Varmint gun(smithing)

[DCFusor]

I've been playing with a Howa in .204 a friend asked me to "breath on" a little. Here are the results, with before and after targets @ 60 yds (my front yard range I use for quick tests).

Upper target is 4 shots of hornady factory ammo "before".
Lower target is 4 shots same ammo "after".

I could do more with this one - I can more often than not put them all in the same hole with guns I've really worked on (and that have better scopes), but this is what it is. Funny, you just don't need a hell of a lot of firepower when you can really put each one right where it belongs.
This ammo gets 4250 fps out of the gun...it's varmint bullets but at this speed they have no trouble at all going through 3/8" steel, making a half inch hole more or less. They "explode" but go on through anyway.

This ain't bad for factory ammo, cold barrel at first (the shot tossed to the right was the first in each case, hmmm). Now, precision reloading and a better scope and I'd bet this would do one holers at 200 yds, if I finish the barrel lapping job - I only "touched" a rough spot I felt, and didn't get it really done. The other thing - factory trigger really stank, so I re-stoned the sear engagement surfaces and put on the magic grease to make it break nicely - before, it was "grinchy" and you couldn't hold on target through all the ick-ick-ick till it went bang.

Not too shabby for a cheap gun, though. Note, I typically don't set the scope for "dead on" for these tests, as it becomes hard to shoot a good group when you destroy the aimpoint.

 

[ancona]

DC,
I have two issues with my AR. The first issue is a common cold barrel problem, with the bullet "pulling" right for the first six or seven rounds, then going where it's supposed to go as the barrel heats up. The second problem is when I am really shooting hard, mag after mag, and the barrel gets smoking hot, when it gets really hot, the rounds tend to start key holing out at 100 yards. While there is little that can be done about the cold barrel pull, can I do anything about the hot barrel or is it simply expanding to the point where the rifling is not turning the bullet?

 

[DCFusor]

To truly answer that one, I'd have to do a little casting of the barrel innards with cero-safe. The first shot flier can be a lot of things - some barrels shoot the first round off simply due to different friction when really clean, or due to a lack of stress relief when they were made (which is fixable with a heat treat). Minor crown issues can also do that - I re-crown almost every barrel I own and that's that (easy in the lathe, sometimes don't even have to remove the stock)

It could also just be getting so fouled that it won't shoot. When I compete, I clean every few rounds as at least that always puts me into a known state. For competition I almost always use moly coated bullets which cuts that fouling way way down as well - those take awhile to start grouping in if you've cleaned all the moly out of the barrel, but that's so hard to do in practice it's not much of an issue unless you use bore paste (abrasive) which you don't do often - can't put metal back after all.

A fluted barrel will cool better, but the truth is - if you shoot very fast, the inside temp is always a lot hotter than the outside. For an instant, it's red hot right after the bullet goes by, and steel is a crappy heat conductor.

Do you have the typical 1::9 twist? That should do with most ammo, but I find my best results with 53 gr sierra flatbase in mine, with straight ammo (no runout). No factory or mil ammo is straight, and with the otherwise sloppy fit in a NATO chamber, it's hard to get them to shoot in the best of times.

On the other hand, here's a target at the same range from my AR after *extensive* work, 5 rounds in 10 seconds, off bags. I keep it in my wallet so it shows when some clerk asks me for my ID, next to the CCW permit and voter card. It's not a fluke - another guy shot one just like it half an hour later with everything else the same and him not as experienced a shooter.

Note, this would be a downright embarrassing target to shoot benchrest at 100 yds. But it's not bad for an AR and going very fast.

 

[benjamen]

DC,
I have two issues with my AR. The first issue is a common cold barrel problem, with the bullet "pulling" right for the first six or seven rounds, then going where it's supposed to go as the barrel heats up. The second problem is when I am really shooting hard, mag after mag, and the barrel gets smoking hot, when it gets really hot, the rounds tend to start key holing out at 100 yards. While there is little that can be done about the cold barrel pull, can I do anything about the hot barrel or is it simply expanding to the point where the rifling is not turning the bullet?

Depending on the rifle build, you can switch out barrels in the middle of a long day of firing. Some barrels can actually be damaged if they get to hot.

 

[DCFusor]

Benjamin is right on that one. And it might not take many rounds to do some harm, but it varies with a lot of other things (some steels work harden and get smoother an tougher with that treatment). Just remember, it's much hotter inside, where it matters, than outside. The normal thing is just to use a reduced rate of fire, and let the heat soak out to the outer part better before the next shot.

Think how long you can hold a piece of steel only an inch or two away from where you're arc welding it without getting burnt - it takes time for that heat to move in steel.

Thus, while I do own two legal class III items - I don't shoot them full auto much, a good barrel is a terrible thing to waste. I do this little demo for people, with either them or me shooting (I do it better, of course).

Shoot a clip full auto at a target at 100 yds. You're usually lucky to get more than 3 on the paper out of 10 (or 30). Now, just shoot as fast as you can semi-auto, and you'll hit the paper every time, and with practice, always in the 10 ring too, and that can be faster than one shot a second once you learn the trick (hand OVER the forearm on the bag to hold her down) and the timing (fire again as you're approaching the bull again from above). Spray and pray just doesn't work as well as in the movies.

I've not seen much in the way of easy to change barrels in AR's though. It hasn't become an issue here - with truly accurate guns, it only takes one shot most of the time anyway.

You can get the inside of a barrel glowing hot in 10 fast rounds - it's not a "middle of the day change" kind of thing.
Ancona - you might be melting the bullets!

 

[ancona]

The rifle I don't have any problems, it is a Kreiger 20". The carbine is the troublemaker. It has a Daniels Defense mid range barrel. Both are 1:7.

 

[DCFusor]

You really could be melting bullets in sustained rapid fire, I've managed it. The cupro-nickel jacket is both very heat conductive (to heat the core) and the base is open on a lot of milsurp and reman-mil. You probably can't get a normal rifle that hot very easily, but I've seen swelled bases and melted cores in bullets I recover. Copper gets soft quick with temperature. A tiny bit of lead leaked from the base is enough to send any bullet end over end - that end (believe it or not) is more important than the tip - and I've proved this even with low velocity pure lead bullets. If I turn the bases really flat on the lathe (I made a special collet for this to be fast) before putting on the gas check, they shoot into half size the group.

Remember, that chamber is hottest of all. This can heat up the round enough to raise the pressure quite a lot and that might contribute to the problem if you're not using a temp-insensitive powder (the milsurp stuff is not great that way).

1::7 is a quick twist and ought to stabilize even heavy long bullets if they spin, but if pressure is too high initially, they might get smeared over the rifling at the start of the leade. You can see that on a recovered bullet if it's bad enough to make them keyhole.

You can try to recover some bullets and see what they look like. Sadly, a fackler box is a PITA and doesn't last long, and it takes quite a few gallon jugs of water in line to really stop a .223, but it might be worth doing for troubleshooting. Or wet phone books work pretty well - you don't care if you bend the bullet, you're going to be looking at the rifling marks to look for clean cut ones (and not some going farther up to the ogive than others, too) - you learn a lot quick that way.

Some guys weld two 55 gal drums together, then shoot into them from the second story of a building (water filled, of course). The smart ones put a screen in the bottom to lift them out with later, more easily. That lasts a long time, and I ought to add that accessory here myself.

Some first shot drift (or the first few) can also be your hold. It actually does matter how tight and how well seated into the shoulder a rifle is as to where things go. When I get out of practice, it happens more to me, FWIW. Remember, it takes some milliseconds for the bullet to get out of there, and recoil and shake start at the drop of the hammer/pin - plenty of time for things to move a little differently if you hold tighter or looser. After a few, you settle in better...

Edit:

With 1::7 you should be trying 69 gr (sierra or nosler) or 70+ gr (berger) bullets seated near the lands if you can get that to fit in the clip. I'm limited to about 2.270 in my clips, so for those I single-load usually. Not for blasting, but they shoot better at fast twists than ligher ones do.
Actually, it's more length than weight - some of the milsurp (green tips) are longer for their mass than "civvie" bullets due to the penetrator core not being as dense. At my 1::9, the 69 grainers are the upper limit - in your 1::7, they ought to be right in the middle of the sweet spot.