Hornady Light Magnum

[SavageSniper]

I see that Hornady offers .270 in 130 and 140 grain rounds that are called light magnum. They say that they are not to be used in semi-auto or gas operated rifles. Is this because of pressures? I only have bolt action .270's but curious.

[oldbillthundercheif]

They may not produce the needed volume / pressure of propellant gas that the semi needs to cycle.

[Fremmer]

I tried them in .30-06, and didn't like them at all. The synthetic stock and terrible trigger didn't help. Lots of recoil.

Not recommended for the semi because of the high pressure. It won't hurt to try them in your bolt; maybe your rifle will like them.

[stevelyn]

It has more to do with the pressure curve rather than higher chamber pressures.

A semi-auto is designed to operate under a pressure impulse of a fixed dwell time to balance sending the bullet on its way with starting the unlocking process after chamber pressures have dropped to a safe level.

Generally, semis perform this feat better with lighter bullets and faster powders. When you start increasing bullet weight and slowing powder burn the action starts its unlocking cycle earlier while pressures are still higher than normal.

It can be best demonstrated by taking a semi auto and shooting a load with a lighter bullet and faster powder, then shooting a heavier load with a slower powder. Examination of the shucked cases usually reveal a normal case from the lighter faster load and a rim tear from the extractor on the heavier one. This is because the extractor started pulling the case from the chamber while the case was smushed up against the chamber walls under decreasing, but yet high pressures.

Light Magnums and High Energy loads only make the problem worse.

[Fremmer]

a rim tear from the extractor on the heavier one

And broken extractors, too.

[Dave Haven]

And bent operating rods on M1's.

[Art Eatman]

Odds are that the pressure's fine, as far as the strength of the action. Probably, the pressure at the gas port is higher than what the operating system is designed for.

The cartridge itself is a Good Thing.

Art

[Unclenick]

What Art said is especially true of the Garand. The gas port is at the muzzle, so dwell time isn't so much the problem as the pressure value. The M14/M1A design has the gas port in mid-barrel, like most gas guns, where bullet barrel time beyond the port has much more influence on op-rod gas pressure exposure. The M14 mechanism is designed to partially compensate for this by closing off the gas port to the admission of more gas once the piston has moved reaward a short distance. Higher pressure moves it faster and stops allowing additional pressurizing gas sooner. That's the compensation. However, starting out faster means some additional impulse energy is still applied to the operating rod, so the compensation isn't perfect and has its limits.

Ironically, despite its age, the M1 Garand is the easiest semi-auto to equip for slow powder and heavy bullets, including the Light Magnum loads. The later version gas cylinder plugs have a valve that opens when using a grenade launcher. You may simply thread the inside of the plugs screwdriver/bleed-off slots for a set screw, and bingo, you can adjust that valve to be open by any amount you choose. Start with it turned in and wide open, then gradually back the screw out just until the gun cycles properly. Some like this for regular ammo, too, since you can tweak it to eject the cases nearby the shooter, rather than tossing them to the next shooter for policing.

You can also buy a gas cylinder plug that accepts any one of a set of fixed diameter port bleeder screws. I believe Brownells carries it. A friend of mine has a Garand set up for 1000 yard match shooting that employs this device. It allows him to run 50 grain + loads of Varget and loads of H4350 with the 175 grain SMK that would not normally be considered within safe limits in the Garand, due to the op-rod's delicate nature.

Nick

[chunk]

do y'all think it would be ok to shoot that round out of a handi rifle? im' a newb, to the .270 win... thanks in advance.

[FirstFreedom]

It's going to be *safe* to shoot it in a Handi. The question is, is it going to stick in the chamber and not eject. Do you have one of the newer handis with an extractor, or one of the classics with ejector? If a classic (ejector), then you're more likely to have a problem. Make sure your chamber is free of oils when you shoot it, and you might want to go to http://www.graybeardoutdoors.com/smf/index.php/board,126.0.html , and look for stickies and threads that discuss polishing chambers, if you're going to shoot hot stuff like the light mags. Follow the instructions, using a dremel and buffer attachment, to smooth/polish the chamber, helping with extraction. And, take a cleaning rod to the range with you, just in case. Then if a case sticks, you can punch it out from the muzzle.

To clarify (some responses indicate confusion), Hornady light mags are on the HOT side, not the weak or "light" side of a given cartridge. They are made to turn *ordinary* cartridges (.270, 30-06, etc) into "LIGHT magnums" just by using special powders which are more efficient, and towards the upper end of saami specs (though still within the pressure specs, to be sure). As has been explained, in a semi-auto, they may make cause the action to cycle TOO fast, which causes jamming because the action closes before the next round has time to pop up and be "caught" and fed into the chamber by the closing bolt.

[chunk]

firstfreedom, thanks for the link !!!!!