Is too much free bore my problem?

[birdiemc]

I have a Rem 700 .308 with factory 20" barrel 1:10 twist, been trying to get it to shoot decent for a couple years now. Out of the box it was 1.5-2 MOA. With or without suppressor, no difference in group size just slight shift in POI. Bedded Talley scope rings, torqued to recommended specs though dont recall now what that was. Lapped rings as they were showing limited contact. I thought maybe changing stocks would help so put it in a magpul hunter, groups opened up a bit and started throwing fliers 6" at 100yds. Pulled it apart checked contact with dykem found some problem areas around rear action screw and magazine, took care of them with a file, no contact on recoil lug except about .030 across the top edge so bedded the lug, still shooting over 2" at 100 yds. Tried different torques on action screws, 70 in/lbs finally brought it back down to where I began 1.5-2" at 100yds.
I finally got around to cracking open my hornady OAL comparator yesterday and found I have what I consider to be excessive free bore. I forgot to write down what it measured to the lands vs. a factory round but if I recall correctly it was about .210.
Today I seated everything to the max the magazine would allow and did write that measurement down, its .167 from the lands.
This is with a 220 gr ELD-X using varget 39.2-40.2 increasing in .2 increments
2240, 2272, 2275, 2285, 2302, 2337 checked using magnetospeed.
The accompanying groups with each load varied from 1.2-2", the tightest group was 39.8 and the POI shift from 39.6 to 39.8 was .143, not as good as .121 between first two charges, but looking at velocity, group size, and POI shift it seems 39.7 might be the ideal load.
Now back to the free bore problem, I'm already at max OAL for the magazine so trying to fine tune with seating depth seems a bit limited, and am I really going to be able to squeeze out an inch with seating depth?
I searched the history and found this thread below and see where many say this excessive free bore isnt necessarily a problem. So what are your thoughts?


https://www.longrangehunting.com/th...shot-out-rem-do-this-on-purpose.120193/page-2

 

[MagnumManiac]

A long jump doesn't necessarily cause poor accuracy.
You can tune AWAY from max mag length, tune powder charge at max mag length.
There are so many variables that it may be bullet choice, powder choice or primer choice causing your woes.
Some bullets don't behave well outside of their happy velocity window. If this is the case, then only increasing velocity or reducing the weight may help.

Have you tried other bullet weights?

Cheers.

 

[AZShooter]

Two thought come to mind. Some there might be other flaws with rifle and try some Berger hybrids which are very seating depth insensitive.

Some ideas on other things that could be wrong with rifle. I don't want to insult your intelligence but must cover some obvious things. Heck I have a list I keep in documents so I don't forget any:

Have you inspected barrel with borescope? I have seen some strange things inside some Rem barrels, including missing lands.

How is the crown?

Action screws shouldn't touch sides of holes in stock. If necessary drill the larger

Be certain the front scope ring base screw is not contacting barrel causing a false tightness

Bolt handle should not touch stock

Mag box must not bind

Recoil lug making early contact in bottom of bedded slot causing the action to sit off bedding

trigger group should make contact with stock

Trigger guard should make contact with trigger


Barrel should not make contact with barrel channel. Due to some flexing some rifles required additional material be removed from stock.

Try some things and get back here to let us know.

Ross

 

[L.Sherm]

Try seating .020 off the lands with a group and see if it shoots better that will answer your question. If it does you could have a wyatt box installed if it shoots to your satisfaction.

 

[birdiemc]

MagnumManiac,

I have tried factory loads in every weight I could find from the 150 -180 gr range, best was 1.5" with the occasional group getting down to 1".
I definitely want to try a different bullet, kinda been considering 175gr. And after reading that thread I linked maybe something from Barnes. I liked the idea of the ELD-X but not married to it.

Ross,

I do not have a borescope so cant look down the barrel. I have thought to check everything you mentioned except the front scope ring base screw. I'll take a look. Thanks.

 

[birdiemc]

Try seating .020 off the lands with a group and see if it shoots better that will answer your question. If it does you could have a wyatt box installed if it shoots to your satisfaction.

Ya know, sometimes I get tunnel vision and forget I can do things like load one at a time into the rifle for testing purposes...

 

[Dosh]

mc, perhaps find a smith with a borescope. This will give you critical info. + on AZShooter's tips, if the barrel scopes out ok. Good luck

 

[Laelkhunter]

Not really sure if it is the same with Weatherbys and other rifles with "free bore", but Weatherbys seem to have more free bore (by design) for some reason, and the Weatherbys I have owned and shot are extremely accurate. Maybe not as accurate as some custom rifles, but when I first got my .340 Weatherby, it shot 1/2 moa with factory 210 Nosler Partition ammo. My reloads were close to that also, but the factory ammo shot the best with the free bore. I'm not sure if I would have any bullet left in the case if I loaded the 210 Noslers to where they were touching the lands.

 

[gohring3006]

I think you need to bore scope it.
The 308 is so forgiving, it's always seems to shoot something good, no matter the rifle make.

 

[cgarb]

If there is a lot of free bore try a flat base bullet. If a bullet with a short bearing surface leaves the casemouth before engagement in the rifling it can cause accuracy problems.

 

[elkaholic]

Not really sure if it is the same with Weatherbys and other rifles with "free bore", but Weatherbys seem to have more free bore (by design) for some reason, and the Weatherbys I have owned and shot are extremely accurate. Maybe not as accurate as some custom rifles, but when I first got my .340 Weatherby, it shot 1/2 moa with factory 210 Nosler Partition ammo. My reloads were close to that also, but the factory ammo shot the best with the free bore. I'm not sure if I would have any bullet left in the case if I loaded the 210 Noslers to where they were touching the lands.

The Weatherbys had more free bore for one reason: VELOCITY!
many of them shot pretty well but people who wanted to shoot them in competition usually shortened the free bore.
Not saying thats the OP's issue. I think it's either bedding or seating depth.

 

[mobenzowner]

I know you have a 1:10 twist and in theory should probably be ok with your bullet, However I have the same gun and it loves 175 SMK's. It likes most bullets in that weight range. It also shot the now discontinues 178 A-Max very well. Both of those bullets shoot under 1/2" for me at 100. As a reference which may help you my CBTO with the 175 smk is 2.347" my LLTO is 2.332". With the 178 A-Max the CTBO is 2.308" and my LLTO is 2.290". Thought this might give you some reference in regards to your chamber dimensions. Good Luck!

I just saw you have tried bullets in the range I suggested. Sorry for my redundancy.

 

[ShtrRdy]

My suggestion, considering all you've done already, is to buy a box of Federal Gold Metal Match with the 168 hr MatchKing and a box with the 175 hr MatchKing. The Sierra MK bullets are very jump insensitive. This should give you an idea if the rifle is capable of grouping.

 

[birdiemc]

Pulled everything apart and looked it over real well. I had put dykem pretty much on anything metal last time I assembled it, looks like it's making contact in all the right places, verified clearance in action screws to ID of pillars, pulled one piece talley rings off, and the front base aft screw was not as tight as the rest, checked clearance between front screw and barrel is good, reinstalled everything (quick search I found recommended tq 25 In lbs for base screws, 20 for ring screws). I know I shouldn't have done it, changing too many variables at once and all, but I threw on the viper HS that arrived this week. I have no reason to believe anything was wrong with the other scope, but figured since I had it all torn down already might as well swap as this is the rifle I bought that scope for.
Now to do as Shtrrdy suggested and go pick up some more 175 Federal, and try the 168 while I'm at it.
Might go make up a few with what I got and just see if tightening that base screw seems to fix everything...2 hour round trip to Academy counting stand in line time