Ever Try This? FeedBack Sought...

[Christchild]

As many may likely know, I load .270 Win. I'm also a fan of the 110gr. Barnes Tipped Triple Shock... TTSX.

I have a good supply of AA4350 and AA3100. AA3100 is similar in Burn Rate to IMR 4831. I easily shoot 1/2" groups from a good rest at 100 yd.s, using AA4350 and the 110gr. TTSX.

I use 150gr. Norma Oryx for my Heavy-For-Caliber/Cartridge loads, and I've developed a load for them using the slower burning AA3100 that groups better than I can.

This is what I'm thinking. If my components were to "work themselves out" in a way that left me with AA3100 "left over" (scenario in my head) and I needed/wanted to use this slower powder with the 110gr. TTSX, what aspects/details/principals should I concern myself with?

I've read that using Lighter-For-Cartridge bullets with a slower powder, often times yields lesser accuracy. With that in mind, suppose I were to use a Large Rifle Magnum primer instead of just Large Rifle?

Could that possibly help ignite the slower powder, resulting in a Better/Safer Pressure Curve more suitable for lighter bullets, and help avoid some/all of the possible negative effects of the Slower Powder/Light Bullet combination?

[Pathfinder45]

Try it and see. Report results here. What's your barrel length? I load for .270 Winchester and .45 Colt almost exclusively. My best 300 yard load consists of 150 grain Nosler Partitions and CCI LR primers stoked with a stiff charge of Norma N-205 powder using Federal cases for about 3,000 fps. I have not tried any of the three powders you mentioned. However, I have used H-450, H-414, H4831, H-4831SC, WMR, IMR-7828, Reloder-22, Magpro, Hunter and perhaps others not so memorable. All of it is just OK at 100 yards. Most 300 yard groups open up considerably; mediocre to dismal. The out-standing exception is the afore-mentioned load using N-205. Of course, that powder was discontinued perhaps three decades ago, [Alas!]. I picked up a lucky find at the gun show that I hope will give Identical results: Norma MRP. Remember that your .270 was designed to be a long range number. Don't think for a minute that your best loads on paper at 100 yards will only be 3x bigger at 300 yards! It's alarming what can happen to those groups over the next 200 yards. Good luck with your experiments and let us know how it all turns out.

[Christchild]

My Browning A-Bolt received a 26" Douglas Air Gauge #4 Contour (Heavy Sporter) a little while back.

As soon as I get the time and opportunity, I'll load a handful of the cartridges with the 110 grainers, AA3100 and Large Rifle Magnum primers, and post my results here.

This thread has received quite a few views but You're the first to reply. I know for a FACT that there are many men (and a few women) on TFL that Flat-Out Know Their Stuff. I was surprised that this thread has been this INactive. I think this could be a good thing, because maybe, this could be new information.

I'm headed upto a friends house today, and MAY bring my rifle, for the SOLE purpose of gathering the information/load data/results to post back to this thread.

I hope I have the time/opportunity to "experiment". I'll post back soon.

My Rifle. http://www.thefiringline.com/forums/...0&d=1253840435

[Unclenick]

Normal concerns are that the lack of Newton's equal and opposite reaction force from accelerating the lighter mass means the powder won't burn fast enough to build pressure well. Slow powders require higher pressure to burn completely and consistently. The lower pressure means you will get more powder fouling and will need bigger charges that throw a lot of unburned powder out of the muzzle. Big fireballs result.

The other concern, though somewhat controversial, is the chance of developing serious secondary muzzle pressure spikes. Texas Gunsmith Charlie Sisk had some photos up on one of the forums showing muzzles he'd blown off .338's, an event he can reproduce at will. The theory is that the light bullet is shot forward so quickly by the rapid acceleration it has under the powder peak pressure that a large pressure drop occurs behind it. That is because the slow burning powder doesn't evolve gas fast enough to keep up with the rate at which the speedy bullet expands the volume behind it, and this pressure drop slows burning of the remaining powder, conserving its chemical energy. The bullet then actually starts to slow from lack of pressure adequate to overcome its bore friction. The forward-moving powder's velocity and inertia are not much damped, however, so the column of burning powder and gas catch up to and slam into the base of the bullet and any unburned powder that was traveling with it at its base. This causes a dramatic pressure rise local to the bullet base. It is the mechanism by which barrel bursts due to obstructions occur, as described in Hatcher's Notebook.

Some images of secondary spikes recorded by a strain gauge instrument are on the page linked to below. Some have claimed this is just a measuring artifact. However, between Sisk's experiments blowing muzzles up and the fact they appear consistently over multiple traces and the fact they always go away when either the bullet weight is increased or a faster powder is used, would make it appear they are authentic. They seem to be strain bulges traversing the barrel that were initiated by a very brief (0.1 milliseconds or so) pressure event further down the tube. The gas itself does not maintain this pressure all the way back to the chamber (it expands), so you don't see pressure signs on the case. That is why some have claimed they are a measuring artifact, but I don't think it is relevant, given the nature of the event and the volume of powder involved, which is not enough to raise pressure throughout the barrel to more than a few thousand psi. You may be inclined, looking at the traces, to think many should not be survivable by those barrels that don't break or bulge from the pressure? Again referring to Hatcher, he reports running regular Springfield barrels to 130,000 cup without damage. He also turned a Springfield barrel down to 1/16" wall thickness, fired three standard service rifle rounds through it (50,000 cup) without visible problems. It was not until he fired a 70-75,000 cup "blue pill" proof round in it that if finally blew out a piece of the barrel near the end of the chamber (Hatcher's Notebook, pp.201-202, 3rd Ed., 1962, Stackpole, Pub.). Steel is strong stuff in a cylindrical form not notched by threads.

Scroll down this page about half way to see the trace examples start.

[Christchild]

Wow.

Thank You, Uncle Nick!

That's the kind of information I need! Well, looks like it won't happen, at least not by MY hand.

I won't be testing the loads In Question.

[Christchild]

This is what I found when I clicked on the link Uncle Nick posted, then went to the Barrel Harmonics page...

The "Catch Up Theory"
We do not know if the above load suffered from an accelerated burn rate (problematic with some ball powders), but agree with ballistic engineers about the probable cause.

The area under the pressure curve directly relates to the energy imparted to the bullet. The rise to peak pressure engraves the bullet into the rifling and establishes it's initial acceleration down the barrel. The highest rate of acceleration occurs just past the point of maximum pressure. As the bullet travels toward the muzzle, lower pressure coupled with bore friction allows the rate of acceleration (not speed) to fall.

If there is insufficient gas produced by the powder (burn rate too slow), pressure behind the bullet will drop excessively. Then, as the bullet's rate of acceleration falls due to bore friction, gases may "catch up" to the bullet before it exits the barrel and produce a secondary pressure event. In the above load we believe the heat generated from initial ignition coupled with a secondary pressure event increased the burn rate of residual ball powder to near detonation.

Note: Secondary pressures readings taken at the chamber are lower and of longer duration then the actual event due to compression of gasses behind the bullet and the time required for expansion and contraction of barrel steel. The above event may have spanned only .1 milliseconds of time but could have reached 150,000 PSI!

Ball powders do not create the phenomenon of secondary pressures but the resultant pressures can be more severe. Indeed, secondary pressures can even occur when using large extruded powder. When using ball powders it is simply more critical that a powder with the proper burn rate be used to avoid secondary pressures entirely.

In every instance when secondary pressures are detected they can be eliminated by using a faster power, heavier bullet or a bullet with more bore contact area. Normal "tweaking" of loads may change the peak of secondary pressures but will not eliminate the problem. Below is the list of factors we now know can cause secondary pressures.

*Powder burn rate too slow for the bullet.
*Bullet weight too light for the powder's burn rate.
*Bullet bore contact area less then normal for the bullet weight
*Barrel longer then normal
*Bore severely worn or incorrectly lapped (loose/worn toward the muzzle)
*Moly in bore or moly coated bullets that reduce bore friction


We are often asked when secondary pressures are too high. Obviously secondary pressures more then 25,000 or 30,000 PSI at the weakest part of a barrel represent a safety issue. On a more practical note, loads that exhibit secondary pressures often show significant variation in barrel timing (when the bullet exits at the muzzle). Even if the timing does not vary shot to shot, it certainly will when the temperature changes so these loads rarely shoot well. Our advice is simply to avoid all loads that produce secondary pressures and keep peak pressures where they are supposed to be, in the chamber. If you shoot factory ammo, try a different brand. If you reload, use a slightly faster powder or heavier bullet.

I recently had the occasion to work with a friend's .223 Douglas barrel that had shot perhaps 6,000 rounds of an off brand ball powder sold as "Data 2200". My understanding is the powder was actually reject 2230, a powder we know produces secondary pressures in small calibers. The owner shot around 2,000 rounds of the load through the barrel each season, then re chamber his good ol' shooter as the throat washed out. When I looked down the barrel with a bore scope I could see rings just down from the muzzle spaced exactly the amount that was removed from the chamber end each time the barrel was re chambered. This convinced me secondary pressures will eventually damage a good barrel.

No doubt there are shooters who will debate our conclusions. We welcome anyone to pose other possible explanations. The "catch up" theory is the only one we have found both fits the evidence and can be used to eliminate these problems. To date, only shooters who do not have access to pressure testing equipment argue adamantly against the "catch up" theory. Professional ballisticians we have talked to whose job it is to formulate powder seem to be in full agreement. Even if the theory is not the "entire" explanation, it is certainly useful.

[Christchild]

I WOULD HAVE been utilizing ALL of the "List", except Moly Bullets, and my barrel only has approx. 100 rounds through it.

Thank You Uncle Nick!!!

If there is anything within my ability that I can do for You, don't hesitate to ask.

I'm still KIND OF "curious" about the Large Rifle Magnum Primer, but with THAT list of Causes, I WILL NOT be trying the loads. Not in THIS lifetime!!!