OAL / Throat question

[sled_mack]

My rifle is a Rem 700 5R in .308. No gunsmithing work done that would affect the throat (new stock, trigger, and bottom metal was added). The rifle has just over 2400 rounds through it.

I recently got a Hornady OAL guage and bullet comparator test kits. I decided to check the max OAL I could run using 178 Amax. I was shocked when they measured 2.335 to the ogive on average. This puts the OAL at about 2.955.

I've been loading the 178 Amax to an OAL of 2.820 to 2.825 (it varies a lot) with an ogive length of about 2.200 (this does not vary by much on the 10 rounds I had left over from last range trip).

This means I am jumping the bullets .135 inch to the lands! I haven't measured, but I'm pretty sure I can not load even close to that in an AICS mag.

Considering that I don't want to have to single load, am I spinning my wheels trying to get a really accurate load with this long of a throat? Do I just load out as long as I can in the AICS mags and see if I can get a better load? Should I consider the Morta mags that allow loading out a bit longer?

At 2400 rounds, I'm not really looking to replace the barrel yet. I've had a few recommendations to have the barrel taken off, cut down a bit on the receiver end, trued up and a new chamber cut. But at the cost of that, having a new match barrel installed is really just the cost of the barrel, so why not go all the way?

So my question is this - Is anyone else jumping that far to the lands with good accuracy? If so, any recommendations on how to get the most out of a rifle with that long of a throat? I don't know if there is anything I could be doing different, but it's worth asking.

If the long throat is truely a limiting factor, let me know that, too. I don't know that I can get it fixed before the snow melts here, but it is something I can start to consider.

Thanks.

 

[Sotahirvi]

Re: OAL / Throat question

I had a Steyr SSG 69 some years ago and i loaded the .308 3 mm off the lands with 110 v max to 190 SMK and got quite good accuracy 1/2 MOA. In my .300 win mag TIKKA T3 i loaded the 180 grain Swift sciroccos 4mm off 1/4 MOA with three shots 100m.

Try crimping your handloads with a crimping die, then you will get a consistent pressure buildup in the cases from shot to shot.

A small fact: Our swedish miracle the 6,5X55 has a throat that jumps the bullet 9-10 mm into the lands but is still one of the most accurate out there.

 

[Victor N TN]

Re: OAL / Throat question

I have 2 load lengths for my bolt action 308. I have a mag length and a single feed length. The mag length was made from a Fed GMM. I used that loaded round to set up that length. I have a length that I can hand feed on the length. But this is a custom chamber. On MOST not all but MOST factory chambers it's almost impossible to do any good trying to bump the lands. If you want to experiment with length that's OK as long as you do it safely.

Good luck.

 

[littlerascal56]

Re: OAL / Throat question

All the Remington factory barrels are that way. My stainless fluted .308 is 2.950 to the rifling also w/AMAX bullets.

My AICS magazine will only let me load to 2.880. I am actually using a COAL of 2.860 and letting them jump. They are shooting great groups (1/2 to 3/4) so I don't worry about it.

The only cost efficient choice would be to have a custom bbl installed, and not mess with setting the factory one back and recutting the chamber.

 

[Mutt]

Re: OAL / Throat question

I was just going through the same thing on my factory 300 WBY.
Your .135" jump has nothing on my .256" jump!

Yikes!
This is my hunting rifle so I normally load 210's to mag length and it shoots <span style="font-style: italic">at</span> 1 moa to 400 yds.
I'm wondering what loading long will do to pressure when one can't even get close to the lands...does pressure go up or down with increased OAL when jamming isn't a factor?

You'll probably end up shooting your current bbl out and re-barreling at some point.

By the way, how does it group with your .135 jump?

 

[sled_mack]

Re: OAL / Throat question

Thanks for the feedback. I knew Rem chambers were long, I didn't realize they were this long. Glad to hear it is not out of the ordinary.

This all has me wondering 2 related things - Will I see any difference testing loads out to the max the mags will allow? And if it's jumping this far, how critical is the OAL/jump?

As far as adding a crimp, I'm thinking if I do I would need to test my loads again working up from a mild load? Right now I'm using 44.7 of Varget behind the 178 Amax, but I've tested up to 45.3 before I get any pressure signs. So I'm comfortable where I'm at, but I don't think I'd want to change anything without working my way up again. Am I on the right track with that?

Secondly, I've got just a plain RCBS seating die. I have it setup not to crimp right now. Would it make a suitable crimp? Would there be a better choice in die for that?

Considering that I don't have to worry about jamming the lands, loading longer (but still within mag length) should not cause any increase in pressure - correct?

How does it group? Well, at 100 yards it is a 1 MOA gun. Hand loads, FGMM, all pretty much the same. I'm stuck pretty hard at that point. I've shot better with a friend's rifle, but I know I have much room to improve.

I've got a class scheduled for this spring, so I'm working on improving me. I still want to be sure that my hand loads are the best they can reasonably be (I'm not a benchrest shooter) so that I have confidence in them and that fact that my targets represent my shooting errors not my hand load errors. Same with the rifle. And that's why every few weeks I shoot a box of FGMM just to see how it compares to my hand loads.

Last question - wouldn't trying to load out to the lands leave too little bullet in the neck? I have NO intention of trying it, as it would serve me no purpose even if it shot well. It's just another bit of information I could learn.

Thanks.

 

[vman]

Re: OAL / Throat question

sled, i have those exact same dimensions on my Remington also.

Alpha Type 2 Mags + a modified feeding ramp = your solution

http://www.alphaindmfg.com/

 

[sled_mack]

Re: OAL / Throat question

vman, How long are you loading your rounds? And if you don't mind, how did you come up with shooting that length?

Thanks.

 

[Sotahirvi]

Re: Oto longer AL / Throat question

I would not say that the crimp will increase your pressure so you cannot use the max load you have now, but let us be careful and back of a couple of grains and start there.

The crimp adds the hold of the bullet so it releases from the case at the same point in the pressure curve and thus increases the consistency between loads= better accuracy.

I use the seating die and screw it down until it touches the case mouth and then adds 1/8 turn. I think this works best with cannelured bullets, for the non cannelured i would use the LEE factory crimp die (dont use it myself but friends do)
It gives a even crimp 1-1.5 mm around the case mouth and is affordable and easy to use.

The reason as i see to put the bullet to the lands is also to get the same effect as a crimp, bullet gets forced into the rifled part of the barrel at the same pressure point.
The thing is that the bullet dont pick up speed and momentum and you will get a mutch sharper pressure spike inside the case.
Berger i know recommends either crimping with freebore or putting the bullet to the lands to get even pressure curves.

The way i do it: I start with the bullet a bit from the lands or magazine lenght, work up some different loads and if i dont get good accuracy i try shifting the COAL to longer and less freebore, backing of one grain or two from my established max load and work it up again.

Also try annealing your case necks so you get the same stiffness in all of them.