Need help with 450 Bushmaster loads.

[ar15barrels]

The 45 Pro as does the 450b have a freebore of .200", which usually means poor accuracy

Long throats are only detrimental when they are oversized and let the bullet bounce around.
A properly centered and sized throat which has a lot of freebore will not necessarily be detrimental to accuracy.
One reason to seat bullets out to touch the lands is that you force the bullet to center up in the barrel where it would normally have 0.001" or more to move within the throat.

[Wildcatter]

Jagermaster,

Of course 60,000 psi is high, although many of us think it is not Danger High. The barrel does not have any problems at these pressures. The .284 specs are 63,000 psi and that includes mountain barrels that have the same chamber dia as does the 450b and then gets smaller than the 450b out to the muzzle. Also consider the 460 S&W's pressures which are in the 60,000 arena. Which do you think is more durable the S&W or an AR? However, having said all this, I would not try to load for 60,000, until you become much more experienced. The only real consideration is bolt thrust. The .223 psi. spec. is for 52,000 psi and if one were to load the 450b for this spec, the bolt thrust will be way lower than the .223's, as per the copper crusher studies as sited by Wayne State University and re-quoted in the gun rags. These were studies done with a special copper crusher placed on the bolt face and then firing the cartridges, so as to compare the 223 to the 45Pro. This was done after they realized that the standard bolt thrust formulas did not apply. I suppose they had to re-learn the principal that bottle necked cartridges have much more thrust. So, maybe this will be over simplified, but in the example of the 450b, not any other AR cartridges, if you have enough wall thickness in the chamber and have a straight case, one can indeed pump up the pressures and stay in the safety margins. That’s the trick, safety margins. The arm chair warriors will do all the nay-saying and because they cannot do it, then neither can you, but I tell you this, it takes guys like you, with the guts, to find out that there are paradigms’ out here and were all along, that are being broken and will yet be broken.

PS. Try sizing the Hornady 350gr. 458 bullet to 452. You are only shrinking them down .003" per side (less than half the size of a human hair) and doing this with other similar bullets has not shown jacket problems in flesh. I don't think this will work with copper/brass solids; of course this trick is only if you just have to have heavy bullets and want to fully realize the full potential of the 450b. Good luck.

[ar15barrels]

Jagermaster,

Of course 60,000 psi is high, although many of us think it is not Danger High. The barrel does not have any problems at these pressures. The .284 specs are 63,000 psi and that includes mountain barrels that have the same chamber dia as does the 450b and then gets smaller than the 450b out to the muzzle. Also consider the 460 S&W's pressures which are in the 60,000 arena. Which do you think is more durable the S&W or an AR? However, having said all this, I would not try to load for 60,000, until you become much more experienced.

The only real consideration is bolt thrust. The .223 psi. spec. is for 52,000 psi

Commonly used maximum bolt thrust loading on AR-15's is 7000 lbs.
A 223 at 55,000 PSI makes about 6300 lbs of thrust.
7.62x39, 6.5 Grenade (grendel) and 6.8 SPC all run right at 7000 lbs.
Using the same formula, a 450 Bushmaster at 60,000 PSI makes 11,775 lbs of thrust.

As a comparison, a 308/7.62x51 makes 10,500 lbs of thrust.
308's use a bigger bolt for obvious reasons...

[Slash2]

I am seating the hornaday 240 XTPs to 2.017" I don't think the 450B has much freebore, the factory rounds only show about .025" before they start to taper. I am loading 36.5 H110 at 1950ft/s. I am staying there because these rounds print on target the same place as the factory rounds. My groups are running abou 2". The same as hornadays factory rounds in my gun. I don't need more speed, I'm Happy.

Went to the range today, 36.5 h110, 240 XTP/MAG, 2.1 OAL.

I didn't crony them, but I got a ragged hole with a four shot group at 100 yrds using bla's recipe. The factory rounds gave me a 1.5" group about 1.5" to the right of the hand loads.

Now, I can understand different loads giving you different altitudes, but different loads being off left to right? What makes one load go left or right more than another?

[ar15barrels]

Of course 60,000 psi is high, although many of us think it is not Danger High. The barrel does not have any problems at these pressures.

All you need is some of that special GM steel to make bolts and barrel extensions and the gun would hold together.
Regular AR-15 bolts and extensions will never hold pressures like you are talking about.

Hi Tim.
Welcome to the fray.

For those not aware, Wildcatter is none other than Tim LeGendre of LeMAG FIREARMS LLC

He loves to push his high pressure 45 professional, but often forgets to mention that it takes a special bolt and barrel extension and that the high pressure rounds would be unsafe with regular parts.

[Boarding-Team-Leader]

Nothing to do with the BM....

Slash2
Nice meeting you and the other two CalGunners today at the range. That 450 puts out some muzzle blast. I was at the forward portion of my lane looking for fired brass (adjacent to yours, left side) when you sent one down range. Glad I was wearing the plugs and muffs. I saw the muzzle blast as well as felt it... big blast.
BTL

[Slash2]

Slash2
Nice meeting you and the other two CalGunners today at the range. That 450 puts out some muzzle blast. I was at the forward portion of my lane looking for fired brass (adjacent to yours, left side) when you sent one down range. Glad I was wearing the plugs and muffs. I saw the muzzle blast as well as felt it... big blast.
BTL

I've been told that I don't even have to hit what I'm shooting at, the muzzle blast alone will scare it to death!

[jagermaster]

thank you ar15barrels.
You have cleared up some very important facts.
At first glance to a novice like me Wildcatters info is very intreging.
Tim if you would like to shear some safe loads with the forum that would be great, we would love the help.

[Wildcatter]

Thanks for the welcome Randall, I've enjoyed your expertise...Just to be clear, one can never really fully prove all the engineering wonders in a forum like this, it wouldn’t matter to some, that you state, Leonardo Da Vinci painted the Mona Lisa. There are some who would belabor the point and then insist that you prove it. I’m not suggesting you are like that at all, it’s just that I want to make a point that will bother some others.

We have not used those special steels for some time now. If you were to follow my examples you’ll find that the 450b at the 52-55,000 psi does indeed exhibit much less bolt thrust than the 223 and the only way you can prove that is two ways, both subjective in nature. First, the copper crusher test and second, is the absolute fact that we have “Never” had a bolt failure.

To say otherwise is to also ignore my examples of a .284 Mountain Rifle and the 460S&W analogies’, which are also subjective.

But I tell you what, between you and I we may be able to solve Slash's loading problems, which as I have pointed out are not low pressure related, I think, assuming we have all the details, subjectively speaking, and the fact we are not standing at his bench, we never will, but we'll help some.

[ar15barrels]

Just to be clear, one can never really fully prove all the engineering wonders in a forum like this, it wouldn’t matter to some, that you state, Leonardo Da Vinci painted the Mona Lisa. There are some who would belabor the point and then insist that you prove it. I’m not suggesting you are like that at all, it’s just that I want to make a point that will bother some others.

I disagree on Bernoulli's principal being the main reason you can get away with elevated pressures that SHOULD be blowing bolts to smithereens.
I believe that the case shape with that nice large cylinder is also playing into it by having really good chamber wall adhesion.

My simplified bolt thrust comparison spreadsheet is only a means of comparison and therefore it does not take chamber adhesion or Bernoulli into account as I don't have a realistic way to quantify those factors.
My spreadsheet calculates thrust more like what you would see with oiled ammo.

I would love to have access to a lab where I could run tests by changing cartridge shape and controlling for pressure to be the same.
It would be eye-opening to know what actual changes you see in bolt thrust loading.

There's always the issue of feeding though.
It's impractical to design some cartridge that has great performance and minimal bolt thrust if it won't feed from a magazine...

[Wildcatter]

Once again Randall, I'm with you. Bernoulli does not explain it all, and really says more about why bottle necked cartridges have less adhesion, as you call it. It is only an engineering guess as to why there is less bolt thrust in the 450b example, making your logic probably correct and very intuitive, on your part. The fact that we can achieve the increased pressures/speeds without blowing the bolt apart is only part of the total equation. One also needs enough steel left over in the chamber to achieve the pressures in the first place. Example, we could chamber an AR in 50 BMG and shoot it, but the pressures and bullet speeds, would be very low, if the AR were to survive, making this exercise wasteful. It appears that the 450b is very close to the end of the line, in this pressure curve idea, before you get into Diminished Returns. Example, same thing happens if far too heavy bullets are used. We could probably build a 1500gr bullet for our test, only to find that, sure it functions the weapon, but what about the speeds? So what is the perfect weight for this family of cartridges, in an AR? The answer in part is in bullet construction and its speed. There are problems in all of this, of course, 300-350gr bullets are great, but if they were design for pistol speeds, they will just blow off the shoulder of a big game, with no penetration, letting the animal to die much later, very bad scene. Thus, the hollow point bullets in .451 cal’s, just are not the one’s to use on big game, that is, at the speeds I’m talking about, unless zero penetration is desired. However, FMJ’s penetrate everything and at these speeds are very cheap and cause catastrophic internal damage, surprisingly with very little meat damage, comparably. I really love the FMJ-FP most of all.

[ar15barrels]

Bernoulli does not explain it all, and really says more about why bottle necked cartridges have less adhesion, as you call it. It is only an engineering guess as to why there is less bolt thrust in the 450b example, making your logic probably correct and very intuitive, on your part.

We observe from experience with the TC contender/encore that when you cut an ackley improved type chamber with straighter walls and load to similar pressures as the parent case, that the thrust actually reduces.
We attribute this to the fact that the angle of the case body changes to a degree that internal pressures are no longer pushing the case rearward out of the chamber, but just making the case stick in the chamber.

You must have read your PO Ackley along the way right?
Remember when he backs out the 30-30 barrel from the receiver and extends the firing pin?

[Wildcatter]

We observe from experience with the TC contender/encore that when you cut an ackley improved type chamber with straighter walls and load to similar pressures as the parent case, that the thrust actually reduces.
We attribute this to the fact that the angle of the case body changes to a degree that internal pressures are no longer pushing the case rearward out of the chamber, but just making the case stick in the chamber.

You must have read your PO Ackley along the way right?
Remember when he backs out the 30-30 barrel from the receiver and extends the firing pin?

[ar15barrels]

I don't know for sure.
I can tell you that the 50 Beowulf or 502 Thunder Sabre will start blowing out case heads due to the extremely rebated brass before it will run into bolt thrust problems.
Not sure about the 500 LeitnerWise as it did not really get sold in volume.
458 Socom runs a larger case head which solves for case problems, but then weakens the bolt by removing a significant portion of the lug roots.

[Wildcatter]

I don't know for sure.
I can tell you that the 50 Beowulf or 502 Thunder Sabre will start blowing out case heads due to the extremely rebated brass before it will run into bolt thrust problems.
Not sure about the 500 LeitnerWise as it did not really get sold in volume.
458 Socom runs a larger case head which solves for case problems, but then weakens the bolt by removing a significant portion of the lug roots.

Interesting. I was taking to Pete Pi about a year ago and Starline was having some kind of a problem with the SOCOM Brass or was it the 50B brass or both, I forget. Anyways, something about splitting, supposedly they have corrected the problem. Do you know anything about that?