Barnes 200gr XPB and 275gr TSX

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Re: Barnes 200gr XPB and 275gr TSX

Postby Bmt85 » Sun Sep 24, 2017 2:25 pm

Bolt thrust calculations only looks at inner case head diameter and pressure. It doesn't take into account rim diameter, case taper, dry or oiled chamber, body taper, shoulder angle, etc. Its a quick and dirty way to get a comparison. If it was the end all, be all, number, a lot of us would be breaking bolts all the time.

As to chamber friction, your correct on pressure effecting it, however, you also have surface area to consider. 450 has a lot more surface area to grab with than 5.56.

I'm not trying to argue or push you, just trying to point out a few things. If you feel you have to stay at/under 40K psi, that is your choice. You will still have a potent hunting round, and as long as your having fun, who cares.
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Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Sun Sep 24, 2017 6:33 pm

There are certainly many nuance to calculating real world bolt thrust compared to the simplified calculation, but most of those nuances are second order at best, pressure times area is the first order factor.

When you look at the quick and dirty calculation (max chamber pressure times case-head or chamber area) for bolt thrust you end up with 450 BM being very similar to 556. I suspect this was a driving reason Bushmaster/Hornady set the SAAMI MAP to 38,500 psi when they created the new cartridge. This is much lower than its progenitor 450 Professional. I also suspect this is why the 30 RAR uses an AR-10 size bolt and barrel extension with its MAP of 55,000 psi. Now if you go and run your 450 BM up to 45,000 or 50,000 psi suddenly your putting loads on the bolt that are comparable to or greater than the thrust of 556 proof loads (125% or 62,366psi) put on that bolt. The lugs are at best equal to 556 lugs in strength and very likely weaker due to the larger case-head recess cut into the bolt.

It seems prudent to watch how much you over pressure 450 BM in an AR. In a bolt gun with a action that is designed to take bolt thrusts from other high pressure large case head cartridge I would think running 450 BM up to 50,000+ psi would be no problem. In an AR though the bolt is the weak link and must be considered.

I love the discussion; push, pull, and discuss this with me all you want, I don't mind. And yes my more conservative Barnes 275gr @1923fps are going to be joy to hunt deer with this year. :D
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Re: Barnes 200gr XPB and 275gr TSX

Postby Al in Mi » Mon Sep 25, 2017 4:03 am

Texas Sheepdawg wrote:
4C1EDF7C-FC36-4605-AF6D-DC9446581D8F.jpeg

This is for my bolt action and single shot. 40.0 grains of 1680 Barnes 275 XPB
2.272”. (Would never fit an AR Mag).
I have yet to test them over a Chrony but I fired one and when it hit the steel plate at 50 yards it sounded like someone hit it with a baseball bat. BOOONNNNGG!!


Dawg, for my 700 and #1, I've seated those 275's at 2.400 OAL. and 10gr more 1680 with no problems. 300MP has really been shining with those 275's too, no chrono data on either yet but soon.

Image
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Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Mon Sep 25, 2017 7:18 am

You guys need to post some chrono data. I am curious how 1680 works with the 275gr bullet.
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Re: Barnes 200gr XPB and 275gr TSX

Postby Texas Sheepdawg » Tue Sep 26, 2017 10:17 am

mcb wrote:You guys need to post some chrono data. I am curious how 1680 works with the 275gr bullet.

I Know.... dang. I’ve got loads piling up for testing.
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Re: Barnes 200gr XPB and 275gr TSX

Postby Al in Mi » Tue Sep 26, 2017 1:38 pm

once these 90*+ days get out of here, I plan to. Hopefully this weekend
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Re: Barnes 200gr XPB and 275gr TSX

Postby plant_one » Tue Sep 26, 2017 10:01 pm

1680 should do well with those. it tends to gets real happy with nice full cases under heavy projo's as a general rule
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