mm, but 7mm hole. Thought maybe a 7 var case fell in box . But after reading it is based off a 308 or lapua case.  Any thoughts on what this case is? barrel is marked 6mm and a 6mm set on rifling looks correct. So I don't think I have any issues as for the barrel , just this odd case.
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MDWS

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Reply with quote  #4 
Quote:
Originally Posted by sleddoc
Not sure if this is quite the topic for my question but what the heck. 
Bought a 6mm mongoose barrel about 6 months ago. just had no extra cash to move the project along.  When I received the barrel there was a sample cartridge in the box. ( so I thought)  Recently I bought some to me from me Christmas presents including a set of dies that were on sale ( so happy).   Went to the reloading shop tonight and one of the boys tagged along asked a ton of good questions while forming some 6mm brass. Then I remembered the sample brass. marked fc 223 rem , case length 1.737 , id on neck .280 .
Shoulder seems to be the same as 6mm, but 7mm hole. Thought maybe a 7 var case fell in box . But after reading it is based off a 308 or lapua case.  Any thoughts on what this case is? barrel is marked 6mm and a 6mm set on rifling looks correct. So I don't think I have any issues as for the barrel , just this odd case.

Did you by chance buy a modified case with your barrel?  Is the base of the case threaded?  If so, that's a mod case to be used with the Hornady OAL gauge to measure seating depth, etc.

The neck is going to be slightly oversize so you can slide 6mm bullets in and out freely while measuring distance to rifling with different bullets.

If not, I'm confused.

Thanks!

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Cabob

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Reply with quote  #5 
7MM TCU, possibly?
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sleddoc

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Reply with quote  #6 
The case is not threaded for a modified case. just a primer pocket. I guess a 7 tcu is possible. I would have to look up measurements for a 7mm tcu case.
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MDWS

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Reply with quote  #7 
Quote:
Originally Posted by sleddoc
The case is not threaded for a modified case. just a primer pocket. I guess a 7 tcu is possible. I would have to look up measurements for a 7mm tcu case.

That's odd... if you ordered a 6mm Mongoose barrel and it is stamped 6mm Mongoose, you're good.  Whatever that random case is that fell in the box or whatever, who knows!

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sleddoc

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Reply with quote  #8 
Didn't think there was any problem with anything I ordered. just the odd case. I don't have any 7 tcu dies to form up a case to compare with. But after measuring it it sure seems like a 7 tcu just a bit short
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MDWS

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Reply with quote  #9 
Quote:
Originally Posted by sleddoc
Didn't think there was any problem with anything I ordered. just the odd case. I don't have any 7 tcu dies to form up a case to compare with. But after measuring it it sure seems like a 7 tcu just a bit short

Is it a fired WLV case maybe?  Fell in the box somehow?  This is fun...

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Cabob

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Reply with quote  #10 
If you form a 7 TCU from a 223 case that is at minimum length, 1.750, it will end up around 1.735-1.740 before it's fire formed. Then it runs about 1.730, sometimes even shorter. If the brass was formed when the 223 was 1.760 or so, add .010 to those measurements. I wish I could show you some cases, but they're at my Ol' man's. It's a great cartridge in a contender, either pistol or rifle! You may have a one-of-a-kind round on your hands!!!!
Good luck.
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RangerJoe

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Reply with quote  #11 
Quote:
Originally Posted by MDWS
Is it a fired WLV case maybe?  Fell in the box somehow?  This is fun...
That would be my guess too!

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