How will a long throat affect accuracy?

Brambles

Regular
Rating - 100%
50   0   1
I am in the process of getting one of my new rifles to shoot. This rifle a Remington Titanium .270 win and it seems to have a very long throat. I can load a round to fit the magazine and it will chamber, this makes for a very long bullet and much longer that the COL of any reloading data I have read. The COL for my load which is with a sierra 150gr sbt is 3.43.

I have noticed a consistant staggered vertical string. Groups are terrible, no signs of pressure at all. Barrel has a pressure point but is floated along the remainder of the lengh of the barrel and is pillar bedded from the factory.

The groups would climb up to 4.5 inches from first shot.
It has a whip for a barrel and heats up fast so I would let it cool after each 4 shot group.

Any help would be great,

Brambles
 
Actually I looked at my targets again and its more like its shooting triangle groups and then throwing a wicked flyer on the 4 shot which spreads the group to 3-5 inches. Smallest 3 shot group was 1.5 inches with the 4th being a flyer that took it to 4.5 inches.

It almost seems like even though it has a long throat the bullets that I was shooting with a COL of 3.26 shot better than the longer ones. Thats one hell of a jump to the lands:confused:
 
It sounds like you should start with your bedding, and float that barrel before you worry about seating depths. A best group of 1 1/2" isn't something that just needs a little fine tuning. If you haven't already, try some different ammo, with different bullets and weights. Save the bullet seating variations for last.
Don't worry too much about the jump to lands. Sako, Tikka and Weatherby all have long throats but are also on the list of makes known for being out of the box shooters. Good luck, you'll find something that $1400 rifle will shoot.
Dogleg
 
That whippy barrel on that Titanium Remmy will not tolerate shooting it hot either. You need to take plenty of time between shots, particularly after the second shot. You may find your groups shrink considerably. I would cut a bit of old credit card and put it under the receiver at the recoil lug area to "float" the barrel off that pressure point and try it before removing the pressure point. That way you may be able to tell if it will help to remove the pressure point. Regards, Eagleye
 
Usually excessively long throats are not good for accuracy. The best accuracy usually occurs when the bullet of the loaded round is close to or in some cases contacting the rifling.
 
Seat a bullet just into the case neck. Just enough so that it doesn't fall out or is wobbly (1/16" into the neck). Put black jiffy marker around the bullet at the ogive (widest point). Chamber the rd.

If the throat is ok, the bullet will engrave in the lands. You will see 6 rectangles on the bullet equally spaced around the circumference. Better yet, when you close the bolt, the bullet will be forced back into the neck.

With a throat like this, you have some freebore but the bullet doesn't actually jump to the lands. This barrel has a chance of working.

You now need to make sure that you use neck sized ammo that is concentric. Runout on neck and bullet no more then 5thou. You will need a proper runout guage to measure and this is where less is better.

Set the OAL length to fit and function from the mag. Work up your load carefully and the rifle should shoot better. 150gr SST have worked very well for me pushed by H4831SC using Fed 210M or CCI BR2 primers. I use a Lee collet neck die whenever possible.

As long as the bullet fully engraves in the lands BEFORE leaving the case neck, you have a chance of making this rifle shoot. If the bullet has to leave the neck and JUMP to the lands, at best you have a MOA rifle. 1.5 to 2MOA is more the norm. You will get flyers for sure.

The only solution is to set back the barrel. However, if this is a new rifle, a call to Remington or wherever you bought the rifle would be in order.

With this heat, you should limit to two shots then let cool. If the gun is going to shoot any load, two or twenty shots will go into small groups. If the first two are wide apart, who cares what the next 8 might do. The load is not consistent enough to be of interest.

My Savage in 7RM is a sub MOA shooter out to 1km. In the fall/winter, I can get 4 to 5 shots away before it overheats. Now it will only take 2 shots before it launches the third shot into the wild blue yonder. Barrel it almost too hot to touch.

For a hunting rifle, the first shot and possible follow up shot are your most important. So tune accordingly.

Personally, I free float all my Rems. Proper bedding is a must and I extend the bedding to the first inch of barrel. With a quality composite stock, there is little chance of the barrel pressure changing due to temp and weather but it is just one more variable in my mind.

By free floating and working up a proper load, I know the rifle is consistent no matter when or where I hunt. That is the type of confidence I need in my gear. I have yet to resort to pressure bedding to make a rifle shoot.

Jerry
 
Last edited:
Thanks for the info guys. I'll give these ideas a shot.

I did that old jiffy marker trick a shot when I loaded up some 130 scirroco's last month and the bullet shoved itself back into the case and marked up the ve a bedded hi-tech specialties stock that I just finished for my mountain rifle and the barrel is free fbullet pretty good so by your descripton I should be able to work with this rifle.
Now if I can get it close to the lands and still function out of the mag is another question, no doubt if I use some 150 roundnose it shouldn't be a problem but thats not my intended bullet.

Your also probably right about the heat, even though its only 4 shots its still to hot to lay your hand on, it seems that the fourth one is the wicked one so maybe I need to invest in some patience.

Will the credit card trick work? I know is should raise the barrel up a bit but won't it change the contact angle on the recoil lug?

Thanks again guys, very interesting read. I welcome any more tips if you have them

Brambles
 
Back
Top Bottom