screwed up 308

[Bruce Hanson]

I hope someone has some ideas. I have a Remington 700P in 308. It was shooting Backhills match into .25 to .3 inch groups. It shot hunting ammo into 2 to 2.25 inches. The right locking lug was only contacting 10 percent, and the left not at all. Evidently the higher velocity was torking the bolt and destroying accuracy. I sent it to the gunsmith and it came back shooting everything about 2.5 inches. Until, after 20 to 25 rounds it shoots sub .2 inch groups. After it cools it again shoots over 2 inches and after 20 rounds again sub .2 inch. What the heck is going on?

 

[Michael Eichele]

I assume your gunsmith fixed the lug problem??

I had a weatherby that would do the same thing, the only time it would shoot worth a crap is when the barrel was nice and warm. I got rid of that one. Several smiths told me to try and chryo the barrel. They said there was stress in the barrel and when it warmed up it would releive the stress. They figured that a chryo job would permanantly relieve the stress. I didnt keep it long enough to find out. 700 pss's are ussually pretty good though.

1. What are your cleaning methods?
2. What kind of ammo are you using?
3. Are you shooting this off a bench and with what rest?

 

[Guest]

Well , first I'd go through and check all the bedding and barrel chanel for proper contact , or lack their off. The check the bore.
Does the gun shoot well when its warm or when its dirty I've seen barrel that were boogered up inside shoot well after a dozen fouling shots , clean it then the accuracy leaves with the bore brush.

If its shooting well only when it has warmed up then ,as was stated before , you could try to have the barrel cryoed to try to even out the metal structure.
You could also check the lug contact again , did the smith just lap the lug or did he do a full on lug to recess machining so they mate correctly

I once new a guy that went round and round with a custom built rifle that would just not shoot , after bad mouthing the smith and the action , barrel , stock and everything else , he sold the gun to me. I replaced the scope and all the accuracy problems went away. The scope was a Leupold to boot.

 

[MAX]

Somethings not happy until it's hot so either carry a portable oven or start tracking the problem down. My first guess is the lug job since that is where the problem originated, and was the apparent source of other malfeasance. I wonder if the action was left in the stock when the 'smith did the lug thingy, and if so, would suspect the bedding is stressing the action, which queered the lug polishing, which...well, you see where I'm going with this right?

 

[Bruce Hanson]

Thanks for the ideas. I have been cleaning with Sweats, or CR10 and finishing up with JB Bore cleaner. It shot best with Blackhills match before. I have been shooting it off sandbags, and from a Hart rest. I lapped the lugs myself with 800 grit garnet. After the lug lap it still grouped Balckhills match .25 inch and brought 150 factory Federal down from 2 inches to under 1 inch. The problem was it took so much lapping that it needed headspacing. When it came back from the smith it shot 2 and 3 inch groups. After 20 rounds it shot a .25 inch group. So I didn't clean the gun and the next day 2 inch groups then back down to .25. I think I'll pull the rifle from the stock and check for something under the recoil lug etc. Thanks again for the ideas.

 

[rjb]

Please pardon the peek at your 308 "problemo"
Some times this done right can equal odd results as you mentioned. Lets assume your
gunsmith was diligent and excellant craftsman. Still your factory action according to above had poor lug contact. How
was the "repaired". No flame here just note
the customary procedure is to use abrasive lapping compound and work the surfaces of
bolt lugs over untill a better more uniform
contact area results. That's OK BUT at same time whatever lug thickness is ground away to make both lugs contact ADDs to the bolt headspace. Headspace being roughly put the
fit of loaded rounds contacting chamber walls
and shoulder area. This fit is key to centering rounds for accuracy. The factory
"fit" is fixed. So it's possible the "cure"
has changed the alighnment (at least until the bolt warms up). Handloaded rounds can compensate i.e. used fireformed brass, neck sized only and bullets seated close to rifling contact. All that componant variables
can change the accuracy +/- of chambered rounds. That's what makes chasing accurate loads so ^^$&*#@ much fun.

rjb

 

[Bruce Hanson]

Max
you were right something was wrong. Not sure what, I did two things. First I slightly lapped the lugs again (very slight). Then I pulled the barrel and action from the stock. The first thing I noticed was a triangular hole behind the forward action screw. It was deep enough to push metal (aluminum bedding block) up around the edges, and it appeared the action was teatering on that high point. I sanded it down, and when I put the action back in the stock it looked like I had twice as much free float. Tonight I went to the range and shot a .28 inch group at 100 yards with my handloads, and with Blackhills match.

 

[MAX]

The best laid plans of mice and men, aft gang aglee.

Glad it was simple to fix. Sometimes the hard part is the details; that's where the devil hangs out.