Dear Sir,
Given the below situation/informatio, can i implore your expertise on helping fix a 308 WInchester chambered gun that throws 6-8" groups at 100yds? and for use of any of your products that might help. I am not sure if its the ammo or the barrel, but I suspect the barrel since its inconsistent with so many brands of ammo; and for the below reasons:
This rifle is a saiga-308, and since it is a semi-auto and the Russian ammo is ~150gr; I try to stick with 150-ish gr ammo. (*) I have tested ~20 brands of 150gr 308 (**). On a fair number, but not all, of the
brass I noticed:
The case necks had expanded concentrically to ~.314 Internal diameter! a new .311 bullet coudl be dropped in easily. Other cases were back to .308-9. OK, seems to me the only way these casenecks could get to expand is if the chamber throat is that big. The other cases must have 'rebounded' back to 308. So if the chamber is so generous, and the projectile is .308, I will have gas blowby, maybe "cutting" or whatever throwing off my accuracy?
I have not done a chamber cast, but I might do just that so I can post all the info?
At this point I see no reason to post any more information, as you have identified a major problem in the greatly oversized chamber neck. Probably the throat is as greatly oversize and the combination allows the short bullets to lean before they get into the rifling. If you handload using jacketed bullets, let us know here, and I'll post the most effective solution to the problem. If this is the problem, which you'll know for sure once you receive the LBT slugs which you say you ordered later in this post. also,
On slugging the bore, the final measurements came out: lands .301, grooves .308. So that at least is OK.
But, and I really need some advice here, here is how the slugging "felt": I used a .312 pure lead ball and rod/small hammer. just out of the chamber, it was tight as expected since the ball had to swage down to size. then it tapped down about as snugly as usual, then hit a tight spot, then slid again. Makes me think my bore is actually too LARGE for most of its lenght, then has a constriction down to .301/308; then widens again to some unknown diameter.
could that constriction be just a snag?
It's the real thing, and a snag is about the same thing as saying constriction. A tight spot of any shape or size is a constriction and will leave the bullet loose after passing through. Lapping will fix this problemCould I be looking at a bore that begs to be.311? and therefore I need to lap out the tight spot to make a uniform .311 bore? Of course, that might leave me with a semi-wildcat .311/308 chambered rifle. But I can cross that bridge later.
You will throughly enjoy being able to provide all the answers to these questions by yourself, once the slugging supplies arrive. YOU will be the expert then! So...
In preparation for accuracy improvement, if possible, i just dropped a check in the mail for a LBT lapping kit, and bought some .311 cast 165gr bullets to use. According to this article:
www.surplusrifle.com/articles2008/trailbosskiss/index.asp9gr of Trail Boss should be (just barely) subsonic.
But I am wondering if I may need something else. Again, any advice you have would certainly be appreciated.
Most sincerely,
cpileri
(*): I am not married to the idea of 150gr loads, just thought to stay with what she was manufactured to fire. But some on the saigaforums report better accuracy with 168gr loads, so I do have some to test (barnes TSX, as that is the bullet I want the most to use, if possible).
(**) to include: Wolf, WInchester Supreme Partition and XP3, Hornady TAP 155gr, Nosler Custon, Barnes VorTX, Federal Premium TSX's, relaods w/ barnes MRX, Prvi Partisan, Sellier and Bellot, and others: as you can see I am looking for a hunting load, suitable for Texas WHitetail/feral pigs. So I have not tested any match loads as the are not the hunting projectile I would prefer. I also have still to test Remington Core-loks and a handload of 150gr Partitions with H4198 as I just read in Handloader a tip that .308 bullets accasionally fire well in .311 bore 303British guns when a faster powder is used to belp 'bump up' the rear of the bullet. We'll see, i suppose.
You've answered one of my first questions here, about whether you would be reloading, so I'll give the information right now. First, regarding the use of 308 bullets in larger bores. If the throat is large, as I suspect you can also go the other way. Use .312 bullets in a 308 bore, without pressure problems, IF the bullets are seated to jump a little before hitting the rifling. Also, again, if the throat is oversize, long loose, use only flat base bullets, not boat tail, as you need all the bearing length possible. Seat them out close to the rifling, if possible, and crimp using the Lee Factory Crimp die. Crush the crimp in deep enough so that the remaining crimp in a fired case will drag against a bullet when inserted with the fingers. This will provide a pilot for the back of the bullet while the nose is getting engraved by the rifling. Plan on lapping out the constriction also, and you should have a VERY accurate hunting rifle. With a big smirk I'll say I'm not authorized to write about jacketed bullets on this 'cast bullet' forum, but understand that understanding all one can about jacketed will broaden his base of understanding about cast, and vice versa. Thanks for 'intruding' with your questions!
