Throat burned out or not???

[bushmotornv]

I have a used 7MM Weatherby mag in a Mark 5 action that will not hold any kind of a group less than about 3". It was made in Japan in Jan. 1994, 26" SS #2 contour. I seat a 175gr Speer GS just into a new case which gives me a total COAL of 3.781. I place in chamber and close the bolt, after removal the total COAL is 3.767. Which leaves only 14 thousands of bullet in case when the bullet hits rifling. That gives me a free bore of about .402. The Speer GS has a lot of bearing surface, any other bullet will leave the case before it hits the rifling, really not good! Am I missing something important here or is the throat gone? What is good free bore on replacement barrel?
I got this weapon for long range Mule Deer and Elk so I want the extra velocity. Now, long range for me is about 500 yds. my eyes and reflex isn't what they were many years ago.
Thanks for any information on this post.
AIRBORNE

So a few thoughts...Weatherby is noted for long freebores,so trying to seat to the lands is next to impossible. Is the bore clean? I don't mean to offend,but I have cleaned "clean" bores and gotten "shot out"rifles to shoot well again. I highly recommend Wipe Out,Patch Out. Many of the agressive bore cleaners creat an oxide over the fouling and show clean by patch color. The Patch Out is non toxic and does not have an offensive odor,and is completely safe on the bore. They also sell an accelerator to speed up the process,but some time here to try out a thorough cleaning is certainly worth it as compared to a re-barrel. I have verified these results with a bore scope,and it has neen nothing short of amazing. I have no affiliation with Wipe Out,just satisfied with their product. Just my 2 cents!

 

[PDRENNER]

Thank you for your thoughts. I have spent hours scrubbing this bore. It was very fouled when I got it so I scrubbed with what I have on hand, bore tech cu+2, Barnes cr-10 and gold medallion. I am satisfied it is copper free.
I am working on the suggested depth test but weather is not good for range work and I am limited with only 87 WBY brass to load for testing. I started out first 3 shot group had coal of 3.366. Each 3 shot group after that was a - 10 thousand. Will see if sweet spot shows up.
AIRBORNE

 

[xsn10s]

Now that you have it well cleaned I'd polish the throat just in case. Use JB Polishing Compound on a solid jag with some tight fitting patches. You can "feel" it the throat is rough by using a new plastic bore brush.

 

[xsn10s]

Your post on the powder residue just on the top of the crown suggests a possible "uneven" crown. Or a crown that isn't perpendicular to the bore.

 

[PDRENNER]

Xsn10s
I just noticed that residue on the crown. Is there a method a layman can use to determine if what you say is a fact? That could be the problem or one of several but if I can eliminate it then that will help narrow the search.

 

[xsn10s]

Xsn10s
I just noticed that residue on the crown. Is there a method a layman can use to determine if what you say is a fact? That could be the problem or one of several but if I can eliminate it then that will help narrow the search.

Well other than having the crown recut not really. Or the equipment needed to determine if any of the problem would cost more than the fixes or work. Which is why when testing a rifle I check the easiest and cheapest fixes first. Like action screws, mounts, scopes, and so on. That's why I said test the rifle on paper at further distances beyond 100 yards before moving on to the more expensive or evasive fixes.

 

[grovey]

From the advice you've been given I'd sell the Weatherby asap, and buy a Tikka t3x in 7rem mag or 270 wsm . 3-6" groups ain't going to shrink into acceptable LR accuracy with just a seating depth change. I agree it's very important, but a slow twist rifle with a mile long throat that shoots like that would be gone.

 

[PDRENNER]

That is my last resort.
AIRBORNE

 

[xsn10s]

It's a bit early to be thinking of getting rid of it. Heck we don't even know what the load was. First thing to do is do all the common checks and then work on a book accuracy load at standard length. Have you even shot it at 300-500 yards on paper or steel?

 

[PDRENNER]

No I have not shot it passed 100. With such poor groups at 100 I didn't see the use of going beyond, but if I did go out to 450yds., which I can do, what would it tell me that I don't already know from my 100 yd groups?
AIRBORNE

 

[grovey]

No I have not shot it passed 100. With such poor groups at 100 I didn't see the use of going beyond, but if I did go out to 450yds., which I can do, what would it tell me that I don't already know from my 100 yd groups?
AIRBORNE

That you'll need a BIG piece of paper. Seriously though... Put a tight fiting patch on your cleaning rod and measure how many inches it moves in till the rod makes a full revolution. A piece of masking tape works for this. One revolution x the length you get equal your bbl's twist. Do it a few times so you know. This will tell you if your bullets are compatible with your rifle.

You didn't mention it, but if you're reloading you really should be using something to measure what you're working with. I suggest Hornady's headspace gauges and bullet comparator's in junction with a hornady modified case to get a reference of where you're at.

Do a coarse seating test at a safe powder charge. I'm not sure how much bullet you have in the neck with your current best load, but as was mentioned I'd start with roughly as much bullet in the neck as the bullet diameter. ( If your leaning on it now with the bullet barely seated back off the powder charge to do your test.) Start at .280 in, and load three groups of three at 0.20, 0.40 and 0.60 closer towards the rifling. Shoot it at 100. You should see a difference on paper.

 

[MudRunner2005]

That is my last resort.
AIRBORNE

Don't sell it, just rebarrel it. Toss on a good stainless aftermarket barrel with a modern twist, have the action blueprinted, and start working up a load.

 

[okie man]

No offense but some people just don't shoot heavy recoiling rifles well and a lightweight 7mm weatherby a bit of a kicker with some loads! Also forget about chasing the lands with one! I've found staying close too length in the manuals works better in the weatherby cartridges. The speer grand slam has never been considered a premium accuracy bullet, nor the hornady spire points. If you do have a slower twist barrel I recommend trying the 145 grain or 160 grain speer btsp

 

[PDRENNER]

Good advise and I thank you. To date have not found anyone willing to rebarrel it! If that is what I decide to do and rebarrel to what cartridge?
AIRBORNE