what should 300 blk brass measure with the hornady headspace comparator?

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Bgd
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by Bgd » Sat Apr 07, 2018 1:48 pm

mr.revolverguy wrote:Though you have already ordered the case holders I believe this is worth a read as the 300blkout headspace is very important and not as forgiving as other cartridges especially if you have a Ruger American in 300blkout.

http://www.dayattherange.com/?page_id=5992

I agree with dellet though SAAMI spec states the headspace according to SAAMI spec is listed as 1.0789Min-1.0889Max as seen by the diagram in the article above.

Die setup is ultra critical I just decided to back my die out a bit, it is still in contact with the shell holder as it required very little adjustment. Following some die holder directions about cam over is junk especially with 300blkout. After firing in my rifles I make sure my case shoulders no matter the cartridge get's bumped back .002-.003. This even works for AR's.
Interesting article, thanks for sharing. seems like attention to die adjustment is very important with the blackout. All my bolt guns I just neck size after I fire them in the rifle. Since this is an autoloader I think I will shoot for a .002 bump like you suggest. Thanks!!
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dellet
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by dellet » Sat Apr 07, 2018 1:56 pm

mr.revolverguy wrote:Though you have already ordered the case holders I believe this is worth a read as the 300blkout headspace is very important and not as forgiving as other cartridges especially if you have a Ruger American in 300blkout.

http://www.dayattherange.com/?page_id=5992

I agree with dellet though SAAMI spec states the headspace according to SAAMI spec is listed as 1.0789Min-1.0889Max as seen by the diagram in the article above.

Die setup is ultra critical I just decided to back my die out a bit, it is still in contact with the shell holder as it required very little adjustment. Following some die holder directions about cam over is junk especially with 300blkout. After firing in my rifles I make sure my case shoulders no matter the cartridge get's bumped back .002-.003. This even works for AR's.
Just for clarity those numbers are for min/max chamber, not base to datum on a sized case. Using those for sizing without confirming chamber fit could be interesting.

Case min/max 1.0707"-0818".

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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by rlandry6 » Sat Apr 07, 2018 3:05 pm

I just finished forming a big batch of 300s using FC .223 brass. I used a RCBS Small Baae FL die to form the cases using the recommended set up of raising the ram all the way, touching the shell holder with the die, then lowering the ram and going down another 1/4 turn on the die for the press camover. Every case fit the slotted gauge perfectly. I got the same result using a Rock Chucker a Redding T-7. I checked every round using a Sheridan slotted gauge and all were perfect.
I don't worry about the shoulder getting bumped because if they are being shot in an AR, they need to be FL sized for every loading anyway.
Also, as a side note, thanks to rmustin for turning me on to the Sheridan gauges. It's the best $60 you can spend for a bench tool. I'm going to order one for .223 and also the Creedmore. Looking for someone who wants to by a couple of Wilson case gauges.. LOL Actually the other case gauges work fine as far as doing the plunk test for length sizing, the the Sheridan actually lets you see if the shoulder is at Saami spec.
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dellet
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by dellet » Sat Apr 07, 2018 3:55 pm

If you don’t load too far over max pressure, and are not over gassed, you can neck size only in an AR.
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by Bgd » Sat Apr 07, 2018 4:18 pm

dellet wrote:If you don’t load too far over max pressure, and are not over gassed, you can neck size only in an AR.
i have an adjustable gas block and try to stay under max pressure always. i have always heard with AR15's you cant neck size only so i have never tried. gues it is worth a try. i was always afraid the bolt may not close all the way on a round if it was to big to fit in the chamber.
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by dellet » Sat Apr 07, 2018 5:10 pm

Bgd wrote:
dellet wrote:If you don’t load too far over max pressure, and are not over gassed, you can neck size only in an AR.
i have an adjustable gas block and try to stay under max pressure always. i have always heard with AR15's you cant neck size only so i have never tried. gues it is worth a try. i was always afraid the bolt may not close all the way on a round if it was to big to fit in the chamber.
It’s tough with a bushing die since most don’t size the full neck. If you have a die that will get the whole neck and touch the shoulder it’s easier.

Slowing down the bolt to give the brass time to shrink before it extracts is the key. Something else that helps that I use is an LMT enhanced BCG. It fully supports the case head using a different extractor and then the pathway for the cam in the carrier has a slightly longer path. The bolt takes longer to open.

If you try it, pull your upper, size your brass and chamber it with finger pressure. That way if you need to, you can tap it out with a cleaning rod.

Ultimately I think I have better accuracy with a full length sizing and bushing neck, but I tried it and it was possible. 3-4 firings before a full sizing was needed.
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by mr.revolverguy » Sat Apr 07, 2018 9:04 pm

Good call Dellet.
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by nksmfamjp » Wed Apr 11, 2018 1:32 pm

1.0818 +0.0000/-0.0070 @ 0.3512 diameter is what I see.

Since Hornady doesn’t make that bushing, I would use the one between 0.3619 and 0.3340. Then measure a fired case. All fired cases should be within 0.001, or you have issues, I think. Then target fired -0.003” for nominal. I don’t think you need that fancy shellholder, but what do I know...

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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by dellet » Wed Apr 11, 2018 4:50 pm

nksmfamjp wrote:1.0818 +0.0000/-0.0070 @ 0.3512 diameter is what I see.

Since Hornady doesn’t make that bushing, I would use the one between 0.3619 and 0.3340. Then measure a fired case. All fired cases should be within 0.001, or you have issues, I think. Then target fired -0.003” for nominal. I don’t think you need that fancy shellholder, but what do I know...
If you size your brass to 1.0818", you will have issues. Min. Chamber is 1.0789".

1.0707" is the reference number for for the datum line on the cartridge.

Hornady's gauge insert to use is .350"
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Re: what should 300 blk brass measure with the hornady headspace comparator?

Post by nksmfamjp » Wed Apr 11, 2018 8:04 pm

nksmfamjp wrote:......Then measure a fired case. All fired cases should be within 0.001, or you have issues, I think. Then target fired -0.003” for nominal. I don’t think you need that fancy shellholder, but what do I know...
That is my real advice....

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