Barnes 200gr XPB and 275gr TSX

Talk about your 450b reloading experience, ask questions, etc...

Moderator: MudBug

Forum rules
Please try and keep it safe!

This information is the responsibility of the community, not the forum. 450bushmaster.net is not responsible if you blow yourselves up.

Re: Barnes 200gr XPB and 275gr TSX

Postby Bmt85 » Mon Sep 18, 2017 3:13 pm

To be able to crimp into the driving band of a 275 TSX, as Hoot talks about, you will be loading out to 2.33-2.34". To be able to run them in an AR mag, you will have to cut a groove out of the front of your mag. Unless of course you have one that is out of spec. I did this and only run the TSX's at that OAL. Never had a feeding issue. If you do load that long I would recommend upping the powder charge a few grains, though. You seem real low as is.
Bmt85
 
Posts: 701
Joined: Wed May 18, 2016 11:13 am
Location: S.E. Michigan

Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Mon Sep 18, 2017 3:31 pm

What type of powder/charge and resultant velocities are you guys getting from this bullet?
User avatar
mcb
 
Posts: 70
Joined: Fri Apr 07, 2017 10:22 pm

Re: Barnes 200gr XPB and 275gr TSX

Postby Bmt85 » Mon Sep 18, 2017 6:21 pm

Don't have velocities yet. Just picked up a chrono and haven't had a chance to use it yet. I do have load data, but it's out of my rifles, so proceed at your own risk.

275 TSX
Hornady once fired brass
Rem 7 1/2
OAL - 2.33"
.473 taper crimp
.473 stab crimp
With Win 296 I started at 85% fill (have to be careful how low you go with Win296/h110) which came out to 37.5gr
With Lilgun, I started at 36gr

If I remember correctly, your running a bushmaster 20" upper which has a carbine length gas system. So if I were you I would keep a very close eye on your case head growth. In other words, use a mic to get readings before loading, then again after firing and resizing.
Bmt85
 
Posts: 701
Joined: Wed May 18, 2016 11:13 am
Location: S.E. Michigan

Re: Barnes 200gr XPB and 275gr TSX

Postby Hoot » Tue Sep 19, 2017 4:58 am

In the case of my load experiments a while back, I could crimp in the groove with my 275 XPB bullets with a COL of 2.29. Again, you just need to see a sliver of it peeking above the mouth. IMHO, if an AR magazine can't tolerate a COL that is 30 thousandths too long, it is too closely toleranced. Never loaded the TSX. I always assumed the two were the same length. I never got too hung up on the 275gr bullets as they are overkill for whitetail deer. The 200gr at 2300-2500 is more than adequate for my needs. Most of the Minnesota rifle zone are woods. They still have more TKO than a 30-06. If you prefer to load the 275 too short to catch the groove at the mouth, you can catch the next one down with a side crimp.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 5083
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Tue Sep 19, 2017 7:14 am

Thanks guys. Went back and looked at my notes and my QL data and I am not sure there is much more velocity to be gained here while staying under SAAMI.

My load as stated earlier:
Bullet: Barnes 275gr TSX
Brass: Hornady (once fired)
Primer: Winchester Small Rifle
OAL: 2.260
Crimp: .475
Powder: Hodgdon H110
Charge 2: 33.5gr
Average: 1923fps (2257 ft-lbs)


When I plug this into Quickloads it tells me I am at 82% fill, predicts a velocity of 1951 fps and a pressure of 37,667 psi. Now me, reality, and Quickloads don't always get along but for 450 Bushmaster and H110 Quickloads has been pretty close to what published data with pressure I can find. This load in particular QL matched reality pretty close (only 1.5% high) If I was in a bolt gun I would not be afraid to go a little over SAAMI but in an AR with the relatively weak 450 bolt I am hesitant to push it much harder.

Would I be better off trying Lil'gun with this bullet? Seems Lil'gun works well with the lighter 200-250 gr bullet and for the heavies 300 gr and up H110/W296 are the choice but the 275 gr Barnes sits in the middle. Just and idea. QL seems to predict that Lil'gun might do better but then again QL's data on Lil'gun is dated given the perceived changes you guys have report with Lil'gun.

I will have to see how much more over the standard 2.260 length my magazines will allow. That might let me safely get another grain or so in there and get to 2000 fps. That said my current 1923 fps and 2257 ft-lbs is going to be more than enough to put some venison on the freezer this season.

On a side not it would be interesting what 450 Bushmaster would have become had they used the 30 RAR bolt and barrel extension rather than the current bolt. 450 Bushmaster would have been a real thumped at a MAP of 55,000 psi instead of only 38,500 psi.
User avatar
mcb
 
Posts: 70
Joined: Fri Apr 07, 2017 10:22 pm

Re: Barnes 200gr XPB and 275gr TSX

Postby Hoot » Tue Sep 19, 2017 9:52 am

This may have been mentioned earlier, but Tim aka Wildcatter, said that when he turned control of his 45 Professional design over to the manufacturers (Hornady/Bushmaster) their risk litigation attorneys castrated it when they dictated the safe pressure rating far below the 284 Winchester parent case. While Tim took that poetic license a little too much to the extreme by my standards, I can attest to the fact that you can safely load the AR 450b a lot higher than 38k.

To answer your other question. While H110 mimics factory ammo pretty closely, Lil Gun has ruled the roost for many members here who reload. I would venture to say that you could extend the weight class of bullets up to include the 275 XPB and TSX. That's where I got my best results. Unfortunately, QL over-predicts the pressure and velocity of Lil Gun. Using a taper crimp in a 1:24 barrel and solid copper bullets, you can compensate it out by changing your start pressure to 1000. Should get your predicted performance and field performance singing from the same sheet. With jacketed lead core bullets and a taper crimp, you can drop that start pressure to zero. That's right, zero.

Quick tip: 275 XPB/TSX, 40gr Lil Gun, again COL that almost buries the groove and .475 taper down into it. Really accurate and somewhere in the vicinity of 2200fps from my factory 20" upper.

Hoot
In Theory, there is no difference between theory and practice. In Practice, there is.
User avatar
Hoot
 
Posts: 5083
Joined: Tue Feb 09, 2010 9:34 am
Location: Minnesota

Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Tue Sep 19, 2017 11:05 am

I have no doubt the cartridge could support higher pressures but I am not sure the 450BM AR bolt can. 450 BM bolt lugs don't have a lot of support at the breach face end of the bolt due to the larger bolt face required by the 450 BM cartridge. I believe the 38,500 psi was selected because that gives you roughly the same bolt thrust as 5.56x45 mm at 62,000 psi. Combine that will the weaker bolt lugs and I not sure I would want to go much over SAAMI in an AR. I also think this is why they made the 30 RAR (55,000 psi) with AR-10 size bolt and extension.

I might also be being a bit overly cautious...
User avatar
mcb
 
Posts: 70
Joined: Fri Apr 07, 2017 10:22 pm

Re: Barnes 200gr XPB and 275gr TSX

Postby Bmt85 » Sat Sep 23, 2017 8:47 am

You are not wrong in your thinking, bolt thrust is a legitimate concern. However, there are a couple things to look at. If I remember correctly, bolt thrust is usually calculated with no concern to case geometry. 5.56 has a pretty good body taper and is shouldered. Compare a 7.62x39 to 5.56. 7.62x39 is again shouldered, has a bigger case head, and also has a lot more body taper. It runs at lower pressure, so calculated bolt thrust is a little more than 5.56, but they break more bolts (good ones not crap) than 5.56. Then look at 6.8 SPC II, bigger case head than 5.56, similar body shape to 5.56, can be ran up to the same pressure as 5.56, yet good bolts hold up. Now taking a 450 case that is straight walled and has less body taper leads to less bolt thrust. If you keep your chamber clean and dry, and shoot loads that completely seal to the chamber, you will have less bolt thrust, to a point anyway. So to say that the bolt thrust calculation is an absolute, is wrong.

Here's another example, I've had a couple factory rounds that had some serious leakage between the brass and chamber. They actually showed very slight imprinting. Those rounds probably equalled the equivalent of 5.56 bolt thrust. Now my 275 reloads using Hornady new brass are way over what would be considered max book loads, yet, my mid level loads show no signs of over pressure. My max loads show very slight imprinting. So if you clean and dry your chamber, and keep a close eye on everything, you can take it above rated pressure.
Bmt85
 
Posts: 701
Joined: Wed May 18, 2016 11:13 am
Location: S.E. Michigan

Re: Barnes 200gr XPB and 275gr TSX

Postby mcb » Sat Sep 23, 2017 12:23 pm

Bolt thrust calculations take into account case geometry. Typically bolt thrust is calculated as chamber pressure times the area of the case head. In the case of a rebated cartridge like 450BM many use the larger chamber diameter. Hence the reason 450 BM at 38,500 psi but a .500 diameter case produces roughly the same bolt thrust as a 5.56x45 with a much higher pressure (62,366psi) but smaller case head diameter of only 0.378.

This bolt thrust calculation is only approximate as it ignores friction between the case and chamber wall (and other lesser factors). That said bolt thrust reduced by case/chamber friction is proportional to chamber pressure since it is the chamber pressure that generates the normal force to generate the friction force so again 556 is going to have more thrust taken by friction than 450BM due to it higher operating pressure.
User avatar
mcb
 
Posts: 70
Joined: Fri Apr 07, 2017 10:22 pm

Re: Barnes 200gr XPB and 275gr TSX

Postby Texas Sheepdawg » Sat Sep 23, 2017 6:42 pm

4C1EDF7C-FC36-4605-AF6D-DC9446581D8F.jpeg
4C1EDF7C-FC36-4605-AF6D-DC9446581D8F.jpeg (1.39 MiB) Viewed 21225 times

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!!
-Texas Sheepdawg

http://youtube.com/c/TexasSheepdawg21
NRA Life Member
User avatar
Texas Sheepdawg
 
Posts: 4731
Joined: Fri Nov 05, 2010 10:55 am
Location: North Texas

PreviousNext

Return to Reloading for the 450b

Who is online

Users browsing this forum: No registered users and 25 guests