Extending the throat..

[DonT]

I have acquired a Rem. 40X in .308 Win. It has a Kreiger barrel with a 1X10 rate of twist and is match chambered to shoot the Sierra matchking bullets and here in lies the problem.

I cannot get a cast bullet to shoot in this rifle to save my life. I have tried bore riders that I swaged down to go up into the barrel, I have tried spire points at 165 gr. both swaged down to go up in the bore farther and full sized set back in the case. I have tried Round nose 220 gr bullets which required they be swaged down or the bolt would not close. None have yeilded anything but very poor Cast Bullet accuracy. I can actually get better groups out of a box stock 700 SPS with the same bullet and not have to go thru the extra step of swaging them down. All bullet are gas checked and being purchased from a local caster.

I have tried AA5744 (21.5 to 27 grains), Alliant 2400 (18.5 to 22 grains), 4759 (22 to 25 grains), I have dabbled with unique and 4198.

It is my thought that this rifle has too abrupt a throat to give me the groups I should be getting from a rifle/barrel combo of this caliber.

So, although trying to fight the urge I am leaning towards using a throater to extend the throat so I can use a longer bullet without having to monkey around swagine a part of it down so it goes up in the barrel.

I am not a gun smith by trade but have done some hobby smithing in the past. I do not wish to remove the barrel to extend the throat so my thought was to get one of the PTG Unithroater.

Thoughts, alternatives, etc.. I am all ears....

DonT

[felix]

NO, DON'T DO IT! Instead, shoot the condoms full speed ahead until the throat wears. In due time the length will become more commensurate for the boolits. The problem is with the twist you have chosen, and perhaps the chamber neck is too large in diameter for best results. I am SURPRISED Kreiger would sell you a barrel, chamber and all, not appropriate for that EXACT matchking you are shooting. That bullet is an industry target standard and desires a 14 twist barrel. Your BOOLITS would shoot fine in the target standard barrel. ... felix

[DonT]

Felix,

Maybe I was not clear. I got the rifle it already had the Kreiger barrel on it and it had already been chambered for shooting Match King Bullets, I am not sure who chambered it. It does this just fine.

I want to shoot Cast Bullets, this it doesn't do well and that is the crux of my issues with the rifle.

Do I lengthen the free bore/throat or leave it alone and sell to someone who likes shooting jacketed bullets...

Sorry for the confusion..
DonT

[Doc Highwall]

DonT, I am shooting a 40x in 308 also and have no problems. I am shooting SAECO #315 175gr TCGC sized .310Dia. lubed with Bullshops NASA lube, 30:1 alloy 9 BHN. Load is as follows Fed case, Rem 9 1/2 primer AA5744 OAL 2.800". I started at 19.0grs and worked up to 21.0grs. At 20.5grs I get my best accuracy. You did not say what size the boolits were or the alloy, I think you exceeded the compressive strength of the alloy.

[felix]

Two choices, rebarrel or sell the gun as is. I would prefer the former because chances are the action was true-ed and therefore the gun shoots good! Are your lugs perfectly square in terms of wear? That would indicate a good action. If not, then sell the gun. If so, get a minimum chambered barrel for that same bullet with 14 twist. Minimum chamber in this situation calls for neck turning to get rid of the high spots on the brass. No need to go further in turning unless you choose to do competition with that gun. Mic your loaded rounds with bullet seated in your match brass as seated for the gun now, and see what that diameter is. If measurement not round per load, write down the average per load. Now, average 10 different loads consisting of the average per loaded round. That is the diameter you desire for the chamber to be cut. ... felix

[felix]

Doc, what are your barrel specs? ... felix

how long is that Saeco boolit?

how long is the Seirra target bullet?

[Doc Highwall]

Felix, the SAECO #315 boolit is 1.037" with the gas check. I will have to see what I got for barrel specs.

[runfiverun]

can you close the bolt on the bore riders?
without swaging them? have you tried them that way?
you might just need a boolit with more bearing surface and less nose ride.
my wifes 0-6 should have been a perfect fir to the rcbs 165 silhouette boolit as i measured it.
don't shoot them worth nothing, but it will shoot the rcbs 150 fn it has more bearing surface and much less [hardly any] bore ride.

[DonT]

Doc,
I can't get something that long in the chamber the bolt will not close. Are you using a factory Remington Barrel with factory throating? What is the twist of your barrel?

Felix,
Are you saying that the 1/10 turn will not shoot cast? The reason I ask is my stock 700 sps will shoot 1.5" - 2" cast loads as will my savage 12bvss. If it will what would be the problem with increasing the freebore/throat to allow clearance?

runfiverun,
No I cannot close the bolt it stops about 1/4 shy of closing and will push the bullet deeper in the case if I force it. This is why I thought the freebore/throat needed to be lengthened.


The only way to get something the size of what Doc is using in the gun is to swage the exposed porttion down to .301" . If I leave 1/8" of the unsized portion of the bullet ahead of the case mouth you can see where it is being slightly squeezed down as it is forced into the throat. Like I said the rifle has a very short throat which works find for the sharply tapered Sierra Match King jacketed bullet.

Thanks all..
DonT

[felix]

Yeah, Don, it will but not with the performance you'd want. I think your other 308s are 12 twist, and that helps. You can always open up the length of your 10 twist throat as an option. Let's delay that option. ... felix

[Doc Highwall]

DonT, the SAECO #315 is a tapered bullet. I just measured one .3026 on the nose .3044,.3058, .3072, .3087, and .3111 at the base. My soft alloy 30:1 allows me to start the bullet into the lands with out too much force. Here is a picture of it with it loaded at 2.750" OAL. I have now increased it to 2.800" OAL. Also here is a target shot at 200 yards with 20.0 grains of AA5744. I think a softer alloy and a lighter charge will help you.

[felix]

Very excellent, Doc! Where do you live in CT? I lived in Bloomfield, 72-76, and worked at Pratt. Shot in the Pistol league and did BR at BlueTrails, winter league mostly. ... felix

[phil218b]

Just a thought, before you change the chamber try cutting the neck down on the brass and seat the bullet a little deeper. Try a couple and see what it does before cutting a lot of brass, but it might give you the clearance you ned to see if the barrel will shoot the boollit.

[S.R.Custom]

I personally don't think the throat is a problem; generally speaking a short throat is a good thing. I've yet to see a rifle whose accuracy improved by increasing the throat/leade. The fact that your box-stock 700 SPS shoots better indicates to me something else is going on, and these two gentlemen kind of hint at it...

...you might just need a boolit with more bearing surface and less nose ride...

...You did not say what size the boolits were or the alloy, I think you exceeded the compressive strength of the alloy.

A few thoughts:

(1) You don't mention alloy. It may be too soft. Take one of your bullets, measure the diameter, seat it, pull it out again, and measure the diameter again. Is it smaller? If it is, Your expander button may be too small and/or your brass too hard. But your other rifle shoots better, so that leads me to...

(2) Match barrels like this typically have much shallower and narrower rifling than box-stock stuff, and frequently don't have enough 'tooth' to hold onto a lead bullet as it's rotationally accellerated. Particularly heavy bore-riding boolits with skinny driving bands. Indeed, the bore riding part may not even be riding at all, causing alignment problems. One-in-ten twist is kinda fast, too, (for boolits) and is probably exacerbating the problem.

(3) Combine (1) and (2) together and you have an accuracy disaster on your hands.

Solution? First off, I'd check the diameter of the bullet like I mentioned in (1). A larger expander button may be in order, as well as annealing your brass. Secondly, you may find accuracy improves if you step up the hardness of your alloy. And like R5R says, a boolit with more bearing surface will probably help too.

If all that doesn't help, I'd sell the rifle if shooting MatchKings isn't your game. It'd be a shame to take a uni-throater to a barrel that does its intended purpose well...

[Junior1942]

Slow that bullet down to 1500 fps/~108,000 rpm to 1600 fps/~115,000 rpm and see if you get much better groups. With my rifles and my alloy, at circa 120,000 rpm bullets fly everywhere.

[DonT]

I got my list of things to do now.. Thanks for much folks will start getting to work...


Again thanks much..

DonT

[Four Fingers of Death]

I got my list of things to do now.. Thanks for much folks will start getting to work...


Again thanks much..

DonT

Yep! We're reallllllllllllll good at giving folk jobs to do and encouraging them into buying new guns. I'm thinking if its a 40X it would have a pretty trued up action anyways. Always wanted one of those suckers, a 222 and a 308 to be exact, one day!