i have a job if anyone is interested

My 9mm likes the 110g soft lead bullets I feed it. A friend cast them for me. I have also shot 125g pistol hard cast lead bullets (Nevada) and they are ok, but once in awhile I’ll get a flyer. Not far out, but maybe an inch out of the group at 21 yards. The rest go into the same hole. Thought it was me at first, but it kept happening. I’ve come to the conclusion the rounds are only just marginally stable since I’m firing them very slow, around 650fps. If I were to speed them up I think the 125g would be fine, the sliight increase in stability would get rid of the flyers.

I don’t speed them up because the gun tends to make a lot more noise when you push them faster than about 700fps. I’ve tuned my 308 pistol to around the same velocity. The 308 rifle is a little hotter, but even that slight increase and you can hear the big difference in noise. Since I’m trying to be as quiet as possible with houses next to me all the time (hawaii property values are nuts), 650fps is just fine for me and the pigs
never complain.

don’t know why you are getting crappy accuracy with light bullets. What weight? Sure it isn’t bullet shape that’s doing it?

walt

The 308 is .308″ diameter, oddly enough. The 9mm is .356″ diameter. For a given weight of bullet, the .308 will be a longer bullet because its diameter is limited to a smaller size than the 9mm, so only 1 dimension to expand along, front to back. Powderburner barrels in .308 tend to be 1:TEN or 1:TWELVE twist and this is sufficient to stabilize a 220g bullet at supersonic velocities. The same twist rate will NOT stabilize a subsonic bullet of the same weight, trust me, I’ve tried many times. The same 1:TEN twist at sub sonic velocities will stabilize only up to around 180g bullets. I once built a .308 with a 1:SIX twist barrel so that I could use the 220g bullets. If you want to experiment in this caliber cheaply with ultra fast twist, get a used AK47 barrel, they come with around a 1:SEVEN twist but they are an oddball size, .311 or .312 if I remember right.

Fucking emoticons.

walt

Crap, that’s a lot of posts. forgive me if I don’t hit each nail on the head, my memory is getting old.

RJ, there is no power differential. That’s a product of mass times velocity. Push it faster, you get more power. Keep velocity same and push more mass, and you get more power. Do both and you get much more power. But, of course, in AG we are limited by speed of sound, so after 950fps or so the only way to get more power is with a heavier bullet. Overpenetration does not count, by the way.

The thing that changes when changing caliber is sectional density, and to a lesser extent, surface resistance of the barrel grooves and lands against the bullet. Larger bullet = more surface area, but area increases as a square of the diameter and mass increases as a cube of the diameter, meaning you can pack a lot more power into larger calibers with less parasitic loss from friction. But that’s a small part of the equation. By far, the most important consideration is bullet selection. In 308 you just have way more bullets to choose from so very easy to pick something that will work in your barrel. 9mm is much more limited and of course, mostly pistol bullets which are not streamlined like rifle bullets. So if long range is your only consideration, 308 is a must have over 9mm. I own both as my only consideration is hunting.

Both 308 and 9mm with similar weight bullets will yield close to same power. Personally I like my 308 better for killing pigs. The 9mm works just fine as well, I have a 201 and shoot 110g soft lead bullets and have always had 1 shot drops on pigs from 60 to 150 lbs… but all were headshot. The 308 seems to give more penetration. an experimental 7mm I had for a year or so had astounding penetration, shot one pig in the top of the head and the bullet passed completely down her neck and exited between her front legs and burrowed deep enough in the dirt under her that I did not recover the bullet. And yes, I looked.

There are equations on the net to help determine the amount of twist you need in a barrel to stabilize a given bullet. You need faster twist for heavier bullets. But the equations are messed up because none of them were designed for airgun use, which looks almost exclusively at subsonic rounds. There is a really hairy one the military uses. I have it in my notes somewhere if you want it. In the end I just ended up having to actually build the guns with different barrels and ordering custom barrels with individual, custom twist rates and actually firing them to test if they were stable or not. The equations did not accurately predict the outcomes.

walt