Home Forums Hunting & Shooting Hunting Rifles Barrel channel clearance and groups size

Likely a Captain Obvious question: what has been the collective experience of the 'Fire from a not so stiff synthetic stock with "adequate" barrel channel clearance and group size? I'm defining adequate as a doubled over dollar bill slides the entire length of the barrel channel with no tight spots. Barrel is centered in the channel.

I have a rifle that shoots submoa with light loads. Crank up the velocity, and groups go to crap, mainly 2 close, 1 out. I've been pondering causes - rifle likes light loads, wrong bullet, wrong powder, primers, on into Infinity. I can live with the light loads because it shoots well - but would like to solve the issue without spending a pile of money on components.

To cover the bases: it's not the scope, mounts, or any other mechanical issue that I can find. Plus it shoots well at lower velocities and minimal recoil. I'd opine its not the shooter because I've shot known rifles along side this one and managed to produce moa/submoa groups. In my mind it's something with the rifle at this point.

My next move is a shim under the forend tip.

Other ideas/thoughts to explore?

What Rifle are we talking about?

My rule of thumb is this, if you can squeeze the end of the forearm and barrel together, and get contact, the barrel is not free floated enough.

Chambering, barrel contour, heavy loads and stock material all come into play

This is why/how I arrived at a possible barrel channel clearance - the amount of pressure to compress the stock against the barrel is remarkably easy to me. I've gotten used to the Kimber Montana stock - I can't make the stock and barrel touch with anything except extreme pressure.

I'm also going to try putting the front bag directly under the action. Normally I place it just in front of the action.

Rifle is a Kimber Hunter.

Slapping the front end tip with the heel of your hand forcefully should not contact the stock. Moving the front bag backward is a very good idea. How is the front lug fit?

All of the above...and maybe a bit more while you have it apart...Barsness and recently Nyhus has written about this. Make sure the magazine box is not acting as a recoil lug, make sure the guard screws have clearance too. Once or twice I have found the root of the bolt handle touching the stock notch causing the occasional wild flyer.

Powder charge does affect group size. Sometimes substantially.

I'm aware of the Montana pre-flight check list and have performed those things when/as needed. On the Hunter, there is no magazine box to bind - it is a magazine that uses the stock as a contact point. The box is held to the rifle but is not binding.

I'll have a look at the bolt handle - new one for me.

Thanks.

Oeh - recoil lug seems to contact fine - but admittedly it tough to tell after it's all bolted together. I'll try the forend tip pressure and placing the bag directly under the action - if that doesn't make a difference, I'll likely bed the action and provide more clearance to the barrel channel.

As noted above
Once or twice I have found the root of the bolt handle touching the stock notch causing the occasional wild flyer.

is often overlooked.

[quote=bwinters]Oeh - recoil lug seems to contact fine - but admittedly it tough to tell after it's all bolted together. I'll try the forend tip pressure and placing the bag directly under the action - if that doesn't make a difference, I'll likely bed the action and provide more clearance to the barrel channel.[/quote
When trying to diagnose flyer problems, as you said, it's tough to tell what is going on with the bedding contact points. It's kinda old fashioned, but I have had good luck just using a very thin coat of candle or propane soot on suspected metal trouble areas. The key here is extreme brain surgery care when re assembling the rifle for the firing test, fire it sufficiently for the soot to leave a fingerprint, and dis assemble with extreme care not smudge the evidence and read the witness marks. You will find your interference points with care and patience.

off hand, I would try different bullets, I seldom changed any part of the recipe and every thing stayed the same

If moving the bag changes or causes POI shift or inaccuracy, that means it is touching the barrel upon firing. The same can be said if you were using a bi-pod. You should never see a shift in POI when going from front rest with a bag vs. using a bi-pod or even shooting off of a pack. This is something that some guys just don't get. I'd say your stock is touching the barrel, even if you think it is not. Your description of, "the amount of pressure to compress the stock against the barrel is remarkably easy to me", just about says it all. Also, since you said, there is "no mechanical issue", I'm assuming you have properly glass bedded this rifle. If not, all of this is for not. Start from the start.. After that, work on the load development.

Good advice, but all can be avoided, if you just properly glass bed from the get go. Hey, that's part of the fun anyway. What I see a lot of the times is it's always the same guys dealing with accuracy issues, and most of the time, they are also the ones that are not fine tuning their rifles. Guys, an out of the box rifle is going to give you good enough results, most times, but if you really want a consistent shooter for the lifetime of the rifle, properly glass bed it and address all the trouble spots right from the start. Why some don't get that, is a mystery to me.

After seeing the barrel whip shown by video in the scope clearance thread, I doubt dollar bill barrel channel clearance is sufficient.

That receiver is bolted to essentially an unmovable platform. Something has to give. You wouldn’t see that with a shoulder fired rifle me thinks.

Holy Shiite! I never realized the barrel whipped that much - and thats not a pencil thin barrel.

Played with it this AM. I have ~ 100 rounds down the tube of that rifle so any signs of the barrel/action hitting something in the stock should be evident. I took it apart this AM - no signs of the stock hitting anywhere. There isn't a ton of play in the action with no screws. I did learn the stock is pillar bedded. I reassembled paying extra attention to making sure the action was seated in the stock and saw no perceptible movement when tightening the action screws. I stopped the torque at 30 lbs on rear, 40 lbs on front. I normally go 35 and 40 on my Montanas. The barrel channel clearance allows 4, 3x5 notecards to pass without obstruction until it hits the barrel shank where it stops dead. If I had opened the barrel channel that much on a gun I was working on, I'd be highly irritated. To me, it looks right on the edge of too much - but that forend still hits the barrel when you squeeze the 2 together.

I'll prob shoot it like this with the front bag close to the action to see what happens - if for nothing else as a learning experiment. If that doesn't seem to work, I'll try the forend pressure point. I don't plan to hunt with this rifle, grandkids might, so I'm in no hurry to do anything. More of learning thing at this point. Plus it does shoot 140 gr Horn SP with IMR 4166 and 4064 at ~ 2400-2450 at sub-moa or a bit better. I have zero doubts they won't bounce off deer at that velocity.

Edited to add: the bolt handle is not in contact at any point with the stock.

All my Remington 700's (wood stocks) shoot better with a forend pressure point. Once I find out the proper point pressure that the gun likes, I place a piece of Teflon thread tape between the pressure point and the barrel.

You get up earlier than I do, very impressed. I have never owned the Kimber Hunter but the pics I see of the stock fore-end look like they went out of their way to try to reinforce it.

You do realize that changing powder charge can affect group size right?