I hope this is not a topic that's been beat to death, I'm new to the site and a brief search didn't answer my question. My father is a gunsmith of over 40 years, and we're building a smallbore rife for my son to use at our local club. Target shooting is a new concept for me.
I've got the barrel threaded and chambered, I'm ready for the length and the contour. So, the question is,
If you could do anything you wanted with a barrel, what would it be? Turn it to shave weight? Flute it? Is there a formula for an optimum length? Any thoughts would be appreciated.
Tim
Barrel length and contour
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Shooting Kiwi
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I'd start with a barrel that has been made as symmetrically as possible, and properly stress-relieved. Then it would be likely to repond to temperature changes in a repeatable way - ideally, by remaining the same shape.
The chamber and lead(e) must likewise be symmetrical and aligned accurately with the barrel axis. The projectile should just be engraved by the rifling when chambered. This gives the projectile the best chance of starting along the barrel properly aligned, not tipped.
If you find that the bore is eccentric (surprisingly not unncommon, although not in target barrels), and turn the outside to make it nice and symmetrical, you might end up with a banana, unless fully stress-relieved before profiling.
The crown should be recessed for protection (but from what?), but I wouldn't care about its shape, as long as everything were symmetrical.
Barrel length is much debated - smallbore target barrels are getting shorter. Probably for the better. If you want a long sight radius, hang the front sight on a 'bloop tube'.
Fluting is stupid for target rifles: it reduces rigidity and saves minimal weight. It's a fashion. Why would you want to save weight anyway? Tapering likewise. The small increase in surface area provided by a fluted barrel probably aids cooling minimally. Anyway, it's not a machine-gun, is it?
Threading into the receiver is a source of possible problems. I think I'd use an easy-fitting thread with lots of Loctite (or equivalent), and hope I'd never have to remove the barrel. The idea is to unite barrel and receiver as completely as possible, not, perhaps, by the last couple of threads. Some funny deforming thread forms have been used, to good effect.
Why not just buy an Anchutz barrelled action and save a lot of worry? It's difficult to re-invent the wheel...
Then I'd find what ammo the rifle works best with, by testing, testing and more testing.
The chamber and lead(e) must likewise be symmetrical and aligned accurately with the barrel axis. The projectile should just be engraved by the rifling when chambered. This gives the projectile the best chance of starting along the barrel properly aligned, not tipped.
If you find that the bore is eccentric (surprisingly not unncommon, although not in target barrels), and turn the outside to make it nice and symmetrical, you might end up with a banana, unless fully stress-relieved before profiling.
The crown should be recessed for protection (but from what?), but I wouldn't care about its shape, as long as everything were symmetrical.
Barrel length is much debated - smallbore target barrels are getting shorter. Probably for the better. If you want a long sight radius, hang the front sight on a 'bloop tube'.
Fluting is stupid for target rifles: it reduces rigidity and saves minimal weight. It's a fashion. Why would you want to save weight anyway? Tapering likewise. The small increase in surface area provided by a fluted barrel probably aids cooling minimally. Anyway, it's not a machine-gun, is it?
Threading into the receiver is a source of possible problems. I think I'd use an easy-fitting thread with lots of Loctite (or equivalent), and hope I'd never have to remove the barrel. The idea is to unite barrel and receiver as completely as possible, not, perhaps, by the last couple of threads. Some funny deforming thread forms have been used, to good effect.
Why not just buy an Anchutz barrelled action and save a lot of worry? It's difficult to re-invent the wheel...
Then I'd find what ammo the rifle works best with, by testing, testing and more testing.
If you believe certain Benchrest gunsmiths, you determine the length by pushing lead slugs through the bore from breech to muzzle and when you find the tightest spot - mark it and cut and crown the barrel there.
It's been suggested that's why Anschutz (et al.) have a larger diameter section at the muzzle - when the barrel is profiled, the bore may open up slightly and by keeping the end larger you get a choke in the last few inches of the barrel.
21" with a tube may be advantageous for the young and for shooting standing but are reputed to be more picky about ammunition.
26" might be more tolerant of ammunition if your son can handle the weight.
I'm not a gunsmith though - so this is all to be taken with a pinch of salt...
K.
It's been suggested that's why Anschutz (et al.) have a larger diameter section at the muzzle - when the barrel is profiled, the bore may open up slightly and by keeping the end larger you get a choke in the last few inches of the barrel.
21" with a tube may be advantageous for the young and for shooting standing but are reputed to be more picky about ammunition.
26" might be more tolerant of ammunition if your son can handle the weight.
I'm not a gunsmith though - so this is all to be taken with a pinch of salt...
K.
There is no one size length that makes everyone happy. MOST prone guys like longer barrels (25-26") and position shooters like shorter (20-21").
What diameter is your barrel now? If your barrel is button rifled you should not contour the barrel unless you know exactly what you are doing. If it is cut rifled, you can contour to your hearts content.
Rimfire barrels are typically straight tubes, no taper at all. They are rarely fluted, but some factory barrels are. The minimum diameter you probably want to go with is .900" straight. The maximum is up to you but weight is a big factor in prone or position shooting. I rarely see bigger than 1.050" and that is a huge rimfire barrel.
Eric U
What diameter is your barrel now? If your barrel is button rifled you should not contour the barrel unless you know exactly what you are doing. If it is cut rifled, you can contour to your hearts content.
Rimfire barrels are typically straight tubes, no taper at all. They are rarely fluted, but some factory barrels are. The minimum diameter you probably want to go with is .900" straight. The maximum is up to you but weight is a big factor in prone or position shooting. I rarely see bigger than 1.050" and that is a huge rimfire barrel.
Eric U
Here's my latest experiment. This bbl was a throw in with another used 2013 bbl I bought. It was 21" which is far too short for my tastes [ BR ]. The bore and chamber looked very nice [ supposedly a Shilen, no idea who cut the chamber ].
Just for the heck of it I mounted it to a 40X and shot it. Shot patterns not groups. Decided to slug it just for the heck of it. Slightly draggy like a modern tapered bore bbl but at the muzzle the slug just STOPPED. Obvious that the gunsmith didn't cut enough off the end of the blank when doing the crown. Had to cut off about 3/4". Now the bbl is definitely too short [ in my mind ].
To try to induce some more taper to the bore I decided to do a ghetto reverse taper on the OD. See pic for results. The bore does feel a bit more draggy [ technical term ] on a slug. I remounted it and fired it for 10 rounds or so after a match a few months back. With no tuner and with some Lapua Center X [ I think even the flags were already put away ] the gun put 10 or so shots in a group that would have scored all 10's if fired at 10 record bulls. I came home and fitted a tuner but haven't been able to shoot the gun since.
Learning to slug a bbl is a skill all serious rimfire shooters need to develop.
Just for the heck of it I mounted it to a 40X and shot it. Shot patterns not groups. Decided to slug it just for the heck of it. Slightly draggy like a modern tapered bore bbl but at the muzzle the slug just STOPPED. Obvious that the gunsmith didn't cut enough off the end of the blank when doing the crown. Had to cut off about 3/4". Now the bbl is definitely too short [ in my mind ].
To try to induce some more taper to the bore I decided to do a ghetto reverse taper on the OD. See pic for results. The bore does feel a bit more draggy [ technical term ] on a slug. I remounted it and fired it for 10 rounds or so after a match a few months back. With no tuner and with some Lapua Center X [ I think even the flags were already put away ] the gun put 10 or so shots in a group that would have scored all 10's if fired at 10 record bulls. I came home and fitted a tuner but haven't been able to shoot the gun since.
Learning to slug a bbl is a skill all serious rimfire shooters need to develop.
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Levergun59
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Tim, it all depends on your Junior. My son was a lightweight at 110 lbs and he was shooting a Model 52, that was lightened but still weighed 12.5 lbs. His standing scores were abysmal. I bought him a Feinwerkbau 700 that weighed 9 lbs and his standing scores took off. So I bought him a Walther UIT that was chopped for a kid and weighed 9 lbs and he shot great with it. It may be an old rifle, but at the State Championships he shot a prone score of 200 out of 200 with 19X, so the rifle is competitive with a sweet trigger. I believe the total weight of the gun compared to your juniors physique will help him out. Let him try different weight guns and watch his standing scores. Then do your rifle build.
Chris
Chris